Background-Angiotensin II (Ang II) is implicated in the development of cardiac ischemic disorders in which prominent neutrophil accumulation occurs. Ang II can be generated intravascularly by the renin-angiotensin system or extravascularly by mast cell chymase. In this study, we characterized the ability of Ang II to induce neutrophil accumulation. Methods and

Angiotensin II (Ang-II) is associated with atherogenesis and arterial subendothelial mononuclear leukocyte infiltration. We have demonstrated that Ang-II causes the initial attachment of mononuclear cells to the arteriolar endothelium. We now report on the contribution of CC chemokines to this response. Intraperitoneal administration of 1 nM Ang-II induced MCP-1, RANTES, and MIP-1α generation, maximal at 4 h, followed by mononuclear leukocyte recruitment at 8 and 24 h. Using intravital microscopy within the rat mesenteric microcirculation 4 h after exposure to 1 nM Ang-II, arteriolar mononuclear cell adhesion was 80–90% inhibited by pretreatment with Met-RANTES, a CCR1 and CCR5 antagonist, or an anti-MCP-1 antiserum, without affecting the increased endothelial expression of P-selectin and VCAM-1. Conversely, leukocyte interactions with the venular endothelium, although inhibited by Met-RANTES, were little affected by the anti-MCP-1. Using rat whole blood in vitro, Ang-II (100 nM) induced the expression of monocyte CD11b that was inhibited by Met-RANTES but not by anti-MCP-1. Stimulation of human endothelial cells (human umbilical arterial endothelial cells and HUVECs) with 1–1000 nM Ang-II, predominantly acting at its AT1 receptor, induced the release of MCP-1 within 1 h, RANTES within 4 h, and MCP-3 within 24 h. Eotaxin-3, a natural CCR2 antagonist, was released within 1 h and may delay mononuclear cell responses to MCP-1. Therefore, Ang-II-induced mononuclear leukocyte recruitment at arterioles and venules is mediated by the production of different CC chemokines. Thus, Ang-II may be a key molecule in the initial attachment of mononuclear cells to the arterial endothelium in cardiovascular disease states where this event is a characteristic feature.

Angiotensin II (Ang-II) exerts inflammatory activity and is involved in different cardiovascular disorders. This study has evaluated the involvement of tumor necrosis factor alpha (TNF␣) in the leukocyte accumulation elicited by Ang-II. Ang-II (1 nM intraperitoneally in rats) induced TNF␣ release at 1 hour followed by neutrophil and mononuclear cell recruitment. The administration of an antirat TNF␣ antiserum had no effect on Ang-IIinduced neutrophil accumulation but in- IntroductionAtherosclerosis is the major cause of myocardial infarction, stroke, and peripheral vascular disease, which accounts for nearly half of all mortality in developed countries. 1 Adhesive interactions between leukocytes and arterial endothelium precede leukocyte infiltration to the subendothelial space in pathological events such as atherosclerosis. 1,2 The migration of leukocytes from the blood to sites of extravascular injury is mediated through a sequential cascade of leukocyte-endothelial cell adhesive interactions that involve an array of cell adhesion molecules (CAMs) present on leukocytes and endothelial cells. 3 Interestingly, whereas leukocyteendothelial cell interactions in postcapillary venules are induced by a wide range of stimuli, leukocyte interactions with the arterial endothelium are only induced by certain risk factors for atherosclerosis such as cytokines like interleukin-1␤ (IL-1␤) or tumor necrosis factor alpha (TNF␣), oxidized low density lipoproteins (LDL), cigarette smoke, or angiotensin-II (Ang-II). [4][5][6][7][8] Activation of the renin-angiotensin system has been demonstrated in myocardial ischemia, acute myocardial infarction, coronary occlusion, and reperfusion models as well as in chronic left ventricular dysfunction after myocardial infarction. [9][10][11] Ang-II, the main effector peptide of the renin-angiotensin system, is implicated in atherogenesis beyond its hemodynamic effects. 12 We demonstrated that 4 hours of exposure to Ang-II in vivo caused arteriolar leukocyte adhesion in the rat mesenteric microcirculation through interaction with its AT 1 receptor subtype, 8 and this effect was not observed under acute (1-hour) stimulation with this peptide hormone. 13 Furthermore, mononuclear cells were found to be the primary cells attached to the arteriolar endothelium whereas the leukocytes interacting with the venular endothelium at the same time were predominantly neutrophils. Despite these findings, the same CAMs were expressed in both the arteriolar and venular endothelia in response to 8 suggesting that other mechanisms were responsible for the differential cellular distribution within the microcirculation.Therefore, this differential effect displayed by Ang-II may be due to different activation mechanisms. Thus, in postcapillary venules, the early response of neutrophil accumulation is primarily mediated by the direct effect of Ang-II on endothelial cells via the expression of P selectin and the rapid release of CXC chemokines. 13,14 In arterioles, leukocyte adhesion probably requires the addition...