Adenosine-induced Bronchoconstriction in Asthma

Abstract

Adenosine by inhalation causes bronchoconstriction in asthmatic but not in normal subjects by an undefined mechanism. This study investigated the roles of cholinergic reflex stimulation and decreased β2-adrenoceptor responsiveness to explain adenosine's bronchoconstrictor action. The protection afforded by the inhaled muscarinic cholinergic antagonist, ipratropium bromide (IB) 1 mg, from bronchoconstriction induced by inhaled adenosine was compared with that of methacholine in 8 allergic asthmatic subjects. After saline placebo, the geometric mean concentrations of adenosine required to produce a 20% fall in FEV1 (PCf20) was 2.20 mg/ml and a 35% fall in SGaw (PCs35) was 1.97 mg/ml, which compared to 0.13 and 0.11 mg/ml, respectively, for methacholine. The IB increased FEV1 by 11 to 15% and SGaw by 69 to 73% and provided a large degree of protection against methacholine, with a geometric mean concentration ratio (CR) of 196 when airway caliber was measured as SGaw (p < 0.001). In contrast, IB provided litt...