QUANTIFYING THE EFFECT OF LOCALLY DELIVERED ANTICOAGULANT DRUGS - MODIFICATION OF AN IN-VIVO MODEL OF VENOUS THROMBOSIS

Increasingly, attention is focusing on the local delivery of antiplate let and fibrinolytic therapy as a means of preventing intravascular th rombosis. A simple, reproducible model of thrombosis, based upon vascu lar damage is needed to test these agents in vivo. We have therefore m odified a rat vena cava model of venous thrombosis based upon vascular injury and stasis. Wistar rats are anaesthetised, the inferior cava d issected free and a segment isolated by slings distally above the ilia cs and proximally above the left renal vein. All other tributaries are ligated. Vascular injury is induced by externally applying soft-jaw c lamps for 5 min. Agents to be tested are introduced into the isolated segment via a left renal vein cannula left in situ for 15 min and then flushed from the cava. Blood is allowed to refill the segment, all re maining slings are tied and the animal left for 30 min before being ki lled. The cava is then opened and thrombus removed and weighed. Scanni ng electron microscopy of the cava after clamping shows areas of norma l endothelium interspersed with areas of denuded endothelium and expos ed subendothelial connective tissue. Histological and immunohistochemi cal staining indicates the thrombus is composed of red cells, platelet s and fibrin. The model was validated by assessing the effects of 2 di fferent doses of locally delivered tissue-type plasminogen activator ( tPA). The mean weights of thrombus were [mg (SD)]: Control (saline; n = 8) 39.0 (8.73), tPA 0.01 mg/ml (n = 6) 45.5 (10.56) and tPA 1 mg/ml (n = 8) 3.5 (3.4). Comparing 1 mg/ml tPA vs. 0.01 mg tPA vs. control, p < 0.001 (Mann-Whitney test). We have thus modified a simple, inexpen sive, reproducible model for assessing the potential of locally delive red agents to reduce platelet-fibrin thrombus formation following vasc ular injury.