FOLLICLE-STIMULATING-HORMONE INDUCES DOSE-DEPENDENT STIMULATION OF IMMUNOREACTIVE INHIBIN SECRETION DURING THE FOLLICULAR PHASE OF THE HUMAN MENSTRUAL-CYCLE

To determine whether FSH is a physiological regulator of the serum immunoreactive inhibin (INH) concentration during the follicular phase of the normal menstrual cycle, purified FSH (Metrodin) was administered in doses of 100 IU (n = 6), 150 IU (n = 5), and 200 IU (n = 5) to normal, regularly cycling volunteers between days 3-7 of the menstrual cycle. A control group (n = 5) received normal saline. There was a linear dose-related increase in serum INH (and in serum FSH) in response to the three doses of FSH, with 200 IU leading to a 107% increase in INH and a 68% increase in FSH. Serum estradiol rose in response to the two higher doses of FSH. There was a significant correlation between the actual increases in INH and estradiol (r = 0.53; P < 0.01). It was concluded that FSH stimulates INH in the follicular phase of the normal menstrual cycle, consistent with a physiological role for FSH in the regulation of granulosa cell production of inhibin.