Williams Robert H, Nollert Matthias U
University of Oklahoma, School of Chemical Engineering and Material Science, 100 East Boyd, Norman, OK 73019, USA.
Thromb J. 2004 Nov 15;2(1):11. doi: 10.1186/1477-9560-2-11.
Nitric oxide (NO) is a free radical that plays an important role in modulating platelet adhesion and aggregation. Platelets are a source of vascular NO, but since erythrocytes avidly scavenge NO, the functional significance of platelet-derived NO is not clear. Our purpose was to determine if NO from platelets affects platelet thrombus formation in the presence of anticoagulated whole blood in an in vitro parallel plate flow system. We studied platelet adhesion and aggregation on a collagen type III surface in the presence of physiologically relevant fluid mechanical shear stress. We found that certain receptor mediated agonists (insulin and isoproterenol) caused a concentration dependent reduction in thrombus formation at a shear rate of 1000 s-1. This effect was mediated by NO since it was abolished in the presence of the NO inhibitor L-nitro-arginine-methyl-ester (L-NAME). As expected, at venous levels of shear rate (100 s-1) neither of the agonists had any effect on thrombus formation since platelet adhesion does not depend on activation at these low levels of shear. Interestingly, at a shear rate of 2000 s-1 the addition of L-NAME caused an increase in platelet coverage suggesting that shear, by itself, induces NO production by platelets. This is the first demonstration of shear stress causing platelets to produce an inhibitor of platelet activation. These results demonstrate that the development of a platelet thrombus is regulated in a complex way and that platelets produce functionally significant amounts of NO even in the presence of whole blood.
一氧化氮（NO）是一种自由基，在调节血小板黏附和聚集方面发挥着重要作用。血小板是血管中NO的一个来源，但由于红细胞能迅速清除NO，血小板源性NO的功能意义尚不清楚。我们的目的是在体外平行板流动系统中，确定在存在抗凝全血的情况下，血小板产生的NO是否会影响血小板血栓形成。我们研究了在生理相关的流体机械剪切应力存在下，血小板在III型胶原表面的黏附和聚集情况。我们发现，某些受体介导的激动剂（胰岛素和异丙肾上腺素）在剪切速率为1000 s-1时，会导致血栓形成呈浓度依赖性降低。这种效应是由NO介导的，因为在存在NO抑制剂L-硝基精氨酸甲酯（L-NAME）时该效应被消除。正如预期的那样，在静脉剪切速率水平（100 s-1）时，这两种激动剂对血栓形成均无任何影响，因为在这些低剪切水平下血小板黏附不依赖于激活。有趣的是，在剪切速率为2000 s-1时，添加L-NAME会导致血小板覆盖增加，这表明剪切力本身可诱导血小板产生NO。这是首次证明剪切应力可使血小板产生血小板激活抑制剂。这些结果表明，血小板血栓的形成受到复杂的调控，并且即使在存在全血的情况下，血小板也会产生具有功能意义的大量NO。
