Abstract
Using intravital microscopy, we examined the role played by B(1) receptors in leukocyte trafficking across mouse mesenteric postcapillary venules in vivo. B(1) receptor blockade attenuated interleukin (IL)-1beta-induced (5 ng intraperitoneally, 2 h) leukocyte-endothelial cell interactions and leukocyte emigration ( approximately 50% reduction). The B(1) receptor agonist des-Arg(9)bradykinin (DABK), although inactive in saline- or IL-8-treated mice, caused marked neutrophil rolling, adhesion, and emigration 24 h after challenge with IL-1beta (when the cellular response to IL-1beta had subsided). Reverse transcriptase polymerase chain reaction and Western blot revealed a temporal association between the DABK-induced response and upregulation of mesenteric B(1) receptor mRNA and de novo protein expression after IL-1beta treatment. DABK-induced leukocyte trafficking was antagonized by the B(1) receptor antagonist des-arg(10)HOE 140 but not by the B(2) receptor antagonist HOE 140. Similarly, DABK effects were maintained in B(2) receptor knockout mice. The DABK-induced responses involved the release of neuropeptides from C fibers, as capsaicin treatment inhibited the responses. Treatment with the neurokinin (NK)(1) and NK(3) receptor antagonists attenuated the responses, whereas NK(2), calcitonin gene-related peptide, or platelet-activating factor receptor antagonists had no effect. Substance P caused leukocyte recruitment that, similar to DABK, was inhibited by NK(1) and NK(3) receptor blockade. Mast cell depletion using compound 48/80 reduced DABK-induced leukocyte trafficking, and DABK treatment was shown histologically to induce mast cell degranulation. DABK-induced trafficking was inhibited by histamine H(1) receptor blockade. Our findings provide clear evidence that B(1) receptors play an important role in the mediation of leukocyte-endothelial cell interactions in postcapillary venules, leading to leukocyte recruitment during an inflammatory response. This involves activation of C fibers and mast cells, release of substance P and histamine, and stimulation of NK(1), NK(3), and H(1) receptors.