The Role of Inhibin on Pituitary FSH Secretion and Maturation of Pituitary-Gonadal Axis in Immature Female Rats.

FUKAYA, T., KAKUTA, C., TOZAWA, H., MANSFIELD, C., TSUIKI, A., YOHKAICHIYA, T. and YAJIMA, A. The Role of Inhibin on Pituitary FSH Secretion and Maturation of Pituitary-Gonadal Axis in Immature Female Rats. Tohoku J. Exp. Med., 1993, 170 (1), 1-9 - The possible physiological significance of endogenous inhibin was evaluated in prepubertal female rats during sexual maturation. Ovarian/serum inhibin, serum FSH levels were measured from 4th day to 35th day of life by RIA. Serum inhibin levels were first detected on 4th day of life, thereafter, progressively increasing up to 27th day. Serum FSH levels gradually increased up to the 14th day with a sharp fall in the FSH levels on day 15 which afterwards was maintained at a lower level. Pregnant mare serum gonadotropin (PMSG) treatment on day 14 and day 22 rats showed different patterns of serum FSH and inhibin changes. In 14 day group, there was no difference between control and PMSG treatment, but in 22 day group, not only significant difference between control and PMSG treatment but also inverted relations between FSH and inhibin after PMSG treatment were found. It can be postulated from these findings that secretion of inhibin from the granulosa cells is initiated by FSH by its direct action on the ovary whereas the level of FSH itself is controlled by inhibin after FSH reaches peak values. Also it can be inferred that the feedback control mechanism of inhibin seems to be established around 3rd week of life. - inhibin; FSH; immature stage; onset of estrous cycle