Changes in serum immunoreactive inhibin during ovulation induction in women with amenorrhea

Changes in serum immunoreactive (IR)-inhibin were measured by RIA in two studies, in order to elucidate, firstly whether the pattern of IR-inhibin secretion is similar to that of estradiol (E2), and secondly, whether inhibin suppresses endogenous FSH release. Study 1: Purified urinary FSH (pFSH) or human menopausal gonadotropin (hMG) were daily injected intramuscularly into women with hypogonadotropic amenorrhea at 12 to 14 week intervals. PFSH and hMG stimulated IR-inhibin release in a similar fashion in the ovulatory cycles, but the increase in estradiol (E2) during pFSH administration was delayed and lower than that during the hMG cycles. This suggests that E2 and IR-inhibin are secreted independently from the granulosa cells. Study 2: Ovulation induction was performed in 18 cycles of 9 women with polycystic ovarian disease (PCOD) by the step-down administration of pFSH. The serum FSH concentration in cycles with premature LH release increased even after the dose of pFSH was reduced, and were significantly higher than those of cycles without premature LH release. It was also found that the serum IR-inhibin concentration in cycles with the premature LH release was 2 to 4 times as high as in cycles without premature LH release. This suggests that IR-inhibin does not suppress endogenous FSH release associated with premature LH release.