Stimulation of Steroidogenesis in Immature Rat Leydig Cells Evoked by Interleukin-1α Is Potentiated by Growth Hormone and Insulin-Like Growth Factors

The cytokine IL-1alpha is produced constitutively by the intact testis, but its function in this organ remains largely unknown. In this study we examined cooperation between IL-1alpha and GH and IGFs with regard to stimulation of steroidogenesis by Leydig cells from 40-d-old rats in vitro. IL-1alpha alone stimulated testosterone (T) and dihydrotestosterone (DHT) production. GH, IGF-I, or IGF-II alone was without effect on T production, but they were found to elevate DHT release, albeit without an obvious dose-response effect. Costimulation with IL-1alpha and GH or with IL-1alpha and IGF-I or IGF-II elevated the rate of steroidogenesis (both T and DHT) above that observed with IL-1alpha alone. GH was found to increase the level of IGF-I in the cultured Leydig cells, an effect that was potentiated by IL-1alpha. The costimulatory effect of GH on steroidogenesis was abolished by treatment with picropodophyllin, a specific inhibitor of the IGF-I receptor, indicating that the action of GH is mediated via IGF-I. Moreover, cells costimulated with IL-1alpha and GH exhibited a marked decrease in the level of intact IGF-binding protein-3 in the culture medium due to the induction of proteolytic activity toward this binding protein. In contrast, secretion of IGF-binding protein-2 was increased by such costimulation. These findings suggest that the stimulation of steroidogenesis in Leydig cells evoked by GH and IGFs requires cooperation with IL-1alpha. This cooperation may play an important role in connection with postnatal Leydig cell maturation and steroidogenesis.