FURTHER OBSERVATIONS ON INDUCED OVULATION IN MICE. A REFRACTORY PERIOD INEARLY PREGNANCY

IN AN EARLIER REPORT, it was shown that ovulation was induced in mice within 18 hrs. after a single subcutaneous injection of a chorionic gonadotrophin (Burdick, Watson, Ciampa and Ciampa, 1943). During the experiment with mated mice it was soon discovered that although ovulation could be regularly induced in animals having implanted embryos, negative results were usually obtained in those animals during the first few days while the fertilized ova were being transported to the uterus. This present investigation was undertaken to collect more data on the duration of this refractory period. Mated mice were selected each morning after ascertaining the presence of the vaginal plug. Single injections of a chorionic gonadotrophin1 were given on different days and in various amounts as indicated in table 1. Injections of 5 I.U. or more were considered adequate for this investigation, since it had been found earlier that 0.7 I.U. was a minimal ovulating dose for mice in later pregnancy.