Abstract
It is widely known that tissue thromboplastin (T. Tbp) is one of the direct trigger factors in DIC. By electron microscopy, purified T. Tbp consists of two types of structures, concentric membrane and amorphous substances, as reported by M. Hvatum et al. We have studied the ultrastructures of T. Tbp to demonstrate how it changes during coagulation.
[Materials and Methods] T. Tbp from lungs of rabbits (Mochida Ltd.) was used for these studies. T. Tbp has been studied on the purificant mixed in plasma, in plasma added with Ca++, in plasmin solution and in plasma added with Ca++ and Urokinase.
Then, attempts were made to demonstrate ultrastructural changes of T. Tbp after intravenous injection, as a model experiment on the pulmonary microthrombi formation induced by T. Tbp circulating from venous return.
The specimens were fixed in phosphate buffered formalin, followed by post-fixation in osmium tetroxide solution. They were examined by transmission electron microscope (TEM) or scanning electron microscope (SEM).
[Results] Morphological appearance of concentrically arranged membrane structure in T. Tbp remained nearly intact during blood coagulation process. T. Tbp, which existed in the sediments following dissolution of fibrin clot by the application of UK, showed an appearance of fine granules adhering to the surface of aggregates of particles through SEM. Through TEM, T. Tbp in the sediments was found to have retained its concentrically arranged membrane structures in some places, while, in some other places the appearance of fused membranes, smaller single vesicles and long sheets of membranes, and the formation of “blebs” etc. were observed. Various morphological changes caused by fibrinolytic substances accompanied the loss in coagulation activities.
Our results showed that coagulation activities of T. Tbp must be completely dependent upon the presence of the membrane structures.
Concentrically arranged membrane structures of the injected T. Tbp disappeared in extremely short time after the injection of te T. Tbp in rabbits. The long sheet membrane of the injected T. Tbp was frequently seen as adhered to the vascular endothelium or to the surface of blood corpuscles. Furthermore, fibrin fibers were formed in contact with the long sheet membrane of T. Tbp.
