Evaluation of iNOS-dependent and independent mechanisms of the microvascular permeability change induced by lipopolysaccharide

1 Subcutaneous injection of lipopolysaccharide (LPS) increases plasma leakage in mouse skin. Pretreatment with LPS conditions mice tolerant to the LPS-induced plasma leakage. Nitric oxide (NO) has been suggested to be involved in these LPS effects. A specific role of inducible NO synthase (iNOS) was investigated in the LPS-induced plasma leakage using iNOS deficient mice. 2 Plasma leakage in mouse skin was measured by the local accumulation of Pontamine sky blue at the site of subcutaneous injection of LPS (Sal. typhimurium). LPS (100-400 mu g site(-1)) produced a dose-related increase in dye leakage in both iNOS deficient and wild-type mice with about 40% less dye leakage in iNOS deficient mice. 3 Indomethacin (5 mg kg(-1)), N-[-2-cyclohexyloxy]-4-nitrophenyl methanesulphonamide (NS-398) (1 mg kg(-1)), diphenhydramine (10 mg kg(-1)) and anti-TNF-alpha antibody (dilution 1:400, 10 mi kg(-1)) inhibited the LPS-induced dye leakage in both iNOS deficient and wild-type mice, whereas N-G-nitro-L-arginine methyl ester (L-NAME) (10 mg kg(-1)) or aminoguanidine (10 mg kg(-1)) inhibited that in wild-type but not in INOS deficient mice. 4 Pretreatment with LPS (0.15 mg kg(-1) i.p.)4 h before decreased the LPS-induced dye leakage in wild-type but not in iNOS deficient mice. LPS pretreatment increased serum corticosterone levels in both mice, while it increased the serum nitrate/nitrite levels in wild-type but not in iNOS deficient mice. 5 These studies indicate that an increase in vascular permeability induced by LPS is mediated by NO produced by iNOS, eicosanoids, histamine and TNF-alpha. The tolerance against LPS-induced vascular permeability change may be mediated by INOS induction but not by an increased release of endogenous corticosteroids.