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The effects of the progestin and glucocorticoid antagonist RU486 on cleavage rate of oviductal embryos from lactating mice was studied. Preliminary experiments suggested that, owing to suppression of follicular activity by lactation, the effects of RU486 during early embryo development could be studied independently of overt oestrogen dominance in mice mated at postpartum oestrus. After treatment with RU486 on days 1–3 of pregnancy in lactating mice, embryos recovered on day 4, but not on day 3, had significantly fewer cells than did those from control animals. However, neither exogenous progestins nor dexamethasone could reverse this effect of RU486. Nevertheless, embryos recovered from lactating mice treated with progestins alone had significantly more cells on day 4 than did those from control animals. In contrast, embryos recovered from mice treated with dexamethasone alone had significantly fewer cells per embryo on day 4 than did those from control mice. These results provide further evidence that the growth rate of oviductal embryos in mice is influenced by the maternal hormone milieu.
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Mink are carnivores of agroforestry fringe habitats and are exposed to pesticides that biomagnify within the food chain. Some pesticides are thought to disrupt reproductive and endocrine functions. In Expt 1, four groups of mink (n = 10) were fed either a control diet, or diets treated with lindane (1 mg kg−1 day−1), carbofuran (0.05 mg kg−1 day−1) or pentachlorophenol (1 mg kg−1 day−1) from before breeding until weaning. Mink were mated twice, at 7–8 day intervals. The treatments had no effect on the proportion of mink accepting the first mating; however, lindane and pentachlorophenol caused a decrease in the percentage of females accepting the second mating. Lindane and pentachlorophenol caused a decrease in whelping rate, although litter size was not affected. Carbofuran had no effect on fertility. Mink that mated only once had a lower whelping rate than mink that mated twice; therefore, it could not be determined whether the decreased whelping rates were due to the lack of a second mating or to increased embryo loss. In Expt 2, two groups of mink (n = 15) were fed a control diet or a diet treated with lindane (1 mg kg−1 day−1) from before mating until weaning. Mink were mated twice on two consecutive days. Lindane did not affect mating response at either mating. Whelping rate, but not implantation rate, was decreased by the lindane treatment. The proportion of embryos lost after implantation (implantation scars not represented by kits at whelping) was increased by the lindane treatment. In conclusion, both lindane and pentachlorophenol decreased fertility in mink, and the lindane effect was primarily a result of embryo mortality after implantation.
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Summary. Adult cyclic beagle bitches were treated for up to 18 months with nafarelin acetate via subcutaneously implanted osmotic pumps, starting during the first week of a pro-oestrous vaginal discharge. The imminent ovulation appeared to be unaffected by treatment, but doses of 8 or 32 μg analogue/day reduced the integrated luteal progesterone values. No new oestrus was detected in 3 bitches during 18 months of treatment with 32 μg/day, which resulted in mean plasma levels of 0·4 ng analogue/ml. A return to oestrus was observed in all 3 bitches between 3 and 18 weeks after cessation of treatment: 2 of the bitches mated at those times and produced normal litters. Another 2 bitches were similarly treated with 32 μg analogue/day; they were mated at the oestrus at start of treatment and dosing was continued for about 63 days. One of the bitches conceived and produced a normal litter. Nafarelin acetate treatment begun during anoestrus resulted in an induced heat 1–2 weeks after the start of treatment. The induced heat consisted of pro-oestrous vaginal discharge, oestrous vaginal cytology, and ovulation (judged by increased circulating levels of progesterone). Three bitches mated at the induced heat and treated for the normal duration of gestation did not litter. Nafarelin treatment of 3 bitches before puberty did not induce signs of oestrus and prevented the occurrence of oestrus through 18 months of treatment. The first oestrus in these bitches occurred 3·5–4 months after cessation of treatment, but mating at that time did not result in pregnancy. These studies have established the feasibility of and dosage requirement for the use of the LHRH agonist as a contraceptive in the bitch.
