BACKGROUND: As a common anticoagulant, heparin is widely used in clinic, but it has remarkable side effects such as severe bleeding and heparin-induced thrombocytopenia, and it cannot inactivate fibrin-bound thrombin. Annexin Ⅴ derivative (AND) is inosculated with C-terminal of hirudin and annexin Ⅴ, and its anticoagulation and anti-thrombosis effects are compared with those of heparin. OBJECTIVE: To investigate the relationship between quantitative effectiveness and time effectiveness of AND on coagulation and thrombosis, and study its reliability. DESIGN: Completely randomized grouping design and controlled study. SETTING: Cardiac Department of amunicipal hospital. MATERIALS: The experiment was conducted at the Animal Laboratory of Jiangsu Provincial People's Hospital from July 2000 to April 2001. Totally 32 male New Zealand white rabbits were randomly divided into 4groups, namely, high dosage AND group, low dosage AND group, common heparin group and saline group with 8 in each group. METHODS: Heparin and AND were diluted with saline.①High dosage AND group: 0.7 mg/kg AND was injected intravenously and followed by intravenous dripping of 0.35mg/(kg ·h)for 2 hours.Low dosage AND group: 0.3 mg/kg AND was injected intravenously and followed by intravenous dripping of 0.15 mg/(kg·h) for 2 hours. Heparin group: 75 IU/kg heparin was injected intravenously and followed by intravenous dripping of 37.5 IU/(kg·h) for 2 hours. Saline group: The same volume of saline and medication were used as those in drug groups.② Blood sample was collected from the femoral vein before administration so as to test blood routine, activated partial thromboplastin time(APTT)and prothrombin time (PT) after 15-, 30- and 60-minute administration and 2-hour withdrawal.③Saccule was separated from endothelium of femoral artery to measure blood pressure of distal femoral artery at 15 minutes after administration.Time of pulse pressure equal to 0 mmHg was recorded when the vessel was occluded completely by a thrombus.Finally the injured femoral arteries whose vessel was stripped were collected to measure its length, wet weight and dry weight. ④Observation of AND toxicity and sideeffects:During the experiment,vital signs of the animals were measured,such as blood pressure,heart rate and breath;in addition,bowelhemorrhage was observed and the number of leucocytes was counted after dissection of some of the animals. MAIN OUTCOME MEASURES:①Effect of AND on blood coagulation system and arterial thrombosis.②AND toxicity and side effects. RESULTS: All the 32 white rabbits entered the final analysis. ① Anticoagulant effect: APTT: Fifteen minutes after administration, APTT in AND group was the longest,which was(136.86±39.46)s in high dosage AND group and (122.90±34.19) s in low dosage ANDgroup.Moreover, APTT was longer than that in saline group [(95.14±24.64) s], but shorter than that in common heparin group [(180.00±0.00) s, P ＜ 0.05, 0.01]. At 30 minutes after administration,AND in high dosage group still had coagulation,and APTT was (124.61±40.19) s in high dosage group, which was longer than that in saline group [(85.57±27.67) s], but APTT was (112.94±43.17) sin low dosage group,which was shorter than that in common heparin group [(85.57±27.67)s,P ＜ 0.05].APTT was shorter in high and low dosage groups than in common heparin group at 60 minutes after administration (P ＜ 0.05),and longer than that in saline group 2 hours after drug withdrawal,but there was not significant difference(P ＞ 0.05).PT:PT in common heparin group was longer than that in high and low dosage groups at 15,30 and 60 minutes after administration (P ＜ 0.05).② Effect on arterial thrombosis:Wet weight of thrombus:It was lighter in AND group than in common heparin group(P ＜ 0.05). Dry weight of thrombus:Thrombus was lighter in high and low dosage groups than in common heparin group, and was lighter in high dosage group than in low dosage group (P ＜ 0.05).Thrombus length:It was shorter in low dosage group than in saline group (P ＜ 0.05), and shorter in high dosage groupthan in common heparin group (P ＜ 0.05). Time of complete occlusion: It was longer in high and low dosage groups than in saline group(P ＜ 0.05).③ AND toxicity and side effects:The behavior of rabbits in high and low dosage groups was similar to that in other two groups. Obvious hemodynamic changes were not found, and bowel hemorrhage was not observed, either. CONCLUSION: AND is an effective anticoagulant and anti-thrombosis agent; the highest anticoagulation effect occurs at 15 minutes afteradminis tration. However, the anticoagulant effect is poor as compared to heparin.The effect is poorer after 60-minute administration. Effect of AND on thrombus is stronger than that of heparin,but the size of thrombus is smaller than that of heparin, and the dosage-dependence manner was found. In addition, the anti-thrombus effect of AND is stronger in high dosage group than in low dosage group.