Inhaled lysine acetylsalicylate (L-ASA) attenuates histamine-induced bronchoconstriction in asthma

When administered by inhalation, histamine provokes dose-related bronchoconstriction in asthmatic subjects mainly by a direct activation of histamine H1-receptors on airway smooth muscle. However, little is known of the change in airway responsiveness to histamine after cyclooxygenase blockade. The aim of the study was to investigate the effect of the potent cyclooxygenase inhibitor, lysine acetylsalicylate (L-ASA), administered by inhalation on histamine-induced bronchoconstriction in a group of 16 asthmatic subjects. The subjects studied attended the laboratory on four separate occasions to receive nebulized L-ASA (solution of 90 mg/ml) or matched placebo (glycine solution of 30 mg/ml) 15 min before bronchoprovocation tests with histamine and methacholine in a randomized, double-blind order. Changes in airway caliber were followed as forced expiratory volume in 1 s (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 histamine in 13 of the 16 subjects studied, the geometric mean (range) values fro PC20 histamine increasing significantly (P < 0.001) from 1.72 (0.13-5.49) mg/ml to 3.31 (0.36-12.00) mg/ml after placebo and L-ASA, respectively. No significant change in airway responsiveness to methacholine was recorded after L-ASA. Acute administration of L-ASA by inhalation protects the asthmatic airways against histamine-induced bronchoconstriction, thus suggesting that endogenous prostaglandins may play a contributory role in the airways response to histamine in human asthma.