Insulin and myocardial blood flow.

The renaissance of glucose-insulin-potassium infusion (GIK) as a treatment of acute myocardial infarction both in diabetic and nondiabetic subjects has raised new interests to clarify the effects and mechanisms of insulin on myocardium. Although the action of insulin on substrate metabolism is quite well studied in heart, the cardiovascular effects were until recent years poorly known. Insulin induces skeletal muscle vasodilation mainly via the endothelium-dependent mechanism and appears to have an important role in normal vascular function. There is increasing amount of evidence that insulin acts as a vasodilatory hormone also in coronary arteries. Insulin enhances myocardial blood flow and decreases coronary vascular resistance in a dose-dependent manner in healthy subjects. Moreover, insulin is able to increase myocardial blood flow also in subjects who are characterized by coronary dysfunction such as subjects with obesity, type 1 diabetes and coronary artery disease. However, vasodilatory effect of insulin may be blunted in these patients. Since already very small increase in myocardial blood flow can reduce significantly myocardial ischemia, these vasodilatory actions of insulin in coronary arteries might partly contribute to beneficial effects of GIK therapy. On the other hand, in contrast to these acute beneficial effect of insulin, epidemiological studies have indentified chronic hyperinsulinemia, a common feature in subjects with insulin resistance to glucose uptake, as an independent risk factor for coronary artery disease. The present article review the physiological and pathophysiological role of insulin in cardiac vasculature and its clinical importance during myocardial ischemia and development of coronary artery disease.