Mechanisms underlying the relaxation response induced by bradykinin in the epithelium-intact guinea-pig trachea in vitro

1 In this study, we investigated some of the signalling pathways involved in bradykinin (BK)-induced relaxation in epithelium-intact strips of the guinea-pig trachea (GPT+E). BK induced time- and concentration-dependent relaxation of GPT+E. Similar responses were observed for prostaglandin E-2 (PGE(2)) or the combination of subthreshold concentrations of BK plus PGE(2). 2 The nonselective cyclooxygenase ( COX) inhibitors indomethacin or pyroxicam, or the selective COX-2 inhibitors DFU, NS 398 or rofecoxib, but not the selective COX-1 inhibitor SC 560, all abolished BK-induced relaxation. 3 The tyrosine kinase inhibitors herbimycin A and AG 490 also abolished BK-induced relaxation in GPT+E. 4 The nonselective nitric oxide synthase ( NOS) inhibitor 7-NINA concentration-dependently inhibited BK effects. 5 BK-induced relaxation was prevented by the selective antagonists for EP3 ( L 826266), but not by EP1 (SC 19221), EP1/ EP2 (AH6809) or EP4 (L 161982) receptor antagonists. 6 Otherwise, the selective inhibitors of protein kinases A, G and C, mitogen-activated protein kinases, phospholipases C and A(2), nuclear factor-kappa B or potassium channels all failed to significantly interfere with BK-mediated relaxation. 7 BK caused a marked increase in PGE(2) levels, an effect that was prevented by NS 398, HOE 140 or AG 490. 8 COX-2 expression did not differ in preparations with or without epithelium, and it was not changed by BK stimulation. However, incubation with BK significantly increased the endothelial NOS ( eNOS) and neuronal NOS ( nNOS) expression, independent of the epithelium integrity. 9 Our results indicate that BK-induced relaxation in GPT+E depends on prostanoids ( probably PGE(2) acting via EP3 receptors) and NO release and seems to involve complex interactions between kinin B-2 receptors, COX-2, nNOS, eNOS and tyrosine kinases.