OBJECTIVE:To investigate the relaxant action of EMD on isolated canine coronary and mesenteric arteries.METHODS:20 and 60mmol/L
KCl were used to pre constricted coronary artery rings with or without endothelium,and relaxant response of EMD was observed.In the presence of glibenclamide,the vasolaxant response to EMD in KCl pre constricted coronary artery was studied and the change of EMD on the dose response curves for KCl induced coronary artery constriction was observed.In addition,EC 50 of EMD on coronary and mesenteric arteries was measured.RESULTS:In the
canine coronary artery rings with or without endotelium,0.7μmol/L EMD caused significant relaxant response of to pre constricted coronary artery with 20mmol/L KCl.When coronary artery was pre constricted with 60mmol/L KCl,relaxant effect of EMD was abolished.In the presence of glibenclamide,the vasolaxant response for EMD in KCl pre contracted coronary artery was antagonized significantly.EMD shifted the dose response curves for KCl(5～30mmol/L) induced constriction to the right,but it had no antagonized response to higher concentration of KCL(≥40mmol/L)(E max was not lowered).EMD produced a markedly concentration dependent reduction of contractile response to phenylephrine or KCl in coronary and mesenteric arteries,their -logEC 50 values were 6.20 and 6.44 respectively.CONCLUSION:EMD is a non endothelium dependent preparation for vascular smooth muscles relaxation,the relaxing action of EMD on
mesenteric artery is two times that of coronary artery.