THE ROLE OF INHIBIN ON PITUITARY FSH-SECRETION AND MATURATION OF PITUITARY-GONADAL AXIS IN IMMATURE FEMALE RATS

The possible physiological significance of endogenous inhibin was eval uated in prepubertal female rats during sexual maturation. Ovarian/ser um 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 l ife, thereafter, progressively increasing up to 27th day. Serum FSH le vels gradually increased up to the 14th day with a sharp fall in the F SH 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 1 4 day group, there was no difference between control and PMSG treatmen t, but in 22 day group, not only significant difference between contro l and PMSG treatment but also inverted relations between FSH and inhib in after PMSG treatment were found. It can be postulated from these fi ndings that secretion of inhibin from the granulosa cells is initiated by FSH by its direct action on the ovary whereas the level of FSH its elf is controlled by inhibin after FSH reaches peak values. Also it ca n be inferred that the feedback control mechanism of inhibin seems to be established around 3rd week of life