BACKGROUND Nitric oxide (NO) is involved in inflammation and host defence of the lung. It has been found in increased concentrations in the airways in asthmatic subjects but its levels in patients with chronic obstructive pulmonary disease (COPD) have not been investigated. A study was undertaken to determine whether markers of NO metabolism (NO in exhaled air, iNOS expression in sputum cells, and nitrite + nitrate (NO₂ ^–/NO₃ ^–) in sputum supernatant) are increased in subjects with COPD, and whether they correlate with inflammatory indices in induced sputum. The associations of these markers with smoking were also assessed.

RESULTS No differences were observed between subjects with COPD and healthy controls in exhaled NO excretion rate (median 5.15 and 6.25 nmol/min), sputum macrophage iNOS expression (14% and 12%), and sputum supernatant NO₂ ^–/NO₃ ^– (46 and 73 μM). NO in exhaled air correlated with the percentage of sputum eosinophils in patients with COPD (rho = 0.65, p = 0.009) but not in healthy individuals. Exhaled NO and supernatant NO₂ ^–/NO₃ ^– levels were lower in healthy smokers than in healthy non/ex-smokers.

CONCLUSIONS Our findings indicate that NO metabolism is not increased in patients with stable COPD. The close association between exhaled NO levels and sputum eosinophils suggests a role for NO in airway inflammation in COPD. Studies performed during exacerbations may clarify this role.