Summary and conclusionsThe effects on diabetic control of the relative cardioselective beta-blocker metoprolol and the non-selective drug propranolol were compared in 20 hypertensive diabetic patients receiving diet alone or diet and oral hypoglycaemic agents. Each drug was given for one month in a double-blind, cross-over study. Fasting, noon, and mid-afternoon blood sugar concentrations rose by 1-0-1-5 mmol/l (18-27 mg/100 ml). The rise with propranolol was not significantly greater than with metoprolol. In a few patients the rise was clinically important.The small overall change observed in diabetic control should not deter the use of beta-blockers in non-insulindependent diabetics, provided control is carefully monitored at the onset of treatment.
IntroductionCatecholamines play a part in the release of insulin' and in the clinical reaction to hypoglycaemia2 and metabolic recovery from it.3 Adrenoceptor-blocking drugs might therefore be expected to influence the way in which patients, particularly diabetics, respond to fluctuations in blood sugar concentrations. Studies on volunteers4-6 show that beta-blockers modify the recovery from hypoglycaemia and suggest that selective, beta1-blocking drugs interfere less than non-selective drugs. The possible metabolic effects of beta-blockers in the presence of a high blood sugar concentration, however, have received relatively little attention, though one study7 showed that glucose tolerance is impaired to a greater extent with non-selective than cardioselective betablockers. One explanation for these results is that insulin secretion may be influenced through a beta 2-receptor in man as it is in dogs.8 The relevance of these observations to the routine management of diabetes is unknown.We decided to see whether long-term treatment with a betablocker materially affects blood sugar control in maturity-onset diabetes and if any advantage is gained from choosing a cardioselective agent. With these aims we compared the relatively cardioselective beta-blocker metoprolol9 with the non-selective agent propranolol in patients with maturity-onset diabetes.
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