HUMAN ENDOTHELIAL-CELLS SUPPRESS PROTHROMBIN ACTIVATION IN NONANTICOAGULATED WHOLE-BLOOD IN-VITRO

Human endothelial cells cultivated on polystyrene microcarrier beads w ere used to study endothelial anticoagulant activity in vitro. Spontan eous whole blood coagulation was inhibited by endothelial cells on mic rocarriers at a surface to volume ratio of 16 cm(2)/ml blood. Thrombin activity generated in nonanticoagulated whole blood during 1 hour and assessed by its fibrinogen clotting effect was reduced by 87% in the presence of endothelial cells. Consistent with this observation, proth rombin fragment(1+2), fibrinopeptide A, and thrombin-antithrombin III- complex release during the same period of time were inhibited by 81%, 47%, and 88%, respectively. Immunoblotting analysis of cell-free super natants derived from the same samples demonstrated that prothrombin ac tivation was strongly suppressed in the presence of endothelial cells. Furthermore, the incubation of nonanticoagulated whole blood with end othelialized beads for only 5 minutes after venipuncture was sufficien t to prevent subsequent prothrombin activation in the cell-free supern atants of the same whole blood sample after centrifugation. These find ings suggest that interruption of the coagulation cascade is probably one major mechanism of endothelial anticoagulant activity in vivo.