Thrombosis induced in vivo in the mesenteric artery of rats. An electron microscopic study of the initial phases.

Local thrombosis was initiated in vivo by applying a weak electric current to the mesenteric artery of rats. The thrombi adhered to areas of arterial wall exhibiting endothelial cell loss and muscle cell damage. They showed no tendency to sustained growth and contained large amounts of vaguely fibrillary substance that enmeshed platelet aggregates and infiltrated the denuded subendothelial layer. The subsequent local administration of dilute ADP led to brisk platelet aggregation and rapid increase in size of the thrombi. The large thrombotic masses disappeared as soon as the administration of ADP was stopped, leaving behind small remnants which, like the initial thrombi, were predominantly composed of enmeshing substance and could be stimulated to renewed growth by resuming the administration of ADP. It appears that the enmeshing substance plays a major role in the stability and cohesion of early thrombi which do not yet contain fibrin. It conceivably is made up of fibrin monomers.