InhibinA Inhibits FSH Action By Suppressing Its Receptor Expression In Cultured Rat Granulosa Cells

Inhibin mainly secreted by granulose cells (GCs). InhibinA/B is composed byαsubunit andβA/βB subunits. Inhibin has long been considered as a suppresser of FSH secretion from the anterior pituitary through pituitary-gonadal negative feedback to regulate follicle development. But we do not know if InhibinA secreted by GCs could target to the FSH receptor (FSHR) and directly affect its expression via an autocrine action.The granulose cells (GCs) isolated from the DES-primed ovaries of immature rats were cultured in a serum-free medium in the presence or absence of FSH and inhibinA. We have demonstrated that inhibinA could suppress the basal and especially the FSH-induced FSHR mRNA level measured by real-time PCR. Furthermore, inhibinA dramatically decreased FSH-induced progesterone and estradiol production, as well as suppressing the P450arom and P450scc level in the cultured GCs. InhibinA was also capable of inhibiting the FSH-induced expression of androgen receptor (AR).Our study has demonstrated for the first time that inhibinA is capable of feedback antagonizing FSH action on granulose cells by reducing FSHR expression at the ovarian level via a short feedback loop. This study enriches the traditional concept and bears an important physiological significance of inhibin in regulation of ovarian function.