In this study, the biochemical mechanisms by which N-nitroso-N-methylurethane (NNMU) induces acute lung injury are examined. Polymorphonuclear neutrophil infiltration into the lungs first appears in the bronchoalveolar lavage (BAL) fluid 24 h after NNMU injection (10.58 ± 3.00% of total cells; P < 0.05 vs. control animals). However, NNMU-induced elevation of the alveolar-arterial O₂ difference requires 72 h to develop. Daily intraperitoneal injections of the inducible nitric oxide (· NO) synthase (iNOS)-selective inhibitor aminoguanidine (AG) initiated 24 h after NNMU administration improve the survival of NNMU-treated animals. However, AG administration initiated 48 or 72 h after NNMU injection does not significantly improve the survival of NNMU-treated animals. These results suggest that · NO participates in events that occur early in NNMU-induced acute lung injury. BAL cells isolated from rats 24 and 48 h after NNMU injection produce elevated · NO and express iNOS during a 24-h ex vivo culture. AG attenuates · NO production but does not affect iNOS expression, whereas actinomycin D prevents iNOS expression and attenuates · NO production by BAL cells during this ex vivo culture. These results suggest that NNMU-derived BAL cells can stimulate iNOS expression and · NO production during culture. In 48-h NNMU-exposed rats, iNOS expression is elevated in homogenates of whole lavaged lungs but not in BAL cells derived from the same lung. These findings suggest that the pathogenic mechanism by which NNMU induces acute lung injury involves BAL cell stimulation of iNOS expression and · NO production in lung tissue.

N-nitroso-N-methylurethane; aminoguanidine; acute respiratory distress syndrome; bronchoalveolar lavage; inducible nitric oxide synthase; polymorphonuclear neutrophil

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