Comparison of Salmeterol and Albuterol-induced Bronchoprotection Against Adenosine Monophosphate and Histamine in Mild Asthma

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Abstract
Short-acting β2-agonists provide greater protection to bronchoconstriction induced by adenosine-5 ′ -monophosphate (AMP) than does methacholine. Because AMP produces bronchoconstriction through release of mediators from mast cells, and methacholine directly constricts airway smooth muscle, this suggests that β2-agonists stabilize mast cells in vivo. This in vivo property has not been demonstrated with long-acting β2-agonists. We undertook two double-blind, randomized, crossover, placebo-controlled studies to investigate the effects of salmeterol and albuterol on airway responsiveness (AR) to AMP and histamine in patients with mild asthma. In the first study, 19 patients attended on four occasions to inhale salmeterol 50 μ g or placebo 2 h before challenge with AMP or histamine. In the second study 16 patients (13 of whom had participated in the first study) were studied in a similar fashion but inhaled albuterol 400 μ g or placebo 30 min prior to challenge. Salmeterol reduced AR to AMP and histamine by 3.4 ± 0.3 and 3.9 ± 0.3 doubling doses, respectively (NS). In contrast, albuterol demonstrated a greater protective effect on AMP than on histamine, reducing AR by 5.1 ± 0.3 and 3.8 ± 0.2 doubling doses, respectively (p < 0.005). Thus, in contrast to albuterol, salmeterol did not demonstrate mast-cell stabilizing properties in vivo at a time corresponding to maximal bronchodilatation. These findings might be explained by the unique pharmacologic profile of salmeterol in combination with the differential β2-adrenoceptor pharmacology of bronchial mast cells and bronchial smooth muscle.

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