摘要:

Platelets are known to contain sialic acid, most of which resides on glycoprotein carbohydrate side-chains. A large proportion of the platelet sialic acid is neuraminidase-labile. The sialic acid of human platelets is of the N-acetyl neuramininic acid type and is implicated in platelet functional events, such as aggregation and adhesion as well as contributing to the platelet's electrophoretic mobility. In this respect the platelet has an overall electronegative charge which is predominately the result of the carboxyl group of the sialic acid moiety. Platelet subpopulations have been isolated with differing amounts of sialic acid and cleavage of platelet sialic acid by neuraminidase is associated with loss of platelets from the circulation. This has relevance to platelet aging in vivo where removal of platelet sialic acid may reveal‘senescence antigens' which could facilitate platelet‘uptake’by the reticuloendothelial system. The importance of platelet sialic acid status has been described in certain platelet disorders such as some thrombocytopenias as well as particular disease states including malignancies and atherosclerosis.

ISSN:0953-7104    

DOI:10.3109/09537109109005496

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Platelets are produced from megakaryocytes. Under normal physiological conditions changes in platelet volume and density are not secondary to ageing but are present at thrombopoiesis. Prolonged increased platelet destruction rate leads to the production of large platelets from large, high ploidy megakaryocytes. In vivo and ex vivo studies show such platelets have more haemostatic potential. Platelets are larger and denser in acute myocardial infarction, where bleeding time is shortened and bleeding time aspirin sensitivity is increased. Thromboxane A2formation is increased in unstable angina pectoris and in acute myocardial infarction. Megakaryocytes are enlarged in acute myocardial infarction and in sudden unexpected cardiac death. Megakaryocyte and platelet changes may precede coronary artery thrombosis.

ISSN:0953-7104    

DOI:10.3109/09537109109005497

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Two fluorescent calcium indicators, Fura 2 and Indo 1 were compared with Quin 2 for the measurement of cytosolic free calcium concentrations (Ca2+)1in intact platelets. The free calcium ions were quantitatively evaluated using a single excitation wavelength fluorimeter before and after stimulation with the Ca2+ionophores ionomycin and A23187, platelet activating factor (PAF) and arachidonic acid (AA). Using Quin 2 no rise in (Ca2+)icould be registered by stimulation with the weak agonists PAF and AA in subthreshold concentrations for aggregation in contrast to Indo 1 and, to a lesser extent, Fura 2. Stimulation with ionomycin and A23187 led to a significant rise in (Ca2+)idetected by all three indicators. The reproducibility was best for Indo 1. The three fluorescence indicators differed in their influence on platelet function and in their physical properties. Higher fluorescence intensities for Fura 2, and especially Indo 1, allowed a much lower indicator concentration of about 2–10% with a 10-fold improvement in the signal/noise ratio with Indo 1. While there was no difference in the volume distribution curves of the dye-loaded platelets, Quin 2-loaded platelets showed a significantly diminished response to collagen-and ADP-induced aggregation.

ISSN:0953-7104    

DOI:10.3109/09537109109005498

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The threshold concentrations of arachidonic acid (AA) required to induce platelet aggregation were measured in platelet-rich plasma (PRP) from patients with acute ischaemic heart disease and healthy controls. The analytical precision of the test was very good (coefficient of variation 0–4%). Analytical accuracy was evaluated by comparing the results with threshold values for collagen-induced platelet aggregation, and a significant correlation was found (r = 0.56; p<0.01). When comparing the serum levels of thromboxane B2to threshold values for AA-induced platelet aggregation an inverse relationship was found (r = -0.37; p<0.01). In the clinical study significantly increased aggregability to AA was seen in patients with unstable angina pectoris (n = 13) compared to patients with stable angina pectoris (n = 14), (p<0.01), and both groups had hyperaggregating platelets compared to healthy controls (n = 27), (p<0.01). The patients with acute myocardial infarction (n = 10) had nearly normoaggregating platelets for the first 2–3 days after admission, but after a week and at day 14 their platelets showed significant hyperaggregability compared to healthy controls (p<0.01). Thus studies of AA-induced aggregation ex vivo suggest that patients with unstable angina pectoris and acute myocardial infarction, in whom coronary thrombus is frequently present, have increased platelet aggregability compared to patients with stable angina pectoris and healthy controls.

ISSN:0953-7104    

DOI:10.3109/09537109109005499

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

The properties of human hepatoma cell lines in relation to their ability to aggregate isolated human platelets were investigated because of the possible relevance to tumour metastasis. Mahlavu, HepG2 and SK55 cells were all able to aggregate platelets irreversibly, but required the presence of small amounts of plasma, which could not be replaced by fibrinogen or other common plasma proteins. They also required the presence of Ca2+. The plasma factor was non-dialysable and heat-labile. In the case of Mahlavu cells and SK55 cells the aggregatory activity was released from the cells as a non-dialysable material of high molecular weight. HepG2 cells were required intact and did not release materials which induced platelet aggregation. In all cases the aggregation was inhibited by hirudin. However, the requirements for plasma factors suggested that the material was not thrombin itself.The aggregatory property of all the cells was inhibited by prostacyclin and in the case of Mahlavu and HepG2 cells, to a lesser extent by nitric oxide. Addition of very small numbers of bovine aortic endothelial cells (but not human umbilical cord cells) inhibited the aggregation induced by Mahlavu and HepG2 cells, but not SK55 cells. If the endothelial cells were pre-treated with aspirin, this inhibitory property was abolished, indicating that a cyclo-oxygenase product was the principal agent.

ISSN:0953-7104    

DOI:10.3109/09537109109005500

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Calcium channel blockers are known to inhibit platelet aggregation in vitro and ex vivo. We studied the influence of a single oral dose of diltiazem (60 mg), nifedipine (10 mg) and verapamil (80 mg) on ADP-, collagen-, and epinephrine-induced platelet aggregation, malondialdehyde formation, serum thromboxane B2and platelet sensitivity to PGI2in 24 patients with coronary artery disease. Ninety minutes after drug intake most platelet function parameters were clearly decreased. Only collagen-stimulated platelet aggregation showed no significant drug effect. Malondialdehyde formation was more affected than ADP-induced platelet aggregation. Platelet sensitivity to PGI2was enhanced after nifedipine. These results suggest an alteration of the prostaglandin system as one of the underlying mechanisms. Diltiazem seems to be the most effective drug with a potent influence on platelet function ex vivo.

ISSN:0953-7104    

DOI:10.3109/09537109109005501

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

Measurement of the plasma concentration of glycocalicin, the extracellular portion of platelet glycoprotein Ib, should prove to be clinically useful in the investigation of causes of thrombocytopaenia and as an indirect method of determining platelet lifespan. We describe an immunoradiometric method for the measurement of glycocalicin in plasma using two murine monoclonal antibodies. The assay has good reproducibility with coefficients of intra- and inter-assay variation of 5.4% and 7.0% respectively, requires standard laboratory skills only and, after overnight coating of the wells, enables analysis of multiple samples in approximately 4 h. With citrated plasma the result of the assay does not appear to be affected by one cycle of freeze-thaw, nor was there any observed difference in result between platelet-poor plasma (PPP) prepared by centrifugation at 1100 g for 15 min and plasma that was confirmed to be platelet-free. The plasma concentrations of citrate and ethylenediaminetetraacetate were found to affect the result of the assay thus making it important that only samples with the same type and similar concentration of anticoagulant be compared and that standards should be diluted in glycocalicin-depleted plasma with the same concentration of these anticoagulants as the unknowns.

ISSN:0953-7104    

DOI:10.3109/09537109109005502

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0953-7104    

DOI:10.3109/09537109109005503

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0953-7104    

DOI:10.3109/09537109109005504

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

ISSN:0953-7104    

DOI:10.3109/09537109109005505

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor