Seiler S, Arnold A J, Grove R I, Fifer C A, Keely S L, Stanton H C
Department of Cardiovascular Biology, Bristol-Myers Pharmaceutical Research and Development Division, Evansville, Indiana.
J Pharmacol Exp Ther. 1987 Nov;243(2):767-74.
Anagrelide (BL-4162A, 6,7-dichloro-1,5-dihydroimidazo[2, 1-6] quinazolin-2[3H]one monohydrochloride hydrate) is a potent and broad spectrum inhibitor of platelet aggregation. Prior studies showed that anagrelide inhibited platelet cyclic AMP (cAMP) phosphodiesterase activity but did not appreciably elevate platelet cAMP levels. We examined the effects of anagrelide on washed human platelets and found that anagrelide caused significant elevation of cAMP levels. Anagrelide treatment also resulted in activation of the platelet cAMP-dependent protein kinase at anagrelide concentrations of 0.1 to 1 microgram/ml, which inhibited platelet aggregation but caused only small increases in platelet cAMP content. When whole platelets were incubated with radiolabeled phosphate, anagrelide increased phosphorylation of platelet proteins with relative molecular weights of 22, 26, 50 and 80 kilodaltons. The pattern of protein phosphorylation stimulated by anagrelide treatment was similar to that observed when the platelets were treated with forskolin. Anagrelide also inhibited the rise in intracellular Ca++ caused by thrombin, as measured using Fura-2-loaded platelets. The inhibition of increased intracellular Ca++ resulted from block of thrombin-induced mobilization of intracellular Ca++, as well as prevention of Ca++ influx through the plasma membrane. Anagrelide itself had no influence on inositol 1,4,5-trisphosphate-induced Caz5++ release from isolated platelet membrane vesicles. These studies suggest that anagrelide inhibits platelet phosphodiesterase activity in intact platelets resulting in an elevation in cAMP levels sufficient to activate the cAMP-dependent protein kinase and inhibit agonist-activated Ca++ fluxes.
阿那格雷（BL - 4162A，6,7 - 二氯 - 1,5 - 二氢咪唑并[2,1 - b]喹唑啉 - 2[3H]酮盐酸盐水合物）是一种强效且广谱的血小板聚集抑制剂。先前的研究表明，阿那格雷可抑制血小板环磷酸腺苷（cAMP）磷酸二酯酶活性，但并未显著提高血小板cAMP水平。我们研究了阿那格雷对洗涤后的人血小板的影响，发现阿那格雷可使cAMP水平显著升高。在阿那格雷浓度为0.1至1微克/毫升时，阿那格雷处理还导致血小板cAMP依赖性蛋白激酶活化，这抑制了血小板聚集，但仅使血小板cAMP含量略有增加。当将完整血小板与放射性标记的磷酸盐一起孵育时，阿那格雷增加了相对分子质量为22、26、50和80千道尔顿的血小板蛋白的磷酸化。阿那格雷处理所刺激的蛋白磷酸化模式与用福斯高林处理血小板时观察到的模式相似。阿那格雷还抑制了凝血酶引起的细胞内Ca++升高，这是通过使用负载Fura - 2的血小板来测量的。细胞内Ca++升高的抑制是由于凝血酶诱导的细胞内Ca++动员受阻，以及防止Ca++通过质膜内流。阿那格雷本身对肌醇1,4,5 - 三磷酸诱导的分离血小板膜囊泡中Ca++释放没有影响。这些研究表明，阿那格雷在完整血小板中抑制血小板磷酸二酯酶活性，导致cAMP水平升高，足以激活cAMP依赖性蛋白激酶并抑制激动剂激活的Ca++通量。
