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

Abstract

Background: This study was designed to examine the role of P-selectin expression in leuko cyte 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^ω-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 mono clonal antibody against P-selectin. Some rings were used for determination of vasoreactivity in response to norepinephrine and acetylcholine, while other rings were incubated with autol ogous 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 nore pinephrine 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-medi ated changes. Intrtperitoneal 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 myelopcroxidase activity and leukocyte deposition in the spleen, but not in the lungs, was abolished by treatment of rats with the P-selectin antagonist CY 1503 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.