Direct evidence of leukocyte adhesion in arterioles by angiotensin II

Although leukocytes adhere in arteries in various vascular diseases, to date no endogenous proinflammatory molecule has been Identified to initiate leukocyte adhesion in the arterial vasculaturs. This study was undertaken to assess angiotensin II (Ang II)-induced leukocyte adhesion in arterioles in vivo. Rats received intraperitoneal injections of Ang II; 4 hours later, leukocyte recruitment in mesenteric microcirculation was examined using intravital microscopy. Ang II (1 nM) produced significant arteriolar leukocyte adhesion of mononuclear cells. Using function-blocking monoclonal antibodies (mAbs) against different rat cell adhesion molecules (CAMs), we discovered that this effect was dependent on P-selectin and β₂-integrin. In postcapillary venules, Ang II also induced leukocyte Infiltration, which was reduced by P-selectin and by β₂- and α₄-integrin blockade. Interestingly, neutrophils were the primary cells recruited in venules. Although β₂-integrin expression in peripheral leukocytes of Ang II-treated animals was not altered, it was increased in peritoneal cells. Immunohistochemical studies revealed increased P-selectin, E-selectin, intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression in response to Ang II in arterioles and venules. These findings provide the first evidence that Ang II causes leukocyte adhesion to the arterial endothelium in vivo at physiologically relevant doses. Therefore, Ang II may be a key molecule in cardiovascular diseases in which leukocyte adhesion to the arteries is a characteristic feature.