Natriuretic properties of melanocyte-stimulating hormones.

Proopiomelanocortin (POMC) is a protein that contains the amino acid sequences of numerous peptide hormones, including the melanocyte-stimulating hormones (MSH). MSH peptides of alpha, beta, and gamma primary structure are present in plasma, and all exhibit natriuretic activity. Intravenous infusion of alpha or beta-MSH leads to a time- and dose-dependent natriuresis, whereas gamma-MSH is reported to be natriuretic at low doses but antinatriuretic at high doses. The natriuretic activity of MSH peptides occurs without change in arterial pressure or renal hemodynamics, suggesting a possible direct tubular inhibition of sodium reabsorption. Intravenously infused gamma-MSH is associated with an increase in the plasma concentration of atrial natriuretic peptide. In addition, gamma-MSH also has a direct intrarenal natriuretic action that is dependent on the renal nerves. In rats, gamma-MSH-related peptides are involved in the reflex control of sodium excretion in situations such as the natriuresis that occurs (a) from the remaining kidney after acute unilateral nephrectomy, (b) from the contralateral kidney shortly after unilateral ureteral pressure elevation, and (c) after unilateral carotid artery traction. POMC-derived peptides (including MSH) are modulated in response to salt loading, and alterations in POMC metabolism and plasma peptide concentrations have been observed in genetically hypertensive rats and during the development of adrenal regeneration hypertension. In addition, plasma gamma-MSH levels are elevated in patients with severe congestive heart failure, and in primary hyperaldosteronism. These observations suggest a possible involvement of MSH-related peptides in sodium homeostasis as well as in certain forms of hypertension.