Stimulation of brook trout ovarian steroidogenesis by gonadotropins I and II is mediated by the cyclic adenosine 3',5'-monophosphate/protein kinase A pathway

In teleosts, ovarian steroidogenesis is under the control of two gonadotropic hormones, GTH I and GTH II, that are struc-turally and functionally homologous to FSH and LH. The intra-cellular mechanisms by which GTH I and GTH II stimulate ste-roidogenesis in the teleost ovary are not well understood. The purpose of this study was to investigate the involvement of the cAMP/protein kinase A (PKA) and protein kinase C (PKC)/Ca 2+ signaling pathways in the steroidogenic actions of GTH I and GTH II in the ovary of the brook trout (Salvelinus fontinalis). The cAMP/PKA pathway mediated the actions of GTH I before germinal vesicle breakdown (preGVBD) and GTH II after GVBD and before ovulation (preOV). Experimental increases in intra-cellular cAMP concentration mimicked the steroidogenic effects of GTH I and GTH II, and an antagonistic analog of cAMP par-tially blocked them. In addition, GTH I and GTH II stimulated the production of cAMP in preGVBD and preOV follicles, re-spectively. Activation of the PKC/Ca 2 + pathway by a phorbol es-ter or a Ca2+ ionophore blocked the GTH I- and GTH I-induced steroid production, whereas inhibition of PKC by specific inhib-itors potentiated the effects of GTH I. These results suggest that the cAMP/PKA signaling pathway mediates the stimulatory ef-fects of GTH I and GTH II on steroidogenesis, and they also suggest the additional involvement of the PKC/Ca2+ signaling pathway in modulating the actions of gonadotropins in brook trout ovarian follicles