血小板释放的ADP通过稳定细胞内钙浓度而稳定PAF诱导的兔血小板 …

AIM: To examine whether platelet-released adenosine diphosphate (ADP) would contribute to the stabilization of rabbit platelet aggregation induced by platelet activating factor (PAF). METHODS: Rabbit platelet aggregation induced by PAF was measured turbimetrically. ADP release from rabbit platelets stimulated by PAF was determined by HPLC. Intracellular Ca2+ was measured using Ca(2+)-sensitive fluorescent indicator Fura 2-AM. RESULTS: PAF > or = 1 nmol.L-1 induced full platelet aggregation, which did not deaggregate over 5 min after aggregation reached peak. Platelet aggregation was deaggregated in a concentration-dependent manner by subsequent addition of ADP scavenger ATP-diphosphohydrolase (apyrase) at 5-100 mg.L-1. PAF 3 nmol.L-1 stimulated release of ADP (29% vs 6% of control), and elicited a rapid rise in intracellular calcium ([Ca2+]i) which peaked at approximately 15 s. Then the [Ca2+]i gradually decayed from 585 +/- 80 nmol.L-1 within 100 s to a low level (364 +/- 82 nmol.L-1). Apyrase 100 mg.L-1, added 2 min after PAF, reduced [Ca2+]i to a lower level (171 +/- 29 nmol.L-1). CONCLUSION: Platelet-released ADP stabilizes PAF-induced rabbit platelet aggregation by stabilizing [Ca2+]i at elevated level.     

Contribution of ADP to the amplification of primary platelet aggregation by platelet activating factor (PAF): modulatory role of aspirin

Platelet Activating Factor (PAF)-induced human platelet aggregation in citrated plasma is accompanied by activation of the cyclo-oxygenase pathway and release of intracellular constituents including Adenosine-5'-diphosphate (ADP). Inhibition of the cyclo-oxygenase pathway by aspirin prevented the amplification of primary platelet aggregation induced by threshold concentrations of PAF. Removal of ADP by enzymatic systems had little or no effect on PAF-induced full aggregation, but reversed the aggregating effect of PAF (at 10 times threshold concentrations) on 'aspirinated' platelets. Aspirin also prevented the synergism between PAF and ADP when subthreshold concentrations of both compounds were combined. Similar results were obtained in heparinized platelet-rich plasma. Thus, ADP may amplify the primary response to PAF but its role is modulated by the availability of the cyclo-oxygenase pathway products.     

眼络通冲剂对血小板聚集和微循环的作用研究

目的探讨眼络通冲剂(YLTG)对血小板聚集和微循环的作用。方法实验用体外ADP诱导法,测定大鼠血小板聚集作用;小鼠灌胃给予眼络通冲剂连续10d,观察对小鼠耳廓微循环的作用。结果YLTG能抑制ADP诱导的大鼠血小板聚集;能明显扩张小鼠耳廓微动脉,使毛细血管开放数增加,血流速度加快。结论YLTG具有预防抑制血栓形成,改善微循环,从而起到改善视力的作用。     

白藜芦醇在体外对ADP诱导人血小板聚集的抑制作用及其机制

白藜芦醇(resveratrol，RESV)是一类广泛存在于葡萄、何首乌、花生等多种天然植物中的多酚类化合物。本研究观察RESV在体外对腺苷二磷酸(adenosine diphosphate，ADP)诱导健康志愿者血小板聚集、血小板膜结合纤维蛋白原(platelet membrane-bound fibrinogen，PFig)的抑制作用及其机制。应用血小板聚集仪、流式细胞仪及蛋白印迹技术(Western blotting)，研究RESV和磷脂酶Cβ抑制剂(phospholipase Cβ inhibitor，U73122)对ADP诱导的健康志愿者血小板聚集、PFig及血小板磷酸化磷脂酶Cβ3(phospho-phospholipase Cβ3，P-PLCβ3)和总磷脂酶Cβ3(total-phospholipase Cβ3，T-PLCβ3)蛋白表达的影响。与对照组相比，RESV(终浓度分别为25、50和100 μmol·L^-1)剂量依赖性地抑制ADP诱导的血小板聚集及Pfig、RESV与U73122对血小板聚集及PFig的抑制有叠加作用。RESV(终浓度为50 μmol·L^-1)还降低血小板P-PLCβ3蛋白的表达，降低血小板P-PLCβ3/T-PLCβ3的表达比率。RESV可能通过抑制健康志愿者血小板磷脂酶Cβ(phospholipase Cβ，PLCβ)的活性，降低了ADP诱导的血小板聚集及PFig，提示RESV有明确的抗血小板作用，具有新型抗血栓药物的研究前景。     

莪术二酮对ADP诱导的兔血小板聚集的抑制作用

莪术为传统的中药，具有行气破血、消积止痛等功效，其主要成分为莪术油和姜黄素类。莪术油具有消炎、止痛、活血化瘀等作用，为莪术的主要活性成分。莪术油主要含有莪术二酮、莪术酮、吉马酮等倍半萜类化合物。从已有的文献报道来看，对莪术油的药理作用研究较多，而对从莪术油中分离单一成分的研究较少。现采用比浊法测定莪术二酮对ADP诱导的免血小板聚集的抑制作用，以阐明莪术在传统的“行气破血”功效中的活性成分，为今后进一步开发新的药物提供试验依据。     

Prostaglandins and human platelet aggregation. Implications for the anti-aggregating activity of thromboxane-synthase inhibitors

Selective pharmacological blockade of thromboxane-synthase in human platelets by dazoxiben resulted in the reorientation of cyclic-endoperoxides towards PGE2, PGD2 and PGF2 alpha. At concentrations which can be reached when thromboxane-synthase is inhibited, PGE2 (100-500 nM) exerted a marked, concentration-dependent pro-aggregatory effect. This required the formation of endogenous or the addition of exogenous endoperoxides and was prevented by PGD2 or 13-aza-prostanoic acid, a selective antagonist of PGH2/TxA2 receptors. The anti-aggregating effect of PGD2 was evident at concentrations lower than those obtained in dazoxiben-treated platelets. It is proposed that in the absence of TxA2 generation, a combination of endoperoxides and PGE2 may result in normal aggregation. The latter may be inhibited by PGD2. No interference of PGF2 alpha on platelet function could be shown.     

Inhibitory mechanism of ifenprodil tartrate on rabbit platelet aggregation

The effects of dl-erythro-4-benzyl-alpha-(4-hydroxyphenyl)-beta-methyl-l-piperidine-eth anol tartrate (ifenprodil tartrate) on rabbit platelet aggregation in vitro and ex vivo were studied. Ifenprodil tartrate inhibited platelet aggregation in vitro induced by ADP, collagen and epinephrine. It also inhibited 5-hydroxytryptamine (5-HT) uptake into platelets and 5-HT release from platelets. Since these inhibitory effects of ifenprodil tartrate on the functions of rabbit platelets were similar to the effects of imipramine, the effects of ifenprodil tartrate may be due to the stabilizing action of ifenprodil tartrate on the platelet membrane. The platelet aggregation by ADP was significantly inhibited in rabbits after oral administration of ifenprodil tartrate, the maximal plasma level of ifenprodil being reached at 20 ng/ml ex vivo, while the maximal level was only 1/40 of the minimal concentration of ifenprodil tartrate necessary to inhibit platelet aggregation in vitro. These results indicate that factors other than ifenprodil tartrate acting directly on the platelets (e.g., PGI2 which is an endogenous inhibitor of platelet aggregation) are involved in inducing the inhibitory effects of ifenprodil tartrate on platelet aggregation ex vivo. The effects of ifenprodil tartrate on both PGI2 release from the aorta and the inhibitory effects of PGI2 on platelet aggregation in vitro were investigated: PGI2 was found to intensify the inhibitory effects of ifenprodil tartrate on platelet aggregation in vitro, but there was little effect, if any, on PGI2 release. Therefore, it is considered that the ex vivo effects of ifenprodil tartrate might be due to its interaction with endogenous PGI2 in the blood.     

Platelet-released ADP stabilizes PAF-induced rabbit platelet aggregation by stabilizing intracellular calcium

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Endothelium-dependent inhibition of platelet aggregation.

In cascade perfusion and superfusion experiments on rabbit tissues, when acetylcholine (ACh) was introduced into the circuit so as to perfuse the aorta under perfusion with noradrenaline (NA), the effluent relaxed the transverse aortic strip which had been denuded of endothelium. The effluent from the perfused aorta which was capable of relaxing the transverse aortic strip also significantly inhibited platelet aggregation induced by arachidonic acid (AA) in a volume-related manner. The inhibitory activity was decreased by the prolongation of transit time before addition of the effluent to platelet-rich plasma. Neither the inhibition of AA-induced aggregation nor the relaxation of the transverse strip by the effluent could be observed after the removal of endothelium from the aorta, or after pretreatment of aorta with mepacrine or nordihydroguaiaretic acid (NDGA). The AA-induced platelet aggregation was unaffected by pretreatment of platelets with mepacrine or NDGA at the concentration tested. Pretreatment of aorta with indomethacin failed to modify the relaxation of the transverse strip induced by the effluent. These results strongly suggest that endothelium-derived vascular relaxant factor (EDRF) possesses inhibitory activity on AA-induced aggregation in addition to its vasodilator activity.     

Inhibition of platelet aggregation by polyaspartoyl L-arginine and its mechanism

AIM: To observe the oral anti-platelet efficacy and the potential action mechanism of polyaspartoyl L-arginine (PDR), a new L-arginine rich compound. METHODS: Platelet aggregation was conducted by Born's method; bleeding time was determined using tail's bleeding time in mice; platelet adhesion was carried out with glass bottle method; nitric oxide (NO) was tested with Griess's method; and cAMP, thromboxane B(2) (TXB(2)) and 6-keto-PGF(1 alpha ) were assessed with commercial kits. RESULTS: The inhibition by PDR (15-60 mg/kg i.g. or 10 mg/kg i.v.) of platelet aggregation induced by adenosine diphosphate (ADP), collagen or thrombin at 1 h after oral administration or at 20 min after i.v. injection for rats (P<0.01), and its (15 mg/kg, i.g.) inhibition of ADP-induced platelet aggregation for rabbits during 6 h after administration were observed. PDR (15-60 mg/kg) prolonged the bleeding time of mice (P<0.05) and (30 mg/kg) increased NO concentration in plasma. On the other hand PDR did not change the contents of cAMP in platelet and TXB2 or 6-keto-PGF(1 alpha) in plasma. CONCLUSION: PDR is a novel, oral effective platelet aggregation inhibitor and its action mechanism possibly related to increasing NO generation.     

Endothelins inhibit serotonin-induced platelet aggregation via a mechanism involving protein kinase C.

Endothelins are a family of three peptides that act as local hormones released by the endothelium. They were found to inhibit rabbit and dog platelet aggregation in vivo, but no effect was observed in vitro. In order to investigate the possible interaction between endothelins and human platelet serotonin receptors, their effects on platelet aggregation induced by serotonin was studied. Endothelin-1, -2 and -3 had a dual action, on platelet aggregation and calcium mobilization induced by serotonin. When added at the same time as serotonin, endothelin potentiated the response to the amine. On the contrary, preincubation of platelet suspension with endothelin resulted in a concentration-dependent inhibition of the serotonin-mediated platelet response. Moreover, endothelin-1 inhibited serotonergic amplification of epinephrine-induced aggregation of platelets. We hypothesize that endothelins can bind to the platelet membrane and interact with serotonin receptors. The diverse effect of endothelins on serotonin-induced aggregation and calcium mobilization may be due to stimulation of protein kinase C.     

烟酰水杨酸对Collagen、ADP、AA诱导的兔血小板聚集的影响

目的观察烟酰水杨酸(NSA)对Collagen、ADP、AA诱导的兔血小板聚集的影响。方法用比浊法测定了NSA体外、体内对兔血小板聚集的影响。结果NSA能明显抑制体外、体内Collagen、ADP诱导的血小板聚集,体外最大抑制率分别为55.7%、61.3%,体内最大抑制率分别为42.2%、74.8%。NSA对AA诱导的兔血小板聚集没有影响。结论NSA具有抑制Collagen、ADP诱导的血小板聚集的作用。其抑制作用具有明显的量效关系。     

Histamine release by platelet aggregation.

Coincubation of rat serosal mast cells with human platelets leads to a significant release of histamine. which dose-dependently increases when platelet aggregation is induced by various concentrations of arachidonic acid. In turn, histamine enhances platelet aggregation induced by different agonists, this effect being mimicked by pyridyl-ethyl-amine (PEA), blocked by mepyramine and amplified by ranitidine. The data suggest the existence of a platelet-derived histamine releasing factor (PDHRF) and indicate the presence of platelet H1 and H2 receptors, capable of modulating platelet aggregation.