Effect of β-blocking agents with and without intrinsic sympathomimetic activity on work efficiency in healthy men

Summary. In order to evaluate the effect of β-blocking agents with and without intrinsic sympathomimetic activity (ISA) on work efficiency in healthy subjects, we studied the haemodynamic and gas exchange parameters, as well as blood lactate concentrations, during a graded maximal bicycle exercise test performed after perorally given propranolol (PRO) and pindolol (PIN) in seven healthy men. The medications (PRO: 80 mg X 2/day, PIN: 10 mg X 2/day, for seven days) were given in a placebo (PLA) controlled, double-blind, randomized, cross-over fashion. Both the drugs reduced heart rate and blood pressure during exercise equally compared with the placebo. The oxygen uptake at submaximal work loads, as well as at the maximum, was constantly and equally reduced by PRO and PIN compared with PLA. The anaerobic threshold was reached at a slightly lower oxygen uptake for both the drugs compared with the placebo (P < 0.05). No significant difference was, however, observed in the work levels at which the ventilatory anaerobic threshold was reached. Moreover, the gross efficiency, i.e. the amount of work performed at a certain energy consumption level (aerobic+anaerobic), was increased by both PRO (26.7 ± 0.5%, P < 0.02 vs PLA: 24–7 ± 0.5%) and PIN (26.5 ± 0–5%, P < 0.05 vs PLA) at a submaximal work load of 240 W. The results indicate that β-blocking agents propranolol and pindolol slightly and equally reduce maximal work performance, but increase the efficiency of submaximal work in a way that a certain amount of external work can be done with smaller consumption of oxygen. These findings may contribute to the benefit of β-blocking agents in patients with coronary heart disease.