Kinetic Studies of Intravascular Thrombus Formation Using Newly Developed Thrombus Model in Microvessels

本实验室发现，用激发光照射结合荧光染料血管内给药可诱导微血管内血小板血栓形成。我们报道了这种新的血小板血栓模型是有用的研究在体内的血液凝固过程和新开发的抗血栓药物的评价。然而，迄今为止，这些机制的细节尚不清楚。在本研究项目中，使用该血栓形成模型在大鼠肠系膜微血管中检查血小板血栓形成的动力学。在血栓形成后不久，血流速度开始增加，并随着血栓的生长而继续增加，特别是在径向方向。流速在达到几乎恒定的狭窄水平后急剧下降。该临界区域狭窄几乎具有恒定值，即，管腔面积的75- 95%。另外还进行了几种药物的抗血栓作用实验。结果表明，前列腺素（PGE_1、PGD_2、PGI_2）可抑制血小板血栓的生长，并呈剂量依赖性。由于预期激发的有色敏化剂（染料）与氧相互作用产生活性氧，因此检查了活性氧对血栓形成的影响。超氧自由基和单线态氧清除剂对延长血栓形成时间有显着作用。此外，从电子显微镜观察，白细胞粘附内皮细胞被认为与血栓形成有关。这些结果表明，光化学反应产生的活性氧对内皮细胞、血小板和/或白细胞的细胞膜损伤起决定性作用。由于这些损伤，血小板似乎开始粘附在内皮上并相互聚集。

It was found in our laboratory that the platelet thrombi were inducible in microvessels by the irradiation of exciting light in combination with the intravascular administration of fluorescent dye. We have reported that this new platelet thrombus model is useful for the studies on blood coagulation processes in vivo and the evaluation of newly developed antithrombotic agents. However, the details of the mechanisms are not clear so far. In this research project, the kinetics of the platelet thrombus formation was examined in microvessels of the rat mesentery, using this thrombus formation model. The blood flow velocity began to increase soon after the initiation of thrombus formation and continued to increase progressively with the growth of the thrombus particularly in the radial direction. The velocity precipitously dropped after reaching an almost constant level of stenosis. This critical area stenosis had almost a constant value, i.e., 75-95 % of the lumen area. The other experiments were also carried out to evaluate the antithrombotic effects of a few drugs. The growth of platelet thrombi was inhibited dose-dependently by the administrations of prostaglandins (PGE1, PGD2, PGI2). Since excited colored sensitizers (dyes) are expected to interact with oxygen to produce active oxygens, the effects of active oxygens on the thrombus formation were examined. The scavengers of superoxide radiacal and singlet oxygen had significant effects to prolong the thrombus formation times. Furthermore, from the electron micoscopic observations, the leucocytes adhered to the endothelial cells were supposed to have relevance to the thrombogenesis. It was suggested from these results that the active oxygens produced by photochemical reaction play decisive roles to induce damage of the cell membranes of the endothelium, platelet and/or leucocyte. Due to these damages the platelets seemed to begin to adhere to the endothelium and aggregate each other.