No effect of propranolol and metoprolol on tolbutamide-stimulated insulin-secretion in hypertensive diabetic and non-diabetic patients.

In a double-blind cross-over study, we compared the effects of placebo, propranolol and metoprolol on tolbutamide-stimulated insulin-secretion in 10 non-insulin-dependent hypertensive diabetics and in 10 hypertensive non-diabetic patients. The patients were randomly allocated to two weeks each of treatment with placebo, propranolol 80 mg or metoprolol 100 mg b.i.d. At the end of each period, an intravenous tolbutamide tolerance test (IVTT, 200mg of tolbutamide i.v.) was performed, which caused a significant rise in peripheral insulin levels, leaving blood glucose concentrations unchanged. Tolbutamide-induced insulin-secretion was unaffected by pretreatment with beta-blockers when blood glucose concentrations were unchanged during the test. Since the serum-concentrations achieved with 200 mg of tolbutamide i.v. are similar to those reported during oral tolbutamide therapy, there seems to be no clinically significant interaction between beta-blockers and tolbutamide with respect to insulin-secretion.