Epidermal growth factor stimulates testosterone production of human Leydig cells in vitro

Epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) have been shown to regulate Leydig cell steroidogenesis in several species. We have investigated the effects, if any, of EGF and IGF-I on in vitro testosterone production of human Leydig cells. Interstitial cells or Percoll purified Leydig cells were isolated from the testes obtained from patients (n = 9) undergoing orchidectomies for treatment of prostate cancer and were cultured for different time periods with hCG, dibutyryl cAMP, EGF and IGF-I. Testosterone in the culture media was measured by radioimmunoassay. While EGF had a stimulatory effect on basal testosterone production of isolated interstitial cells or purified Leydig cells, IGF-I was ineffective. When the interstitial cells were cultured in the presence of hCG or EGF for 3, 6 or 24 h, the stimulatory effects of EGF on testosterone production were only evident after 24 h. On the other hand, hCG stimulated testosterone production at all time points (i.e after 3, 6, 24 h of incubation). When added in the presence of maximal concentrations of hCG and dibutyryl cAMP, EGF did not further enhance steroidogenesis. On the other hand, IGF-I potentiated the effects of hCG on testosterone production. These studies suggest that EGF and IGF-I may play a regulatory role in steroidogenic function of the human testes.