Characterization of Ile-His-Arg-Phe, a novel rice-derived vasorelaxing peptide with hypotensive and anorexigenic activities.

SCOPE: Recently, we found that dipeptide Arg-Phe (RF) had cholecystokinin (CCK)-dependent vasorelaxing activity. The RF sequence is often observed in the primary structure of natural food proteins. In the current study, we investigated enzymatic conditions for the release of RF-related peptides from rice glutelin, a major storage protein, using gastrointestinal proteases. RF-related peptides were then characterized. METHODS AND RESULTS: It was found that RF and Ile-His-Arg-Phe (IHRF) were released in the chymotrypsin digest of the partial structure of rice glutelin. We then focused on previously unidentified IHRF, corresponding to rice glutelin(155-158). IHRF had vasorelaxing activity in the mesenteric artery of spontaneous hypertensive rats (SHRs). Orally administered IHRF lowered systolic blood pressure in SHRs. The antihypertensive activity of IHRF was more potent and long-lasting than that of RF. IHRF-induced vasorelaxing activity was not blocked by inhibitors of nitric oxide synthase and cyclooxygenase, but by an antagonist for CCK1 receptor. IHRF also had CCK-like suppressive activities in food intake and gastrointestinal transit. IHRF increased intracellular Ca²âº flux and CCK release in the enteroendocrine cell STC-1. CONCLUSION: IHRF, a novel CCK-dependent vasorelaxing peptide, decreases both blood pressure and food intake in rodents.

Novel CCK-dependent vasorelaxing dipeptide, Arg-Phe, decreases blood pressure and food intake in rodents.

SCOPE: We found that a dipeptide, Arg-Phe (RF), had vasorelaxing activity in mesenteric artery isolated from spontaneously hypertensive rats (SHRs) (EC(50) = 580 nM). We then investigated its mechanism of action, and elucidated its physiological functions. METHODS AND RESULTS: Vasorelaxing activities of RF-related peptides were tested. The retro-sequence dipeptide FR was inactive, suggesting that the RF sequence is important for a potent vasorelaxing effect. RA and AF were also inactive. RF-nh(2) had vasorelaxing activity, implying that the C-terminal amidation of RF is tolerated. Nitric oxide (NO) and prostaglandins (PGs) are known to be vasorelaxing factors; however, the vasorelaxing activity of RF was inhibited by neither N(G) -nitro-l-arginine methyl ester (l-NAME), an NO synthase inhibitor, nor indomethacin, a COX inhibitor. Interestingly, the activity was blocked by lorglumide, an antagonist of the cholecystokinin (CCK)(1) receptor; however, RF had no affinity for CCK receptors, suggesting that RF stimulates CCK release. Orally administered RF decreased blood pressure in SHRs, and this antihypertensive activity was also blocked by a CCK(1) antagonist. RF had CCK-like suppressive effects on food intake and gastrointestinal transit. RF increased intracellular Ca(2+) flux and CCK release in enteroendocrine STC-1 cells. CONCLUSION: A novel CCK-dependent vasorelaxing RF decreases both blood pressure and food intake.