Prazosin, an alpha 1-adrenoceptor antagonist, partially inhibits exercise-induced asthma

The effect of prazosin, a potent and specific alpha 1-adrenoceptor antagonist given by inhalation (total nebulized 2 mg) was compared with placebo in a double-blind randomized study of 10 atopic asthmatic children. Prazosin significantly (p less than 0.01) reduced the severity of post-exercise bronchoconstriction (maximum fall in peak expiratory flow after exercise 21.4% +/- SEM 6.3% after prazosin compared with 42.5% +/- 7.3% after placebo). This protective action of prazosin suggests that activation of alpha 1-adrenoceptor may be involved in the pathogenesis of exercise-induced asthma either by facilitation of mast-cell mediator release or by direct contraction of bronchial smooth muscle. Prazosin did not significantly change resting bronchomotor tone or histamine-induced bronchoconstriction, suggesting no effect on bronchial smooth muscle contractility.