ERYTHROPOIETIN AND TESTICULAR STEROIDOGENESIS - THE ROLE OF 2ND-MESSENGERS

It has been demonstrated that erythropoietin (EPO) influences rat and human Leydig cell steroidogenesis, stimulating testosterone production through a direct and specific receptor-mediated mechanism. The aim of this study was to investigate the mechanism by which recombinant huma n erythropoietin (rHuEPO) exerts its stimulatory effect on rat Leydig cells. Recombinant human EPO did not induce, at any dose tested (10(-1 0) to 10(-13) mol/l), an increase in either cAMP or cGMP, suggesting t hat in Leydig cells the effect of rHuEPO does not involve the adenylat e or guanylate-cyclase systems. The role of transmembrane calcium flux in rHuEPO-stimulated steroidogenesis was studied by evaluating the ef fect of calcium channel blocker, verapamil, and by the Ca-45(2+) uptak e method. Verapamil did not influence rHuEPO-induced testosterone secr etion and rHuEPO did not modify calcium recycling, indicating that cal cium transmembrane flux is not involved in the rHuEPO effect. The prot ein kinase C inhibitor staurosporine (10, 30, 100 and 300 nmol/l) inhi bited rHuEPO-stimulated testicular steroidogenesis in a dose-dependent manner. This indirect evidence suggests that the stimulatory effect o f rHuEPO on rat Leydig cells may involve protein kinase C activation.