Non-adrenergic, non-cholinergic nervous system and overnight airway calibre in asthmatic and normal subjects

Increased parasympathetic tone does not fully explain the night-time bronchoconstriction responsible for nocturnal cough and wheezing in asthmatic subjects. The overnight variation in function of the other neural pathway innervating bronchial smooth muscle--the non-adrenergic, non-cholinergic (NANC) system--was thus examined. NANC function was tested after parasympathetic and beta-adrenergic blockade in 12 normal subjects and 12 patients with mild asthma by comparing the bronchodilator effect (measured as oscillatory resistance, Ros) of capsaicin (an NANC stimulant) at 0400 h with that at 1600 h. The order in which capsaicin or diluent was given was randomised, and observers were blind as to which substance had been inhaled. Bronchodilatation was greater at 1600 h than at 0400 h in both the normal subjects (mean decrease in Ros 1-3 min after capsaicin at 1600 h 9% [SEM 1], at 0400 h -2% [1]; p less than 0.001) and the asthmatic group (1% [1], -7% [2]; p = 0.001). The results suggest that inhibition of NANC function in the early morning may contribute to overnight bronchoconstriction.