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Direct and Vagally Mediated Chronotropic Effects of Morphine Studied by Selective Perfusion of the Sinus Node of Awake Dogs

1975; Elsevier BV; Volume: 68; Issue: 2 Linguagem: Inglês

10.1378/chest.68.2.222

1931-3543

Ferdinand Urthaler, James H. Isobe, Thomas N. James,

Cardiovascular Syncope and Autonomic Disorders

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 (10µg/ml) into the sinus node artery and did not prevent the initial sinus tachycardia. Selective perfusion of the sinus node with atropine sulfate solution (1µg/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. 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 (10µg/ml) into the sinus node artery and did not prevent the initial sinus tachycardia. Selective perfusion of the sinus node with atropine sulfate solution (1µg/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.