Nitric oxide: an endogenous modulator of leukocyte adhesion.

Open Access
Publisher Website
Google Scholar
Abstract
The objective of this study was to determine whether endogenous nitric oxide (NO) inhibits leukocyte adhesion to vascular endothelium. This was accomplished by superfusing a cat mesenteric preparation with inhibitors of NO production, NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine methyl ester (L-NAME), and observing single (30-microns diameter) venules by intravital video microscopy. Thirty minutes into the superfusion period the number of adherent and emigrated leukocytes, the erythrocyte velocity, and the venular diameter were measured; venular blood flow and shear rate were calculated from the measured parameters. The contribution of the leukocyte adhesion glycoprotein CD11/CD18 was determined using the CD18-specific monoclonal antibody IB4. Both inhibitors of NO production increased leukocyte adherence more than 15-fold. Leukocyte emigration was also enhanced, whereas venular shear rate was reduced by nearly half. Antibody IB4 abolished the leukocyte adhesion induced by L-NMMA and L-NAME. Incubation of isolated cat neutrophils with L-NMMA, but not L-NAME, resulted in direct upregulation of CD11/CD18 as assessed by flow cytometry. Decrements in venular shear rate induced by partial occlusion of the superior mesenteric artery in untreated animals revealed that only a minor component of L-NAME-induced leukocyte adhesion was shear rate-dependent. The L-NAME-induced adhesion was inhibited by L-arginine but not D-arginine. These data suggest that endothelium-derived NO may be an important endogenous modulator of leukocyte adherence and that impairment of NO production results in a pattern of leukocyte adhesion and emigration that is characteristic of acute inflammation.