Actions of tachykinins on the rabbit mesenteric artery: substance P and [Glp6,L‐Pro9]SP6–11 are potent agonists for endothelial neurokinin‐1 receptors

1. Identification of the subtype of neurokinin receptor on the endothelium of the rabbit mesenteric artery was demonstrated by comparing the relative potencies of the naturally occurring tachykinins, substance P, neurokinin A and neurokinin B and the highly selective agonists [Glp6,L-Pro9]SP6-11 (L-Pro), [Glp6,D-Pro9]SP6-11 (D-Pro) and N-succinyl-[Asp6,MePhe8]SP6-11 (senktide). 2. Relaxations of the rabbit mesenteric artery to substance P, neurokinin A and neurokinin B were concentration-dependent and were abolished by the removal of the endothelium. 3. Substance P was more potent than neurokinin A or neurokinin B and L-Pro was more potent than D-Pro or senktide. 4. Substance P, neurokinin A and neurokinin B all significantly reduced the nerve-mediated contractile response in the presence of the endothelium at a concentration of 0.1 microM, with a rank order of potency substance P greater than neurokinin A greater than neurokinin B. 5. At a concentration of 0.1 microM, L-Pro also significantly reduced the nerve-mediated contractile response, unlike D-Pro and senktide. 6. It is concluded that the relaxation of the rabbit mesenteric artery produced by substance P is mediated by neurokinin-1 receptors (NK-1) located on the endothelium. Furthermore, of the analogues, L-Pro was particularly potent for these receptors.