Antithrombin effects on endotoxin-induced microcirculatory disorders are mediated mainly by its interaction with microvascular endothelium

Objective: To investigate whether the protective effect of antithrombin III, which has been shown to exert beneficial effects during septic disorders, including reduction of endotoxin-associated leukocyte/endothelial cell interaction and capillary perfusion failure, is mainly based on its anticoagulant capacity or direct effects on the microvascular endothelium. Design: Animal study with three treatment groups. Setting: Animal research facility. Subjects: Syrian golden hamsters, 6-8 wks old with a body weight of 60-80 g. Interventions: In skinfold preparations of hamsters, normotensive endotoxemia was induced by intravenous administration of 2 mg/kg endotoxin (lipopolysaccharide, 2 mg/kg). Antithrombin III (n = 7 animals; 250 units/kg) or tryptophan(49)-blocked antithrombin III (n = 6; 250 units/kg) was substituted intravenously 5 mins before lipopolysaccharide administration. Saline-treated animals (n = 11), receiving only lipopolysaccharide, served as controls. Tryptophan(49)-blocked antithrombin III binds to glycosaminoglycans at the endothelial surface to a significantly lower extent while retaining its progressive anticoagulant effects. Measurements and Main Results: Compared with controls, antithrombin III significantly reduced lipopolysaccharide-induced arteriolar and venular leukocyte adherence (p < .01) and prevented depression of functional capillary density (p < .01), whereas tryptophan(49)-blocked antithrombin III failed to significantly improve both variables. As measured in vivo by a monoclonal fluorescein isothiocyanate-labeled anti-antithrombin III antibody and intravital microscopy, the lack of effect of tryptophan(49)-blocked antithrombin III was associated with significantly lower antithrombin III/endothelium binding coefficients after 1 hr, 3 hrs, and 24 hrs of endotoxemia (p < .01). Conclusions: We conclude that specific antithrombin III interactions with cell-surface glycosaminoglycans on the endothelium rather than anticoagulant properties are the mechanism of antithrombin III-mediated attenuation of leukocyte/endothelial cell interaction and capillary perfusion failure.