[Organization of experimental thrombi in arteries and veins. A comparative study (author's transl)].

Thrombi were produced in 62 female white rats (Sprague-Dawley) by injection of thrombin in the right common carotid artery and in the left vena iugularis as well. Partly the vessels were ligatured proximal and distal of the thrombus, partly they were closed with one ligature. In this latter group (one ligature) the thrombus was exposed to the blood-pressure, while in the first group the thrombus was protected against the blood-waves. After 2, 4, 6, 8, 10 and 14 days as after 4 and 6 weeks the rats were sacrificed and the thrombosed vessel-segments were studied by light-microscope. In the arterie we found occlusive thrombi. In the veins the thrombi were higher in fibrin content than in the arteries. Between the thrombus and the endothelium of the vein-wall there was a sinus which became wider with aging of the thrombus. In the first days the progression of thrombus-organization was more rapid in veins than in arteries; endothelial cells, fibroblasts and capillary buds invaded the thrombus more extensive. In veins there was no difference in composition and organization of the thrombi of the two groups. In the thrombosed veins often small capillaries could be seen running through the vessel wall into the tissue of the organized thrombus but not in arteries. 6 weeks after thrombus-formation wide capillaries recanalized the veins, but the arteries were obturated by fibrous tissue with only a few small capillaries. Elastic fibres could be seen in the organized arterial thrombi earlier and more extensive than in the venous. In double ligatured arteries the organization of thrombi was more rapid than in arteries, in which the thrombus was influenced by the pulsating blood-pressure. In this latter group with only one ligature the organization-process was pronounced in the proximal part of the thrombus, which was higher in fibrin content. Next the ligature the thrombus was composed mainly of erythrocytes and hematoidin-needles. In this part of the thrombus the organization-process started with delay. From our findings we may conclude that the composition of a thrombus, the influence of the blood-pressure and the structure of the vessel-wall are important factors to explain the different temporal course and morphological pattern of thrombus-organization.