Direct and vagally mediated chronotropic effects of morphine studied by selective perfusion of the sinus node of awake dogs.
Two milliliters of a morphine sulfate solution (1 mg/ml) perfused selectively into the sinus node artery of five trained unanesthetized dogs caused an immediate brief sinus tachycardia followed by a delayed but prolonged sinus bradycardia. Beta-receptor blockade was achieved by selective perfusion of propranolol hydrochloride solution (10 mug/ml) into the sinus node artery and did not prevent the initial sinus tachycardia. Selective perfusion of the sinus node with atropine sulfate solution (1 mug/ml), however, did prevent morphine from causing further sinus rate increase. The immediate positive chronotropic action of morphine was thus attributable to a peripherally located vagolytic action. The exact opposite was true with regard to the delayed bradycardia; it was due to a centrally mediated generalized increase in vagal tone regularly elicited by morphine.
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries; D001285:Atropine / Q000494:pharmacology; D004285:Dogs; D004562:Electrocardiography; D006339:Heart Rate / Q000187:drug effects*; D007275:Injections, Intravenous; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D010477:Perfusion; D012849:Sinoatrial Node / Q000187:drug effects*; D013268:Stimulation, Chemical; D013610:Tachycardia / Q000139:chemically induced; D013997:Time Factors
D000319:Adrenergic beta-Antagonists; D009020:Morphine; D001285:Atropine