α-MSH at physiological concentrations stimulates “Late pathway” steroid products in adrenal zona glomerulosa cells from sodium restricted rats

Abstract

alpha-MSH stimulates steroid secretion by rat adrenal zona glomerulosa cells and tissues but not fasciculata/reticularis cells when added to in vitro incubations. With glomerulosa cells from control animals on a normal sodium intake, production of corticosterone was significantly stimulated at an alpha-MSH concentration of 10(-9) moles per 1, with ED50 at 10(-8) moles per 1. Other steroid products, including 18-hydroxycorticosterone (18-OH-B), 18-hydroxydeoxycorticosterone (18-OH-DOC) and aldosterone were only significantly stimulated at 10(-7) moles alpha-MSH per 1. In contrast, in cells taken from animals subjected to dietary sodium restriction, aldosterone and 18-OH-B were significantly stimulated at 10(10) moles alpha-MSH per 1, whereas corticosterone and 18-OH-DOC were unaffected at all concentrations tested. Circulating plasma levels of alpha-MSH in control animals were 2.5 +/- 0.4 x 10(-10) moles per 1, but were unchanged by dietary sodium restriction or by sodium loss induced by diuretic (LASIX) administration. However, the threshold concentration at which alpha-MSH induces increased aldosterone secretion in cells from sodium depleted rats clearly falls well within the physiological range, and it is therefore likely that alpha-MSH contributes to the support of aldosterone secretion in these animals in vivo.