INDUCTION OF SUPEROVULATION BY IMMUNONEUTRALIZATION OF ENDOGENOUS INHIBIN THROUGH THE INCREASE IN THE SECRETION OF FOLLICLE-STIMULATING-HORMONE IN THE CYCLIC GOLDEN-HAMSTER

The present study was conducted to study the effect of immunoneutraliz ation against endogenous inhibin on FSH, LH, oestradiol-17 beta and pr ogesterone secretion and to investigate the effect of removal of endog enous inhibin on subsequent follicular development in the hamster. Aft er treatment with anti-inhibin serum (inhibin-AS) at 1100 h on day 2 o f the oestrous cycle (day 1=day of ovulation), a marked increase in pl asma levels of FSH and a slight increase in plasma levels of LH were n oted and pituitary contents of FSH, but not LH, were also increased. I n the group treated with inhibin-AS, superovulation occurred on day 1 of the following cycle. Plasma levels of oestradiol-17 beta markedly i ncreased with the increase in the number of ovulations induced by huma n chorionic gonadotrophin (hCG) as compared with those in control anim als. In the second cycle, plasma concentrations and pituitary contents of FSH in the animals given 200 mu l inhibin-AS still showed high val ues as compared with those in the animals treated with control serum, although superovulation did not occur on day 1 of the third cycle. Pla sma concentrations and pituitary contents of LH in the hamster given 2 00 mu l inhibin-AS tended to decrease as compared with those in contro l animals during the second cycle. Plasma concentrations of oestradiol -17 beta in the animals treated with 200 mu l inhibin-AS changed in a similar way to controls. A marked increase in plasma concentrations of progesterone was noted on days 1 and 2 of the second cycle in the gro up receiving inhibin-AS. The twice daily injection of 1 IU hCG during the second cycle to the animals given 200 ttl inhibin-AS induced super ovulation on day 1 of the third cycle. These results indicate that cir culating inhibin may be an important indicator of the number of develo ping follicles and may maintain the species-specific number of develop ing follicles through suppression of FSH secretion in the cyclic hamst er. They also suggest that high levels of inhibin slightly suppress pl asma levels of LH, indicating that plasma LH may also regulate follicu lar development in the cyclic hamster.