The role of alpha-receptors in bronchoconstriction induced by beta-blockade

We examined 10 patients with an exercise-induced asthma. Physical exercise was carried out under placebo, 40 mg propranolol, 5 mg pindolol and 50 mg metoprolol, respectively, before and after alpha blockade. After exercise, we noted a distinct increase of airway resistance in all cases, the increase of which, however, was lower after a preceding alpha blockade. Under propranolol, the increase of the airway resistance and of norepinephrine, as compared with pindolol, metoprolol, and placebo, was most intensive.