Inhibition of endotoxin-induced leukocyte/endothelial cell interaction by antithrombin III

Antithrombin III (AT III) is an important inhibitor of thrombin activity, as well as of many other proteases of the coagulation system. AT III administration showed beneficial effects onseptic multiple organ dysfunction in clinical and experimental studies. This study investigates the AT III effect on leukocyte/endothelial cell interaction and microvascular perfusion. In the skin fold preparation of the hamster severe endotoxinemia was induced by repeated administration of endotoxin (LPS, 2 mg/kg, at t₀= 0 h and t₃= 48 h. AT III (250 U/kg) was substituted intravenously at t₀, t₂= 24 h, and t₃ (n = 6 animals, AT III group). In control animals (n = 5, controls) LPS was given without AT III substitution. By intravital fluorescence microscopy (FITC dextrane, rhodamine 6G) venular leukocyte adherence was determined at t₀, t₁ = 8 h, t₂, t₃, t₄ = 56 h, and t₃ = 72 h. Functional capillary densiry (FCD) served as a measure of capillary perfusion. AT III resulted in a significant modulation of LPS-induced leukocyte adherence and in a modulation of the LPS-induced depression in FCD (P < 0.0l, MANOVA). Thus, the number of sticking leukocytes after induction of endotoxin-emia was significantly lower in the AT III group compared with control animals (AT III: t₁ = 182 ± 35 cells/mm², t₂= 176 ± 21, t₃= 210 ± 51, t₄= 243 ± 48, t₅= 144 ± 29; control: t₁= 630 ± l05, t₂= 465 ± 113, t₃= 404 ± 50, t₄ = 542 ± 93, t₅= 356 ± 102; P < 0.05). AT III downregulated LPS-induced leukocyte/endothelial cell interaction and prevented the depression in FCD which served as a measure of capillary perfusion. Both mechanisms may explain beneficial AT III effects in patients with severe sepsis.