Although the molecular mechanism by which eNOS expression and activity were negatively regulated in pulmonary arteries of COPD patients had not been studied in this study, it might be due to the harmful effect of cigarette smoke on pulmonary endothelial cells via inflammatory mediators and free radicals as demonstrated previously (Raij et al. 2001; van der Vaart et al. 2004). This evidence concerns the gene NOS3 and chronic obstructive pulmonary disease.