Cardiac responses to acute insulin-induced hypoglycemia in humans

The effects of acute hypoglycemia on the heart and cardiovascular system were examined in humans using radioisotopic techniques, complemented by measurement of heart rate and blood pressure. The heart rate increased from 62 +/- 3 to 87 +/- 3 beats/min in response to hypoglycemia; this increase was accompanied by a significant increase in systolic blood pressure, a fall in diastolic blood pressure, with no change in the mean arterial blood pressure. The left ventricular ejection fraction increased from 47 +/- 3 (SE) to 72 +/- 5% in response to hypoglycemia. The increases in heart rate and ejection fraction were abolished during parenteral nonselective beta-adrenergic blockade with propranolol but were unaffected by either alpha-adrenergic blockade with phentolamine or cholinergic blockade with atropine. During beta-adrenergic blockade, there were significant increases in diastolic and mean arterial blood pressure in response to hypoglycemia. During alpha-adrenergic blockade the systolic, diastolic, and mean arterial pressures fell significantly after hypoglycemia. The blood pressure responses to hypoglycemia were unaffected by cholinergic blockade. Thus the increases in ejection fraction and in heart rate in response to hypoglycemia are mediated by beta-adrenoreceptors, whereas the blood pressure responses to hypoglycemia are mediated by alpha- and by beta-adrenoreceptors.