Intracoronary thrombus formation is associated with epicardial vasoconstriction distal to the thrombotic site. To investigate the mechanisms of abnormal vasomotor function of the artery distal to the thrombotic site, we studied coronary vessels in dogs with cyclic flow variations (CFVs) of the left anterior descending coronary artery (LAD) stenosis with endothelial injury. Coronary rings isolated from the LAD (proximal, stenotic, and distal sites) and control circumflex coronary arteries were tested for responsiveness to endothelium-dependent (acetylcholine and A23187) and endothelium-independent vasodilators (NaNO2). Endothelium-independent relaxation was intact in all 4 sites. Endothelium-dependent relaxation was intact in the control and proximal sites and impaired in the stenotic sites. Relaxations not only to acetylcholine and A23187 but also to serotonin, ADP, and thrombin were impaired in the distal sites after observing CFVs for 80 minutes. Electron microscopy revealed the loss of endothelial integrity with leukocyte adherence to the endothelium in the distal sites. Immunohistochemical expression of P-selectin on the endothelial cells was more upregulated in the distal site than in the proximal site, and P-selectin mRNA expression was significantly greater in the ischemic region distal to the thrombotic site than in the proximal nonischemic region. PB1.3, a neutralizing monoclonal antibody against P-selectin, and sialyl LewisX (SLeX)-containing oligosaccharide SLeX, a carbohydrate analogue of selectin ligand, preserved endothelial function without affecting CFVs. SLeX-containing oligosaccharide preserved endothelial integrity of the distal site and inhibited P-selectin expression of the distal site. Thus, the adhesive interaction between endothelial P-selectin and leukocyte SLeX may play an important role in endothelial injuries of the coronary artery distal to the thrombotic site.