Regulation of testicular steroid production in vitro by gonadotropins (GTH I and GTH II) and cyclic AMP in coho salmon (Oncorhynchus kisutch).

The ability of coho salmon gonadotropins GTH I and GTH II to stimulate testicular production of 11-ketotestosterone (11-KT) and 17 alpha,20 beta-dihydroxy-4- pregnen-3-one (17,20 beta-P) in vitro, as well as the involvement of cyclic AMP (cAMP) as a mediator of the actions of GTH I and GTH II, were investigated in maturing male coho salmon. Testicular tissue was incubated in the presence or absence of the test substances at 15 degrees. Both GTH I and GTH II stimulated the in vitro production of 11-KT and 17,20 beta-P in a concentration- and time-dependent manner. In testicular tissue at stage IV of spermatogenesis, GTH I and GTH II stimulated the in vitro production of steroids with similar potency. The steroidogenic activity of GTH I and GTH II appeared to be mediated, at least in part, by cAMP as indicated by the ability of dibutyryl cAMP and forskolin to mimic the steroidogenic actions of GTHs, and the similar ability of GTH I and GTH II to increase intracellular cAMP levels in the testicular tissue. The calcium ionophore A23187 stimulated basal but not GTH-stimulated production of steroids in vitro. In addition, differential effects of a protein kinase C inhibitor, H-7, on 11-KT and 17,20 beta-P production were found. Basal and GTH-stimulated production of 11-KT were inhibited by H-7; whereas basal and GTH-stimulated production of 17,20 beta-P were stimulated by H-7. These results suggest that protein kinase C may also be involved in the steroidogenic actions of GTH I and GTH II.