The influence of lead ions on uterine activity in the rat

Prenatal exposure to lead in relation to risk of preterm low birth weight: A matched case-control study in China

We investigated the association between prenatal exposure to lead (Pb) and the risk of preterm low birth weight (PLBW). Pb concentrations in maternal urine collected at birth from 408 subjects (102 cases and 306 matched controls) were analyzed and adjusted by creatinine. The median Pb concentration in the PLBW cases (10.60μgPb/g creatinine) was higher than that of the controls (7.28μgPb/g creatinine). An adjusted odds ratio (OR) of 2.96 (95% CI=1.49-5.87) for PLBW was observed when the highest tertile was compared to the lowest tertile of Pb levels. The association was more pronounced among female infants (adjusted OR=3.67 for the highest tertile; 95% CI=1.35-9.93) than male infants (adjusted OR=1.91 for the highest tertile; 95% CI=0.74-4.95). Our study suggests that prenatal exposure to levels of Pb encountered today in China is associated with an elevated risk of PLBW.

Congener-specific effects of PCBs on contractions of pregnant rat uteri

Both increased and decreased gestation lengths have been reported following exposures to polychlorinated biphenyl (PCB) mixtures and congeners. Because oscillatory uterine contractions are essential for parturition, we hypothesized that the disparate findings on gestation length may be the result of distinct PCB congener-specific actions on oscillatory uterine contractions. This study examined the acute effects of PCB congeners on isometric contractions of isolated pregnant uteri and the structure-activity relationship for individual congeners. After cumulative exposure to individual PCB congeners (0.5 microM to 150 microM), oscillatory contractions were: 1) not altered by 2,4,5,2',4',5'-hexachlorobiphenyl, 3,4,5,3',4'-pentachlorobiphenyl, or 3,4,3',4'-tetrachlorobiphenyl; 2) significantly inhibited by 4-hydroxy-2',4',6'-trichlorobiphenyl; and 3) markedly increased by 2,4,6-trichlorobiphenyl and 2,4,2',4'-tetrachlorobiphenyl, when compared to solvent controls. The uteri were more sensitive to PCB congeners with ortho-substituted light chlorination than those highly chlorinated, or those interacting with the Ah-receptor.

The relationship between cadmium and lead burdens and preterm labor

OBJECTIVE

To study the possible involvement of lead and cadmium in mechanisms of preterm labor.

METHOD

Estimations of lead and cadmium in blood, myometrium and placenta of Swedish and Polish women in preterm labor (n = 17) or delivered at term (n = 13).

RESULT

There was a positive correlation between pregnancy week and content of lead in blood. The mean blood concentration of cadmium in preterm delivered women, 2.0 micrograms/l, was significantly higher than that in term delivered patients, 0.6 microgram/l. In Polish patients the concentration of lead in blood, 37.9 micrograms/l, was higher than that in Swedish women of 11.2 micrograms/l. Cadmium concentrations in myometrium and placenta of Polish women, 0.2 and 0.3 microgram/g, respectively, were also significantly higher than the corresponding concentrations in Swedish patients, 0.04 and 0.1 microgram/g and this difference remained when only nonsmokers were compared. Smokers and nonsmokers did not have significantly different cadmium levels.

CONCLUSION

These results do not support the concept of lead causing increased myometrial activity in preterm labor, but indicate a higher uptake of lead and cadmium of Polish than of Swedish women. Further investigations are warranted to delineate the importance of the elevated concentration of cadmium in the blood of women with preterm labor.

Influence of high lead and cadmium soil content on human reproductive outcome

The influence of lead and cadmium on human reproductive outcome was studied in areas of Eastern Poland with high specific soil contamination with these heavy metals. By personal interviews, information on socioeconomic background factors as well as obstetrical and gynecological histories were obtained from 136 women living in villages with high amounts of lead and cadmium and from 269 women of nearby villages with no increased content of these metals. Physical examination and estimations of blood concentrations of lead and cadmium were also performed in 89 and 175 women from these areas, respectively. In the contaminated areas, there were significantly fewer women with three or more pregnancies (39 vs. 52%) and deliveries at full term (35 vs. 44%) than in nearby villages with normal concentrations of these heavy metals, and the weight of preterm newborns was lower (1930 vs. 2225 g). Furthermore, hypertension was more common (15 vs. 22%) and of higher magnitude (mean blood pressure 140 vs. 129 mmHg) in the study group than in the control women. The mean blood concentrations of lead in the two groups. 675 and 621 micrograms/dl did not differ statistically, whereas the concentrations of cadmium of 29 and 25 micrograms/dl were significantly higher in the study than in the control group. There was a significant correlation between cadmium levels and number of preterm deliveries. These results suggest that cadmium and lead could be factors of importance in reproductive outcome.

Neutral metalloendopeptidase associated with the smooth muscle cells of pregnant rat uterus

The pregnant rat uterus contains a membrane-bound metalloendopeptidase that is biochemically and immunologically similar to kidney enkephalinase (E.C.3.4.24.11). The uterus enzyme readily cleaved specific neutral endopeptidase substrates and oxytocin as well as the synthetic elastase substrate, Suc(Ala)3-pNA, yet did not digest native elastin. Using specific inhibitors, the uterus endopeptidase was identified as a metallopeptidase and not a serine protease, having an absolute requirement for zinc and perhaps calcium for maximal activity. The uterus endopeptidase cross-reacted with polyclonal antiserum to kidney microvillar endopeptidase and a monoclonal antibody to common acute lymphocytic leukemia antigen. Immunohistochemical localization of the enzyme in a 17 day pregnant uterus indicated that the enzyme was localized on the smooth muscle bundles of the myometrium and the endometrial epithelium. Total enzyme activity was 25 times higher in the late-term pregnant uterus (17th day of pregnancy) than in the nonpregnant uterus. Enzyme levels dropped rapidly prior to parturition and within 4 days after delivery the enzyme activity had returned to control levels. Inhibition of NEP in uterine strips with phosphoramidon resulted in a marked potentiation of oxytocin-induced contractions. Our results suggest that the uterine endopeptidase may have an important role in regulating uterine smooth muscle cell contraction during the later stages of pregnancy through its action on oxytocin and perhaps other biologically active peptides.