Endothelium-dependent relaxant effect of neurokinins on rabbit aorta is mediated by the NK1 receptor

Several neurokinins, namely substance P, neurokinin A, neurokinin B, [beta-Ala8]neurokinin A-(4-10) and senktide, were tested on noradrenaline-precontracted rabbit aortic rings to characterize the receptor mediating their endothelium-dependent relaxant effect in this preparation. CP-96,345, the new nonpeptide antagonist selective for the NK1 receptor, was also studied. Substance P, neurokinin A and neurokinin B, in that order of potency, were effective in relaxing precontracted rings, indicating the involvement of the NK1 receptor; [beta-Ala8]neurokinin A-(4-10) and senktide, which are selective agonists for NK2 and NK3 receptors, respectively, had no significant relaxant effect. The relaxant effects of substance P, neurokinin A and neurokinin B were competitively antagonized by nanomolar concentrations of CP-96,345. These findings support the view that the NK1 receptor mediates the endothelium-dependent relaxant effect of the neurokinins in rabbit aorta.