Effect of beta blockade and intrinsic sympathomimetic activity on exercise performance

Abstract

Beta-adrenergic receptor blocking drugs with intrinsic sympathomimetic activity may have the advantage of not depressing myocardial function and pulse rate at rest. Little is known about their effects during exercise. Thus, the effects of small and large doses of pindolol, a nonselective beta-adrenergic blocking drug with intrinsic sympathomimetic activity, were compared with the effects of small and large doses of propranolol in 13 normal men during treadmill exercise. Compared with placebo, all drug regimens decreased exercise duration (p less than 0.001). There were no significant differences in duration between pindolol and propranolol, or between the small and large dose of each drug. Maximal oxygen consumption tended to be lower with all preparations compared with placebo (p less than 0.10). With smaller doses, decrements of maximal heart rate (HR) and HR-blood pressure (BP) product were equivalent for pindolol and propranolol (decreases of 46 vs 43 beats/min, and 13,000 vs 12,000 units). The HR-BP product decreased more with high-dose propranolol than high-dose pindolol (decrease of 18,000 vs 14,800 units) due to a greater decrement in HR with propranolol (decrease of 65 +/- 3 vs 53 +/- 3 beats/min). At both submaximal levels, for both low- and high-dose preparations, HR, BP and HR-BP product were lower for propranolol than for pindolol. Thus, in healthy subjects, pindolol and propranolol at doses that produced equivalent reductions in maximal oxygen consumption, exercise duration and, for the smaller dose, HR, had different effects on submaximal HR-BP product, an index of myocardial oxygen consumption, as a result of a higher HR and BP with pindolol.