Epidermal Growth Factor Directly Stimulates Steroidogenesis in Primary Cultures of Porcine Leydig Cells: Actions and Sites of Action*

The actions and the mechanisms of action of epidermal growth factor (EGF) in testicular steroidogenesis were investigated using a model of primary culture of purified porcine Leydig cells from immature intact animals. EGF decreased (1.7-fold) human CG (hCG)-induced dehydroepiandrosterone (DHEA) accumulation in the medium whereas it enhanced (2.5- fold) that of testosterone. The maximal and half-maximal effects on both DHEA and testosterone secretions were observed at similar concentrations which were, respectively, 3 (5 × 10-10 M) and 0.7 (11 × 10-11 M) ng/ml EGF, after 72-h treatment. EGF effect on DHEA and testosterone secretion was similarly observed whether the cells were acutely (3 h) stimulated with hCG (1 ng/ml) or with 8-bromo-cAMP (10-3 M). TO further localize the steroidogenic biochemical steps affected by EGF, the growth factor action on steroidogenic enzyme activities was investigated. EGF increased Δ5 steroid intermediate (i.e. pregnenolone and DHEA) formation [evaluated in the presence of 10...