Central alpha 1-adrenergic and opiate systems in the control of the vagal tone in normotensive and spontaneously hypertensive rats.
In anesthetized, normotensive beta-blocked rats, the alpha 1-adrenoceptor blocking drug, AR-C 239 (300 micrograms/kg, i.v.) induced a bradycardic effect related to a central increase in the vagal tone. This bradycardia was inhibited by previous administration of naloxone, intravenously (1 mg/kg) or centrally (100 micrograms/kg, i.c.) injected. Naloxone, by itself did not change the heart rate. In brainstem membranes from normotensive rats, AR-C 239 did not influence the stereoselective binding of [3H]naloxone. In spontaneously hypertensive (SH) rats, naloxone peripherally or centrally administered did not influence the activation of the vagal tone induced by AR-C 239, in beta-blocked animals. These results suggest the possible involvement of opiate release in the AR-C 239-induced vagal bradycardia, in normotensive rats. They also afford new arguments for the existence of close interactions between central alpha-adrenergic and opiate systems in the cardiovascular regulation. The possible participation of kappa-receptors in this effect is discussed. In addition, such an opiate mechanism triggered by central alpha 1-adrenoceptor blockade seems to be either absent or inactive in SH rats.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000139:chemically induced / Q000503:physiopathology; D001933:Brain Stem / Q000378:metabolism; D006973:Hypertension / Q000378:metabolism / Q000503:physiopathology*; D007546:Isoquinolines / Q000494:pharmacology*; D008297:Male; D009270:Naloxone / Q000378:metabolism / Q000494:pharmacology*; D010879:Piperazines; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D014628:Vagotomy; D014630:Vagus Nerve / Q000503:physiopathology*
D000317:Adrenergic alpha-Antagonists; D007546:Isoquinolines; D010879:Piperazines; D011942:Receptors, Adrenergic, alpha; D011957:Receptors, Opioid; D009270:Naloxone; C032994:AR-C239