PROGESTERONE-INDUCED AUGMENTATION OF PITUITARY GONADOTROPHIN RESPONSES TO LUTEINIZING HORMONE-RELEASING HORMONE IN OESTROGEN-PRE-TREATED AMENORRHOEIC WOMEN

Abstract

Modulating effects of estradiol-17.beta. and progesterone on the pituitary responsiveness to luteinizing hormone-releasing hormone (LRH) were investigated in 12 women with functional amenorrhea. The pituitary reserve capacity for gonadotropin section was investigated with repeated i.v. LRH tests before and after administration of estradiol-1.beta. followed by progesterone or saline. I.m. injection of 1 mg of estradiol-17.beta. benzoate suppressed the basal gonadotropin levels in serum and the gonadotropin responses to LRH 24 h later. Progesterone, 25 mg i.m., was then administered in 11 experiments. Six hours later, when the mean serum progesterone level had increased to levels similar to those seen in the early post-ovulatory phase of the menstrual cycle, there was a marked augmentation of the pituitary capacity to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in response to LRH. This was not found in 8 experiments where saline was given instead of progesterone after estrogen pretreatment. The greatly increased pituitary sensitivity to LRH at midcycle may be caused not only by the estradiol increase in blood during the late follicular phase but also in part by the small pre-ovulatory rise of progesterone during the mid-cyclic LH peak. Further support was added to the hypothesis that progesterone and estradiol is involved in the induction of the LH peak at midcycle. Progesterone may be of importance to secure the release of enough LH for ovulation and normal corpus luteum formation to occur.