PMSG responsiveness during adult life after partial oogonia destruction with misulban in the rat embryo

Pregnant rats were given one of the following doses of misulban on day 15 of pregnancy : 0.25, 0.36, 0.52, 0.75, 0.82, 0.88 or 0.95 mglkg. In the three-month old offspring it was observed that : 1) The number of cyclic rats decreased according to the dose of misulban given to the mothers ; 2) Cyclic rats were given an injection of 20 IU of PMSG at metcestrus followed by an injection of 150 IU of HCG the evening the presumed oestrus. The following observations were made after such a treatment : a) there was no difference in ovulation rate between rats born from mothers treated with misulban (0.25-0.75 mg/kg) and untreated mothers ; b) there was no difference in ovulation rate between rats born from mothers treated with misulban (0.75-0.95 mg/kg) and controls receiving 10 IU PMSG and 150 IU HCG. It is suggested that : a) the oogonia population is sensitive to increasing doses of misulban ; b) a sufficient number of primordial follicles is necessary at birth in order to maintain cyclicity in the adult ; c) the rate of superovulation is dependant on the number of growing and preantral follicles at the time of treatment with PMSG.