Dexamethasone attenuated endotoxin-induced acute lung injury through inhibiting expression of inducible nitric oxide synthase

Application of glucocorticoids in sepsis or severe infection is disputable in clinic. In this experiment, we studied the effect of dexamethasone on nitric oxide synthases and whether dexamethasone could attenuate endotoxin-induced acute lung injury (ALI). SD rats received 5 mg/kg lipopolisaccharide (LPS) injection. Then arterial oxygen partial pressure (PaO₂), lung histology, lung tissue nitric oxide (NO) production and expression of nitric oxide synthases (NOS) were detected at 0.5, 1, 2, 3 or 4 h after LPS injection. PaO₂ and lung injury deteriorated upon time. Production of NO in lung tissue increased significantly particularly in the first two hours, and this change was mainly due to the over-expression of inducible NOS (iNOS), but not endothelial NOS (eNOS). Furthermore, a tight positive correlation was observed between lung injury score (LIS) and NO production level in lung tissue. Dexamethasone could ameliorate PaO₂ and lung damage evidently, which were paralleled by significant decreases in the production of NO and in the expression of iNOS mRNA. In conclusion, dexamethasone could effectively attenuate endotoxin-induced lung injury through inhibiting iNOS expression and activation in the very early stage of ALI.