THE INDUCTION OF OVULATION BY OVARIAN STEROIDS IN THE ADULT RAT

Abstract

SUMMARY When oestrogen was administered early in the oestrous cycle of the rat on the day of metoestrus, the inhibitory effect of progesterone injected at dioestrus on ovulation was lost and a facilitatory effect was observed; ovulation was advanced by one day. The advancement of ovulation by oestrogen injected at the dioestrus — 1 stage of a 5-day cycle was confirmed; it was shown that this response could be elicited by as little as 0·13 μg. oestradiol benzoate. These results are discussed in relation to other studies on the time of oestrogen secretion in the normal cycle, the alteration of the response of the pituitary to progesterone injection from an inhibitory to a facilitatory effect by previous exposure to oestrogen, and the mechanism of induction of ovulation by oestrogen in the 5-day cycle and in pregnancy. The relevance of these and similar experiments on the induction of ovulation by ovarian steroids in the rat as a guide to what is occurring during the normal cycle is questioned, principally because when ovulation was induced by these means the changes in the activity of the thyroid gland that are associated with ovulation in the normal cycle were not reproduced.