The induction of LH receptors by FSH in cultured rat granulosa cells and the effects of ovarian steroids on this process were examined. Granulosa cells were isolated from the ovaries of untreated immature rats (25 days old) and cultured with highly purified FSH (Sairam; 250 ng/ml). After culture (48- 96 h in chemically defined media), both the binding of [125I]hCG and the responsiveness (cAMP and progesterone production) to an acute LH stimulus (100 ng/ml; NIH B8) were measured. The appearance of LH/hCG-binding sites and LH responsiveness indicates the presence of functional LH receptors. The induction of LH receptors by FSH requires a lag period of 24-48 h. After 48 h, the concentration of LH receptors in cultured granulosa cells continues to increase with time in culture with FSH; the continuous presence of FSH is required to maintain the induction process. If granulosa cells are cultured without hormone for 24-48 h before FSH is added, no induction of LH receptors occurs. However, if 17β-estradiol (5 x 10-7 M) is added during this initial period, then the cells are responsive to the later addition of FSH. This maintenance of FSH responsiveness is not observed when dihydrotestosterone or progesterone is substituted for 17β-estradiol in the initial culture period. The FSH-dependent induction of LH receptors in cultured rat granulosa cells can be blocked if an inhibitor of steroidogenesis, such as aminoglutethimide phosphate (AGP; 1 mM), is added along with FSH at the initiation of the culture. The inclusion of progesterone, dihydrotestosterone, or 17β-estradiol (but not 20α-dihydroprogesterone) in the culture together with FSH and AGP will overcome the inhibition by AGP and restore the induction of LH receptors. These results suggest that steroids produced by the developing follicle can modulate the FSH-dependent induction of LH receptors, and this may play a role in the development of follicular responsiveness to LH.
ASJC Scopus subject areas