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.
SCOPE: We found that a dipeptide, Arg-Phe (RF), had vasorelaxing activity in mesenteric artery isolated from spontaneously hypertensiverats (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.