EPA-600/8-83-028B
February 1986
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LEAD EFFECTS ON CARDIOVASCULAR FUNCTION AND STATURE:
AN ADDENDUM TO THE U.S. EPA*1986 DOCUMENT,
AIR QUALITY CRITERIA FOR LEAD
February, 1986
Environmental Criteria and Assessment Office
Office of Research and Development (ORD)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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LEAD EFFECTS ON CARDIOVASCULAR FUNCTION AND STATURE:
AN ADDENDUM TO THE U.S. EPA 1986 DOCUMENT,
AIR QUALITY CRITERIA FOR LEAD
INTRODUCTION
The earlier U.S. EPA criteria document, Air Qua!ity Criteria for Lead
(EPA-600/8-77-071) has been updated and revised pursuant to section 108 and 109
of the Clean Air Act, as amended, 42 U.S.C. 7408 and 7409, and will be used as
a basis for review and, as appropriate, revision of the National Ambient Air
Quality Standard (NAAQS) for lead. As part of this process, EPA released two
external review drafts of the revised criteria document, Air Qua!ity Criteria
for Lead (EPA-600/8-82-028A&B), which were made available both for public com-
ment and peer review by the Clean Air Scientific Advisory Committee (CASAC) of
the Agency's Science Advisory Board. A final version of that criteria document
incorporating revisions made in response to public comments and CASAC review of
earlier drafts is in the final stages of preparation.
Not fully evaluated in the revised Criteria Document, however, are
recently published papers concerning: (1) the relationship between blood lead
levels and blood pressure; and (2) lead exposure effects on early growth and
stature. The present Addendum to the revised document, Air Quality Criteria
for Lead, evaluates newly published information on cardiovascular effects of
lead, including assessment of both human and animal toxicology studies. The
Addendum also discusses newly published data regarding lead effects on growth
and stature, as evaluated by epidemiology and animal toxicology studies.
1. Lead Effects on the Cardiovascular System
Lead has long been reported to be associated with cardiovascular effects,
in both human adults and children. This section assesses pertinent literature
on the subject, including: (1) studies of cardiotoxic effects in overtly
lead-intoxicated individuals; (2) epidemiologic studies of associations between
lead exposure and increased blood pressure, including observations for non-
overtly intoxicated subjects; (3) toxicologic data providing experimental evi-
dence for lead-induced cardiovascular effects in animals and (4) information on
possible mechanisms of action underlying cardiovascular effects of lead exposure.
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1.1	Cardiotoxic Effects in Overtly Lead-Intoxicated Human Adults and Children.
Structural and functional changes suggestive of lead-induced cardiac
abnormalities have been described for both adults and children, always in
individuals with clinical signs of overt intoxication. For instance, in
reviewing five fatal cases of lead poisoning in young children, Kline (1960)
noted that degenerative changes in heart muscle were reported to be the proxi-
mate cause of death; it was not possible, however, to establish that the ob-
served changes were directly due to lead intoxication per se. In another
study, Kosmider and Petelenz (1962) found that 66 percent of a group of adults
over 46 years old with chronic lead poisoning had electrocardiographic abnor-
malities, a rate four times the adjusted normal rate for that age group.
Additional evidence for a possible etiological role of higher level lead expo-
sure in the induction of disturbances in cardiac function derives from obser-
vations of the disappearance of electrocardiographic abnormalities following
chelation therapy in the treatment of many cases of lead encephalopathy (Myer-
son and Eisenhauer, 1963; Freeman, 1965; Silver and Rodriguez-Torres, 1968).
The latter investigators, for example, noted abnormal electrocardiograms in 21
(20 percent) of 30 overtly lead-intoxicated children prior to chelation therapy,
but abnormal electrocardiograms remained for only four (13 percent) after such
therapy (Silver and Rodriguez-Torres, 1968). None of the above studies pro-
vide definitive evidence that lead induced the observed cardiotoxic effects,
although they are highly suggestive of an etiological role of lead in producing
such effects. Some recently reported human autopsy study results (Voors et al.,
1982) showing associations between heart-disease mortality and elevated aortic
lead levels also point toward possible involvement of lead in cardiotoxic di-
sease processes.
1.2	Epidemiologic Studies of Blood-Lead/Blood-Pressure Relationships
Hypertension or, more broadly, increased blood pressure represents the
single main type of cardiovascular effect long studied as possibly being asso-
ciated with excessive lead exposure. As long ago as 1886, Lorimer reported
that high blood lead levels increased the risk of hypertension. However, from
then until only recently, relatively mixed and often apparently contradictory
results have been reported concerning associations between high-level lead
exposures and hypertension effects. That is, numerous investigators reported
significant associations between hypertension and lead poisoning (Oliver, 1891;
Legge, 1901; Vigdortchik, 1935; Emmerson, 1963; Dingwall-Fordyce and Lane,
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1963; Richet et al. , 1966; Morgan, 1976; Beevers, et al., 1976), whereas other
studies failed to find a statistically significant association at p <0.05
(Belknap, 1936; Fouts and Page, 1942; Mayers, 1947; Brieger and Rieders, 1959;
Cramer and Dahlberg, 1966; Malcolm, 1971; Ramirez-Cervantes et al., 1978). The
potential contribution of lead to hypertension was difficult, if not impossi-
ble, to determine based on the results of the above studies, due to many metho-
dological differences and problems (e.g., lack of comparable definitions of
lead exposure and prospective control populations, variations in how hyperten-
sion was defined or measured as the key health endpoint, etc.).
In contrast to the confusing array of results derived from the above stu-
dies, a much more consistent pattern of results has begun to emerge from more
recent investigations of relationships between lower-level lead exposures and
increases in blood pressure or hypertension. For example, Khera et al (1980)
reported a case control study showing higher blood lead levels in hypertensive
patients and those with other cardiovascular diseases than for hospital control
subjects. Also, Kromhout and Couland (1984) and Kromhout et al (1985) reported
associations between hypertension and blood lead among 152 elderly men in the
Netherlands; Batuman et al. (1983) reported an association between hypertension
and chelatable lead burdens in veterans; and Moreau et al. (1982) reported
significant associations (p <0.001) between blood-lead levels and a continuous
measure of blood pressure among 431 French policemen (age 24 to 55 years),
after controlling for important potential confounding variables such as age,
body mass index, smoking, and drinking.
In a larger recent study, Pocock et al. (1984) evaluated relationships
between blood lead concentrations, hypertension, and renal function indicators
in a clinical survey of 7735 middle-aged men from 24 British towns. Results
for the overall group studied indicated correlation coefficients of r = +0.03
and r = +0.01 for associations between systolic and diastolic blood pressure,
respectively, and blood lead levels. The systolic blood pressure correlation,
though small in magnitude, was nevertheless statistically significant at
p <0.01. However, analyses of data for men categorized according to blood lead
concentrations only suggested increases in blood pressure at lower blood lead
levels; no further significant increments in blood pressure were observed at
higher blood lead levels (either before or after adjustment for factors such as
age, body mass index, alcohol consumption, social class, and observer). Eval-
uation of prevalence of hypertension defined as systolic blood pressure over
160 mm Hg revealed no significant overall trend; but of those men with blood
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lead levels over 37 pg/dl, a larger proportion (30 percent) had hypertension
when compared with the proportion (21 percent) for all other men combined
(p <0.08). Similar results were obtained for diastolic hypertension defined
as >100 mmHg, i.e., a greater proportion (15 percent) of men with blood lead
levels over 37 pg/dl had diastolic hypertension in comparison with the pro-
portion (9 percent) for all other men (p <0.07). Pocock et al. (1984) inter-
preted their findings as being suggestive of increased hypertension at blood
lead levels over 37 pg/dl, but not at lower concentrations typically found in
British men. However, more recent analyses reported by Pocock et al. (1985)
for the same data indicate highly statistically significant associations
between both systolic (p <0.003) and diastolic (p <0.001) blood pressure and
blood lead levels, when adjustments are made for variation due to site (town)
in multiple regression analyses. The regression coefficients for log blood
lead versus systolic and diastolic pressure were +2.089 and +1.809, respecti-
vely, when adjusted for town as well as body mass, age, alcohol, smoking,
social class and observer.
Relationships between blood lead and blood pressure among American adults
have also been recently evaluated, as reported by Harlan et al. (1985) and
Pirkle et al. (1985). These analyses were based on evaluation of NHANES II
data, which provide careful blood lead and blood pressure measurements on a
large-scale sample representative of the U.S. population and considerable
information on a wide variety of potentially confounding variables as well. As
such, these analyses avoided the problem of selection bias, the healthy-worker
effect, workplace exposures to other toxic agents, and problems with appropri-
ate choice of control groups that often confounded or complicated earlier,
occupational studies of blood-lead, blood-pressure relationships. The analyses
reported by Harlan et al. (1985) demonstrated statistically significant linear
associations (p <0.001) between blood lead concentrations and blood pressure
(both systolic and diastolic) among males and females, aged 12 to 74 years.
However, using a model controlling for a number of other potentially confound-
ing factors, blood lead was not independently related to blood pressure in
women after adjusting for the effects of other variables in the model.
Further analyses reported by Pirkle et al. (1985) focussed on white males
(aged 40 to 59 years) in order to avoid the effects of collinearity between
blood pressure and blood lead concentrations evident at earlier ages and
because of less extensive NHANES II data being available for non-whites. In
the subgroup studied, Pirkle et al. (1985) found significant associations
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between blood lead and blood pressure even after including in multiple
regression analyses all known factors previously established as being corre-
lated with blood pressure. The relationship also held when tested against
every dietary and serologic variable measured in the NHANES II study. Inclu-
sion of both curvilinear transformations and interaction terms altered little
the coefficients for blood pressure associations with lead (the strongest rela-
tionship was observed between the natural log of blood lead and the blood pres-
sure measures). The regression coefficients for log blood lead versus systolic
and diastolic blood pressure were 8.436 and 3.954, respectively. No evident
threshold was found below which blood lead level was not significantly related
to blood pressure across a range of 7 to 34 MQ/dl. In fact, the dose-response
relationships characterized by Pirkle et al. (1985) are indicative of large
initial increments in blood pressure at relatively low blood lead levels,
followed by leveling off of blood pressure increments at higher blood lead
levels. This pattern is consistent with biphasic blood pressure increases
observed in response to blood lead increases in the rat (Victery et al.,
1982a,b) and may also account for the failure of other studies to find con-
sistent relationships between blood pressure and blood lead in study groups
with mild to moderate elevations of blood lead concentrations. Pirkle et al.
(1985) also found lead to be a significant predictor of diastolic blood pres-
sure greater than or equal to 90 mmHg, the criterion blood pressure level now
standardly employed in the United States to define hypertension.
Additional analyses were performed by Pirkle et al. (1985) to estimate the
likely public health implications of their findings concerning blood-lead,
blood-pressure relationships. Changes in blood pressure that might result from
a specified change in blood lead levels were first estimated. Then coeffi-
cients from the Pooling Project and Framingham studies (Pooling Project
Research Group, 1978 and McGee and Gordon, 1976, respectively) of cardiovas-
cular disease were used as bases: (1) to estimate the risk for incidence of
serious cardiovascular events (myocardial infarction, stroke, or death) as a
consequence of lead-induced blood pressure increases and (2) to predict the
change in the number of serious outcomes as the result of a 37 percent decrease
in blood lead levels for adult white males (aged 40-59 years) observed during
the course of the NHANES II survey (1976-1980). The following declines in
serious outcomes were thusly estimated: (1) a 4.7 percent decrease (77,300
fewer events) for fatal and non-fatal myocardial infarctions; (2) a 6.7 percent
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decrease (27,500 fewer events) for fatal and non-fatal strokes; and (3) a 5.5
percent decrease (73,900 fewer events) for death from all causes.
Unpublished reanalyses of the NHANES II data have been provided by Schwartz
(1985a,b) which confirm that the regression coefficients remain significant for
both systolic and diastolic blood pressure when site is included as a variable
in multiple regression analyses. Schwartz (1985a,b) reported coefficients of
1.41 (p <0.05) and 3.30 (p <0.01) for blood lead relationships versus systolic
and diastolic blood pressure, respectively, for all men over 20 years old and
3.12 (p <0.05) for diastolic pressure for men aged 40 to 59, after controlling
for 64 sites included in the NHANES II study. No coefficient was reported for
systolic pressure for the latter age group after controlling for site, but it
would be expected to be significant since the systolic results are consistently
higher than for the diastolic in all other analyses.
Overall, the analyses reported by Harlan et al. (1985), Pirkle et al.
(1985), and Schwartz (1985a,b) provide convincing evidence for strong associ-
ations between blood pressure increases and blood lead levels, even at blood
lead concentrations below 30 jjg/dl and, possibly, down to as low as 7 (jg/dl.
Furthermore, their results are consistent with similar findings of statistically
significant associations between blood lead levels and blood pressure increases
as derived from other recent epidemiologic studies, such as those of Moreau et
al. (1982), Kromhout and coworkers (1984, 1985) and Pocock et al. (1984, 1985).
Whether the blood-lead blood-pressure associations observed in these studies
are causal or not remain to be more definitively established and the quantifi-
cation of likely consequent risks for serious cardiovascular outcomes estimated
by Pirkle et al. (1985) more precisely characterized.
The specific magnitudes of risk obtained for serious cardiovascular out-
comes in relation to lead exposure, estimated on the basis of lead-induced
blood-pressure increases, depend crucially upon the size of coefficients esti-
mated for blood-lead blood-pressure associations. Some uncertainty exists in
regard to the most appropriate blood-lead blood-pressure coefficients to use in
attempting to project more serious cardiovascular outcomes. For example, the
coefficients obtained in reanalyzing the NHANES II data, adjusting for site,
are smaller than those reported based on analyses unadjusted for site and,
thus, it might be argued that Pirkle et al (1985) overestimated probable risks
of consequent serious cardiovascular outcomes. On the other hand, adjusting
for site would be expected to result in loss of sensitivity and increased bias
toward lower coefficients for blood-lead blood-pressure associations, which may
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underestimate the strength of the underlying biological relationship and thusly
lead to underestimates of risk for more serious outcomes. The best estimates
of risk for more serious outcomes may, therefore, fall somewhere between those
obtained using blood-lead blood-pressure coefficients unadjusted and adjusted
for site in the NHANES II data set. Also complicating the situation at present
are the weaker associations between blood-lead and blood-pressure reported by
Pocock et al.(1984, 1985). Further analyses of additional large scale epide-
miologic data sets may be necessary in order to resolve more precisely quanti-
tative relationships between blood-lead and blood-pressure, and more serious
cardiovascular outcomes as well.
Support for the plausibility of causal relationships between lead expo-
sures and hypertension, as well as consequent more serious cardiovascular
effects, is provided by the information discussed below in relation to poten-
tial mechanisms underlying lead effects on blood pressure and experimental
findings bearing on the subject.
1.3 Mechanisms Potentially Underlying Lead-Induced Hypertension Effects
The underlying causes of increased blood pressure or "hypertension" (dia-
stolic blood pressure above 90 mm Hg), which occurs in as many as 25 percent of
Americans, are not yet fully delineated (Frolich, 1983; Kaplan, 1983). Many
factors contribute to development of this disease, including hereditary
traits, nutritional factors and environmental agents. The relative roles of
various dietary and environmental factors in influencing blood pressure and the
mechanisms by which they do so is a matter of intense investigative effort and
debate (see proceedings of conference "Nutrition and Blood Pressure: Current
Status of Dietary Factors and Hypertension," McCarron and Kotchen, 1983). This
section discusses plausible biochemical-physiological mechanisms by which lead
potentially influences the cardiovascular system to induce increased blood
pressure, followed by the evaluation of experimental evidence concerning the
contribution of lead exposure to development of hypertension.
Blood pressure is determined by interaction of two factors: cardiac out-
put and total peripheral resistance. An elevation of either or both results in
an increase in blood pressure. A subsequent defect in a critical regulatory
function (e.g., renal excretory function) may influence central nervous system
regulation of blood pressure, leading to a permanent alteration in vascular
smooth muscle tone which sustains blood pressure elevation. The primary defect
in the pathophysiology of hypertension is thought to be due to alteration in
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calcium binding to plasma membranes of cells; this change in calcium handling
may in turn be dependent upon an alteration in sodium permeability of the
membrane (Blaustein, 1977; Rasmussen, 1983; Postnov and Orlov, 1985). This
change affects several pathways capable of elevating pressure: one of which is
a direct alteration of the sensitivity of vascular smooth muscle to vasoactive
stimuli; and the other of which is indirect, by altering neuroendocrine input
to vascular smooth muscle including changes in renin secretion rate.
1.3.1 Role of disturbances in ion transport of plasma membranes
Many stimuli activate target cells in the mammalian body via changes in
ion permeabilities of the plasma membrane, primarily for sodium, potassium, and
calcium ions (Carafoli and Penniston, 1985); the change in calcium ion con-
centration is the primary intracellular signal controlling muscle contractions,
hormone secretion, and other diverse activities. Extracellular fluid contains
high concentrations of sodium and calcium, while intracellular potassium is
high. Intracellular calcium is present in two forms, bound and free ion, with
the concentration of the free ion normally about 0.1 pM. These concentration
gradients across cell membranes are maintained via the action of membrane-bound
energy-requiring or voltage-dependent exchange pumps. For sodium and potas-
sium, the regulatory pump is a sodium/potassium-dependent ATPase which extrudes
sodium in exchange for potassium ions and in the process is important in
maintaining the cell membrane potential. For calcium, there is a membrane
potential-dependent sodium/calcium exchange pump which extrudes one calcium ion
in exchange for three sodium ions. In addition, there are calcium ATPase pumps
located at cell membranes and at intracellular membrane storage sites (endo-
plasmic reticulum and mitochondria). As calcium ions move in and out of the
cell and in and out of intracellular storage sites, the intracellular free
calcium ion ([Ca2+]) changes from its resting value to something higher or
lower. The ion interacts with several calcium-binding proteins which in turn
activate cell contractile or secretory processes.
It has been postulated (Blaustein and Hamlyn, 1983) that sodium pump inhi-
bition by some endogenous factor (thought to be a hormone) could be ultimately
causatory for development of both essential and volume-expanded hypertension by
affecting vascular tone or resistance. As explained above, the sodium pump
maintains and restores the membrane potential subsequent to depolarization
events. Decreased sodium pump activity may directly increase membrane perme-
ability to calcium and increase reactivity to calcium-dependent stimuli. Small
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changes in the distribution of intracellular and extracellular sodium ions
affect the membrane potential and cause a much larger decrease in activity of
the sodium/calcium exchange pump, resulting in a proportionately much greater
elevation in intracellular free calcium ion which in turn increases reactivity
to calcium-activated stimuli. Some of the newest antihypertensive therapeutic
agents (calcium channel blockers) act to lower intracellular [Ca2+] by reducing
movement of extracellular calcium into cells, thereby reducing activation of
processes requiring such movement. Diuretic drugs may reduce the postulated
rise in intracellular sodium concentration related to the decreased Na/K ATPase
activity and thereby reduce elevated intracellular calcium by stimulation of
the Na/Ca exchange pump.
If lead exposure could be shown to affect sodium transport (which then
indirectly alters vascular resistance) or to directly affect vascular resis-
tance (by changing calcium ion permeability or transport), it could contribute
to the development of hypertension. Highlighted concisely below is evidence
that lead acts to alter sodium balance and calcium-activated cell activities of
vascular smooth muscle. Changes in either or both of these could be expected
to produce changes in blood pressure regulation.
1.3.2 Role of renin-angiotensin in control of blood pressure and fluid balance
One major endogenous factor regulating total peripheral resistance of the
vascular smooth muscle is angiotensin II (All), a small peptide generated in
plasma via the action of a renal hormone, renin. Renin is synthesized and
stored in juxtaglomerular (JG) cells of the kidney and is released when JG
cells receive stimuli indicating a decrease in arterial pressure, as sensed by
cardiovascular baroreceptors and transmitted to the central nervous system
(CNS) with subsequent activation of efferent p-adrenergic signals to the kid-
ney. Changes in the intracellular calcium ion concentration of the JG cell are
thought to be involved in renin release (Churchill, 1985), with an increase in
intracellular [Ca2+] producing a decrease in renin secretion, while a decrease
in intracellular [Ca2+] produces an increase in renin release.
Renin is the first enzyme in a series which splits a small peptide, angio-
tensin I (AI) from angiotensinogen, or renin substrate, a large protein synthe-
sized by liver and found in circulation. AI is converted to All by angiotensin
converting enzyme (ACE), an enzyme found in plasma and lung tissue. All is
degraded to All I and other breakdown products by various proteolytic enzymes.
Renin is cleared from plasma by the liver.
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All acts to increase total peripheral resistance by: (1) direct action on
vascular smooth muscle to increase vasoconstriction (it is 10 to 40 times more
potent than norepinephrine and acts to elevate cytosolic calcium of vascular
smooth muscle to activate the contraction of actin and myosin); and (2) indi-
rectly, by acting on the area postrema of the medulla oblongata to increase the
discharge rate of sympathetic neurons (which increases norepinephrine release,
decreases its reuptake, and increases vascular sensitivity to norepinephrine).
All also influences renal function and overall salt and fluid balance in
several ways: (1) Renal hemodynamics: glomerular filtration rate is altered
by All-related changes in renal blood flow or indirectly by increased norad-
renergic transmission to the kidney resulting from CNS action of AIL (2)
Salt and water metabolism: All-induced changes in renal sympathetic tone alter
reabsorption of sodium and potassium; All stimulates aldosterone secretion
which affects sodium and potassium balance; All may have direct action on the
renal tubules to increase electrolyte and water reabsorption. In addition, All
appears to act directly on the CNS to increase thirst.
The renin-angiotensin system thus has a major influence on regulation of
blood pressure; for this reason, investigators interested in hypertension have
studied the system in detail. Because renal disease may be an important initi-
ating event in subsequent development of hypertension and because lead is an
important renal toxicant, some investigative reports of patients with lead
intoxication have evaluated blood pressure changes and changes in the renin-
angiotensin system. For example, Sandstead et al. (1970) found that dietary
sodium restriction produced smaller increases in plasma renin activity and
aldosterone secretion rates in lead-poisoned men than expected. The mechanism
of action on the renin-aldosterone system was not known. Gonzalez et al.
(1979) studied renin activity, aldosterone, and plasma potassium levels in a
group of lead-toxic patients. The patients had low plasma renin activity in
response to a furosemide challenge (a volume-depleting stimulus) and were
hyperkalemic (evidence that aldosterone levels were low). Bertel et al.,
(1978) presented a clinical case report of reduced beta-adrenoceptor-mediated
function in a lead-toxic man (blood lead >250 pg/dl) with hypertension
(160-170/100-105 mm Hg). Prior to administration of the test dose of isoprena-
line, the patient had high plasma norepinephrine levels and low PRA activity.
The dose of isoprenaline required to increase heart rate 25 beats/min was
15-fold greater than that required in control subjects. The raised plasma
norepinephrine level suggests that reactive sympathoneural activity could cause
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alpha-adrenoceptor-mediated vasoconstriction which contributes to elevated
blood pressure. Lead interference with the receptor-adenylate cyclase system
could reduce beta-adrenoceptor-mediated vasodilatation as well as tachycardia
and renin release. Recently, Campbell et al. (1985) found Pb-related increases
in the concentrations of PRA and angiotensin I in lead-exposed normotensive
men. These changes may be precedent to development of hypertension.
The paucity of experimental data linking lead and changes in the renin-
angiotensin system stimulated most of the following experimental studies,
although many questions remain unanswered.
1.4 Experimental Studies of Lead Effects on Blood Pressure and the
Renin-Angiotensin System.
Several questions can be posed regarding how lead might affect the renin-
angiotensin system, such as:
(1)	Does lead affect sodium handling by the renal tubule?
(2)	Does lead directly affect renin release? If so, is All elevated to
an appropriate level? Do normal homeostatic mechanisms function to
adjust renin levels under conditions of fluid and electrolyte loss?
(3)	Does lead alter renin synthesis (as measured by renal renin content)?
(4)	Does lead affect rate of production of All by altering angiotensin
converting enzyme activity?
(5)	Does lead alter All catabolism?
(6)	Does lead affect renin substrate production?
(7)	Does lead affect renin clearance by the liver?
(8)	Does lead affect vascular reactivity directly?
(9)	Does lead directly affect aldosterone release?
Many of these questions have been addressed by studies discussed below.
1.4.1 Acute In-Vivo Lead Exposure
Lead injected iv in dogs and rats, at doses as low as 0.1 mg/kg (whole
blood lead < 5 |jg/dl and renal lead of 1.2 pg/g) produced over the next several
hours significant increases in plasma renin activity (PRA) and in excretion of
sodium, other cations, and water (Mouw et al., 1978). There was no change in
glomerular filtration rate; therefore, the increased sodium excretion could be
attributed to decreased sodium reabsorption. The mechanism of lead's action on
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tubular reabsorption was not determined but it was suggested that lead could
affect mitochondrial ATP production necessary for active transport processes or
action directly on carrier molecules or enzymes, e.g., Na/K ATPase, specifi-
cally involved in tubular transport. In this report, the mechanism by which
lead increased renin secretion was not determined.
In a subsequent report, Goldman et al. (1981) found that the rise in PRA
after acute lead injection was not due to increased renin secretion in six of
nine dogs; rather, there was elimination of hepatic renin clearance, without
evidence for other interference in liver function. In the remaining three
dogs, renin secretion increased; this was thought to be due to lead activation
of normal mechanisms for renin secretion, although none of the classic pathways
for influencing renin secretion were altered. The authors postulated that lead
might produce alterations in cytosolic calcium concentration in renin-secreting
cells. (Further evidence that cytosolic calcium concentration is indeed
important in renin release has been reviewed in detail by Churchill, 1985.) In
addition, although angiotensin II (All) levels in lead-exposed animals were
elevated because of increased PRA, the All levels were not increased propor-
tionately as much as the PRA, leading to a further suggestion that angio-
tensin-converting enzyme (which converts AI to All) was suppressed or that
All-degrading enzyme was enhanced. The authors noted that multiple actions of
lead on the renin-angiotensin system may help explain confusion about the
ability of lead to cause hypertension. At certain exposure conditions, there
could be elevated PRA without simultaneous inhibition of angiotensin-converting
enzyme, thereby contributing to hypertension, while higher doses or longer ex-
posure might inhibit converting enzyme and thereby cause loss of hypertension.
1.4.2 Chronic Lead Exposure
The literature of experimental findings of lead-induced changes in the
renin-angiotensin system and blood pressure in animals is complicated by
apparently inconsistent results when comparing one study to another. All
studies report changes in the renin-angiotensin system, yet some studies fail
to find an effect on blood pressure and others do report hypertension. Doses
and exposure periods employed vary widely, but in general, hypertension is
observed most consistently with relatively low doses over relatively long
exposure periods. The papers reviewed here make specific mention of lead dose
employed and blood lead concentration achieved (if measured). For comparison
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with human exposure findings, it is helpful to recognize that blood lead
concentrations seldom exceed 40 (jg/dl in the general population.
Perry and Erlanger (1978) found that chronically feeding rats either
cadmium or lead at doses of 0.1, 1.0, or 0.5 ppm produces statistically signi-
ficant increases in systolic blood pressure. The mechanisms for this finding
were not discussed but the implications for human populations exposed to very
low doses of these metals were pointed out. Victery et al. (1982a) reinvesti-
gated the question, using lead doses of 100 and 500 ppm administered in the
drinking water to rats beginning while animals were i_n utero and continuing
through six months of age. At 3h mo of age, the male rats drinking 100 ppm
lead first demonstrated a statistically significant increase in systolic blood
pressure (152 ±3.7 vs. 135 ±5.6 mm Hg); this difference persisted for the
remainder of the experiment. Animals drinking 500 ppm had lower pressures which
were not significantly different from controls. Female rats drinking 100 ppm did
not demonstrate pressure changes. At termination of the experiment PRA was
significantly decreased by 100 ppm lead exposure, but not at 500 ppm. All
values tended to be lower (controls: 22 ± 8 pg/ml, 100 ppm: 13 ± 7, 500 ppm:
10 ± 2). There was a dose-dependent decrease in AII/PRA ratio for lead-exposed
rats. Renal renin was depressed in lead-exposed animals. The hypertension
observed in these animals was not secondary to overt renal disease (as opposed
to an effect on renal cell metabolism), as evidenced by lack of changes in renal
histology and plasma creatinine.
With regard to possible mechanisms of the lead-induced hypertension, the
animals had low-renin hypertension (which is characteristic of 30 percent of
people with hypertension). Thus elevated renin was not responsible for main-
tenance of the hypertension. Volume expansion may be a factor, as suggested by
slight increases in body weight and decreased hematocrit (also possibly related
to lead effects on heme synthesis). There was no change in plasma sodium and
potassium, although more sensitive determinations of fluid balance and exchange-
able sodium were not done. A second potential hypertensive mechanism, increased
vascular responsiveness to catecholamines, was examined and is discussed below.
Victery et al. (1983) examined changes in the renin-angiotensin system of
rats exposed to lead doses of 5, 25, 100, or 500 ppm during gestation until
1 month of age. All had elevated plasma renin activity, while those at 100 and
500 ppm also had increased renal renin concentration. Lead-exposed animals
anesthetized to obtain the blood sample secreted less renin than control
animals. It appears that lead has two chronic effects on renin secretion, one
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inhibitory and one stimulatory; the magnitude of effect on PRA reflects the
dose and timing of the lead exposure as well as the physiological state of the
animal.
In another study, Victery et al. (1982b) reported that rats fed 5 or 25
ppm lead for 5 months (blood lead of 5.6 and 18.2 pg/dl respectively) did not
develop hypertension but at 25 ppm had significantly decreased PRA. Both
groups of animals had a decrease in the All to PRA ratio. Thus, lead exposure
at levels generally present in human population caused observable effects in
renin synthesis, and were consistent with either inhibition of conversion of AI
to All or enhanced All catabolism. No measurements of ACE activity were made.
The failure to observe hypertension in these animals may have been due to a
number of factors, but additional studies may be required to verify this
finding.
Iannaccone et al. (1981) administered 50 ppm lead to male rats for 160
days (average blood lead of 38.4 pg/dl) and found a marked increase in arterial
pressure of lead-exposed animals (systolic/diastolic 182 ± 6/138 ± 7 mm Hg)
versus pressures in controls of 128 ± 5/98 ± 3. No measurements of hormone
levels were performed; determination of vascular reactivity in these animals
is discussed below.
Male pigeons fed a diet containing added calcium (100 ppm), magnesium
(30 ppm), lead (0.8 ppm), or cadmium (0.6 ppm) in a 2x4 factorial design for a
six-month period were observed for alterations in aortic blood pressure and
atherosclerotic changes (Revis et al., 1981). Diastolic pressures were 25 mm
Hg higher in pigeons exposed to Mg, Pb, or Cd than in Ca-exposed pigeons.
Systolic pressure was greatest in Cd-exposed birds. Calcium in the diet
resulted in lowered systolic pressures in animals exposed to combinations of
other metals (presumably by decreasing their gastrointestinal absorption).
Similarly, there was a decrease in number and size of aortic plaques in presence
of calcium and an increase with lead exposure.
Keiser et al. (1983b) tested lead-exposed rats (500 or 1000 ppm for 3-4
mo, blood leads of 41 and 55 pg/dl) for the ability of the liver to clear
exogenous renin and a test substance (sulfobromophthalein) following nephrec-
tomy and found no difference from control clearance times. Thus, elevations in
plasma renin observed in chronically exposed animals must be the result of
increased renin secretion. However, the finding of decreased renin activity
after some long-term exposure periods (see above) illustrates that lead must
also act in an inhibitory way to decrease renin secretion and the finding of
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decreased, increased, or no change in renin activity depends on the balance of
the stimulatory and inhibitory input to the juxtaglomerular cells. Angiotensin-
converting enzyme, which was postulated to be low in lead-exposed animals (see
above), was found to be normal in both plasma and lungs.
1.4.3	Renin Secretion by Kidney Slices In-Vitro
The effects of renin-secretion stimuli on the ability of kidney slices to
secrete renin i_n vitro either after chronic i_n vivo exposure or i_n vitro expo-
sure to lead have been studied by several investigators. Keiser et al. (1983a)
reported that rabbit kidney cortex slices exposed to 10-5 or 10-6 M lead
secreted significantly less renin than controls. Slices obtained from lead-
exposed rabbits (500 or 1000 ppm for 7 wk, with blood lead levels of 66 and 109
jjg/dl respectively) secreted significantly more renin j_n vitro than controls.
They postulated that lead could compete with Ca2+ for influx into juxtaglo-
merular cells and thereby stimulate renin release. Responsiveness to a beta-
adrenergic stimulus was less in the higher-dose slices. Since p-adrenergic
stimuli are thought to act via reduction of intracellular [Ca2+] (by increased
Ca efflux or intracellular sequestration), it was proposed that lead may inter-
fere with these calcium fluxes and interfere with the response to £ agonists.
Meredith et al. (1985) found somewhat contradictory results, with lead
able to provoke renin secretion from rabbit kidneys both i_n vivo and i_n vitro
(at comparable dose levels to that used by Keiser). Calcium channel blockers
attenuated this response. These authors propose that lead is able to act at
the cellular level to stimulate renin secretion. Since most experimental
evidence suggests that increased intracellular calcium decreases renin release,
whereas calcium efflux stimulates renin secretion, the authors further postu-
late that lead uptake by the juxtaglomerular cells promotes calcium efflux
which then leads to an increase in renin secretion.
1.4.4	Effects of Lead on Vascular Reactivity
Piccinini et al. (1977) and Ravalli et al. (1977) studied the effects of
lead on calcium exchanges in the isolated rat tail artery; lead in concentra-
tions of up to 15 |jmol i_n vitro produced contractions which required the pre-
sence of calcium in the perfusion solution. Therefore, calcium influx was not
affected by lead. The fact that tissue calcium content was increased is
compatible with the sites of lead action at the cell membrane; lead inhibits
calcium extrusion, and at intracellular stores, lead decreases calcium-binding
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capacity. Both processes produce an increase in intracellular exchangeable
calcium.
Tail arteries obtained from the hypertensive rats in the study performed
by Victery et al. showed an increased maximal contractile force when tested i_n
vitro with the alpha-adrenergic agents norepinephrine and methoxamine (Webb et
al., 1981). This finding is apparently related to an increase in the intra-
cellular pool of activator calcium in the smooth muscle cells in the artery.
This change may also be responsible for decreased relaxation of the muscle
after induced contractions.
In vivo tests of cardiovascular reactivity in rats exposed to 50 ppm lead
(blood lead 38.4 ±3.6 pg/dl) for 160 days were performed by Iannaccone et al.
(1981). Systolic and diastolic blood pressure readings obtained under anesthe-
sia were 182 ± 6/138 ± 7 mm Hg for lead-exposed rats versus 128 ± 5/98 ± 3 for
controls. Humoral agents, norepinephrine and angiotensin II (but not bradykinin
and angiotensin I), produced significant increases in systolic and diastolic
pressure. This suggests there is decreased conversion of Al to AIL At high
doses, epinephrine produced an equal increase in pressure in lead-exposed and
control animals; at lower doses, only slight increases in mean arterial pressure
were observed. Bilateral carotid artery occlusion under conditions of autonomic
blockade produced a two fold greater decrease in blood pressure and heart rate
in lead-exposed rats. The data suggest that the lead-related increase in
arterial pressure is due at least in part to greater sympathetic tone, with the
metal affecting neural control of blood pressure.
1.4.5 Lead Effects on Cardiac Muscle
Lead has been hypothesized to contribute to cardiomyopathy (Asokan, 1974)
and to have cardiotoxic properties. Rats fed 1 percent lead acetate for 6
weeks (with blood lead of 112 ± 5 jjg/dl) had structural changes in the myocar-
dium. These included myofibrillar fragmentation and separation with edema
fluid, dilation of the sarcoplasmic reticulum, and mitochondrial swelling.
These changes were observed before any measured changes in myocardial electro-
lyte concentrations.
Williams et al. (1977a,b) exposed young rats to lead (2000 ppm; blood lead
at 21 days of age was 43 pg/dl but was not different from controls at 170-200
days) via maternal milk, from birth to 21 days of age. Animals were studied
for cardiovascular response to norepinephrine at 170-200 days of age. There
were no differences in the blood pressure increase to norepinephrine but there
16

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was a five- to ten-fold increase in cardiac arrhythymias in lead-exposed
animals. There were no differences in the basal or norepinephrine-stimulated
cyclic AMP levels in cardiac tissue.
In a subsequent study (Hejtmancik and Williams, 1979), it was reported
that only part of the arrhythmogenic activity of norepinephrine in lead-exposed
rats was due to reflex vagal stimulation; there was also a direct cardiac
effect, probably at the alpha receptor level. Lead appeared to have no effect
on beta receptors.
Kopp et al. (1978) worked out an j_n vitro system for monitoring the
cardiac electrical conduction system, electrocardiogram, and systolic tension,
and were able to demonstrate that i_n vitro lead (3 x 10-2 mM) or cadmium
(3 x 10-2 mM) depressed systolic tension and prolonged the PR interval of the
ECG. Both ions increased conduction times in the His bundle electrograms but
conduction blocks occurred at different sites (atrioventricular node for
cadmium and distal to the His-Purkinje cell junction for lead).
In a subsequent paper, Kopp and Barany (1980) found that cadmium or lead
added to heart tissue perfused in vitro (3 x 10-3 mM and 3 x 10-4 mM, respec-
tively) inhibited the positive inotropic activation of the heart by calcium and
isoproterenol, and the concomitant increase in phosphorylation of cardioregula-
tory proteins. There was no effect of lead or cadmium on the positive chrono-
tropic effects of the beta-adrenergic agonist.
Hearts obtained from rats exposed to low levels of cadmium and/or lead
(5 ppm) for 20 months were found to have similar changes in the heart's elec-
trical conduction system (Kopp et al., 1980) with significant prolongation of
the P-R interval. In lead-fed animals, this was due to increased conduction
time through the His-Purkinje cell system.
Williams et al. (1983) suggested that much of the negative inotropic
effect of lead on cardiac tissue and ECG abnormalities can be related to lead's
interference with calcium ion availability and/or membrane translocation. In
addition, even those lead exposure-related effects that appear to occur through
autonomic nerves may be understood in terms of effects on calcium ion which is
required for neurotransmitter release.
Evis et al. (1985) studied the effects of chronic low lead treatment (5
and 25 ppm, with blood leads < 10 pg/dl) and hypertension (spontaneously
hypertensive rats) on blood pressure and the severity of cardiac arrhythmias in
rats. The animals were studied up to 16 months of age and the authors reported
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that there were no consistent lead-related effects on ischemia-induced cardiac
arrhythmias, blood pressure or P-R interval in the electrocardiogram.
1.5 Summary of Lead-related Effects on the Cardiovascular System
To briefly summarize, lead can directly inhibit renal tubule reabsorption
of sodium, probably via action on the sodium/potassium ATPase. Na/K ATPase
inhibition may occur in other cell types as well. Some volume depletion may
occur which could contribute to elevation in plasma renin activity. The lead
effect on PRA can be stimulatory, inhibitory, or without effect, depending on
the length of exposure and the exposure level. Lead exposure reduces the
increase in PRA which occurs with noradrenergic stimulation. It is not likely
that the chronic increase in PRA is due to decreased hepatic clearance of
renin. Depending on the length and dose of lead exposure, renal renin concen-
tration is elevated followed by decreased concentrations. In response to
elevations in PRA, there are increased levels of All, but the levels are
inappropriately low; this does not appear to be due to a lead-related decrease
in ACE, but rather to increased All catabolism. Aldosterone levels are also
inappropriately low, possibly due to a lead-related defect on calcium ion-
dependent release of aldosterone. Vascular smooth muscle isolated from lead-
exposed animals has increased reactivity to noradrenergic stimuli, probably due
to an increase in intracellular calcium ions. There appears to be increased
sympathetic activity in lead-exposed animals. Cardiac arrhythmias are usually
observed to be more frequent in lead-exposed animals.
Although the exact mechanisms involved in lead-induced changes in renin
secretion rate have not been examined, it is likely that lead could be affec-
ting the cytosolic free calcium ion of the juxtaglomerular cells. When there
is a stimulation of renin release, there is presumably a decrease in intracell-
ular [Ca2+] due to lead blockage of calcium entry through voltage-sensitive
calcium channels. After lead enters the juxtaglomerular cells, lead could
enhance or block calcium exit via Na/Ca exchange pumps or increase or decrease
the intracellular sequestration of calcium in storage compartments. It is not
yet clear whether lead stimulates or antagonizes calcium fluxes that occur in
the JG cells; therefore it is not possible to state definitely which of these
possibilities is more correct. Renin release in response to adrenergic stimuli
binding to receptor-operated calcium channels appears to be inhibited. The
reasons for this are not known, but lead may decrease the number of receptor
sites or change the intracellular calcium response which is normally elicited
18

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when these channels are stimulated. For example, if intracellular free calcium
ion levels are already elevated and there were to be a smaller decrease in
[Ca2+] than normal due to blocking of calcium efflux via the Na/Ca exchange
pumps or lowered pumping into intracellular stores, renin secretion would be
less under conditions of adrenergic stimulation.
The changes in vascular reactivity which have been reported in animals
chronically exposed to lead are probably the key finding which can lead to an
understanding of how lead can contribute to development of hypertension. The
vascular smooth muscle changes are necessary and sufficient in themselves to
account for the increase in blood pressure and the fact that these changes are
observed in animals exposed to relatively low lead levels makes it increasingly
important to evaluate these findings in additional experimental studies. There
may be additional changes (not yet evaluated) in the entire sympathetic neural
control of vascular tone which acts to amplify the contractile response to any
endogenous vasoconstrictor substance.
Two authors (Audesirk, 1985, and Pounds, 1984) have recently reviewed
experimental evidence on the influence of lead on calcium movements at the
subcellular level in a variety of cell types including neurons, neuromuscular
synapses, and hepatocytes. The reader should consult these reviews for experi-
mental documentation of the postulated changes in calcium-activated systems.
Lead may interact with any process normally influenced by calcium ions and,
depending on the system, lead may act as a calcium antagonist or as an agonist.
In addition, lead interferes with the function of many proteins, especially
enzymes such as Na/K ATPase and the mitochondrial respiratory enzymes. These
interactions may influence calcium ion concentrations and movements. If lead
interferes with calcium ion movement through calcium channels, either by
blocking entry or blocking efflux, there will be a decrease or an increase in
cytosolic free calcium ion. Lead may alter the distribution and uptake rates
of calcium ion in cell storage sites with the result that mitochondrial and
endoplasmic reticulum levels can be increased or decreased; this in turn would
affect cytosolic free calcium levels. Lead binds to calcium-binding sites on
calcium regulatory proteins (calmodulin, in particular [Cheung, 1984]) and
thereby can alter enzyme systems such as Ca-specific ATPase, which would then
alter calcium efflux from the cytosol.
This review has discussed some of the major experimental data concerning
lead-related changes in blood-pressure regulatory systems. Further research
efforts are necessary to evaluate more fully cellular mechanisms by which lead
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exposure produces its effects. Most data, however, are consistent with an
effect of lead (even at very low levels) on the renin-angiotensin system and on
vascular reactivity. Both of these effects are probably related to lead-
induced changes in intracellular free calcium ion concentration, in juxta-
glomerular cells of the kidney, in neural centers controlling blood pressure,
and in cardiac and vascular smooth muscle. The result is altered renin and All
levels, and increased responsiveness of the vascular smooth muscle to vaso-
constricting stimuli. As long as these factors are stimulated by lead exposure,
it would be logical to expect that increased blood pressure would result.
However, there appear to be other effects of lead, particularly at higher doses
for longer exposure periods, at which blood pressure is no longer elevated.
This may reflect more extensive deterioration of the hemeostatic controls of
blood pressure so that further increases in pressure do not occur. Additional
experimental studies will be necessary to explain the so-called biphasic
dose-response curve for the lead-related changes in blood pressure, which
appear to parallel those observed in humans as delineated by epidemiologic
studies of blood-lead blood-pressure relationships discussed earlier.
2.0	Lead Effects on Growth and Stature
The effects of lead exposure early in development on physical growth and
stature have recently become a matter of increasing interest and potential
concern, in light of certain newly published epidemiologic observations. The
new epidemiologic results, coupled with earlier reports of findings from human
and experimental animal studies, point toward retardation or "stunting" of
physical growth or stature due to lead exposure during early prenatal or post-
natal development, including at relatively low lead exposure levels encountered
in the general population.
2.1	Epidemiologic Observations
Among the earliest indications of lead effects on stature are observations
reported by Nye (1929) regarding "runting," along with squint and foot drop, as
physical signs characteristic of overtly lead-poisoned Australian children seen
in the 1920's. Remarkably, since then very few systematic evaluations of
possible stunting of physical growth have been included among the health end-
points examined in the numerous epidemiologic studies of lead effects on early
human development.
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In one such study, Mooty et al. (1975) obtained physical measurements
(weight, height) for children (2-4 years old) chosen according to low (x ±
S.D.= 20.4 ±4.3 pg/dl) and high (56.9 ± 8.3 pg/dl) blood lead levels. The 21
high-lead children, with blood lead levels in the range 50-80 pg/dl, were both
shorter (x = 32.1 percentile on Stuart's Boston Growth Charts) and weighed less
(x = 43.8 percentile) than the 26 low-lead children with blood leads of 10-25
(jg/dl (height = 41.1 percentile, weight = 48.7 percentile). The average age
for the control subjects was 34 months and was comprised of 12 Puerto Rican, 8
Black and 5 Caucasian children, whereas the high-lead group's mean age was 33
mos. and was comprised of 4 Puerto Rican, 17 Black and no Caucasian children.
Because of the slightly younger age and lack of Caucasian children in the
high-lead group (as well as other differences, e.g., dietary intakes), it is
not possible to clearly determine the relative contribution of lead to the
observed smaller stature of the high lead subjects versus other factors.
In a later study, Johnson and Tenuta (1979) studied the growth and diets
of 43 low-income Milwaukee children (aged 1 to 6 yrs) in relation to their
blood lead levels. Children with low (12-29 pg/dl; N = 15), moderate (30-49
(jg/dl; N = 16) and high (50-67 [jg/dl; N = 12) blood lead levels had average
daily calcium intakes of 615, 593, and 463 mg, respectively. Also, there was a
relative decrease (p <0.075) in individual height percentile with increasing
blood lead level (the high blood lead children had means of 25.7 percentile for
height and 42.2 percentile for weight; no specific data for other lead groups
reported), and higher incidence of pica (eating of plaster and paint) on the
part of the children with blood leads ranging from 30 to 67 pg/dl. Unfortu-
nately, the specific racial composition and age of the different blood lead
groups were not reported, making it impossible to determine the relative con-
tribution of such factors (or the differences in calcium intake or other die-
tary factors) versus lead to the observed smaller stature among the high lead
children.
In another study, Routh et al. (1979) examined a sample of nonurban chil-
dren (N = 100; mainly from lower socio-economic families in NC) with develop-
mental and learning disabilities for previously undiagnosed lead intoxication.
One child with "moderately" elevated blood lead (according to the then-existing
CDC classification, 50-79 |jg/dl) and nine with "minimal" elevations (30-49
pg/dl) were identified. Of these 10 children, seven were microencephalic
(defined as head circumferences at or below the third percentile for the
child's age on standard growth charts). This was a markedly greater proportion
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of microencephaly (17 of 62; 25 percent) than that seen among the remaining
children with blood leads below 29 pg/dl. Most of the microencephaly syndrome
children were Black. Five of the elevated blood-lead children also showed more
general growth retardation, in that their height, weight, or both were at or
below the third percentile for age and sex. These results, as those from the
previously discussed studies, are highly suggestive of possible stunting of
growth due to lead exposure early in development resulting in blood lead levels
generally above 30 (jg/dl. However, again it is not possible to clearly sepa-
rate the relative contribution of lead from other factors (racial, dietary,
etc.) that may have affected growth of the children studied by Routh et al.
(1979).
Much stronger evidence for lead exposure producing retardation of growth
and decreased stature has more recently emerged in the 1980's from both animal
toxicology studies (discussed below) and evaluation of larger scale epidemio-
logic data sets. In regard to the latter, Schwartz et al. (1986) have reported
results of analyses of data from the NHANES II study described earlier in
relation to evaluation of blood-lead blood-pressure relationships. More
specifically, Schwartz et al. (1986) analyzed results for anthropometric
measurements, as well as numerous other factors (age, race, sex, dietary, etc.)
likely to affect rates of growth and development, among the NHANES II children.
Linear regressions of adjusted data from 2695 children (aged 7 yrs or
younger) indicated that 9 percent of the variance in height, 72 percent of the
variance in weight, and 58 percent of the variance in chest circumference were
explained by the following five variables: age, race, sex, blood lead, total
calories or protein, and hematocrit or transferrin saturation. The step-wise
multiple regression analyses further indicated that blood lead levels were a
statistically significant predictor of childrens's height (p <0.0001), weight
(p <0.001) and chest circumference (p <0.026), after controlling for age in
months, race, sex and nutritional covariates. The strongest relationship was
found between blood lead and height, with threshold regressions indicating no
evident threshold for the relationship down to the lowest observed blood lead
level of 4 pg/dl. At their average age (59 mo.), the mean blood lead level of
the children appears to be associated with a reduction of about 1.5 percent
below the height expected if their blood lead level had been zero. Similarly,
the relative impacts on weight and chest circumference were of the same magni-
tude.
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Overall, the above findings of Schwartz et al. (1986) appear to be highly
credible, being based on well-conducted statistical analyses of a large-scale
national survey data set (which was subjected to rigorous quality assurance
procedures) and having taken into account numerous potentially confounding
variables. Other recent results, newly emerging from independent, well-con-
ducted prospective studies of prenatal and early postnatal lead exposure
effects on human development, also appear to substantiate the likelihood of
lead retarding early growth. For example; Dietrich et al. (1986) report that
prenatal maternal blood lead levels and early postnatal (10-day) blood lead
levels were negatively correlated with birth weight (p <0.001) and gestational
age (p <0.05) for 185 infants from low socio-economic inner-city Cincinnati
families. The plausibility of reported epidemiologic findings of associations
between early lead exposure and retardation of growth reflecting causal rela-
tionship is supported by some limited animal toxicology results concisely
discussed below.
2.2 Animal Toxicology Studies
Numerous experimental animal studies on the neurobehavioral or other
effects of lead exposure early in development have taken into account lead
effects on maternal nutrition or postnatal growth of exposed animals as possi-
ble confounding factors. Few, however, have systematically evaluated lead
effects in growth per se as one of the major health endpoints measured.
One study, by Grant et al. (1980), does provide detailed experimental data
relating external lead exposure doses to consequent blood lead levels and
growth rate measured in terms of both weight and length. Continuous prenatal
and postnatal exposures to lead were accomplished via lead adulteration of the
drinking water: (1) of dams prior to conception, throughout pregnancy, and
nursing; and (2) of the drinking water consumed post-weaning by their offspring
through 180 days (6 mo.). Females from lead exposure groups averaging blood
lead levels in the range 18-48 ng/dl were significantly shorter in crown-to-
rump length from postnatal days 7 to 180, but lead-exposed males exhibited a
transient retardation of growth and were not significantly different in length
than control animals by the end of the 180 day observation period. Decreased
body weight, (with no decrease in food consumption per unit of body weight) was
found in animals with blood leads of 40-60 (jg/dl, whereas deficits in rate of
neurobehavioral development and indications of specific organic or functional
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alterations (Fowler et al., 1980) were observed at blood lead levels in the
range of 20-40 pg/dl.
The mechanisms by which lead exposure early in development may affect
growth remain to be more fully delineated. One of the more likely possibili-
ties is an effect of lead on neural pathways in the brain regulating neuro-
endocrine functions mediated by the pituitary gland and/or direct effects of
lead on other developing endocrine organs, which may in turn alter feedback
mechanisms resulting in disruption of normal CNS neuroendocrine control. In
that regard, Petrusz et al., (1979) have reported effects of early postnatal
lead exposure on pituitary and serum gonadotropins in neonatal rats - effects
which might be part of a complex chain of neuroendocrine alterations that could
result in growth disturbances. Similarly, other reports of lead effects on
neuroendocrine central mechanisms in animals (e.g., Govani et al., 1980) and
man (e.g., Sanstead et al., 1969, 1970) provide additional support for possible
involvement of lead effects on endocrine function that could result in growth
retardation. Of particular interest are reported observations on somatomedin
activity before and after chelation of lead-intoxicated children (Rohn, 1982).
2. 3 Summary and Conclusions Regarding Lead Effects on Growth and Stature
The earlier epidemiologic studies discussed above (Mooty et al., 1975;
Johnson and Tenuta, 1929; Routh et al., 1979) provided suggestive evidence for
lead effects on early growth and stature. However, it is difficult to appor-
tion relative degrees of contribution of lead to observed growth deficits in
comparison to other factors due to the manner in which the data from these
small scale studies were reported. Much stronger evidence has emerged from the
Schwartz et al. (1986) evaluation of the large-scale NHANES II nationwide data
set and some additonal data beginning to emerge from prospective studies, such
as that of Dietrich et al. (1986).
The plausibility that the observed epidemiologic associations between lead
exposure and retarded growth reflect causal relationships is supported by
certain limited parallel experimental toxicology observations in the rat by
Grant et al. (1980), albeit at blood lead levels distinctly higher than the
lower values in the range of blood lead levels of children included in the
Schwartz et al. (1986) analysis. Furthermore, the possibility of lead effects
on neuroendocrine mechanisms mediating lead-induced retardation of growth is
also supported by certain studies, e.g., those of Petrusz et al. (1979) and
others, showing effects of lead in neuroendocrine functions in animals and man.

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Much remains to be done, however, in regard to more fully characterizing
quantitative relationships between lead exposure and growth retardation in
children, as well as determining the specific physiological mechanisms under-
lying such effects.
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REFERENCES
Asokan, S. K. (1974) Experimental lead cardiomyopathy: myocardial structural
changes in rats given small amounts of lead. J. Lab. Clin. Med. 84: 20-25.
Audesirk, G. (1985) Effects of lead exposure on the physiology of neurons.
Prog. Neurobiol. 24: 199-231.
Batuman, V. ; Landy, E. ; Maesaka, J. K. ; Wedeen, R. P. (1983) Contribution of
lead to hypertension with renal impairment. N. Engl. J. Med. 309: 17-21.
Beevers, D. G. ; Erskine, E. ; Robertson, M. ; Beattie, A. D.; Campbell, B. C. ;
Goldberg, A.; Moore, M. R.; Hawthorne, V. M. (1976) Blood-lead and hyper-
tension. Lancet 2(7975): 1-3.
Belknap, E. L. (1936) Clinical studies on lead absorption in the human: III.
blood pressure observations. J. Ind. Hyg. Toxicol. 18: 380-390.
Bertel, 0.; Buhler, F. R.; Ott, J. (1978). Lead-induced hypertension: blunted
beta-adrenoceptor-mediated functions. Br. Med. J. 1(6112): 551.
Blaustein, M. P. (1977) Sodium ions, calcium ions, blood pressure regulation,
and hypertension: a reassessment and a hypothesis. Am. J. Physiol. 232:
C165-C173.
Blaustein, M. P.; Hamlyn, J. M. (1983) Role of a natriuretic factor in
essential hypertension: an hypothesis. In: McCarron, D. A.; Kotchen, T.
A., eds. Nutrition and blood pressure control: current status of dietary
factors and hypertension, a symposium; September 1982; Arlington, VA. Ann.
Intern. Med. 98 (5, pt. 2): 785-792.
Brieger, H.; Rieders, F. (1959) Chronic lead and mercury poisoning: contem-
porary views on ancient occupational diseases. J. Chronic Ois. 9: 177-184.
Campbell, B. C.; Meredith, P. A.; Scott, J. J. C. (1985) Lead exposure and
changes in the renin-angiotensin-aldosterone system in man. Toxicol. Lett.
25: 25-32.
Carafoli, E. ; Penniston, J. T. (1985) The calcium signal. Sci. Am. 253(5):
70-78.
Cheung, W. V. (1984) Calmodulin: its potential role in cell proliferation and
heavy metal toxicity. Fed. Proc. Fed. Am. Soc. Exp. Biol. 43: 2995-2999.
Churchill, P. C. (1985) Second messengers in renin secretion. Am. J. Physiol.
249 (2, pt. 2) F175-F184.
Cramer, K.; Dahlberg, L. (1966) Incidence of hypertension among lead workers: a
follow-up study based on regular control over 20 years. Br. J. Ind. Med.
23: 101-104.
26

-------
PRELIMINARY DRAFT
Dietrich, K. N. ; Krafft, K. M. ; Shukla, R.; Bornschein, R. L. ; Succop, P. A.
(1986) The neurobehavioral effects of prenatal and early postnatal lead
exposure. In: Schroeder, S. R., ed. Toxic substances and mental
retardation: neurobehavioral toxicology and teratology. Washington, DC:
AAMD monograph series; in press.
Dingwal1-Fordyce, I.; Lane, R. £. (1963) A follow-up study of lead workers. Br.
J. Ind. Med. 20: 313-315.
Emmerson, B. T. (1963) Chronic lead nephropathy: the diagnostic use of calcium
EDTA and the association with gout. Australas. Ann. Med. 12: 310-324.
Evis, M. J.; Kane, K. A.; Moore, M. R. ; Parratt, J. R. (1985) The effects of
chronic low lead treatment and hypertension on the severity of cardiac
arrhythmias induced by coronary artery ligation in anesthetized rats.
Toxicol. Appl. Pharmacol. 80: 235-242.
Favalli, L. ; Chiari, M. C. ; Piccinini, F. ; Rozza, A. (1977) Experimental
investigations on the contraction induced by lead in arterial smooth
muscle. Acta Pharmacol. Toxicol. 41: 412-420.
Fouts, P. J.; Page, I. H. (1942) The effect of chronic lead poisoning on
arterial blood pressure in dogs. Am. Heart J. 24: 329-331.
Fowler, B. A.; Kimmel, C. A.; Woods, J. S.; McConnel, E. E.; Grant, L. D.
(1980) Chronic low level lead toxicity in the rat. III. An integrated
assessment of long term toxicity with special reference to the kidney.
Toxicol. Appl. Pharmacol. 56: 59-77.
Freeman, R. (1965) Reversible myocarditis due to chronic lead poisoning in
childhood. Arch. Dis. Child. 40: 389-393.
Frohlich, E. D. (1983) Mechanisms contributing to high blood pressure. In:
McCarron, D. A.; Kotchen, T. A., eds. Nutrition and blood pressure
control: current status of dietary factors and hypertension, a symposium;
September 1982; Arlington, VA. Ann. Intern. Med. 98 (5, pt. 2): 709-714.
Goldman, J. M.; Vander, A. J.; Mouw, D. R.; Keiser, J.; Nicholls, M. G. (1981)
Multiple short-term effects of lead on the renin-angiotensin system. J.
Lab. Clin. Med. 97: 251-263.
Gonzalez, J. J.; Werk, E. E., Jr.; Trasher, K. ; Behar, R.; Loadholt, C. B.
(1979) Renin aldosterone system and potassium levels in chronic lead
intoxication. Sov. Med. J. 72: 433-437.
Govoni, S. ; Lucchi, L.; Battaini, F.; et al. (1980) Effect of chronic lead
treatment affects dopaminergic control of prolactin secretion in rat
pituitary. Toxicol. Letters 20: 237-241.
Grant, L. D. ; Kimmel, C. A.; West, G. L. ; Marti nez-Vargas, C. M. ; Howard,
J. L. (1980) Chronic low-level lead toxicity in the rat: II. effects on
postnatal physical and behavioral development. Toxicol. App. Pharmacol.
56: 42-58.
27

-------
PRELIMINARY DRAFT
Harlan, W. R.; Landis, J. R.; Schmouder, R. L. ; Goldstein, N. G.; Harlan, L. C.
(1985) Blood lead and blood pressure: relationship in the adolescent and
adult US population. JAMA J. Am. Med. Assoc. 253: 530-534.
Hejtmancik, M. R., Jr.; Williams, B. J. (1979) Effect of chronic lead exposure
on the direct and indirect components of the cardiac response to
norepinephrine. Toxicol. Appl. Pharmacol. 51: 239-245.
Iannoccone, A.; Carmignani, M. ; Boscolo,	P. (1981) Reattivita cardiovascolare
nel ratto dopo cronica esposizione a	cadmio o piombo [Cardiovascular reac-
tivity in the rat following chronic	exposure to cadmium and lead]. Ann.
1st. Super. Sanita 17: 655-660.
Johnson, N. E. ; Tenuta, K. (1979) Diets and lead blood levels of children who
practice pica. Environ. Res. 18: 369-376.
Kaplan, N. M. (1983) Hypertension: prevalence, risks, and effect of therapy.
In: McCarron, D. A.; Kotchen, T. A., eds. Nutrition and blood pressure
control: current status of dietary factors and hypertension, a symposium;
September 1982; Arlington, VA. Ann Intern. Med. 98 (5, pt. 2): 705-709.
Keiser, J. A.; Vander, A. J.; Germain, C. L. (1983a) Effects of lead on the
secretion and disappearance of renin in rabbits. Toxicol. Appl. Pharmacol.
69: 117-126.
Keiser, J. A.; Vander, A. J.; Germain, C. L. (1983b) Clearance of renin in
unanesthetized rats: effects of chronic lead exposure. Toxicol. Appl.
Pharmacol. 69: 127-137.
Khera, A. K. ; Wibberley, D. G. ; Edwards, K. W.; Waldron, H. A. (1980) Cadmium
and lead levels in blood and urine in a series of cardiovascular and
normotensive patients. Intern. J. Environ. Studies 14: 309-312.
Kline, T. S. (1960) Myocardial changes in lead poisoning. Am. J. Dis. Child.
99: 48-54.
Kopp, S. J.; Barany, M. (1980) Influence of isoproterenol and calcium on
cadmium- or lead-induced negative inotropy related to cardiac myofibrillar
protein phosphorylations in perfused rat heart. Toxicol. Appl. Pharmacol.
55: 8-17.
Kopp, S. J.; Glonek, T.; Erlanger, M.; Perry, E. F.; Perry, H. M., Jr.; Barany,
M. (1980) Cadmium and lead effects on myocardial function and metabolism.
J. Environ. Pathol. Toxicol. 4: 205-227.
Kopp, S. J.; Baker, J. C. ; D'Agrosa, L. S.; Hawley, P. L. (1978) Simultaneous
recording of His bundle electrogram, electrocardiogram, and systolic
tension from intact modified Langendorff rat heart preparations I: effects
of perfusion time, cadmium, and lead. Toxicol. Appl. Pharmacol. 46:
475-487.
Kosmider, S.; Petelenz, T. (1962) Zmiany elektrokardiograficzne u starszych
osob z przewleklym zawodowym zatruciem olowiem [Electrocardiographic
changes in elderly patients with chronic professional lead poisoning].
Pol. Arch. Med. Wewn. 32: 437-442.
28

-------
PRELIMINARY DRAFT
Kromhout, D. ; Wibowo, A. A. E. ; Herber, R. F. M. ; Dalderup, L. M. ; Heerdink,
H.; Coulander, C. de L. ; Zielhuis, R. L. (1985) Trace metals and coronary
heart disease risk indicators in 152 elderly men (the Zutphen study). Am.
J. Epidemiol. 122: 378*385.
Kromhout, D.; Couland, C. L. (1984) Trace metals and CHD risk indicators in 152
elderly men (the Zutphen study). Eur. Heart J. 5(abstr. suppl. 1): 101.
Legge, T. M. (1901) Industrial lead poisoning. J. Hyg. 1: 96-108.
Lorimer, G. (1886) Saturnine gout, and its distinguishing marks. Br. Med. J.
2(1334): 163.
Malcolm, D. (1971) Prevention of long-term sequelae following the absorption of
lead. Arch. Environ. Health 23: 292-298.
Mayers, M. R. (1947) Industrial exposure to lead. Occup. Med. 3: 77-83.
McCarron, D. A.; Kotchen, T. A., eds. (1983) Nutrition and blood pressure
control: current status of dietary factors and hypertension, a symposium;
September 1982; Arlington, VA. Ann. Intern. Med. 98 (5, pt. 2).
McGee, D.; Gordon, T. (1976) The results of the Framingham Study applied to
four other U.S.-based epidemiologic studies of coronary heart disease:
section 31. In: Kannel, W. B. ; Gordon, T. , eds. The Framingham Study: an
epidemiological investigation of cardiovascular disease. Washington, DC:
U.S. Department of Health, Education, and Welfare, National Institutes of
Health; DHEW publication no. (NIH) 76-1083. Available from GPO,
Washington, DC; S/N 017-040-00396-0.
Meredith, P. A.; Campbell, C. B. ; Blower, A.; Derkx, F. H. M.; Reid, J. L.
(1985) The effects of lead on the renin-angiotensin system. Xenobiotica
15: 521-528.
Mooty, J; Ferrand, C. F. ; Harris, P. (1975) Relationship of diet to lead
poisoning in children. Pediatrics 55: 636-.
Moreau, T. ; Orssaud, G.; Juguet, B.; Busquet, G. (1982) Plombemie et pression
arterielle: premiers resultats d'une enquete transversale de 431 sujets de
sexe masculin [Blood lead levels and arterial pressure: initial results of
a cross sectional study of 431 male subjects] [letter]. Rev. Epidemol.
Sante Publique 30: 395-397.
Morgan, J. M. (1976) Hyperkalemia and acidosis in lead nephropathy. South. Med.
J. 69: 881-886.
Mouw, 0. R.; Vander, A. J.; Cox, J.; Fleischer, N. (1978) Acute effects of lead
on renal electrolyte excretion and plasma renin activity. Toxicol. Appl.
Pharmacol. 46: 435-447.
Myerson, R. M.; Eisenhauer, J. H. (1963) Atrioventricular conduction defects in
lead poisoning. Am. J. Cardiol. 11: 409-412.
Nye, L. J- J- (1929) An investigation of the extraordinary incidence of chronic
nephritis in young people in Queensland. Med. J. Aust. 2: 145-159.
29

-------
PRELIMINARY DRAFT
Oliver, T. (1891) Lead poisoning in its acute and chronic forms. London, United
Kingdom: Young J. Pentland.
Perry, H. M., Jr.; Erlanger, M. W. (1978) Pressor effects of chronically
feeding cadmium and lead together. In: Hemphill, D. D., ed. Trace sub-
stances in environmental health-XII: [proceedings of University of
Missouri's 12th annual conference on trace substances in environmental
health]; June; Columbia, MO. Columbia, MO: University of
Missouri-Columbia; pp. 268-275.
Petrusz, P.; Weaver, C. M. ; Grant, L. D. ; Mushak, P.; Krigman, M. R.
(1979) Lead poisoning and reproduction: effects on pituitary and serum
gonadotropins in neonatal rats. Environ. Res. 19: 383-391.
piccinini, F.; Favalli, L. ; Chiari, M. C. (1977) Experimental investigations on
the contraction induced by lead in arterial smooth muscle. Toxicology
8: 43-51.
pirkle, J. L. ; Schwartz, J.; Landis, J. R.; Harlan, W. R. (1985) The relation-
ship between blood lead levels and blood pressure and its cardiovascular
risk implications. Am. J. Epidemiol. 121: 246-258.
Pocock, S. J.; Shaper, A. G. ; Ashby, D. ; Delves, T. ; Whitehead, T. P. (1984)
Blood lead concentration, blood pressure, and renal function. Br. Med. J.
289: 872-874.
Pocock, S. J.; Shaper, A. G.; Ashby, D.; Delves, T. (1985) Blood lead and blood
pressure in middle-aged men. In: Lekkas, T. D., ed. International
conference: heavy metals in the environment: v. 1; September; Athens,
Greece. Edinburgh, United Kingdom: CEP Consultants, Ltd; pp. 303-305.
pooling Project Research Group. (1978) Relationship of blood pressure, serum
cholesterol, smoking habit, relative weight and ECG abnormalities to
incidence of major coronary events: final report of the pooling project.
J. Chronic Dis. 31: 201-306.
postnov, Y. V.; Orlov, S. N. (1985) Ion transport across plasma membrane in
primary hypertension. Physiol. Rev. 65: 904-945.
pounds, J. G. (1984) Effect of lead intoxication on calcium homeostasis and
calcium-mediated cell function: a review. Neurotoxicology 5: 295-332.
Ramirez-Cervantes, B.; Embree, J. W.; Hine, C. H. ; Nelson, K. M.; Varner, M.
0.; Putnam, R. D. (1978) Health assessment of employees with different
body burdens of lead. J0M J. Occup. Med. 20: 610-617.
Pasmussen, H. (1983) Cellular calcium metabolism. Ann. Intern. Med. 98:
809-816.
Revis. N. W. ; Zinmeister, A. R.; Bull, R. (1981) Atherosclerosis and hyperten-
sion induction by lead and cadmium ions: an effect prevented by calcium
ion. Proc. Natl. Acad. Sci. U.S.A. 78: 6494-6498.
30

-------
PRELIMINARY DRAFT
Richet, G.; Albahary, C.; Morel-Maroger, L.; Guillaume, P.; Galle, P. (1966)
Les alterations renales dans 23 cas de saturnisme professionnel [Renal
changes in 23 cases of occupational lead poisoning]. Bull. Mem. Soc. Med.
Hop. Paris 117: 441-466.
Rohn, R. D.; Shelton, J. E. ; Hill, J. R. (1982) Somatomedin activity before
and after chelation therapy in lead-intoxicated children. Arch. Environ.
Health 37: 369-373.
Routh, D. K.; Mushak, P.; Boone, L. (1979) A new syndrome of elevated blood
lead and microcephaly. J. Pediatr. Psychol. 4: 67-76.
Sandstead, H. H. ; Michelakis, A. M.; Temple, T. E. (1970) Lead intoxication:
its effects on the renin-aldosterone response to sodium deprivation. Arch.
Environ. Health 20: 356-363.
Sandstead, H. H. ; Orth, D. N.; Abe, K. ; Steil, J. (1970) Lead intoxication:
effect on pituitary and adrenal function in man. Clin. Res. 18: 76.
Sandstead, H. H.; Stant, E. G.; Brill, A. B.; Arias, L. I.; Terry, R. T. (1969)
Lead intoxication and the thyroid. Arch. Intern. Med. 123: 632-635.
Schwartz, J. (1985a) Evidence for a blood lead-blood pressure relationship
[memorandum to the Clean Air Science Advisory Committee]. Washington, DC:
U.S. Environmental Protection Agency, Office of Policy Analysis. Available
for inspection at: U.S. Environmental Protection Agency, Central Docket
Section, Washington, DC; docket no. ECAO-CD-81-2 IIA.F.60.
Schwartz, J. (1985b) Response to Richard Royal 11s questions on the blood
lead-blood pressure relationships in NHANES II [memorandum to Dr. David
Weil]. Washington, DC: U.S. Environmental Protection Agency, Office of
Policy Analysis. Available for inspection at: U.S. Environmental Protec-
tion Agency, Central Docket Section, Washington, DC; docket no. ECAO-CD-
81-2 IIA.C.5.
Schwartz, J.; Angle, C.; Pitcher, H. (1986) The relationship between childhood
blood lead and stature. Pediatrics: in press.
Silver, W. ; Rodriguez-Torres, R. (1968) Electrocardiographic studies in
children with lead poisoning. Pediatrics 41: 1124-1127.
Victery, W.; Vander, A. J.; Markel, H.; Katzman, L.; Shulak, J. M.; Germain, C.
(1982a) Lead exposure, begun jjn utero, decreases renin and angiotensin II
in adult rats (41398). Proc. Soc. Exp. Biol. Med. 170: 63-67.
Victery, W.; Vander, A. J.; Shulak, J. M. ; Schoeps, P.; Julius, S. (1982b)
Lead, hypertension, and the renin-angiotensin system in rats. J. Lab.
Clin. Med. 99: 354-362.
Victery, W.; Vander, A. J.; Schoeps, P.; Germain, C. (1983) Plasma renin is
increased in young rats exposed to lead in utero and during nursing
(41517) Proc. Soc. Exp. Biol. Med. 172: 1-7.
Vigdortchik, N. A. (1935) Lead intoxication in the etiology of hypertonia. J.
Ind. Hyg. 17: 1-6.
31

-------
PRELIMINARY DRAFT
Voors, A. W.; Johnson, W. D.; Shuman, M. ?. (1982) Additive statistical effacts
of cadmium and lead on heart-related disease in a North Carolina autopsy
series. Arch. Environ. Health 37: 98-102.
Webb, R. C. ; Winquist, R. J.; Victery, W.; Vander, A. J. (1981) In vivo and i_n
vitro effects of lead on vascular reactivity in rats. Am. J. Physiol. 241:
H2TFH216.
Williams, B. J.; Griffith, W. H.; Albrecht, C. M.; Pirch, J. H. ; Hejtmancik, M.
R., Jr.; Nechay, B. R. (1977a) Cardiac effect of chronic lead poisoning.
In: Brown, S. S., ed. Clinical chemistry and chemical toxicology of
metals. New York, NY: Elsevier/North-Holland Biomedical Press; pp.
127-130.
Williams, B. J.; Griffith, W. H. , III; Albrecht, C. M. ; Pirch, J. H. ;
Hejtmancik, M. R. , Jr. (1977b) Effects of chronic lead treatment on some
cardiovascular responses to norepinephrine in the rat. Toxicol. Appl.
Pharmacol. 40: 407-413.
Williams, B. J.; Hejtmancik, M. R., Jr.; Abreu, M. (1983) Cardiac effects of
lead. Fed. Proc. Fed. Am. Soc. Exp. Biol. 42: 2989-2993.
32

-------
PRELIMINARY DRAFT
Voors, A. W.; Johnson, W. D.; Shuraa.7, M. 5. (1982) Additive statistical effects
of cadmium and lead on heart-re la'ted disease in a North Carolina autopsy
series. Arch. Environ. Health 37: 98-102.
Webb, R. C. ; Winquist, R. J.; Victery, W. ; Vander, A. J. (1981) In vivo and i_n
vitro effects of lead on vascular reactivity in rats. Am. J. Physiol. 241:
H2TFH216.
Williams, B. J.; Griffith, W. H.; Albrecht, C. M.; Pirch, J. H.; Hejtmancik, M.
R. , Jr.; Nechay, B. R. (1977a) Cardiac effect of chronic lead poisoning.
In: Brown, S. S., ed. Clinical chemistry and chemical toxicology of
metals. New York, NY: Elsevier/North-Holland Biomedical Press; pp.
127-130.
Williams, B. J.; Griffith, W. H., III; Albrecht, C. M.; Pirch, J. H.;
Hejtmancik, M. R. , Jr. (1977b) Effects of chronic lead treatment on some
cardiovascular responses to norepinephrine in the rat. Toxicol. Appl.
Pharmacol. 40: 407-413.
Williams, B. J.; Hejtmancik, M. R. , Jr.; Abreu, M. (1983) Cardiac effects of
lead. Fed. Proc. Fed. Am. Soc. Exp. Biol. 42: 2989-2993.
32

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