Abstract
In order to assess the role of the bronchial circulation in the pathogenesis of exercise-induced asthma (EIA), we conducted a double-blind, randomized study of the effects of pretreatment with an inhaled alpha 1-adrenergic agonist, methoxamine (Mx), in nine asthmatic teenagers with known EIA. Exercise consisted of 5 min cycle ergometry at a submaximal, constant work-load, while the subjects breathed dry air at ambient temperature. Forced expiratory volume in one second (FEV1) was measured at baseline, 15 min after pretreatment of either Mx or saline, and serially after exercise. Mx significantly reduced the exercise-induced fall of FEV1 without modifying baseline FEV1 in five of the eight subjects, had little or no effect in three and caused an acute asthmatic attack in the remaining subject. Mx has potent constrictor effects on both bronchial and vascular smooth muscles through stimulation of postjunctional alpha 1-adrenoceptors. Therefore, the protective effect of Mx on EIA may be attributed to vasoconstriction of tracheobronchial vessels opposing the hyperaemia and mucosal airway oedema that may cause, at least in part, the exercise-induced acute bronchial obstruction in EIA. Alternatively, Mx stimulates mucus, water and electrolyte secretion by airway epithelium and may, therefore, oppose the dehydration of airway surface that could be a causative factor of EIA.
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