Surface phenomena of coagulation factors in vivo, observed by fluorescence intravital microscopy

The microcirculatory blood vessels of the exposed rat mesentery have been observed by incident fluorescence microscopy using various optical systems as well as image-intensifier devices and fast-scanning fluorometry techniques. As fluorescence-labeled proteins, albumin, gamma-globulin, fibrinogen, fibronectin, factor VIII-derived polypeptides, and antithrombin III have been injected intravenously. In some experiments two different-labeled proteins were administered consecutively. Whereas albumin and gamma-globulin did not accumulate at the inner surface of the microcirculatory blood vessels , fibrinogen and fibronectin showed a significant affinity to the vessels inner lining, mostly in venular vessels. Both substances accumulated at the same places of the microcirculatory endothelium. Blocking the fibrinolytic system of the animal increased the deposition of both substances. Factor VIII-derived polypeptides accumulated at the vessel inner surface in a different way. Antithrombin III did not show any affinities to the vascular wall. A receptor at the endothelial cell surface for both fibrinogen and fibronectin is postulated.