Increases in heart rate and blood pressure produced by injections of dermorphin into discrete hypothalamic sites

Central cardiovascular sites of action for dermorphin were determined by injecting 40 pmol of the peptide into discrete sites within the hypothalamus of halothane anesthetized rats. Blood pressure and heart rate in 101 rats were 88 +/- 1 mm Hg and 338 +/- 3 beats/min, respectively, prior to 100 nl intrahypothalamic injections of either vehicle or dermorphin. In the caudal anterior hypothalamic nucleus (A5800-5300), dermorphin, but not vehicle, increased blood pressure 8% and heart rate 26%, without changing respiration rate. The peak response was at 32 +/- 5 min, the duration greater than 90 min. Injections of naloxone (30 nmol) into the same anterior hypothalamic site, or 3 mg/kg naloxone administered i.m., completely reversed the cardiovascular actions. Similar increases in heart rate and blood pressure occurred at A6600-6300, the region between medial preoptic and anterior hypothalamic nuclei. Small increases in heart rate, but not blood pressure, resulted from dermorphin injections into the septal area, medial preoptic nucleus, paraventricular hypothalamic nucleus and the lateral ventricle, while injections in the posterior and dorsomedial hypothalamic nuclei were without effect on blood pressure and heart rate. These data provide support for anterior hypothalamic and medial preoptic sites for the cardiovascular actions of the opiate receptor agonist, dermorphin, and indicate greatest effects with this dose (primarily on heart rate) are produced at discrete sites (A6600-6300 and A5800-5300) within these nuclei.