THE ROLE OF MYOCARDIAL CATECHOLAMINES IN THE RESPONSE TO TYRAMINE

¹ Cardiology Branch, National Heart Institute, Bethesda, Maryland

The relationship between the dose of tyramine and heart rate, myocardial contractile force and mean arterial pressure was studied in 5 normal, 3 reserpine pretreated, and 3 chronically cardiac denervated dogs, before and after the infusion of norepinephrine. In the reserpine pretreated dogs these responses were clearly reduced below those observed in the control dogs. In the cardiac denervated dogs the myocardial contractile force, heart rate, and pressor responses to tyramine were essentially the same as in the reserpine pretreated dogs. The infusion of norepinephrine increased the contractile force response to tyramine in the reserpinized dogs whereas in the cardiac denervated dogs only the pressor response was augmented. Cardiac denervation and reserpine pretreatment reduced atrial norepinephrine to less than 0.05 µg/g. The infusion of norepinephrine increased the myocardial norepinephrine in the reserpine pretreated dogs to approximately 30% of normal. These results indicate that most of the inotropic and chronotropic effects of tyramine observed in the intact dog are the result of the release of only myocardial catecholamines and that the norepinephrine content of the reserpine pretreated dog heart can be partially repleted by a prolonged infusion of high concentrations of norepinephrine.