Follicle-stimulating hormone-inhibin B interactions during the follicular phase of the primate menstrual cycle revealed by gonadotropin-releasing hormone antagonist and antiestrogen treatment

The aim was to determine the pattern of inhibin A and inhibin B secretion d uring the ovulatory cycle of the macaque and to explore the effects of mani pulating follicular phase FSH on inhibin B secretion by: 1) blocking the ea rly follicular phase rise in FSH with GnRH antagonist treatment; 2) adminis tering FSH in GnRH antagonist-treated animals; and 3) preventing the midfol licular phase decline in FSH by a specific antiestrogen. Treatment with GnRH antagonist, starting on day 25 of the cycle, abolished the early follicular phase rise in FSH and the associated increase in inhib in B. The same treatment, followed by exogenous FSH, restored the secretion of inhibin B. Treatment with antiestrogen, commencing during the midfollic ular phase, induced a supraphysiological rise in FSH, followed by a marked stimulation of inhibin B and estradiol secretion. Despite continued antiest rogen treatment, FSH secretion declined before peak values of inhibin B and estradiol were attained, implying a potential endocrine role for inhibin B , in addition to estradiol, in the negative feedback regulation of FSH. The se results show that follicular phase FSH is the major stimulus for inhibin B secretion. (J Clin Endocrinol Metab 84: 1365-1369, 1999).