Signal transduction mechanisms mediating secretion in goldfish gonadotropes and somatotropes

The intracellular signal transduction mechanisms mediating maturational gon adotropin and somatotropin secretion in goldfish are reviewed. Several majo r signaling mechanisms, including changes in intracellular [Ca2+], arachido nic acid cascades, protein kinase C, cyclic AMP/protein kinase A, calmoduli n, nitric oxide, and Na+/H+ antiport, are functional in both cell types. Ho wever, their relative importance in mediating basal secretion and neuroendo crine-factor-regulated hormone release differs according to cell type. Simi larly, agonist- and cell-type-specificity are also present in the transduct ion pathways leading to neuroendocrine factor-modulated maturational gonado tropin and somatotropin release. Specificity is present not only in the act ions of different regulators within the same cell type and with the same li gand in the two cell types, but this also exists between isoforms of the sa me neuroendocrine factor within a single cell type. Other evidence suggests that function-selectivity of signaling may also result from differential m odulation of Ca2+ fluxes from different sources. The interaction of differe nt second messenger systems provide the basis by which regulation of matura tional gonadotropin and somatotropin release by multiple neuroendocrine fac tors can be integrated at the target cell level.