Inhibition of acetylcholine-induced bronchoconstriction in asthmatics by nifedipine

The calcium-dependent constriction of bronchial smooth muscle cells and release of mediators derived from mast cells is important in the pathophysiology of asthma. We hypothesized that nifedipine, a slow calcium channel blocker, would inhibit or attenuate acetylcholine-induced bronchoconstriction in asthmatics. Because one consequence of mast cell activation is the release of platelet-activating factor, we wondered whether thromboxane levels would be increased during acute bronchial constriction in asthmatics. Bronchoconstriction was induced in 8 asthmatics (6 men, 2 women) by acetylcholine; each subject was pretreated either with placebo or nifedipine (20 mg sublingually) on 2 separate days. Vital capacity, forced expiratory volume in 1 s, peak expiratory flow rates and oscillatory resistance were measured prior to and after the intake of placebo or nifedipine as well as after an acetylcholine challenge. Pretreatment with nifedipine significantly attenuated acetylcholine-induced changes in all four lung function parameters studied, but did not significantly influence the increase in thromboxane B2 plasma concentrations observed after the acetylcholine challenge. From these data we conclude that nifedipine inhibits the acetylcholine-induced bronchoconstriction in asthmatics. This effect may be either a direct action on bronchial smooth muscle or may be due to the inhibition of mediators other than thromboxane.