Proopiomelanocortin-derived peptides, phosphoinositides, cAMP, and aldosterone secretion

Since the intracellular messengers of various proopiomelanocortin-derived peptides remain ambiguous at best, we have investigated the possible involvement of phosphoinositide metabolism in aldosterone secretion evoked by α-MSH, β-LPH, as well as ACTH in rat and calf adrenal glomerulosa cells. We have also examined the cAMP responses in the adrenal glomerulosa cells to α-MSH comparing it with those of ACTH. Our results showed that neither α-MSH, β-LPH, nor ACTH increased inositol triphosphate (IP₃) or other inositol phosphates in adrenal glomerulosa cells while increasing aldosterone secretion from the same cells. Angiotensin II, known to cause hydrolysis of the phosphoinositides, increased IP₃ in these adrenal cells in a dose-dependent manner. Both ACTH and α-MSH raised the cAMP levels in the calf adrenal glomerulosa cells, although the magnitude of the increase of cAMP in response to ACTH was greater. These findings suggest that IP₃ as a mediator of α-MSH-and β-LPH-induced aldosterone secretion is not likely and other mediator(s) may be involved.