THE ROLE OF OESTROGEN IN THE INDUCTION OF OVULATION IN THE GONADOTROPHIN-TREATED IMMATURE RAT

Abstract

SUMMARY The effects of different doses of pregnant mare serum gonadotrophin (PMS) were examined in 29-day-old immature rats; a dose great enough to produce follicles capable of ovulating in response to the additional injection of human chorionic gonadotrophin (HCG) 56 hr. later in the majority of animals also caused significant oestrogen secretion as judged by uterine weight. Maximal uterine growth resulted from doses of PMS that led to a significant incidence of 'spontaneous' ovulation. In contrast, administration of ovine follicle-stimulating hormone (FSH) resulted in the ripening of large numbers of follicles with much less evidence of oestrogen secretion; 'spontaneous' ovulation did not occur in FSH-treated animals but ovulation could be induced by additional treatment with oestrogen and progesterone in combination but not by either steroid alone. Previous exposure to oestrogen appears to be necessary for the facilitatory action of progesterone on luteinizing hormone release to be demonstrable and the FSH-primed immature rat is a convenient preparation to study this interaction.