Sensitivity to diethylstilbestrol-(DES)-induced abortions is influenced by the Whitten effect

Group-housed female mice, when introduced to a male, will undergo a synchronized estrous cycle with a characteristic pattern of mating where the majority of animals mate on the third day. This phenomenon is termed the Whitten effect. Exposure of pregnant mice to diethylstilbestrol (DES), a potent nonsteroidal estrogen, is capable of inducing premature parturition. The purpose of this study was to evaluate abortion induced by a single injection of DES on day 15 of gestation and compare the sensitivity depending on the day of mating. Initial observations confirmed that those animals that mated on day 3 were significantly more susceptible to DES-induced abortion than animals that mated on any other day. The possibility that this increase in sensitivity to abortion may be the result of differences in number or size of embryos at the time of DES exposure was examined. No significant difference was observed in the number of embryos at day 4 of gestation, at day 15 of gestation, or at birth. There was no difference in the weight of embryos at day 15 of gestation or at birth. A significant increase in the ratio of embryos between uterine horns was observed in the animals that mated on day 3 (ratio = 2.13) compared to animals mating on other days (ratio = 1.23 to 1.48). The cause of increased sensitivity to DES in animals that mated on day 3 is unclear. Our results may indicate that the induction of ovulation associated with the Whitten effect causes unequal embryo distribution leading to functional differences in sensitivity of the pregnancy to exogenous stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)