N itric oxide (NO), a vasodilator involved in the regulation of pulmonary vascular tone, is synthesized by a family of enzymes, nitric oxide synthases (NOS). To investigate whether adenoviral-mediated overexpression of constitutive endothelial NOS (ceNOS) would attenuate hypoxic pulmonary vasoconstriction, we aerosolized 3 X 10(9) plaque forming units of a recombinant adenovirus containing the ceNOS gene (AdCMVceNOS) into rat lungs. Four days after infection, transgene expression was confirmed using immunoblot techniques. Diffuse ceNOS immunostaining was detected in alveoli and medium-sized and small pulmonary vessels of AdCMVceNOS-transduced lungs. AdCMVceNOS-transduction was associated with an 86% increase in [3H]arginine to [3H]citrulline conversion and a rise in pulmonary cGMP levels from 7 +/- 1 to 59 +/- 9 pmol/mg protein in lungs from AdCMVceNOS versus control rats, (P < 0.05). During acute hypoxia (FIO2 = 0.10) for 25 min, mean pulmonary artery pressure (PAP) increased significantly from 17 +/- 1 to 27 +/- 1 mmHg in rats aerosolized with saline (n = 4) and from 18 +/- 1 to 28 +/- 1 mmHg in rats given an adenoviral vector expressing a nuclear-targeted beta-galactosidase gene (AdCMV beta gal, n = 8). In contrast, in AdCMVceNOS-transduced rats (n = 8) the hypoxia-induced increase in PAP was significantly attenuated (18 +/- 1 to 23 +/- 2 mmHg). Systemic blood pressure was not affected by aerosol gene transfer. Thus, adenoviral-mediated ceNOS gene transfer to rat lungs increases ceNOS expression and activity, and reduces acute hypoxic pulmonary vasoconstriction. Aerosolized recombinant adenovirus overexpressing vasodilatory proteins can act as a selective pulmonary vasodilator and may hold promise as a future therapeutic strategy for pulmonary hypertension.