Coronary Vascular Effects of Glucagon in the Isolated Dog Heart

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Abstract
Glucagon decreases peripheral vascular resistance by direct action on the arterioles. The present experiments were performed to study the effect of glucagon on the coronary resistance vessels. In isolated hearts from eight dogs the coronary arteries were perfused at a constant rate and the change in coronary pressure was used as an index of change in resistance after the intracoronary injections of glucagon (50 µg/kg). In the beating heart, glucagon caused a 22% decrease in the average coronary pressure (from 102 to 80 mm Hg); however, with this decrease in coronary resistance, myocardial contractility rose an average of 45% (from 11 to 16 units), the average heart rate increased 38% (from 156 to 213 beats/min), and the average coronary venous oxygen saturation decreased from 79.7% to 63.7%. However, when similar intracoronary injections of glucagon were made after cardiac arrest by potassium there was no change in coronary venous oxygen saturation and no significant decrease in coronary pressure. We conclude that the decrease in coronary resistance in the beating heart after glucagon injection is secondary to the metabolic effects of the increased myocardial contractility and heart rate, and that there is no significant direct vasodilating effect on the coronary resistance vessels.

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