Biochemical changes in endothelial cell monolayers induced by fibrin deposition in vitro

Endothelial cells in vivo come into contact with fibrin during numerous physiological and pathological processes, but the nature of this interaction is poorly understood. The interaction of fibrin and endothelial cells was examined by incubating bovine aortic endothelial cell monolayers in vitro with fibrinogen (100 micrograms/ml) in medium supplemented with 10% calf serum. This treatment produced a layer of fibrin above the endothelial cell monolayer, which induced disorganization of the monolayer and remained associated with the monolayer even after washing. Endothelial cell pinocytosis of 14C-sucrose was elevated by 25% and 60% after incubation with fibrin for 8 hours and 2 days, respectively. Fibrin deposition on endothelial cell monolayers increased the rate of DNA synthesis (3H-thymidine incorporation) for 1 to 3 days by as much as 60% over controls. Concomitant with the lysis of fibrin above endothelial cells and the reorganization of the monolayer at Days 4 or 5 was a reduction of endothelial cell pinocytosis and DNA synthesis to control values. In contrast, there was no effect on the cell density at any time after incubation with fibrin. These results indicate that fibrin interacts with endothelial cells and induces a disorganization of the monolayer that is accompanied by changes in the rate of pinocytosis and in the rate of DNA synthesis.