Cadmium: its effects on ovulation, egg transport and pregnancy in the rabbit

The subcutaneous administration of cadmium chloride (CdCl2) 24 h before hCG-induced ovulation in rabbits sacrificed 14 h after induction of ovulation leads to a dose-dependent decrease in the number of oviductal eggs and the number of eggs shed. While a dose of 1.25 mg/kg CdCl2 imposed no effect, only 50-67% of the dogs treated with 2.5 or 5 mg/kg CdCl2 ovulated and of those ovulated eggs 35.6 and 45%, respectively, were found in the oviducts. At a dose of 7.5 mg/kg CdCl2, a higher proportion (57.1%) of the does failed to ovulate and only 16% of the eggs were recovered from the oviducts. Ligature of the uterotubal junction failed to increase the rate of eggs recovered from the oviducts. A sharp increase in serum progesterone (delta4 P) level within 2 h after induction of ovulation suggests that the reduction in the percentage of eggs recovered from the oviducts probably occurred due to altered fimbrial functions. On the other hand, in does treated with 5 mg/kg CdCl2 1 or 7 days before mating, pregnancy was interrupted in 60 and 75% of the does together with reduced delta4 P concentration and the conception rate (no. of implantations/CL) was significantly reduced. CdCl2 given 21 days before or 3 days after mating did not affect pregnancy and delta4 P concentration remained unaltered. Results suggest that the developing or mature follicles are sensitive to CdCl2 treatment. Once the CL is formed, the effect of CdCl is reduced. The receptivity of CdCl2-treated females indicates that probably the circulating estrogens were not affected and the ability to ovulate in response to hCG and mating reflects that, at least at the doses used, the hypothalamic-pituitary gonads functions are functional in the rabbit.