Insulin-induced increase in heart rate and its prevention by propranolol

Acute hyperinsulinaemia in the absence of changes in blood glucose increases heart rate in man. Animal studies have suggested that beta-adrenergic blockade does not prevent the insulin-induced increase in heart rate. The aim of the present study was to investigate the acute effect of insulin on heart rate and blood pressure in non diabetic subjects and, in particular, to determine whether beta-adrenergic receptor blockade would significantly influence the effect. On separate days 9 healthy young volunteers were pretreated with either 80 mg propranolol or placebo p.o. After a 60-90 min period of heart rate and blood pressure stabilization, a placebo injection was given intravenously and heart rate and blood pressure were then monitored every 5 min. After 30 min insulin Actrapid MC 0.2 IU/kg body weight was given i.v. A 20% glucose infusion was given to maintain blood glucose at its fasting level. After insulin administration, a rapid and statistically significant increase in heart rate was observed when the patients were pretreated with placebo; pretreatment with propranolol completely prevented this effect. Serum insulin levels were significantly higher than baseline at all times and there was no significant change in blood glucose. The results are consistent with the hypothesis that the insulin-induced increase in heart rate in man may result from stimulation of cardiac sympathetic activity.