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Effects of Glucagon on Myocardial Metabolism in Patients With and Without Coronary Artery Disease

The metabolic effects of glucagon on the heart were studied in subjects with and without coronary artery disease. In both groups, a moderate rise in the arterial glucose level occurred with practically unchanged glucose uptake by the myocardium. Myocardial oxygen extraction was also unchanged in both groups of subjects. In individuals with normal coronary arteries, myocardial extraction ratio of lactate was normal before and unchanged after glucagon administration. In patients with significant coronary artery disease, mean extraction ratio of lactate was very low before glucagon and increased markedly following its administration. Seven of 18 patients had production of lactate by the myocardium before glucagon, and this reverted to lactate extraction 5 min after glucagon administration. Left ventricular work index was found to increase more than indices of myocardial contractility and oxygen consumption, and improved aerobic lactate utilization during glucagon action may be partly related to the lower oxygen cost of work performance or improved cardiac efficiency. Arterial serum potassium level decreased in both groups of subjects after glucagon administration, with the appearance of a slightly negative potassium balance across the myocardium. The possible relationship of the cardiac inotropism induced by glucagon to intramyocardial ionic exchanges is discussed.