GENETIC AND HORMONAL INFLUENCES ON OVULATION AND IMPLANTATION IN ADULT MICE TREATED WITH GONADOTROPHINS

Abstract

SUMMARY The innate oestrous cycle, the dose of hormone, and the strain of mouse used influence ovulation and implantation in adult mice treated with pregnant mares' serum (PMS) and human chorionic gonadotrophin (HCG). Almost all of the treated mice in some strains will mate, while those from other strains are less responsive. Excess of hormone reduced the mating response and also suppressed ovulation through the formation of atretic corpora lutea and atretic follicles. Provided that the amount of hormone was not excessive, ovulation was induced in almost all mice of all strains irrespective of age, body weight, or stage of the oestrous cycle when treatment began. In one strain more eggs were recovered from females in metoestrus than from those in oestrus or dioestrus at the beginning of treatment, but this effect of the oestrous cycle was only found with low doses of PMS. The proportion of mice with implanted embryos after treatment was influenced by the dose of hormone, strain differences, and the stage of the oestrous cycle when treatment began. This proportion was low after large amounts of PMS and HCG, and generally higher in strains of high natural fertility than in those of low fertility. Fewer of the mice in dioestrus, when injected with PMS, had implanted embryos than had those in oestrus or metoestrus. A strain of mice containing many acyclic females was least successful in implanting embryos. The proportion of embryos that implanted decreased with increasing doses of hormone, apparently because of the increased competition between them for uterine sites.