Effects on physical performance of intrinsic sympathomimetic activity (ISA) during selective β₁-blockade

Summary

In 15 healthy, not specifically trained volunteers (age: 26.6±2.7 years) single equipotent doses of a selective β₁-blocker with intrinsic sympathomimetic activity (ISA) (200 mg Epanolol-Visacor; V) and of a selective β₁-blocker without ISA (100 mg Metoprolol; M) were compared with placebo (P) with respect to their influence upon physical performance capacity and metabolism in a random, double blind, cross-over experimental setting. The subjects underwent three step by step incremental treadmill tests and three treadmill endurance tests until volitional exhaustion. Maximum running speed and maximum oxygen uptake were used as measures of maximum performance capacity. Running speed and oxygen uptake related to individual anaerobic threshold, and running time and running distance in the endurance tests were used as measures of endurance capacity. Both maximum and endurance performances were reduced significantly by β-blockade. No relevant differences were discerned between V and M. The uniform reduction in exercise heart rate with both β-blockers demonstrated the application of equipotent doses. At rest, heart rate was significantly higher under V than under M. Carbohydrate metabolism was unaffected, both βblockers showing equal inhibition of lipolysis during exercise. We conclude that intrinsic sympathomimetic activity has no influence upon physical performance and metabolism during selective β₁-blockade.