Cadroy Y, Horbett T A, Hanson S R
Department of Basic and Clinical Research, Institute of Scripps Clinic, La Jolla, CA 92037.
J Lab Clin Med. 1989 Apr;113(4):436-48.
To study mechanisms of complex thrombus formation in vivo, and to compare the relative antithrombotic effects of anticoagulants and antiplatelet agents, a model was developed in baboons. Segments of collagen-coated tubing followed by two sequentially placed expansion chambers exhibiting disturbed flow patterns were exposed to native blood under laminar flow conditions. The device was incorporated for 1 hour into an exteriorized arteriovenous shunt in baboons under controlled blood flow (20 ml/min). Morphologic evaluation by scanning electron microscopy showed that thrombi associated with collagen were relatively rich in platelets but thrombi in the chambers were rich in fibrin and red cells. Deposition of indium 111-labeled platelets was continuously measured with a scintillation camera. Platelet deposition increased in a linear (collagen-coated segment) or exponential (chambers 1 and 2) fashion over time, with values after 40 minutes averaging 24.1 +/- 3.3 x 10(8) platelets (collagen segment), 16.7 +/- 3.4 x 10(8) platelets (chamber 1), and 8.4 +/- 2.4 x 10(8) platelets (chamber 2). Total fibrinogen deposition after 40 minutes was determined by using iodine 125-labeled baboon fibrinogen and averaged 0.58 +/- 0.14 mg in the collagen segment, 1.51 +/- 0.27 mg in chamber 1, and 0.95 +/- 0.25 mg in chamber 2. Plasma levels of beta-thromboglobulin (beta TG), platelet-factor 4 (PF4), and fibrinopeptide A (FPA) increased fourfold to fivefold after 60 minutes of blood exposure to the thrombotic device. Platelet deposition onto the collagen segment, chamber 1, and chamber 2 was linearly dependent on the circulating platelet count. Platelet accumulation in chamber 1 and chamber 2 was also dependent on the presence of the proximal collagen segment. An anticoagulating dose of standard heparin decreased platelet deposition in the chambers (p less than 0.05) but did not decrease deposition onto the collagen segment. Although beta TG and PF4 levels remained elevated after the administration of standard heparin, the elevation in plasma FPA was interrupted. Further evidence that the thrombotic process was dependent on platelets was provided by the finding that prostaglandin I2 at high concentration (35 ng/ml) decreased platelet deposition onto the collagen segment and in chambers 1 and 2, decreased beta TG and PF4 release, and reduced FPA formation. The combination of standard heparin and PGI2 produced the most potent inhibition of platelet thrombus formation and prevented the increases in plasma PF4, beta TG and FPA.
为研究体内复杂血栓形成的机制，并比较抗凝剂和抗血小板药物的相对抗血栓作用，在狒狒身上建立了一个模型。将涂有胶原蛋白的管道段，随后是两个依次放置的呈现紊乱血流模式的扩张腔，在层流条件下暴露于天然血液中。该装置在控制血流（20毫升/分钟）的情况下，在狒狒的体外动静脉分流中植入1小时。通过扫描电子显微镜进行形态学评估显示，与胶原蛋白相关的血栓中血小板相对丰富，但腔室内的血栓富含纤维蛋白和红细胞。用闪烁相机连续测量铟111标记血小板的沉积情况。血小板沉积随时间呈线性（涂有胶原蛋白的段）或指数（腔室1和2）方式增加，40分钟后的平均值分别为24.1±3.3×10⁸个血小板（胶原蛋白段）、16.7±3.4×10⁸个血小板（腔室1）和8.4±2.4×10⁸个血小板（腔室2）。40分钟后总纤维蛋白原沉积通过使用碘125标记的狒狒纤维蛋白原测定，在胶原蛋白段平均为0.58±0.14毫克，在腔室1为1.51±0.27毫克，在腔室2为0.95±0.25毫克。血液暴露于血栓形成装置60分钟后，血浆β-血小板球蛋白（βTG）、血小板因子4（PF4）和纤维蛋白肽A（FPA）水平增加了四倍至五倍。血小板在胶原蛋白段、腔室1和腔室2上的沉积与循环血小板计数呈线性相关。腔室1和腔室2中的血小板积聚也取决于近端胶原蛋白段的存在。标准肝素的抗凝剂量可降低腔室内的血小板沉积（p＜0.05），但不会降低在胶原蛋白段上的沉积。尽管给予标准肝素后βTG和PF4水平仍升高，但血浆FPA的升高被阻断。高浓度（35纳克/毫升）的前列腺素I2降低了血小板在胶原蛋白段以及腔室1和2上的沉积，降低了βTG和PF4的释放，并减少了FPA的形成，这一发现进一步证明血栓形成过程依赖于血小板。标准肝素和PGI2的联合使用对血小板血栓形成产生了最有效的抑制作用，并防止了血浆PF4、βTG和FPA的升高。
