Objective To investigate the effect of cerebral ischemia on functional parameters of affected arteries and probe into the possible pathogenesis of ischemia-reperfusion injury.Methods Intraluminal suture ischemic model was used by occlusion of left middle cerebral artery in rats.Two hours later,the middle cerebral artery segments were isolated from both ischemia and control groups for measurement of changes in vessel diameter induced by increasing pressure and vasoactive compounds.And then,distensibility,myogenic tone,reactivity to 5-HT and ACh were calculated and compared between groups.Results In lower pressure range,ischemic vessels showed an increased myogenic tone(at 40 mm Hg,1 mm Hg=0.133 kPa,19.3%±0.4% vs 10.0%±0.2%,t=20.568,P=0.000)and decreased diameter.In higher pressure range,ischemic vessels showed an increased diameter.distensibility and decreased myogenic tone(at 120 mm Hg,12.0%±0.2% vs 21.8%±0.4%,t=-23.575,P=0.000).In normal pressure range,myogenic tone was not altered after ischemia. Both groups constricted to 5-HT and dilated to ACh,however,the response was significantly diminished after ischemla.Conclusion These findings demonstrate that contractile and diastolic function of affected artery was impaired after ischemia,a result that may contribute to ischemia-reperfusion injury by losing upstream cerebrovascular resistance and increasing perfusion on the microcirculation.