The role of blood flow in platelet adhesion, fibrin deposition, and formation of mural thrombi.

Abstract Rabbit aortas were selectively denuded of endothelium by a balloon catheter, thus exposing the subendothelial surface. The interaction of platelets with this surface was examined by light and electron microscopy and measured with a morphometric technique. At unaltered flow in vivo platelets formed a tight and continuous layer within 10–20 min, no fibrin deposition was found, and formation of platelet thrombi was transient. A similar pattern of platelet interaction with subendothelium was observed in vitro after exposure to citrated blood which was pumped through a newly developed perfusion chamber at an average flow velocity similar to that measured in vivo . In contrast, at reduced blood flow in vivo markedly fewer platelets adhered to the subendothelial surface within a given period of time, areas with fibrin deposits at the subendothelial surface and in close association with platelets and red blood cells were observed and mural platelet thrombi were virtually absent. Similarly, fewer platelets adhered to the subendothelial surface at lower blood flow velocities in vitro and no platelet thrombi formed. These experimental data indicate that platelet adhesion and aggregation play a predominant role only at high, i.e., arterial, blood flow velocities and function independent of coagulation. Fibrin deposition at the subendothelial surface on the other hand appears to require stagnant blood.