Background-Angiotensin II (Ang II) plays a critical role in the development of vascular lesions in hypertension, atherosclerosis, and several renal diseases. Because Ang II may contribute to the leukocyte recruitment associated with these pathological states, the aim of the present study was to assess the role of Ang II in leukocyte-endothelial cell interactions in vivo. Methods and Results-Intravital microscopy of the rat mesenteric postcapillary venules was used. Sixty minutes of superfusion with 1 nmol/L Ang II induced a significant increase in leukocyte rolling flux (83.8Ϯ20.7 versus 16.4Ϯ3.1 cells/min), adhesion (11.4Ϯ1.0 versus 0.8Ϯ0.5 cells/100 m), and emigration (4.0Ϯ0.7 versus 0.2Ϯ0.2 cells/field) without any vasoconstrictor activity. These effects were not mediated by mast cell activation. Intravenous pretreatment with AT 1 (losartan) or AT 2 (PD123,319) receptor antagonists significantly reduced Ang II-induced responses. A combination of both receptor antagonists inhibited the leukocyte rolling flux, adhesion, and extravasation elicited by Ang II at 60 minutes. Pretreatment of animals with fucoidin or an adhesion-blocking anti-rat P-selectin monoclonal antibody abolished Ang II-induced leukocyte responses. Furthermore, rat platelet P-selectin expression was not affected by Ang II stimulation. Conclusions-Ang II induces significant leukocyte rolling, adhesion, and emigration, which may contribute not only to hypertension but also to the onset and progression of the vascular damage associated with disease states in which plasma levels of this peptide are elevated.

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