Exercise metabolism during 1 hour of treadmill walking while taking high and low doses of propranolol, metoprolol, or placebo.

Aerobic exercise and beta-blocking drugs are regularly prescribed as treatment for hypertension and as a prophylactic for patients at risk from coronary heart disease and for those recovering from an infarct. Some beta blockers, particularly non-beta 1-selective drugs, may make exercise more difficult, possibly by interfering with substrate metabolism during exercise. This study examined the effects of low and high doses of a beta 1-selective blocker, metoprolol, and a non-selective beta blocker, propranolol, on exercise metabolism. The study involved 20 healthy subjects (10 men, 10 women) who walked on a treadmill at 50% of their maximal oxygen uptake for 1 h on five occasions, separated by 7 days. On each of the five occasions they received one of the following treatments, given in random order: placebo, metoprolol 50 mg, metoprolol 100 mg, propranolol 40 mg, or propranolol 80 mg, all taken twice daily. Fat oxidation, expressed as a percentage of total energy expenditure, was significantly lower than with placebo for all of the active treatments except metoprolol 50 mg (placebo: 42.7 +/- 11.6%; metoprolol 50 mg: 38.7 +/- 14.1%, p = NS; metoprolol 100 mg: 36.3 +/- 13.7%, p = 0.05; propranolol 40 mg: 31.2 +/- 9.3%, p = 0.01; propranolol 80 mg: 29.5 +/- 10.9%, p = 0.01); and significantly lower with propranolol than with metoprolol (propranolol 40 mg: p = 0.0036; propranolol 80 mg: p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)