OBJECTIVE: To determine whether nitric oxide (NO) might modulate ventilator-induced lung injury. DESIGN: Randomized prospective animal study. SETTING: Animal research laboratory in a university hospital. SUBJECTS: Isolated, perfused rabbit heart-lung preparation. INTERVENTIONS: Thirty-six isolated, perfused rabbit lungs were randomized into six groups (n = 6) and ventilated using pressure-controlled ventilation for two consecutive periods (T1 and T2). Peak alveolar pressure during pressure-controlled ventilation was 20 cm H2O at T1 and was subsequently (T2) either reduced to 15 cm H2O in the three low-pressure control groups (Cx) or increased to 25 cm H2O in the three high-pressure groups (Px). In the control and high-pressure groups, NO concentration was increased to approximately equal to 20 ppm (inhaled NO groups: CNO, PNO), reduced by NO synthase inhibition (L-NAME groups: CL-Name, PL-Name), or not manipulated (groups CE, PE). MEASUREMENTS AND MAIN RESULTS: Changes in ultrafiltration coefficients (deltaKf [vascular permeability index: g.min(-1).cm H2O(-1).100 g(-1)]), bronchoalveolar lavage fluid 8-isoprostane, and NOx (nitrate + nitrite) concentrations were the measures examined. Neither L-NAME nor inhaled NO altered lung permeability in the setting of low peak alveolar pressure (control groups). In contrast, L-NAME virtually abolished the change in permeability (deltaKf: PL-Name (0.10 +/- 0.03) vs. PNO [1.75 +/- 1.10] and PE [0.37 +/- 0.11; p <.05]) and the increase in bronchoalveolar lavage 8-isoprostane concentration induced by high-pressure ventilation. Although inhaled NO was associated with the largest change in permeability, no significant difference between the PE and PL-NAME groups was observed. The change in permeability (deltaKf) correlated with bronchoalveolar lavage NOx (r2 =.6; p <.001). CONCLUSIONS: L-NAME may attenuate ventilator-induced microvascular leak and lipid peroxidation and NO may contribute to the development of ventilator-induced lung injury. Measurement of NO metabolites in the bronchoalveolar lavage may afford a means to monitor lung injury induced by mechanical stress.