EFFECT OF CARDIOSELECTIVE AND NON-SELECTIVE β-BLOCKADE ON THE HYPOGLYCÆMIC RESPONSE IN INSULIN-DEPENDENT DIABETICS

Abstract The response to intravenous insulin was studied in seven diabetics after a dose of placebo, propranolol (40 mg), or metoprolol (50 mg). Two of the seven subjects also had a week's course of each of the same agents taken three times daily. Neither of the β-blockers potentiated the effect of insulin as judged by the rate of reduction in blood-glucose. However, blood-glucose recovery was reduced significantly by propranolol, but not significantly by metoprolol. Propranolol caused severe bradycardia and raised diastolic blood-pressure during hypoglycaemia; these effects were milder with metoprolol. Propranolol inhibited the free- fatty-acid levels after hypoglycaemia to a greater extent than did metoprolol. The results strongly suggest that propranolol (and presumably other non-selective β-blockers) is hazardous in subjects prone to hypoglycaemia. When diabetics require β-blockade a cardioselective β 1 -blocker should be used.