Thrombosis triggered by severe arterial lesions is inhibited by oral administration of a glycoprotein IIb/IIIa antagonist

Platelet aggregation and thrombosis play an important role in the onset of acute coronary events. Regardless of the stimulus for activation, platelet thrombus formation is ultimately regulated through the IIb/IIIa receptor complex. The effects of oral administration of xemilofiban, a non-peptide mimetic of the RGDF sequence of the IIb/IIIa receptor complex, on thrombus formation were evaluated in a canine model. Xemilofiban significantly reduced platelet deposition on severely damaged arterial wall. Platelet deposition was reduced at both low (13 ± 1 from 56 ± 18 × 10⁶ platelets cm⁻²; P  < 0.05) and high (23 ± 2 from 111 ± 21 × 10⁶ platelets cm⁻²; P  < 0.01) shear rates. Platelet deposition was reduced to a monolayer as seen by electron microscopy (platelet–vessel wall interaction). Therefore, the availability of an orally active IIb/IIIa antagonist for chronic use may have significant value in preventing thrombus formation in those clinical situations associated with severe arterial injury, such as atherosclerotic plaque disruption.     

The assembly of the factor X-activating complex on activated human platelets

Summary.  Platelet membranes provide procoagulant surfaces for the assembly and expression of the factor X-activating complex and promote the proteolytic activation and assembly of the prothrombinase complex resulting in normal hemostasis. Recent studies from our laboratory and others indicate that platelets possess specific, high-affinity, saturable, receptors for factors XI, XIa, IX, IXa, X, VIII, VIIIa, V, Va and Xa, prothrombin, and thrombin. Studies described in this review support the hypothesis that the factor X-activating complex on the platelet surface consists of three receptors (for the enzyme, factor IXa; the substrate, factor X; and the cofactor, factor VIIIa), the colocalization of which results in a 24 million-fold acceleration of the rate of factor X activation. Whether the procoagulant surface of platelets is defined exclusively by procoagulant phospholipids, or whether specific protein receptors exist for the coagulant factors and proteases, is currently unresolved. The interaction between coagulation proteins and platelets is critical to the maintenance of normal hemostasis and is pathogenetically important in human disease.     

适量饮酒对健康成年男性血浆TXB2,6-Keto-PGF2a及血小板聚集功能的影响

①目的　观察适量饮酒对健康成年男性的血小板聚集功能及血浆血栓素B2 (TXB2 ) ,6 酮 前列腺素F2a(6 Keto PGF2a)的影响。②方法　将 80例健康成年男性随机分成 4组 ,分别空腹饮用矿泉水、啤酒、干红葡萄酒各 2 0 0mL ,白酒 50mL加矿泉水至 2 0 0mL .于饮前及饮后 2h分别测定血小板的聚集率及解聚率 ,并采血测定血浆TXB2 ,6 Keto PGF2a.③结果　矿泉水组饮后上述指标无变化 (t=0 .0 3～ 0 .84,P >0 .0 5) ;白酒、啤酒、红葡萄酒组饮后血小板聚集率减低 (t=8.1 2～ 2 4 .39,P <0 .0 1 ) ,解聚率升高 (t=2 8.48～ 35 .2 2 ,P <0 .0 1 ) ,血浆TXB2 降低 (t=2 5 .69～ 89.83 ,P <0 .0 1 ) ,而血浆 6 Keto PGF2a升高 (t=2 1 .0 6～ 2 3 .2 9,P <0 .0 1 )。④结论　健康成年男性适量饮酒可减低其血小板聚集功能 ,降低其血浆TXB2 ,提高其血浆 6 Keto PGF2a水平     

Influence of a calcium dependent protease inhibitor on platelet activation and secretion

Continuous proteolysis resulting in consumption of major cytoskeletal proteins may be essential for platelet activation and aggregation. In this study we evaluated the effect of a known protease inhibitor, Leupeptin, on agonist induced platelet aggregation and secretion. Platelets exposed to 10 ugs/ml of Leupeptin did not aggregate in response to the action of thrombin (0.2u/ml). However, a concentration of Leupeptin as high as 250 ugs/ml did not prevent arachidonate induced aggregation and secretion. Leupeptin (100 ugs/ml) effectively blocked thrombin (0.2 u/ml) induced elevation of cytosolic calcium, but did not affect arachidonate induced elevation of platelet intracellular calcium levels. At a concentration of 100 ug/ml, Leupeptin effectively blocked thrombin (0.5u/ml) induced clot formation of platelet poor plasma, suggesting that it can exert its effect on thrombin by preventing fibrinogen degradation. Effective K_i for the competitive inhibition of thrombin induced hydrolysis of a chromogenic substrate, S2238, by Leupeptin was 2.4 uM. Leupeptin inhibition of platelet function was reversible by washing platelets free of the polypeptide. Results of our study demonstrate that Leupeptin inhibits thrombin induced platelet activation, probably by interfering with its proteolytic activity on the platelet surface membrane. However, inhibition of platelet surface membrane associated proteases did not prevent activation of platelets by other agonists.     

检测各型乙肝患者血小板功能的临床意义

检测198例各型乙肝患者血小板功能的五个项目：血小板总数、粘附试验、聚集试验、血块退缩、血小板第3因子有效性，发现各期乙肝患者血小板功能的异常有显著性差异（P＜0．01）．并提示乙肝患者除有血小板数量的改变外，还有质量的改变，因此，全面的血小板功能检测可作为估计乙肝患者肝损害程度的辅助指标．     

Effect of dipyridamole with or without aspirin on urine protein excretion in patients with membranous glomerulonephritis

Summary The antiproteinuric effect of the antiplatelet agent dipyridamole has been assessed after inhibiton of thromboxane B₂ (TxB₂) synthesis in 8 patients with confirmed membranous glomerulonephritis. There were three study periods, each of 30 days, and 45 days apart, namely a washout period, treatment with dipyridamole 300 mg/d, and dipyridamole 225 mg/d plus aspirin 150 mg/d. On Days 1 and 30 of each study period serum and urine creatinine, 24-h excretion of protein, creatinine clearance, platelet aggregometry on whole blood and serum TxB₂ were measured. Treatment with dipyridamole alone or with aspirin produced significant inhibition of platelet aggregation and a fall in 24-h protein excretion; the latter amounted to 54% with dipyridamole alone and 56 % with dipyridamole plus aspirin (NS). Dipyridamole plus aspirin caused an 82 % reduction in serum TxB₂.     

凝血酶受体结构与功能的研究现状

凝血酶（ｔｈｒｏｍｉｂｉｎ，Ⅱａ）是一种生成于损伤处血管内皮细胞多功能蛋白酶，它是参与凝血过程各个环节反应中的关键酶。在发挥止血作用的同时，还可能诱导炎症、增生及修复等反应。最近发现的凝血酶受体（ｔｈｒｏｍｂｉｎ ｒｅｃｅｐｔｏｒ，ＴＲ）分子可能为解释上述现象提供了一个理论框架。同时，ＴＲＮ端被Ⅱａ切下的４１个氨基酸片段是否具有特殊功效，值得研究探讨。     

Chronic isolated macrothrombocytopenia with autosomal dominant transmission: a morphological and qualitative platelet disorder

Abstract: We studied 47 subjects belonging to 13 unrelated families with a history of mild haemorrhagic diathesis and chronic thrombocytopenia. 36 patients presented some degree of thrombocytopenia: 7/36 (19%) had slight thrombocytopenia (100–150×10⁹/L); 26/36 (72%) had mild thrombocytopenia (50–100×10⁹/L) and 3/36 (8%) had severe thrombocytopenia (<50×10⁹/L). No correlation was observed between platelet count and the degree of haemorrhagic diathesis, which was mild in the majority of patients. Transmission was autosomal dominant. Platelet anisocytosis, increased percentage of large platelets and absence of leukocyte inclusions were observed in 26/30 (87%) of the examined blood smears. The ultrastructural appearance of platelets was normal. Megakaryocytes appeared normal in number in 10/10 patients, but showed asynchronous nuclear-cytoplasm maturation and mainly nonlobulated nuclei. Platelet aggregation was studied in 26 patients and either increased or decreased curves were variably observed in response to different aggregating agents. Platelet-associated IgG (PAIgG) was increased in 18/31 (58%) patients, while serum autoantibodies against platelet glycoproteins Ib/IX or IIb/IIIa were demonstrable in only 1 case. An increased expression of platelet surface glycoproteins Ib and IIb/IIIa, as studied by murine monoclonal antibodies binding in 17 cases, was observed. Platelet survival performed by 111In-oxine-labelled autologous platelets was normal in the 3 studied patients. Congenital macrothrombocytopenia confirms to be a distinct clinical disorder for which the name of “chronic isolated hereditary macrothrombocytopenia” is proposed.     

Blood platelets in severely injured burned patients

Unbelievable decrease of blood-platelet in the severely burned patients during the treatment of skingrafting caused two patients to unexpected death. From the records of changes of platelet number, a certain ‘platelet curve’ was made. By observing the curve, our treatments of skingrafting were carried out during the stable period and from then on we had no death cases.     

Comparison of the effect of intravenous ketoprofen, ketorolac and diclofenac on platelet function in volunteers

Background : Nonsteroidal anti–inflammatory drugs (NSAIDs) inhibit prostaglandin synthesis which may result in impaired platelet function. Because NSAIDs have different abilities to inhibit cyclo–oxygenases we compared the effect of intravenous ketoprofen, ketorolac and diclofenac on platelet function in volunteers. Methods : Ten healthy male volunteers were given ketoprofen 1.4 mg kg^-1, ketorolac 0.4 mg kg^-1 and diclofenac 1.1 mg kg^-1 in saline i.v. on three different occasions, at more than one–week intervals, in a randomized double–blind crossover study. Platelet function was evaluated before (sample 0), 2 (sample 2) and 24 h (sample 3) after the beginning of the infusion. Results : Two of the volunteers had no secondary platelet aggregation in their aggregation curves before the experiment (sample 0, studied three times) and their results were excluded from the final analysis. Diclofenac inhibited adrenaline (0.9 μg–ml^-1) induced platelet aggregation less (median maximal aggregation 22.5%) than ketoprofen (18.3%) and ketorolac (15.7%) (P<0.05) in sample 2. In the ketorolac group in sample 3 an impairment of adrenaline (0.9 ng ml^-1) induced platelet aggregation was still seen (26.7%) (P<0.05) but not in the other groups. Diclofenac did not affect adenosine diphosphate (ADP) induced platelet aggregation. However, ketorolac caused an impairment in ADP (3 μM and 6 μM) induced platelet aggregation and ketoprofen in ADP (6 μM) induced platelet aggregation in sample 2. Bleeding time was prolonged (P<0.05) after ketoprofen and ketorolac (sample 2) but not after diclofenac. Platelet retention on glass beads was unaffected by the tested drugs. Conclusion : Ketoprofen, ketorolac and diclofenac caused a reversible platelet dysfunction. Diclofenac had the mildest effect, while platelet dysfunction was still seen 24 h after the beginning of ketorolac.