Leydig cell steroid production in the presence of LH is further stimulated by rat testicular fluid, fetal calf serum and bovine follicular fluid, but not by rat and bovine serum.

LH-dependent steroid production by isolated rat Leydig cells is fourfold stimulated by the addition of charcoal-stripped rat testicular fluid. Fetal calf serum and bovine follicular fluid have similar stimulatory effects. In contrast, rat and bovine serum suppress steroid production in the presence of LH in a dose-dependent manner. The results show that stimulatory and inhibitory factors can modulate Leydig cell steroidogenesis and these factors appear not to be organ or species specific.