Beta‐adrenoceptor blockade and hypoglycaemia. A randomised, double‐ blind, placebo controlled comparison of metoprolol CR, atenolol and propranolol LA in normal subjects.

1. The effect of 1 week of treatment with propranolol LA (160 mg), atenolol (100 mg) and metoprolol CR (100 mg) on awareness of and the physiological responses to moderate hypoglycaemia were compared with placebo using a randomised, cross‐over design in 12 healthy volunteers. 2. All three beta‐adrenoceptor antagonists reduced resting heart rate, systolic blood pressure and heart rate responses to submaximal exercise compared with placebo. 3. Under hyperinsulinaemic (60 mu m‐2 min‐1) clamp conditions, at a blood glucose of 2.5 mmol l‐1, atenolol prevented the rise in systolic and atenolol and metoprolol CR prevented the fall in diastolic blood pressure usually associated with hypoglycaemia. At this level of hypoglycaemia, the expected increase in heart rate was inhibited by atenolol but not metoprolol CR. Pre‐ treatment with propranolol LA resulted in a significant pressor response and a bradycardia during hypoglycaemia. In addition the normal increase in finger tremor was abolished by propranolol LA. 4. During hypoglycaemia all three beta‐adrenoceptor blockers augmented sweating compared with placebo but hypoglycaemic symptoms, awareness and slowing of reaction time were the same with drugs and placebo. 5. The rise in plasma adrenaline and other counter‐regulatory hormones during hypoglycaemia was enhanced by beta‐adrenoceptor blockade. 6. We conclude that beta‐adrenoceptor antagonists modify the physiological and hormonal responses to, but do not adversely affect awareness of, moderate hypoglycaemia in healthy volunteers.