Inducible nitric oxide synthase expression is increased in the alveolar compartment of asthmatic patients

Increased exhaled nitric oxide ( NO ) levels in asthma are suggested to be through inducible NO synthase (i NOS ). The aim of this study was to investigate the expression of i NOS in bronchoalveolar lavage ( BAL ) cells and tissue from central and peripheral airways and compare it with the exhaled bronchial and alveolar NO levels in patients with asthma vs a control group. Methods Thirty‐two patients with asthma (defined as controlled or uncontrolled according to Asthma Control Test score cut‐off: 20) and eight healthy controls were included. Exhaled NO was measured, and alveolar concentration and bronchial flux were calculated. i NOS was measured in central and peripheral lung biopsies, as well as BAL cells. Bronchoalveolar lavage macrophages were stimulated in vitro , and i NOS expression and NO production were investigated. Results Expression of i NOS was increased in central airway tissue and the alveolar compartment in uncontrolled as compared to controlled asthmatics and healthy controls. There were no differences, however, in i NOS m RNA levels in total BAL cells in uncontrolled as compared to controlled asthma. Bronchoalveolar lavage cell m RNA levels of i NOS or i NOS expression in central and alveolar tissue did not relate to alveolar NO , nor to bronchial flux of NO . In vitro stimulation with leukotriene D 4 increased i NOS m RNA levels and NO production in cultured BAL macrophages. Conclusion The levels of both bronchial and alveolar i NOS are increased in uncontrolled as compared to controlled asthma. However, levels of i NOS in BAL macrophages were not reflected by alveolar NO . Both central and distal i NOS levels may reflect responsiveness to steroid treatment.