MICROVASCULAR RESPONSES TO INHIBITION OF NITRIC-OXIDE PRODUCTION - ROLE OF ACTIVE OXIDANTS

The objective of this study was to assess the potential contribution o f hydrogen peroxide (H2O2) to the leukocyte-endothelial cell adhesion and increased microvascular permeability observed in rat mesenteric ve nules after inhibition of nitric oxide synthesis with N-G-nitro-L-argi nine methyl ester (L-NAME). Leukocyte adherence and emigration and lea kage of fluorescein isothiocyanate-labeled albumin were monitored in p ostcapillary venules before and after exposure of the tissue to L-NAME . H2O2 production in mesenteric tissue was monitored by using dihydror hodamine 123 (DHR), the H2O2-sensitive fluorochrome. L-NAME elicited a rapid increase in both the rate of albumin extravasation and oxidatio n of DHR, which was followed by an increased adherence and emigration of leukocytes in postcapillary venules. Treatment with either catalase or dimethylthiourea attenuated the L-NAME-induced oxidative stress, a lbumin leakage, and leukocyte-endothelial cell adhesion. Oxidation of DHR was enhanced in animals treated with either 3-amino-1,2,4-triazole (ATZ), an inhibitor of endogenous catalase, or a combination of ATZ a nd maleic acid diethyl ester, which depletes intracellular glutathione . Animals receiving a CD11/CD18-specific antibody to prevent leukocyte adhesion/emigration exhibited a reduced oxidation of DHR in response to L-NAME. These findings indicate that most of the H2O2 (and secondar ily derived oxidants) generated in mesenteric tissue exposed to an inh ibitor of nitric oxide production is due to accumulation of activated leukocytes.