Y2-Melanocyte-Stimulating Hormone

Peptides of the pro-opiocortin class produce pronounced cardiovascular and natriuretic actions. We have investigated the acute cardiovascular effects of one of the most potent members of this class, y2-melanocyte stimulating hormone (y2-MSH), in rats. Pressor actions of y2MSH administered systemicaMy were eliminated by ganglionic blockade with chlorisondamine. Peripheral cholinergic blockade failed to affect either the pressor or cardioaccelerator responses to y2MSH. Administration of yrMSH (2.0-10.0 /xg) produced vasoconstriction primarily in the mesenteric and hindlimb vascular beds, while the renal bed showed little response. Infusions of phenylephrine produced pressor responses similar to those found with y2-MSH, which were accompanied by a decrease in heart rate and vasoconstriction in the mesenteric and renal vascular beds. Hemodynamic changes produced by y2-MSH and phenylephrine were blocked or attenuated by a,-adrenergic receptor blockade with pra/.osin. Direct injection of y2-MSH into the renal artery produced an acute renal vasoconstriction that was not attenuated by a,-adrenergic or ganglionic blockade. These findings and the results of previous publications are consistent with the hypothesis that y2-MSH may produce a centrally mediated activation of the sympathetic nervous system, have direct vasoconstriction actions on the renal vasculature, and inhibit baroreceptor function to produce an increase in blood pressure without an accompanying bradycardia. (Hypertension 7 [Suppl I]: 1-145—1-150, 1985)