Purified FSH stimulates production of inhibin by the human ovary

Abstract

ABSTRACT Ovarian inhibin production is stimulated by the administration of human menopausal gonadotrophins or following a rise in endogenous LH and FSH. In order to determine whether FSH specifically stimulates inhibin secretion in vivo, immunoassayable serum inhibin levels were measured following the administration of a highly purified preparation of urinary FSH free of significant contamination with LH. Ten anovulatory women underwent a protocol of induction of ovulation with purified FSH and human chorionic gonadotrophin (hCG). During the induction of ovulation, blood samples were taken for radioimmunoassay of FSH, LH, oestradiol, progesterone and inhibin. During the administration of FSH there were increases in plasma concentrations of FSH, oestradiol and inhibin (P < 0·01) but no significant change in the concentration of LH. Oestradiol and inhibin concentrations rose in parallel and were closely correlated (τ = 0·920, n = 110, P < 0·001). There was also a direct correlation between the measured level of FSH and inhibin (τ = 0·512, n = 110, P < 0·05), but there was no correlation between LH and oestradiol, inhibin or FSH. Inhibin (τ− = 0·702, n = 10, P < 0·01) and oestradiol (τ− = 0·691, n = 10, P < 0·01) were correlated with the number of follicles seen on ovarian ultrasound. Levels of oestradiol and inhibin reached a peak on the day of hCG administration or on the following day. Inhibin levels then fell over the next 2 days in all cycles. In an ovulatory cycle resulting in conception, inhibin and oestradiol then rose in parallel with progesterone. We conclude that inhibin appears to be a follicular product which, in the follicular phase of the cycle, is stimulated by FSH alone, with granulosa cells being the probable site of production. Journal of Endocrinology (1989) 122, 279–285