Effect of Prolonged Thrombus Exposure on the Development of Secondary Venous Wall Changes in a Rat Venous Thrombosis Model

ABSTRACT

PURPOSE: There is growing evidence that thrombosis and inflammation are closely interrelated and that the inflammatory response may play a role in the development of the syndrome of post-thrombotic, chronic venous insufficiency. A thrombus contains biologically active factors that stimulate cellular and structural alterations and lead to post-thrombotic venous abnormalities. Prolonged exposure to thrombus may result in the development of more severe pathologic conditions. To assess the effect of prolonged thrombus exposure on the development of secondary venous wall changes, the level of D-dimer test and the microscopic findings of thrombosed vein were analyzed in a rat venous thrombosis model. METHOD: The left iliac vein of male Sprague-Dawley rats weighing of 250 to 300 gm were thrombosed by means of either proximal ligation or temporary 24-hour occlusion with a microvascular clamp. The rats were divided into three groups control group (n=10), thrombosis model by proximal ligation of the iliac vein only; group A (n=10), thrombosis model by proximal ligation of the iliac vein with treatment of low molecular weight heparin (LMWH; Clexane(r) 0.5 mg/kg, s.c.b.i.d); and group B (n=10), thrombosis model by temporary 24-hours clamp of the iliac vein without treatment of LMWH. The vein located 2 cm below from the initial ligation was harvested at time intervals of 7 and 14 days after ligation or clamp. Thrombi were identified by gross findings and indirectly quantitated with D-dimer test. RESULT: The levels of D-dimer test on days 7 and 14 after ligation or occlusion were significantly higher in the control group than in groups A and B (P<0.05). However, gross findings of intraluminal thrombosis were not present only in group B. These findings suggest that injection of LMWH did not prevent the development of thrombi around the ligation area. The neutrophilic infiltration of the perivascular area was evaluated microscopically (Hematoxylin-Eosin stain, x100). Severe perivascular neutrophilic infiltration was found in the control group and group A, whereas in group B neutrophilic infiltration was decreased to a mild or moderate degree. The vein wall thickness was evaluated by counting cells on representative sections through the mid vein area and by direct measuring of the vein wall usinga scale bar. The rat vein walls on days 7 and 14 were significantly thicker in the control group and group A than in group B (P<0.05). CONCLUSION: These results suggest that prolonged exposure of thrombus plays a major role in the development of secondary venous wall changes. However, the injection of LMWH did not prevent the development of secondary venous wall changes during the prolonged exposure of thrombus.