Lead poisoning in monkeys during pregnancy and lactation

Lead and cadmium in human placentas and maternal and neonatal blood (in a heavily polluted area) measured by graphite furnace atomic absorption spectrometry

OBJECTIVE

To measure the concentrations of the trace elements lead and cadmium in human placenta and in maternal and neonatal (cord) blood. To assess the influence of the strongly polluted environment on the content of metals in tissues and on the permeability of placenta to cadmium and lead. Various methods of mineralisation were tested before analysis.

METHODS

Graphite furnace atomic absorption spectrometry was used for the determination of lead and cadmium. The samples for analysis were prepared by mineralisation under pressure in a Teflon bomb (HNO3, 110 degrees C), by wet ashing under normal pressure (HNO3 + H2O2 for 12 hours), and by microwave digestion in concentrated nitric acid.

RESULTS

In analysed samples the following mean concentrations of cadmium and lead were found: in venous blood Pb = 72.50 ng/ml, Cd = 4.90 ng/ml; in placenta Pb = 0.50 microgram/g, Cd = 0.11 microgram/g; in cord blood Pb = 38.31 ng/ml, Cd = 1.13 ng/ml.

CONCLUSION

High concentrations of lead and cadmium were found in placentas and in maternal blood whereas in neonatal blood there was an increased concentration of lead and only traces of cadmium. It is concluded that the placenta is a better barrier for cadmium than for lead. Among the examined methods of mineralisation, microwave digestion was the best.

Reproductive toxicity of chronic lead exposure in the female cynomolgus monkey

The effect of chronic lead (Pb) exposure on menstrual function and circulating concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol (E2) and progesterone (P4) were studied in female nulliparous cynomolgus monkeys (n = 32). Pb acetate (1500 micrograms/kg BW/day) was administered by capsule to monkeys in teh following groups; exposure from birth to 10 years (lifetime, n = 8), postnatal day 300 to 10 years (adolescent, n = 8), and postnatal days 0 to 400 (childhood, n = 8). Monkeys in the control group (n = 8) received gelatin capsules containing the vehicle only. Reproductive assessment of these monkeys was performed between 9 and 10 years, during which time the blood Pb levels in the lifetime and adolescent exposure groups were approximately 35 micrograms/dL. No overt signs of Pb-induced toxicity were found in the general health or menstrual function. However, Pb treatment significantly suppressed circulating levels of LH (P less than 0.042), FSH (P less than 0.041), and E2 (P less than 0.0001) during the menstrual cycle. Pb treatment had no effect on plasma concentrations of P4. These data indicate that chronic Pb exposure results in subclinical suppression of circulating concentrations LH, FSH, and E2 without producing overt signs of menstrual irregularity.

The comparative developmental neurotoxicity of lead in humans and animals

The effects of lead on neurobehavioral development have been extensively investigated in humans as well as animals. This valuable lode of research findings offers a basis for comparing the developmental neurobehavioral toxicity of lead across species and for assessing the validity of animal models of developmental neurotoxicity. Comparisons of human and animal findings suggest that the greatest qualitative similarities involve relatively complex behavioral processes such as cognition and learning. Quantitative comparisons based on dose-response relationships for these endpoints are difficult to make because the relationships are sometimes nonmonotonic (U-shaped) and because blood lead levels may not be directly comparable between species. However, the lowest levels of exposure at which developmental neurobehavioral effects have been observed are similar: 10-15 micrograms/dl in children, less than 15 micrograms/dl in primates, and less than 20 micrograms/dl in rodents. Although the convergence between animal and human findings for other neurobehavioral endpoints is not as striking, sensory-evoked potentials and communicative processes offer two promising areas for continued investigation and cross-species comparison.

Congenital lead encephalopathy in monkeys

Thirty-one squirrel monkey fetuses were exposed to lead acetate given to the mothers perorally during the last three-fourths or two-thirds of pregnancy. The mean maternal blood lead concentration of the group was 37 micrograms/100 ml and the individual means ranged from 22-82 micrograms/100 ml. Examination of the central nervous system was performed in 15 of the offspring (one abortion, eight stillborns, three neonatal deaths, two killed fetuses and one killed newborn). The mean cerebral weight was reduced for the fetal age (about 10%). Three cerebra were paradoxically overweight for the fetal age as well as for the body weight, probably due to edema. Neurohistology revealed large numbers of characteristic perivascular, petechial hemorrhages in the white matter in six of the fifteen cerebra. In two of these cases, such hemorrhages were also found in the white matter of the cerebellum, brain stem and spinal cord. Examination of four recovered placentas (two after delivery and two at hysterotomies) indicated a lead dose-dependent weight reduction and revealed various pathological lesions. The extensive brain hemorrhages, as well as varying degrees of edema, were seen in stillborns and neonates, while prenatally sacrificed fetuses showed few or no petechial hemorrhages and no signs of edema. It is suggested that lead is involved in the parenchymal growth retardation and the endothelial changes in the prenatal brain, as well as the placental damage, and that prematurity, birth-associated mechanical stress and asphyxia contribute to or precipitate vascular lesions, which may form the basis of acute, or later apparent, neurobehavioral disturbances.