Interference of lead with implantation in the mouse: effect of exogenous oestradiol and progesterone.

The implantation inhibiting effect of an intravenous injection of 75 ppm of lead chloride, giving blood levels of about 32 mumol/l, could be counteracted by exogenous steroid hormones. Subcutaneous injections of 0.1 microgram of oestradiol-17 beta and 1 mg of progesterone were given together with the lead on day 4 of pregnancy, and the same hormone doses were given also on day 5. The frequency of animals having implantations on day 6 of pregnancy in this group was the same as in the control group (75%), whereas in animals given lead and no hormones, the frequency of pregnancies was only 20%. Morphological examination by light microscopy of implantation sites on day 6 of pregnancy in the lead + hormone-treated group showed that the decidual swellings contained implanted embryos of a normal appearance. Serum levels of oestradiol-17 beta and progesterone in nontreated and lead-treated mice were not significantly different between the two groups on day 5 of pregnancy. It is suggested that the implantation failure may be due to an effect of lead on uterine responsiveness to ovarian steroids.