Growth factors have been shown to modulate differentiation of cultured ovarian granulosa cells. Transforming growth factors (TGFs) constitute a family of polypeptide growth factors capable of reversibly inducing anchorage-independent growth in normal cells. Epidermal growth factor (EGF), which has significant structural homology with TGF alpha, has been shown to modulate differentiation of granulosa cells in vitro. Similarly, TGF beta (TGFB) has been found to have significant structural homology with ovarian follicular fluid inhibin. To examine whether TGFB might affect granulosa cell growth or differentiation, rat granulosa cells were cultured in serum-free medium containing insulin for up to 3 days with varying concentrations of TGFB in the presence or absence of FSH. TGFB caused a dose-dependent increase in FSH-stimulated LH/hCG receptor binding, but had no effect on binding in the absence of FSH; TGFB (10.0 ng/ml) further increased FSH-stimulated LH/hCG receptor binding by 48 +/- 8% (P less than 0.02). Similarly, FSH-stimulated progesterone production was increased by TGFB in a dose-dependent manner; TGFB (1.0-10.0 ng/ml) increased FSH-stimulated progesterone production 2- to 3-fold (P less than 0.02). In contrast, EGF (10.0 ng/ml) decreased FSH-stimulated LH/hCG receptor binding by 93 +/- 1% (P less than 0.02). Neither FSH-stimulated intracellular nor extracellular cAMP accumulations were affected by TGFB treatment. However, EGF (10.0 ng/ml) diminished extracellular and intracellular FSH-stimulated cAMP accumulation at 48 and 72 h of culture. Culture protein and DNA content were not significantly affected by TGFB. These results suggest that TGFB may enhance FSH-stimulated LH receptor induction and steroidogenesis by mechanisms that do not further increase net cellular cAMP accumulation; TGFB and EGF can have opposite effects on gonadotropin-dependent differentiation; and products of the TGFB/inhibin gene family may have a capacity for autocrine or paracrine modulation of granulosa cell differentiation.