IN-VIVO ANALYSIS OF ANTITHROMBOTIC EFFECTIVENESS OF RECOMBINANT HIRUDIN ON MICROVASCULAR THROMBUS FORMATION AND RECANALIZATION

Purpose: This study was undertaken to evaluate in vivo the effect of r ecombinant hirudin (r-hirudin [HBW 023]), a potent thrombin inhibitor, on the process of microvascular thrombus formation and recanalization . Methods: Thrombosis was induced photochemically in distinct arteriol es (n = 25) and venules (n = 30) of the ear of 16 hairless hr/hr mice (8 to 10 weeks old, 25 to 30 g of body weight). r-Hirudin (1 mg/kg of body weight) was administered intravenously directly before thrombus i nduction; saline-treated animals served as controls. Thrombus formatio n (i.e., first platelet deposition at the endothelial Lining [FPD]; in ner luminal diameter reduction to 50% [D/2]; complete vessel occlusion [CVO]), vessel recanalization, microcirculatory parameters, and leuko cyte-endothelial cell interaction were analyzed by means of intravital fluorescence microscopy. Results: Hirudin significantly delayed the p rocess of thrombus formation compared with saline-treated controls in both arterioles (FPD: 381 +/- 80 vs 137 +/- 25 seconds, P < 0.05; D/2: 627 +/- 49 vs 501 +/- 71 seconds; CVO: 925 +/- 78 vs 854 +/- 60 secon ds) and venules (FPD: 173 +/- 11 vs 59 +/- 4 seconds; D/2: 342 +/- 54 vs 228 +/- 27 seconds; CVO: 541 +/- 85 vs 344 +/- 43 seconds; P < 0.05 ). In addition, r-hirudin-treated animals showed an increased rate of vessel recanalization at 24 hours after thrombus induction (arterioles : 54% [7 of 13] vs 0% [0 of 12], P < 0.05; venules: 77% [10 of 13] vs 53% [9 of 17]), whereas microcirculatory parameters and leukocyte-endo thelial cell interaction were not affected. Conclusion: Our data indic ate that r-hirudin not only counteracts the process of thrombus format ion but also promotes vessel recanalization, thus supporting its use i n clinical microvascular surgery.