Comparison of the effects of propranolol and MJ 1999 on cardiac β‐adrenoceptors in man

Summary 1 . Propranolol, a β-adrenoceptor blocking drug with local anaesthetic and a direct myocardial depressant action, and MJ 1999, a β-adrenoceptor blocking drug which has no local anaesthetic or intrinsic sympathomimetic action, were compared for β-adrenoceptor blocking activity in man. 2 . Propranolol was 2·67 times more active than MJ 1999 in reducing by 50% the tachycardia produced by the intravenous infusion of isoprenaline in healthy volunteers. 3 . Propranolol and MJ 1999 intravenously both reduced resting heart rate in the standing position and an exercise tachycardia, but there was no qualitative or quantitative difference between them. 4 . On oral administration, both propranolol and MJ 1999 reduced resting heart rate and an exercise induced tachycardia; propranolol was only slightly more active than MJ 1999. 5 . In patients with thyrotoxicosis propranolol was about twice as active as MJ 1999 in reducing the heart rate.