Contribution of β-adrenergic receptors to exercise-induced bronchodilatation in healthy humans

Exercise in healthy subjects is usually associated with progressive bronchodilatation. Though the decrease in vagal tone is deemed to be the main underlying mechanism, activation of bronchial β₂-receptors may constitute an additional cause. To examine the contribution of β₂-adrenergic receptors to bronchodilatation during exercise in healthy humans, we studied 15 healthy male volunteers during maximum exercise test at control conditions and after a non-selective β-adrenergic blocker (carvedilol 12.5mg twice a day until heart rate decreased at least by 10beats/min) and inhaled β₂-agonist (albuterol 400μg). Airway caliber was estimated from the partial flow at 40% of control forced vital capacity (V̇part40) and its changes during exercise from the slope of linear regression analysis of V̇part40 values against the corresponding minute ventilation during maximal exercise until exhaustion. At control, V̇part40 increased progressively and significantly with exercise. After albuterol, resting V̇part40 was significantly larger than at control increased but did not further increase during exercise. After carvedilol, V̇part40 was similar to control but its increase with exercise was significantly attenuated. These findings suggest that β₂-adrenergic system plays a major role in exercise-induced bronchodilation in healthy subjects.