Effects of galanin on the secretory activity of the rat adrenal cortex: in vivo and in vitro studies.

Galanin, a 28-amino-acid peptide originally isolated from pig intestine, was found to cause dose-dependent rises in the plasma concentration of corticosterone in hypophysectomized rats and in both basal and submaximally ACTH-stimulated in vitro corticosterone production by adrenal quarters and isolated zona fasciculata/reticularis cells. These findings indicate that galanin exerts a direct glucocorticoid secretagogue effect on the inner adrenocortical zones and suggest that galanin, high concentrations of which are contained in adrenal chromaffin cells, may be included in that group of regulatory peptides, by way of which adrenal zona medullaris is thought to exert a paracrine control on the function of the zona corticalis. Galanin was also found to increase the plasma level of aldosterone in hypophysectomized rats in a dose-dependent manner without inducing changes in natremia, kalemia, plasma renin activity, or ACTH plasma concentration. Galanin did enhance both basal aldosterone output and that following submaximal ACTH or angiotensin II stimulation aldosterone output from adrenal quarters, but not from isolated zona glomerulosa cells. This last, rather unexpected, result suggests that galanin exerts an indirect mineralocorticoid secretagogue action, which seems to require the structural integrity of the adrenal cortex and the presence of the adrenal medulla. The hypothesis is advanced that galanin may control the release of some medullary peptides, which in turn may affect mineralocorticoid secretion of the zona glomerulosa in a paracrine manner.