Schafer A I, Crawford D D, Gimbrone M A
J Clin Invest. 1984 Apr;73(4):1105-12. doi: 10.1172/JCI111296.
An important determinant of platelet-vessel wall interactions is the local balance of production of endothelial prostacyclin (PGI2) and platelet thromboxane (TX) A2, labile eicosanoids with opposing effects on hemostasis. Disputed evidence suggests that platelet-derived prostaglandin endoperoxide intermediates may be utilized as substrates for vascular PGI2 synthesis. Using several different approaches, we have found that platelets can transfer endoperoxides to cultured endothelial cells for efficient conversion to PGI2, but a reciprocal transfer of endothelial endoperoxides for utilization by platelet thromboxane synthetase does not occur under the same experimental conditions. However, platelets can utilize arachidonic acid released by endothelial cells for lipoxygenase metabolism. We have directly demonstrated the production of [3H]6-keto-PGF1 alpha (the breakdown product of [3H]PGI2) by aspirin-treated endothelial cells in the presence of platelets stimulated with [3H]arachidonic acid. In coincubation experiments using either arachidonate or ionophore A23187 as a stimulus, radioimmunoassay of the net production of arachidonic acid metabolites showed that 6-keto-PGF1 alpha generation by aspirin-treated endothelial cells in the presence of platelets may actually exceed its generation by uninhibited endothelial cells alone. In functional assays, platelet aggregation was inhibited in the presence of aspirin-treated endothelial cells after stimulation with either arachidonate or ionophore A23187. In contrast, the inverse experiments, using aspirin-treated platelets and uninhibited endothelial cells, failed to demonstrate platelet utilization of endothelial endoperoxides for TXA2 production by any of the above methods. These studies thus provide evidence that efficient unidirectional transfer and utilization of platelet-derived endoperoxides for endothelial PGI2 production can occur. This process may serve to amplify PGI2 generation adjacent to areas of vascular injury and permit tight localization of platelet plug formation at these sites.
血小板与血管壁相互作用的一个重要决定因素是内皮前列环素（PGI2）和血小板血栓素（TX）A2生成的局部平衡，这两种不稳定的类花生酸对止血具有相反的作用。有争议的证据表明，血小板衍生的前列腺素内过氧化物中间体可能被用作血管PGI2合成的底物。通过几种不同的方法，我们发现血小板可以将内过氧化物转移到培养的内皮细胞中，以有效地转化为PGI2，但在相同的实验条件下，内皮内过氧化物不会反向转移以供血小板血栓素合成酶利用。然而，血小板可以利用内皮细胞释放的花生四烯酸进行脂氧合酶代谢。我们直接证明了在用[3H]花生四烯酸刺激的血小板存在的情况下，经阿司匹林处理的内皮细胞产生了[3H]6-酮-PGF1α（[3H]PGI2的分解产物）。在使用花生四烯酸盐或离子载体A23187作为刺激物的共孵育实验中，对花生四烯酸代谢产物净生成的放射免疫分析表明，经阿司匹林处理的内皮细胞在血小板存在的情况下生成的6-酮-PGF1α实际上可能超过未受抑制的内皮细胞单独生成的量。在功能测定中，在用花生四烯酸盐或离子载体A23187刺激后，经阿司匹林处理的内皮细胞存在时血小板聚集受到抑制。相比之下，使用经阿司匹林处理的血小板和未受抑制的内皮细胞进行的反向实验，未能通过上述任何方法证明血小板利用内皮内过氧化物生成TXA2。因此，这些研究提供了证据，表明血小板衍生的内过氧化物可有效地单向转移并用于内皮PGI2的生成。这一过程可能有助于放大血管损伤区域附近的PGI2生成，并使血小板栓子形成紧密定位在这些部位。
