Recently, a protein fraction [follicle regulatory protein (FRP)] which inhibits FSH-induced granulosa cell aromatase activity was isolated from both human and porcine follicular fluid. In this study, the actions of FRP on 3 beta-hydroxysteroid dehydrogenase (3 beta-HSDH) activity were examined using granulosa cells obtained from hyperstimulated patients undergoing oocyte aspiration for in vitro fertilization. Granulosa cells were cultured with 0, 167, or 500 micrograms/ml FRP with or without human menopausal gonadotropin (hMG; 10 mIU/ml). After 48 h, the medium (S) was removed and stored. Cells then were mechanically lysed and centrifuged at 10,000 X g. The supernatant was further centrifuged (100,000 X g) to obtain a microsomal fraction (M) and cytosol (C). The M fraction was resuspended in medium 199 with 10(-6) M pregnenolone plus 5 microM NAD+ and incubated for 2 h to determine 3 beta-o1 dehydrogenase activity. The S, C, and M fractions were all assayed for progesterone (P) by RIA. hMG markedly increased P concentrations in the S and C fractions. The M fraction demonstrated a hMG-dependent enhancement in 3 beta-HSDH activity. However, the hMG-associated S, C, and M P levels were decreased in granulosa cells coincubated with FRP. In conclusion, ovarian steroidogenesis may be dependent on the integrated interactions of both gonadotropins and local nonsteroidal paracrine/autocrine modulators of granulosa cell function.