Fibroblast growth factor is a regulator of testosterone secretion in cultured immature Leydig cells.

The regulatory effect of fibroblast growth factor (FGF) on testosterone secretion was studied by using a model of immature porcine Leydig cells cultured in serum-free defined medium. FGF enhanced in a dose-dependent manner hCG-stimulated testosterone secretion (ED50 = 11 ng/ml FGF). The stimulatory effect of FGF on testosterone accumulation was time dependent; testosterone increased to a maximal value at 24 h treatment and then dramatically declined to near control value following 48 and 72 h treatment with FGF; such a decline was not related to FGF degradation in culture medium. Although FGF increased maximal secretion of testosterone, it did not affect the human chorionic gonadotrophin (hCG) concentrations required for maximal and half-maximal secretion of testosterone (1 and 0.2 ng/ml hCG, respectively). These effects of FGF are probably exerted in the context of the local control of testicular steroidogenesis.