RESUMO
OBJECTIVES: To compare the effects of a highly beta1-selective adrenoceptor antagonist bisoprolol with those of atenolol and placebo on endurance exercise capacity in young, healthy male volunteers. DESIGN: Twelve subjects randomly received oral placebo, atenolol (100 mg/day) or bisoprolol (10 mg/day) for 3 weeks, following a double-blind cross-over design. METHODS: At the end of each period, the subjects performed an endurance exercise test on the bicycle ergometer at 70% of maximal aerobic power. Cardiac output was measured by means of an automated CO2-rebreathing method. Venous blood was sampled before, during and after exercise. RESULTS: Exercise duration was not significantly different between the two drugs tested. Total exercise duration was significantly reduced by bisoprolol (-19.4 +/- 6.7%, P< 0.01) (mean +/- SEM) and by atenolol (-29.8 +/- 6.6%, P< 0.001), compared with placebo. Atenolol and bisoprolol were equally effective in lowering resting plasma renin activity, heart rate and systolic blood pressure. Resting and exercise stroke volume were significantly increased by both drugs, so that cardiac output was not significantly affected. Both drugs induced significant decreases in plasma-free fatty acid concentrations during recovery and blunted the exercise-induced increase. There were no significant relationships between the reduction of exercise duration and the haemodynamic changes or the degree of impairment of the exercise-induced increase in free fatty acid release resulting from beta-blockade. CONCLUSIONS: It is concluded that both drugs affect endurance exercise capacity in young, normotensive men, with a tendency to a smaller reduction during bisoprolol treatment. Haemodynamic variables are unlikely to be involved in the reduction of endurance exercise capacity. The role of the reduced availability of plasma free fatty acids remains unclear.
