Role of airway endogenous nitric oxide on lung function during and after exercise in mild asthma

We hypothesized that nitric oxide (NO), a known mild bronchodilator that can be released by several cell types within pulmonary airways, might protect airways during exercise in asthmatic subjects. We studied 17 individuals with documented exercise-induced asthma (screening exercise evaluation) on 2 study days: after treatment with inhaled NO synthase inhibitor N^G-monomethyl-L-arginine (L-NMMA; 2 ml of 25 mg/ml mist) and after treatment with saline vehicle. Pulmonary resistance (RL, esophageal manometry) rose and forced expiratory volume in 1 s fell more after L-NMMA compared with saline treatment, suggesting a bronchoprotective role for NO at baseline. The rise in RL seen after L-NMMA treatment was nearly completely reversed early in exercise, suggesting a non-NO-mediated bronchodilation. A slow rise in RL during constant-load exercise and dramatic increase in RL after exercise were the same on the 2 treatment days, indicating little role for NO in regulating airway function during and after exercise. We conclude that endogenous NO plays little role in regulating airway function during and after exercise in subjects with mild asthma.