The effect of beta-blockade on glucose tolerance and insulin release in adult diabetes.

Blood glucose and plasma insulin levels were studied in ten adult diabetics treated in a cross-over fashion for at least three weeks with alprenolol, a non-selective beta-blocker, or with metoprolol, a cardioselective beta 1-blocker. Dietary intake was controlled three days prior to the study which comprised both i.v. and oral glucose tolerance tests. Mean fasting blood glucose levels were significantly higher on alprenolol than on metoprolol. The increase in fasting blood glucose was particularly pronounced in two patients. In these subjects the glucose tolerance following both an i.v. and an oral glucose load was reduced when treatment was switched from metoprolol to alprenolol. Lower plasma insulin levels in response to glucose were also found in these patients on alprenolol than on metoprolol. The mean insulin levels for all ten patients did not differ significantly between the two treatment periods. These data show that treatment with a non-selective beta-blocker can in some patients cause a considerable deterioration of the glucose tolerance, presumably due to inhibition of insulin release.