Mating and embryo yield of mice injected with gonadotropins on specific days of the estrous cycle and in acyclic periods.

Pregnant mare serum gonadotropin and human chorionic gonadotropin, hormones that can be used to induce superovulation, were administered to hybrid female mice (C57BL/6J X CBA/J) on known days of the estrous cycle, or when the mice were known to be acyclic, in order to determine whether certain reproductive states of the animals either enhanced or inhibited effects of the exogenous gonadotropins. Days of the estrous cycle on which the hormones were given did not significantly affect the numbers of animals that mated and in most cases did not affect embryo yield. When hormone treatment was initiated on the day of estrus in the 5-day cycle, the embryo yield was greater than when treatment was initiated on the first day of diestrus but even the difference between these groups had only marginal significance. Mice that were not exhibiting regular estrous cycles, some of which had been rendered acyclic by exposure to constant light, did not differ from mice with regular cycles in numbers that mated or in embryo yield following gonadotropin administration. When gonadotropin injection of regularly cycling mice was initiated on metestrus, on the first day of diestrus, or on estrus, the vaginal cycle was retarded as indicated by failure of cornified cells subsequently to predominate in vaginal smears at proestrus, estrus, or metestrus but initiation of hormone treatments on the second day of diestrus advanced the occurrence of vaginal cornification. Following gonadotropin injection, vaginal cornification became less reliable as a predictor of the time at which the animals would mate and ovulate.(ABSTRACT TRUNCATED AT 250 WORDS)