Inhaled lysine acetylsalicylate (L-ASA) attenuates the bronchoconstrictor response to adenosine 5'-monophosphate (AMP) in asthmatic subjects

Abstract

When administered by inhalation, adenosine 5'-monophosphate (AMP) provokes dose-related bronchoconstriction in asthmatic subjects by a mechanism believed to involve mast cell mediator release. However, little is known of the change in airway responsiveness to AMP after cyclo-oxygenase blockade. The aim of this study was to investigate the effect of the potent cyclo-oxygenase inhibitor, lysine acetylsalicylate (L-ASA) administered by inhalation, on AMP-induced bronchoconstriction in a group of nine asthmatic subjects. The subjects studied attended the laboratory on six separate occasions to receive nebulized L-ASA (solution of 90 mg·ml-1) or matched placebo (glycine solution, 30 mg·ml-1) 15 min prior to bronchoprovocation tests with AMP, histamine and methacholine in a randomized, double-blind order. Changes in airway calibre were followed as forced expiratory volume in one second (FEV1) and agonist responsiveness was expressed as the provocative concentration causing a 20% fall in FEV1 from baseline (PC20). Administration of both L-ASA and glycine solution caused a small but significant acute fall in FEV1 from baseline, which returned to normal within 15 min. When compared to placebo, inhaled L-ASA reduced the airway responsiveness to AMP in all the subjects studied, the geometric mean (range) values for PC20 AMP increasing significantly from 36.3 (7.9-250.5) to 101.8 (27.2-1300) mg·ml-1 after placebo and L-ASA, respectively. Moreover, nebulized L-ASA induced a small but significant reduction in airway responsiveness to histamine, the geometric mean (range) PC20 values for histamine increasing from 2.77 (1.05-5.49) to 436 (1.69-11.24) mg·ml-1 after placebo and L-ASA, respectively. No significant change in airway responsiveness to methacholine was recorded after L-ASA. Administration of L-ASA by inhalation protects the asthmatic airways against AMP and, to a lesser extent, histamine-induced bronchoconstriction, thus suggesting that endogenous prostaglandins may play a contributory role in the airways response to AMP in human asthma.