Growth hormone-dependent potentiation of gonadotropin-stimulated steroid production by ovarian follicles of the goldfish

The possible involvement of growth hormone (GH) in the regulation of ovarian function in the goldfish was investigated by determining the effects of common carp GH on steroid production by vitellogenic and preovulatory ovarian follicles incubated in vitro. Carp GH acts in a dose-dependent manner to potentiate the actions of common carp gonadotropin (GtH) on the production of 17 beta-estradiol and testosterone by vitellogenic ovarian follicles and the actions of human chorionic gonadotropin (hCG) on testosterone production by preovulatory ovarian follicles. Carp GH alone had no effect on basal steroid secretion by either class of ovarian follicles. Chum salmon GH but not bovine GH also enhanced carp GtH-induced production of 17 beta-estradiol by vitellogenic ovarian follicles. Common carp prolactin had no effects on basal or GtH-stimulated steroid production by vitellogenic or preovulatory ovarian follicles. The actions of carp GH on preovulatory follicles were not apparent when tested with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, suggesting that GH may act to enhance either the formation or actions of cAMP. In summary, these data demonstrate that GH has a direct modulatory effect on GtH-stimulated steroid production and suggest that GH may be an important regulator of follicular development in the goldfish.