Hyperbaric oxygen increases plasma exudation in rat trachea: involvement of nitric oxide

1 This study investigates the microvascular permeability changes in trachea l tissue of rats exposed to hyperbaric oxygen (HBO). 2 Rats, following exposure to HBO or ambient air (control animals) for 1.5, 3 and 6 h, were prepared for recording of nitric oxide exhaled (FENO) in a ir using a chemiluminescence analyser. The level of FENO was not statistica lly different in the two groups. Plasma exudation, evaluated by measuring t he leakage of Evans blue (EB) dye into the tracheal tissue, was significant ly elevated (48, 86 and 105% at 1.5. 3 and 6 h. respectively) in HBO-treate d rats. 3 Plasma exudation in the trachea of control rats was significantly increas ed (42%, P < 0.05) by N-G-nitro-L-arginine methyl ester (L-NAME), whereas i t was significantly reduced (31%, P < 0.05) in rats exposed to HBO for 3 h. 4 N-acetylcysteine (NAC) and flunisolide significantly prevented the increa se in plasma leakage in HBO-treated rats. In contrast, indomethacin was dev oid of anti-exudative activity in these experiments. 5 Western immunoblot showed a significant increase in the level of inducibl e nitric oxide synthase (iNOS) protein in the tracheal homogenates of HBO-t reated rats, as compared to basal levels. 6 These results indicate that nitric oxide (NO) is involved in the maintena nce of microvascular permeability in tracheal tissue of rats. The protectiv e effect observed with the steroid seems to support this hypothesis. Furthe rmore, the beneficial action of NAC underlines that reactive oxygen species participate in the microvascular permeability changes observed in tracheal tissue of rats exposed to HBO.