Pathophysiological effects of fibrin on arterial endothelial cells in vivo: an electron microscopic study

Interactions between fibrin and arterial endothelial cells of rat iliac arteries in vivo were studies electron microscopically using a newly devised method. The microvilli became attached to the fibrin threads in an initial period of fibrinolysis. These threads had a fine granular appearance in the lysed areas. Fibrinolytically active endothelial cells had an active vesicular transport for ferritin particles injected concomitantly with the fibrinogen-thrombin mixture, thereby implying the enhancement of endothelial permeability in the lysed areas. However, fibrinolytically inactive endothelial cells coexisted in the same arteries. The denuded intima showed no lytic changes in the fibrin threads. These results indicate that the microvilli of the endothelial cells may plan an important role in the releasing plasminogen tissue activator from the endothelial cells and that there is a heterogeneity with regard to reactivity of each endothelial cell to fibrin.