In vivo arterial platelet-vessel wall interaction and thrombosis: induction, on-line registration and ultrastructural control.

A technique for induction and on-line quantification of local platelet thrombi in mesenteric arteries of small laboratory animals was developed and standardized in our laboratory. In the past, this model was used to study the nature of platelet-vessel wall interaction in the living animal. The ultrastructure of the experimental intimal lesion and the vessel wall regeneration were assessed by transmission electron microscopy (TEM), both in normal and pathologic conditions. Scanning electron microscopy (SEM) now shows the ultramorphology of platelet thrombi on the experimentally injured arterial segment following topical superfusion with ADP, mepacrine or platelet-activating factor (PAF). The application of these substances, each with proper bio-activity, leads to distinct types of platelet thrombi. Mepacrine or PAF superfusion causes large thrombotic masses, as compared to control, ADP induced thrombi, and seems toxic for the endothelial cells. Mepacrine thrombi differ significantly from PAF thrombi in their platelet density, degree of platelet activation and in their relation to the endothelium that surrounds the experimental lesion. Furthermore, PAF superfusion induces a phenomenon of spontaneous regeneration of the thrombus after its forced embolization. This is probably due to some unknown bio-action of PAF in the vessel wall.