Haslam R J, Davidson M M, Desjardins J V
Biochem J. 1978 Oct 15;176(1):83-95. doi: 10.1042/bj1760083.
Whereas adenosine itself exerted independent stimulatory and inhibitory effects on the adenylate cyclase activity of a platelet particulate fraction at low and high concentrations respectively, 2-substituted and N6-monosubstituted adenosines had stimulatory but greatly decreased inhibitory effects. Deoxyadenosines, on the other hand, had enhanced inhibitory but no stimulatory effects. The most potent inhibitors found were, in order of increasing activity, 9-(tetrahydro-2-furyl)adenine (SQ 22536), 2',5'-dideoxyadenosine and 2'-deoxyadenosine 3'-monophosphate. Kinetic studies on prostaglandin E1-activated adenylate cyclase showed that the inhibition caused by either 2',5'-dideoxyadenosine or compound SQ 22536 was non-competitive with MgATP and that the former compound, at least, showed negative co-operativity; 50% inhibition was observed with 4 micron-2',5'-dideoxyadenosine or 13 micron-SQ 22536. These two compounds also inhibited both the basal and prostaglandin E1-activated adenylate cyclase activities of intact platelets, when these were measured as the increases in cyclic [3H]AMP in platelets that had been labelled with [3H]adenine and were then incubated briefly with papaverine or papaverine and prostaglandin E1. Both compounds, but particularly 2',5'-dideoxyadenosine, markedly decreased the inhibition by prostaglandin E1 of platelet aggregation induced by ADP or [arginine]vasopressin as well as the associated increases in platelet cyclic AMP, so providing further evidence that the effects of prostaglandin E1 on platelet aggregation are mediated by cyclic AMP. 2'-Deoxyadenosine 3'-monophosphate did not affect the inhibition of aggregation by prostaglandin E1, suggesting that the site of action of deoxyadenosine derivatives on adenylate cyclase is intracellular. Neither 2',5'-dideoxyadenosine nor compound SQ 22536 alone induced platelet aggregation. Moreover, neither compound potentiated platelet aggregation or the platelet release reaction when suboptimal concentrations of ADP, [arginine]vasopressin, collagen or arachidonate were added to heparinized or citrated platelet-rich plasma in the absence of prostaglandin E1. These results show that cyclic AMP plays no significant role in the responses of platelets to aggregating agents in the absence of compounds that increase the platelet cyclic AMP concentration above the resting value.
腺苷本身在低浓度和高浓度时分别对血小板微粒体部分的腺苷酸环化酶活性产生独立的刺激和抑制作用，而2-取代和N6-单取代腺苷具有刺激作用，但抑制作用大大降低。另一方面，脱氧腺苷的抑制作用增强，但没有刺激作用。按活性增加顺序，发现的最有效的抑制剂是9-(四氢-2-呋喃基)腺嘌呤(SQ 22536)、2',5'-二脱氧腺苷和2'-脱氧腺苷3'-单磷酸。对前列腺素E1激活的腺苷酸环化酶的动力学研究表明，2',5'-二脱氧腺苷或化合物SQ 22536引起的抑制作用与MgATP无竞争性，并且至少前一种化合物表现出负协同性；4微摩尔的2',5'-二脱氧腺苷或13微摩尔的SQ 22536可观察到50%的抑制作用。当以用[3H]腺嘌呤标记然后与罂粟碱或罂粟碱和前列腺素E1短暂孵育的血小板中环状[3H]AMP的增加来测量时，这两种化合物还抑制完整血小板的基础和前列腺素E1激活的腺苷酸环化酶活性。这两种化合物，尤其是2',5'-二脱氧腺苷，显著降低了前列腺素E1对ADP或[精氨酸]加压素诱导的血小板聚集的抑制作用以及相关的血小板环状AMP的增加，从而进一步证明前列腺素E1对血小板聚集的作用是由环状AMP介导的。2'-脱氧腺苷3'-单磷酸不影响前列腺素E1对聚集的抑制作用，这表明脱氧腺苷衍生物对腺苷酸环化酶的作用位点在细胞内。2',5'-二脱氧腺苷和化合物SQ 22536单独都不诱导血小板聚集。此外，当在不存在前列腺素E1的情况下，将次优浓度的ADP、[精氨酸]加压素、胶原或花生四烯酸添加到肝素化或枸橼酸化的富含血小板的血浆中时，这两种化合物都不会增强血小板聚集或血小板释放反应。这些结果表明，在不存在使血小板环状AMP浓度高于静息值的化合物的情况下，环状AMP在血小板对聚集剂的反应中不起重要作用。
