To investigate the mechanisms underlying the proinflammatory effects of bradykinin, we used intravital microscopic techniques to examine leukocyte/endothelial cell adhesive interactions and venular protein leakage in single postcapillary venules of the rat mesentery. Superfusion of the mesentery with bradykinin at 0.1 or 1.0 µM, but not 0.01 µM, for 60 min increased the number of rolling, firmly adherent (stationary), and emigrated leukocytes, decreased erythrocyte velocity (at 1.0 µM only), and increased venular protein leakage. These bradykinin-induced changes were completely blocked by topical application of the bradykinin-B₂ receptor antagonist HOE 140. Neither treatment with inhibitors of nitric oxide synthase, cyclooxygenase, or platelet-activating factor, nor a mast cell stabilizer were effective in preventing bradykinin-induced leukocyte recruitment and albumin leakage. While oxypurinol (a xanthine oxidase inhibitor), PR-39 (an inhibitor of NADPH oxidase), or superoxide dismutase (SOD, a superoxide scavenger) were also ineffective, treatment with a cell-permeant SOD mimetic (Mn-TBAP) or antioxidant (mercaptoproprionyl glycine) attenuated the increases in leukocyte adhesion and venular protein leakage, as did inhibition of cytochrome P450 (CYP)epoxygenase activity with sulfaphenazole. Protein kinase C inhibition was also effective in reducing the proinflammatory effects of bradykinin. Immunoneutralizing P-selectin or intercellular adhesion molecule-1 (ICAM-1) completely prevented bradykinin-induced leukocyte adhesion and emigration, but did not affect venular albumin leakage. On the other hand, stabilization of F-actin with phalloidin prevented bradykinin-induced leukocyte emigration and microvascular barrier disruption but did not alter leukocyte adhesion. These data indicate that bradykinin induces leukocyte/endothelial adhesive interactions in rat mesenteric venules via a B₂-receptor-initiated, CYP-epoxygenase-, oxidant- and PKC-mediated, P-selectin- and ICAM-1- dependent mechanism. Bradykinin also produced venular protein extravasation, an effect that was initiated by stimulation of B₂ receptors, involved CYP epoxygenase activation and oxidant generation, and was mediated by PKC activation and cytoskeletal disruption, but was independent of leukocyte adherence and emigration.