Rapakinin, an anti-hypertensive peptide derived from rapeseed protein, dilates mesenteric artery of spontaneously hypertensive rats via the prostaglandin IP receptor followed by CCK 1 receptor

Abstract

The anti-hypertensive peptide Arg-Ile-Tyr, which was isolated based on its inhibitory activity (IC 50 = 28 μM) for angiotensin I-converting enzyme (ACE) from the subtilisin digest of rapeseed protein, exhibited vasorelaxing activity (EC 50 = 5.1 μM) in an endothelium-dependent manner in the mesenteric artery of spontaneously hypertensive rats (SHRs). We named the peptide rapakinin. ACE inhibitors are reported to induce nitric oxide (NO)-dependent vasorelaxation by elevating the endogenous bradykinin level; however, the vasorelaxation induced by 10 μM of rapakinin was blocked only insignificantly by HOE140 or N G-nitro- l-arginine methyl ester ( l-NAME), antagonists of bradykinin B 2 receptor and an inhibitor of NO synthase, respectively. On the other hand, the vasorelaxation induced by 10 μM rapakinin was significantly blocked by indomethacin and CAY10441, a cyclooxygenase (COX) inhibitor and an antagonist of the IP receptor, respectively. The vasorelaxing activity of rapakinin was also blocked by lorglumide, an antagonist of the cholecystokinin (CCK) CCK 1 receptor, although rapakinin has no affinity for the IP and CCK 1 receptors. The vasorelaxation induced by 10 μM iloprost, an IP receptor agonist, was also blocked by lorglumide, suggesting that CCK–CCK 1 receptor system is activated downstream of the PGI 2–IP receptor system. The anti-hypertensive activity of rapakinin after oral administration in SHRs was also blocked by CAY10441 and lorglumide. These results suggest that the anti-hypertensive activity of rapakinin might be mediated mainly by the PGI 2–IP receptor, followed by CCK–CCK 1 receptor-dependent vasorelaxation.