Aim To study the vasodilation of MS23,a brand new phosphodiesteras inhibitor,on contractions induced by various stimuli in rings of arteries isolated from rat different organs.Method Tension of aortic and microvessel rings were recorded isometrically by PowerLab and DMT system respectively.Results MS23 concentration-dependently shifted the noradrenaline(NA)-induced concentration-contraction curves rightward in a non-parallel manner with the maximal contraction depressed by 74.7%.MS23 and aminophylline(Ami) produced concentration-dependent relaxation on KCl or NA-induced precontraction.Endothelium deprivation and NO synthesis inhibition induced by L-NAME failed to affect the relaxation.MS23 and Ami relaxed KCl-induced precontraction of rat coronary,middle cerebral,renal and mesenteric arterial rings in a concentration-dependent manner,and showed no organ preference in this respect.Conclusion MS23 antagonizes and relaxes contractions induced by various stimuli in the rings of arteries isolated from different organs of rat without marked preference among the organ origin of artery and stimuli.The vasorelaxation induced by MS23 is related neither to endothelium nor to nitric oxide synthesis.

Objective: To investigate the effect with its possible mechanisms of zacopride on vasodilatation of isolated coronary arterial rings in experimental rats.
Methods: The tension of vasodilatation of isolated coronary arterial rings of male SD rats was recorded by Powerlab and DMT system. The rats were divided into 4 groups: +Endo (vehicle) group, +Endo (zacopride) group and -Endo (vehicle) group, –Endo (zacopride) group.n=6 in each group. The vasodilatation effects of zacopride on KCl (60 mmol/L) and U46619 (10-6 mol/L) pre-constricted arterial ring were recorded; the effects of different agents on zacopride caused vasodilatation were studied.
Results: In both +Endo (zacopride) and –Endo (zacopride) groups, zacopride showed a dose dependent vasodilatation effect on coronary ring pre-constricted by KCl and U46619. The maximum vasodilatation effect of zacopride in KCl treated+Endo (zacopride) group was (90.15 ± 6.38) %, in U46619 treated-Endo (zacopride) group was (81.67 ± 4.97 ) %; the maximum vasodilatation effect of zacopride in KCl treated-Endo (zacopride) group was (85.48±5.04) %, in U46619 treated–Endo (zacopride) group was (79.65 ± 3.51) %, compared to each corresponding vehicle group, allP<0.05. The inhibitor of IK1 channel, BaCl2 could signiifcantly reduce the vasodilatation effect of zacopride in KCl and U46619 pre-constricted coronary ring,P<0.05. However, the inhibitor of eNOS (L-NAME), the blocker of KCa channel (TEA), blocker of Kv channel (4-AP) and blocker of KATP channel (Glib) had no such signiifcant effects, allP>0.05.
Conclusion: Zacopride had vasodilatation effect on coronary arterial ring which was pre-constricted by KCl and U46619, which might be related to the channel of IK1.