Abstract: AIM: The present study was designed to investigate the relaxing effects and mechanism of PRF in rat mesenteric arterial bed(MAB) and isolated mesenteric artery(MA). METHODS: Isolated the MAB and MA of the rat,and the MAB and MA were cuted into artery rings, the tension of MAB and MA rings was measured by Myograph System. RESULTS: PRF could induce a concentration-dependent relaxation of MAB rings which was pre-contracted with phenylephrine(Phe), the relaxation rate was 70%(compared to the control). This effect was significantly reduced by the nitric oxide(NO) Synthase inhibitor N-nitro-L-arginine(L-NOARG) or high K⁺ solution and completely inhibited by KCl plus L-NOARG. But the vasorelaxant effect could not be altered by indometacin,atropine,yohimbine,pyrilamine K channel inhibitor: BACl₂, glibenclamide,ouabain,4-aminopyridine. In Phe pre-contracted MA rings, PRF also induced a concentration-dependent relaxation,which was inhibited by endothelial removal, charybdotoxin(ChTx), and ChTx plus apamin, respectively.Moreover the relaxant functiont was not altered by HOE140 and apamin given alone. CONCLUSION: The vasorelaxing effect of PRF is dependent upon the NO-cGMP pathway and in combinaton with hyperpolarization due to activation of Ca²⁺-dependent K⁺ channels.

Key words: Proanthocyanidins, Nitricoxide, K channel