Nitric Oxide Synthesis Inhibition and Role of P-selectin in Leukocyte Adhesion to Vascular Tissues

BACKGROUND: This study was designed to examine the role of P-selectin expression in leukocyte adhesion to endothelium caused by inhibition of nitric oxide synthesis. METHODS AND RESULTS: Rat aortic rings were treated with the nitric oxide synthesis inhibitor N(omicron)-nitro-l-arginine methyl ester (l-NAME) for 2 hours. Parallel sets of aortic rings were pretreated with the nitric oxide precursor l-arginine or posttreated with a specific monoclonal antibody against P-selectin. Some rings were used for determination of vasoreactivity in response to norepinephrine and acetylcholine, while other rings were incubated with autologous unlabeled leukocytes or Biotin-FITC labeled leukocytes for 30 minutes. Leukocyte adhesion to vascular endothelium was determined by scanning electron microscopy. l-NAME enhanced the contractile response in response to norepinephrine, suppressed the relaxant response to acetyleholine, promoted leukocyte adherence to the endothelium and resulted in P-selectin expression on the aortic endothelium. Pretreatment of aortic rings with l-arginine reversed the l-NAME-mediated changes in vasoreactivity in response to norepinephrine and acetyleholine and attenuated the l-NAME-enhanced leukocyte adhesion to endothelial intima. P-selectin treatment, on the other hand, had no effect on l-NAME-mediated changes. Intraperitoneal administration of l-NAME resulted in a significant decrease in plasma nitrite level, a small, but significant, increase in lung and spleen myeloperoxidase activity, and a significant increase in leukocyte deposition in lung and spleen. The l-NAME-mediated increase in myeloperoxidase activity and leukocyte deposition in the spleen, but not in the lungs, was abolished by treatment of rats with the P-selectin antagonist CY1503 administered 30 minutes prior to l-NAME. CONCLUSIONS: These observations indicate that a reduction in nitric oxide synthesis enhances leukocyte adhesion to aortic endothelium and in visceral tissues. While P-selectin expression is evident in some of the experimental models of leukocyte adhesion to endothelium under conditions of nitric oxide inhibition, the role of P-selectin expression remains unclear.