Exercise responses of healthy subjects in the evaluation of cardioselectivity of beta-blockers.

The effects of intravenous propranolol, metoprolol, acebutolol and placebo on exercise-induced changes in heart rate and peak flow rate (PFR) have been studied in a group of healthy subjects. The three beta-blockers produced significant and comparable reductions in exercise-induced tachycardia and the magnitude of the reduction was related to the log plasma concentration of each drug. Significant cardiac beta-blockade was detectable for three hours after giving propranolol and for four hours after metoprolol and acebutolol. The exercise-induced changes in PFR were small and variable and were not significantly affected by any of the drugs. We conclude that, contrary to published reports, exercise-induced changes in heart rate and PFR in healthy subjects do not provide a satisfactory test system for assessing the selectivity of beta-blockers.