Evangelou A M, Malamas M P, Vezyraki P, Karkabounas S C
Laboratory of Experimental Physiology, University of Ioannina, Greece.
In Vivo. 1998 May-Jun;12(3):321-5.
Catecholamines play an important role in platelet activation and aggregation, epinephrine being the most potent one. Catecholamines are substantially increased during stress, exercise or smoking and could result in clinically important platelet activation if their action was not rapidly regulated. In the present study the possible fast regulation of epinephrine-induced platelet aggregation by its metabolic degradation products is investigated.
Human platelet rich plasma (hPRP) and washed rabbit platelets(wRP) were used for the study. The platelets irreversible aggregation induced by epinephrine and ADP were monitored by an aggregometer prior to and after the addition of the catecholamines degradation products metanephrine, 3-methoxy-4-hydroxy-phenyl-glycole-aldehyde (MHPGA),3-methoxy-4-hydroxy-phenyl-mandelic acid (VMA) 3,4-dihydroxy phenyl glycole (DHPG),3,4-Dihydroxy-phenyl-glycole-aldehyde (DHPGA) and the trimethoxy-phenyl-methyl-piperazine(TMP), a known free radical scavenger and calcium antagonist. Linoleic acid-lipoxygenase reaction, in vitro was monitored in the presence and absence of VMA.
Metabolic degradation products possessing a methoxy group at position 3 of the phenolic ring markedly inhibited epinephrine and ADP-induced platelet aggregation at microM concentrations. The most potent inhibitor of both agonists was metahephrine, followed by MHPGA and VMA. TMZ also inhibited platelet aggregation at concentrations similar to VMA. Dihydroxy-phenyl compounds failed to induce any inhibition. None of the substances tested induced any aggregatory effect even at high concentrations (1 mM). VMA significantly inhibited linoleic acid-lipoxygenase reaction at 0.1 microM.
Results indicate that catecholamines' degradation products possessing methoxy (-OCH3) groups can rapidly inhibit in vitro and ex vivo epinephrine-induced platelet aggregation. The inhibitory effects of methoxy phenolic derivatives on epinephrine-induced platelet aggregation may possibly be attributed to their free radical scavenging properties. There is substantial evidence to conclude that an internal rapid autoregulation of epinephrine-induced platelet aggregation, caused by its metabolic degradation products, takes place in vivo.
儿茶酚胺在血小板活化和聚集过程中发挥重要作用，其中肾上腺素作用最为显著。在应激、运动或吸烟期间，儿茶酚胺水平会大幅升高，若其作用不能被迅速调节，可能导致具有临床意义的血小板活化。在本研究中，我们探讨了儿茶酚胺代谢降解产物对肾上腺素诱导的血小板聚集可能存在的快速调节作用。
本研究采用富含人血小板的血浆（hPRP）和洗涤后的兔血小板（wRP）。在添加儿茶酚胺降解产物甲氧基肾上腺素、3 - 甲氧基 - 4 - 羟基苯乙二醇醛（MHPGA）、3 - 甲氧基 - 4 - 羟基苯扁桃酸（VMA）、3,4 - 二羟基苯乙二醇（DHPG）、3,4 - 二羟基苯乙二醇醛（DHPGA）以及已知的自由基清除剂和钙拮抗剂三甲氧基苯基甲基哌嗪（TMP）之前和之后，通过血小板聚集仪监测肾上腺素和ADP诱导的血小板不可逆聚集。在有或无VMA存在的情况下，监测体外亚油酸 - 脂氧合酶反应。
在酚环3位带有甲氧基的代谢降解产物在微摩尔浓度下可显著抑制肾上腺素和ADP诱导的血小板聚集。两种激动剂最有效的抑制剂是甲氧基肾上腺素，其次是MHPGA和VMA。TMP在与VMA相似的浓度下也能抑制血小板聚集。二羟基苯化合物未能产生任何抑制作用。即使在高浓度（1 mM）下，所测试的物质均未诱导任何聚集作用。VMA在0.1微摩尔浓度下可显著抑制亚油酸 - 脂氧合酶反应。
结果表明，带有甲氧基（-OCH3）的儿茶酚胺降解产物能够在体外和体内迅速抑制肾上腺素诱导的血小板聚集。甲氧基酚类衍生物对肾上腺素诱导的血小板聚集的抑制作用可能归因于其自由基清除特性。有充分证据表明，在体内存在由儿茶酚胺代谢降解产物引起的肾上腺素诱导的血小板聚集的内部快速自动调节机制。
