ENHANCED ENDOTHELIAL TISSUE FACTOR BUT NORMAL THROMBOMODULIN IN ENDOTOXIN-TREATED RABBITS

Exposure of cultured endothelial cells to bacterial endotoxin induces an enhancement of cell procoagulant activity (PCA) and a simultaneous reduction of thrombomodulin activity (TM). We evaluated the effect of endotoxin on the expression of both endothelial PCA and TM in vivo, in rabbits. Animals were given a single i.v. injection of endotoxin (E. coli 0111:B4 LPS, W, 10-200 mug/kg); the thoracic aorta was harvested after 2 or 4 hours and placed in an ad hoc device to expose the endoth elial surface only. Endotoxin treatment resulted in a dose-dependent i ncrease of endothelial PCA (p < 0.001, at 100 mug/kg or more), which w as totally dependent on factor VII and thus identified as tissue facto r. In contrast, endothelial TM activity, as measured by the rate of th rombin-induced protein C activation, was similar in control and endoto xemic rabbits, even when the animals were given two injections (50 mug /kg, 24 h apart), or a continuous infusion (40 mug/kg/h during 4 hours ) of endotoxin. To explore the effect of endotoxin on TM activity at t he microcirculation level, we measured the extent of protein C activat ion in vivo, induced by a continuous infusion of low doses of thrombin (1 NIH U/kg/min for 60 min). Again, endotoxin administration was not associated with significant changes in TM-dependent protein C activati on, as assessed by the anticoagulant activity present in a barium citr ate plasma eluate obtained at the end of thrombin infusion. Although r eduction of TM during persistent endotoxemia cannot be definitively ex cluded, our data support a major role of endothelial PCA in LPS-induce d coagulative changes.