[Studies on inhibin in human follicular fluid]

In order to investigate whether inhibin (FSH-suppressing activity) is present in human follicular fluid (hFF) and whether inhibin in hFF could be correlated with the FSH level in peripheral serum, the effect of hFF on FSH secretion was studied using monolayer culture of rat anterior pituitary cells. Dextran-coated charcoal (DCC)-treated hFF exerted an inhibitory effect on pituitary FSH secretion but not on LH. The inhibitory effect of hFF upon basal FSH secretion was different from those of steroids such as estradiol, progesterone, testosterone and androstenedione. hFF inhibited the LHRH-stimulated secretion of both FSH and LH. Since hFF and porcine follicular fluid (pFF) produced a parallel dose-dependent decrease of basal FSH secretion, the same suppressing activity may be present in both hFF and pFF. Inhibin activity increased gradually during the follicular phase, but decreased in the luteal phase. Inhibin activity in hFF except during preovulatory surge showed a significant inverse correlation with the FSH level in peripheral serum. These results might indicate that inhibin activity in hFF increased according to follicular maturation and that inhibin (non-steroidal substance) may be one of the important regulators of FSH secretion in the human pituitary.