Objective To explore the protective effect of uridine 5'-triphosphate (UTP) on cerebral ischemia reperfusion injury in rats.Methods One hundred adult male SD rats were randomly divided into five groups (20 each):sham operation group,saline control group,G_ 10 group,G_ 30 group and G_ 90 group.Ischemia was induced by intraluminal suture embolism of mesocephalic artery (MAO) of the rats in all the groups except sham operation group.UTP solution was delivered through an indwelling tail venous catheter via microinfusion pump 30min after the occlusion of mesocephalic artery at a rate of 5ml/(kg?min),and rats in G_ 10,G_ 30 and G_ 90 group received 10,30 and 90?g/kg UTP,respectively.Rats in sham group and saline control group received normal saline.The total fluid volume was the same,1ml/kg,in all groups.Neurological deficit score (NDS) was determined 24h after reperfusion.Eight SD rats were then randomly selected from each group,and water content of cerebral hemispheres was measured.Two rats from each of sham operation group,saline control group and G_ 90 group were selected for studying the ultrastructure of brain tissue by electron microscopy.Infarct volume was determined by 2,3,5-triphenyl-tetrazolium chloride (TTC) staining with another 10 rats in each group.Results The protective effect of UTP was determined on cerebral ischemia-reperfusion injury in rats,and in G_ 90 group showed the most significant protective effect.For the rats in saline group and G_ 90 group,NDS score was 0.7 and 1.8 (P