Nakamura T, Ariyoshi H, Kambayashi J, Ikeda M, Shinoki N, Kawasaki T, Monden M
Department of Surgery II, Osaka University Medical School, Japan.
Thromb Res. 1997 Jan 15;85(2):83-93. doi: 10.1016/s0049-3848(96)00225-3.
We recently reported the high prevalence of impaired platelet responsiveness only to epinephrine in healthy Japanese. This abnormality was associated with a 50% decrease in the number of alpha 2-adrenergic receptors. Platelets from non-responders (NR) do not undergo secondary platelet aggregation even after exposure to 100 microM epinephrine, but they can potentiate the effect of ADP to provoke platelet aggregation. To further define the nature of the defect and to delineate controversial steps of epinephrine stimulated signal transduction, a signaling pathway of epinephrine was investigated in platelets from NR and R(normal responder to epinephrine). In a unique particle counting apparatus, epinephrine initially triggered the formation of small platelet aggregates composing of 10-1000 cells from both R and NR, but the aggregates became larger (4600 > cells) only in platelets from R. Thus, platelets from NR lack the ability to form larger aggregates. A similar defect was reproduced by treating normal platelets with aspirin. In the presence of fibrinogen, platelets from NR lacked phospholipase A2 activation, determined by arachidonic acid liberation in the presence of inhibitors to cyclooxygenase and lipoxygenase. In the absence of fibrinogen, aggregation and phospholipase A2 activation were not evident in R and NR. The surface expression of GPIIb/IIIa was markedly decreased in platelets from NR after stimulation by epinephrine, in comparison with those from R. The resting level and epinephrine stimulated increase in cAMP were not significantly different between NR and R. Incubating R platelets with a half saturating dose of yohimbine rendered them insensitive to epinephrine. These results indicated that the impaired platelet aggregation induced by epinephrine was due to the impaired surface exposure of glycoproteins GPIIbIIIa integral to the activation of phospholipase A2, which requires the full and normal occupancy of the alpha 2-adrenergic receptor by epinephrine.
我们最近报道，在健康的日本人中，血小板仅对肾上腺素反应性受损的情况十分普遍。这种异常与α2 - 肾上腺素能受体数量减少50%有关。无反应者（NR）的血小板即使在暴露于100微摩尔肾上腺素后也不会发生继发性血小板聚集，但它们可以增强ADP引发血小板聚集的作用。为了进一步明确缺陷的本质，并描绘肾上腺素刺激信号转导中存在争议的步骤，我们在NR和R（对肾上腺素正常反应者）的血小板中研究了肾上腺素的信号通路。在一种独特的粒子计数装置中，肾上腺素最初触发了由R和NR的10 - 1000个细胞组成的小血小板聚集体的形成，但聚集体仅在R的血小板中变得更大（>4600个细胞）。因此，NR的血小板缺乏形成更大聚集体的能力。用阿司匹林处理正常血小板也会出现类似的缺陷。在有纤维蛋白原存在的情况下，通过在环氧化酶和脂氧合酶抑制剂存在下花生四烯酸的释放来测定，NR的血小板缺乏磷脂酶A2的激活。在没有纤维蛋白原的情况下，R和NR中的聚集和磷脂酶A2激活均不明显。与R的血小板相比，肾上腺素刺激后NR的血小板中糖蛋白GPIIb/IIIa的表面表达明显降低。NR和R之间静息水平和肾上腺素刺激引起的cAMP增加没有显著差异。用半饱和剂量的育亨宾孵育R血小板会使其对肾上腺素不敏感。这些结果表明，肾上腺素诱导的血小板聚集受损是由于糖蛋白GPIIbIIIa的表面暴露受损，而GPIIbIIIa的激活是磷脂酶A2激活所必需的，这需要肾上腺素完全正常地占据α2 - 肾上腺素能受体。
