Hypertensive response following stimulation of opiate receptors in the caudal ventrolateral medulla.
In urethane-anesthetized rats, vasodepressor neuron pools were located bilaterally in and adjacent to the A1 area of the ventrolateral medulla by injecting the neuroexcitatory amino acid, L-glutamate. Ventrolateral vasodepressor areas included the caudalateral part of the nucleus reticularis gigantocellularis, the rostrolateral part of the nucleus reticularis ventralis, and the dorsal nucleus reticularis lateralis. In the ventrolateral vasodepressor areas L-glutamate elicited a transient fall in blood pressure (BP) and heart rate (HR). The opiate agonist (D-ala2-met5)-enkephalinamide (DAME) was used to stimulate opiate receptors in vasodepressor sites, identified with L-glutamate. In these sites, bilateral injections (0.1 microliter/site) of DAME caused a dose-related (2.5-500.0 ng) increase in blood pressure and heart rate, as well as exaggeration of the response to occlusion of the carotid. The effects of DAME on blood pressure were completely abolished by alpha-adrenergic blockade (phentolamine, 2 mg/kg, i.v.) and all effects of DAME were reversed by the administration of naloxone HCl (1 mg/kg, i.v.). Naloxone reversal was accompanied by an unexpected "rebound" hypertension. Saline had no significant effects when injected, or administered intravenously, in the absence or presence of DAME. It was concluded that stimulation of opiate receptors in the ventrolateral vasodepressor areas activated sympathetic outflow. An enkephalinergic system in this area of the brain stem may serve to modulate blood pressure, heart rate and cardiovascular reflexes.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D002339:Carotid Arteries / Q000502:physiology; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*
D005971:Glutamates; D011957:Receptors, Opioid; D009270:Naloxone; D018698:Glutamic Acid; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-