Cardiovascular effects of intrahypothalamic injections of α-melanocyte stimulating hormone

Abstract

Injection of α-melanocyte stimulating hormone (α-MSH, 0.6–12 nmol in 100–300 nl) into the rostral dorsomedial hypothalamic nucleus of the halothane anesthetized rat resulted in a 12% increase in heart rate (41 ± 4bpm) which was accompanied by a slight increase in blood pressure (5 ± 1mm Hg). The response was characterized by a gradual onset, with a peak increase at 7 ± 1 min and a duration of 51 ± 6 min. Tachyphylaxis to the response was apparent for at least 180 min following initial exposure to the peptide. In contrast to the increase in heart rate observed following α-MSH injection into the dorsomedial nucleus, injections into the medial preoptic, anterior, paraventricular or posterior hypothalamic nuclei had no significant effects on blood pressure and heart rate. These data suggest a possible role for brain α-MSH in the central control of heart rate at a site within the dorsomedial nucleus of the hypothalamus.