NOS3 and pulmonary arterial hypertension: While endothelial NOS (NOS3,also known as eNOS) expression is decreased in lung sections from PAH patients[19], it is paradoxically increased in plexiform lesions [20]; however, eNOS isunlikely to contribute significantly to NO synthesis in this environment where itprobably exists in an uncoupled state and catalyzes the formation of thesuperoxide radical, promoting oxidative stress and pulmonary vascular remodeling[21].