摘要:

Just as the mythical Pheonix arose from the ashes, so too has Platelets. Reluctantly, it had been decided that the December issue of Volume 6, 1996 had to be the final one. Despite considerable success in attracting and publishing high quality papers relating to platelets and platelet-related research, the previous publishers had decided that the journal should come to an end.

ISSN:0953-7104    

DOI:10.3109/09537109609079502

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Although dipyridamole was identified as a potential antithrombotic agent many years ago,1its effectiveness as a single agent in secondary prevention of arterial thrombosis in man has never been proven in properly conducted clinical trials with sufficient power. In many clinical trials it has been tested in combination with aspirin, and until recently meta-analyses have failed to show any significant benefit of the combination of aspirin and dipyridamole beyond that shown with aspirin alone.2,3

ISSN:0953-7104    

DOI:10.3109/09537109609079503

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Human blood platelets can be activated by a variety of physiological activators such as adenosine diphosphate (ADP), thrombin or collagen, leading to activation of GPIIb-IIIa into a high-affinity receptor for Fg (FgR), binding of fibrinogen (Fg), and subsequent platelet aggregation required for normal hemostasis. Although enormous progress has been made in the biochemistry of platelet activation, of the platelet membrane GPIIb-IIIa, and of solution Fg, much less is known of the dynamics of expression of FgR, of its occupancy by Fg, and of their relation to the dynamics of platelet aggregation. Since platelet activation and aggregation occur within∼1 s of stirring with activators such as ADP, a methodology was required for determining the rapid dynamics of expression of FgR and binding of Fg, and their correlation with platelet aggregation kinetics. We therefore developed the theoretical and experimental base for determining these dynamic changes under non-equilibrium conditions, using fluorescently-labelled probes and flow cytometry. This approach has yielded a novel general technique for assessing the rapid dynamics of any cell surface molecule, as well as unexpected new insights into the kinetic expression and nature of FgR formed on platelet surfaces activated with ADP and PMA. The same approach has been extended to an analysis of the size-dependent (subpopulation) behaviour of platelets in expressing FgR, obtainable by analytically selecting platelets of different size from forward scatter profiles obtained in studies of the whole population. Parallel measurements of kinetics of platelet recruitment into microaggregates and expression and Fg occupancy of FgR as a function of ADP concentration, led to an unexpected new model for platelet activation and recruitment based once again on the selective recruitment of platelet subpopulation and an‘all or none, quantal’response of any single platelet in expressing all of its FgR and becoming recruitable for aggregation, but at a critical ADP concentration dependent on its own subpopulation characteristics. This approach has also led to novel insights into problems associated with platelet‘activation’arising with different isolation procedures. Dynamic binding studies of Fg to FgR on activated platelets has become possible using appropriately FITC-labelled Fg and flow cytometry. This has also led to studies of the relation between shear-dependent capture efficiency of platelets into doublet formation and the fraction of Fg-occupied receptors. In addition, we have successfully used FITC-labelled human and bovine Fg to demonstrate a delayed expression of FgR and Fg binding to ADP-activated platelets from bleeding Simmental cattle, although the final expression of numbers and accessibility of FgR, measured at equilibrium, were normal. Some future directions for dynamic flow cytometric studies of platelet activation and function are discussed.

ISSN:0953-7104    

DOI:10.3109/09537109609079504

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Actin is the most abundant platelet protein. It is present in two forms - a globular monomeric form (G-actin), and a filamentous polymeric form (F-actin). The F-actin is present both at the periphery of the cell in the form of a membrane skeleton which helps maintain cell shape, and also contributes to a three dimensional network that exists throughout the cell known as the cytoskeleton.1In the resting platelet, G-actin and F-actin exist in equilibrium, but on platelet activation this is disturbed in favour of the production of F-actin, with a corresponding decrease in the amount of G-actin. This process is known as actin polymerization.

ISSN:0953-7104    

DOI:10.3109/09537109609079505

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

We have explored both the independent and combined effects of aspirin on cultured endothelial cells and platelets, and its influence on platelet deposition onto an extracellular matrix. Blood was circulated through a flat perfusion chamber with two coverslips placed sequentially with respect to blood flow. The first coverslip (upstream) was covered with a cultured endothelial cell monolayer, and the second (downstream) coated with extracellular matrix obtained after endothelial cell removal. Platelet interaction was measured on the second coverslip. Treatment of endothelial cells on the first coverslip with 100μM aspirin strongly reduced 6-keto-PGF1alevels recovered in the perfusates (118.3±35.8 vs 1038.0±308.5 pg/ml) and significantly increased platelet deposition on the downstream coverslip (% covered surface: 38.6±6.4% vs 14.6±1.8%;P<0.001). Increased platelet deposition (% covered surface: 24.9 f 3.1%;P<0.01) was observed in perfusions performed with blood containing aspirinized platelets, in the presence of intact endothelial cells. Treatment with aspirin of both platelets and endothelial cells had no additional effect on platelet adherence. Pretreatment of cultured endothelial cells with aspirin did not influence the adhesive properties of their underlying extracellular matrix. Our results indicate that, although endothelial cell cyclooxygenase is important in regulating platelet adhesion, its blockade seemed to have minimal effect on platelet deposition once platelet-cyclooxygenase was already inhibited.

ISSN:0953-7104    

DOI:10.3109/09537109609079506

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Epinephrine is the only physiological platelet activator which induces platelet aggregation without a preceding change in platelet shape. The reason why epinephrine cannot induce this shape change is not known. Electron microscopically, we could show that during the first phase of epinephrine-induced platelet aggregation, the platelet aggregate is composed of discoid platelets, lying in rather loose contact with neighbouring platelets. During the second wave of epinephrine-induced aggregation (this is when thromboxane (TX)A2production has taken place), platelets have completely lost their discoid shape and are very tightly bound. In EDTA-platelet rich plasma (PRP), we could demonstrate a clear synergistic action of epinephrine 10–20μM on the first phase of shape change (disc-to-sphere transformation), induced by low concentrations of arachidonic acid (AA), collagen, adenosine diphosphate (ADP) and platelet activating factor (PAF). In combination with moderate concentrations of AA or collagen, epinephrine induced a clear aggregation-independent secretion of platelet granules, which in the absence of epinephrine, only takes place with higher inducer concentrations. All these synergistic actions could be demonstrated in the aggregometer and electron microscopically. To explain these findings, we hypothesize that the inability of epinephrine to induce a shape change that precedes aggregation is due to slow generation of TXA2which is only formed as a positive feedback mechanism of aggregation. This TXA2will bind to its own receptor and produce a shape change coinciding with the second wave of epinephrine-induced aggregation. Collagen, in contrast, induces very rapid TXA2generation, causing Ca2+mobilization and myosin light chain-phosphorylation, leading to shape change, clearly before aggregation starts.

ISSN:0953-7104    

DOI:10.3109/09537109609079507

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Equine platelet aggregation was stimulated by collagen fibres or platelet-activating factor. The action of both ligands was blocked by forskolin or prostaglandin E1agents which are known to activate adenylate cyclase. Equine platelet membranes were found to contain adenylate cyclase activity which was inhibited in dose-dependent fashion by both collagen and platelet-activating factor. Platelet-activating factor-induced inhibition was antagonised by WEB2086.

ISSN:0953-7104    

DOI:10.3109/09537109609079508

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The endogenous content of serotonin in human platelets has been used in many clinical studies to indicate platelet activation. A decrease in platelet serotonin compared with controls has been regarded as an indicator of platelet activation. However, the results published are difficult to compare, because of huge variations in endogenous serotonin between control groups in different investigations. This is likely to be because of lack of standardization. Several factors that influence the endogenous platelet serotonin content were studied in more than 200 blood donors. The most important factor was the totalgforce of the centrifugation used to isolate platelets. Also the age and sex of platelet donors, number of platelets in platelet-rich plasma, and mean platelet volume influenced normal serotonin values. Using a standardized centrifugation procedure (2700 g min) the mean endogenous serotonin was 2.80 nmol/109platelets in young women and 2.58 in elderly women, and 2.67 in young men and 2.30 in elderly men. The differences both for age and sex were statistically significant. Endogenous platelet serotonin shows intrapersonal stability over time, since endogenous platelet serotonin did not change on repeated venepuncture for 9 weeks. Factors such as age, sex and isolation procedure must therefore be considered when endogenous platelet serotonin are studied in relation to disease and treatment.

ISSN:0953-7104    

DOI:10.3109/09537109609079509

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Human platelets with a high content of endogenous serotonin took up more serotonin when incubated with exogenous serotonin, than platelets with a low endogenous content of serotonin. Also, thrombin-stimulated serotonin secretion (%) was high when endogenous serotonin was high. This was not found with fresh platelets, but was found when platelets were stored as platelet concentrates for 5 and 7 days. With platelets stored for 5 or 7 days, both uptake and secretion were increased after preincubation of the platelets with an amount of exogenous serotonin that was completely taken up. Inhibition of the reuptake of serotonin by imipramine during thrombin-induced secretion increased the secretion in stored platelets. Agonists like collagen, ADP, and a prostaglandin analogue (U46619) gave only 3–7% secretion. Imipramine increased the secretion induced by U46619, but not the secretion induced by ADP or collagen. The specific 5-HT2receptor inhibitor, ketanserin, had no effect on agonist stimulated secretion, or secretion stimulated by a calcium ionophore (A23187).Both the uptake and the thrombin-induced secretion of serotonin correlated significantly with endogenous serotonin in stored platelets. In fresh platelets the uptake of serotonin correlated positively, although not significantly, with endogenous serotonin. It is speculated that endogenous serotonin may affect secretion through stimulation of the thrombin receptor, at least in stored platelets.

ISSN:0953-7104    

DOI:10.3109/09537109609079510

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

A new murine monoclonal antibody, MDP-1, specific for human platelet glycoprotein IIIa has been produced and characterized. Following SDS-polyacrylamide gel electrophoresis, MDP-1 reacted with a 94kDa protein immobilized on a nitrocellulose membrane. Upon reduction, MDP-1 no longer bound to the 94kDa protein indicating an epitope requiring at least one disulfide bond. On crossed immunoelectrophoresis MDP-1 reacted to the same peak as the GP IIb-IIIa complex-specific antibody AP-2. After dissociation of the GP IIb-IIIa complex with EDTA, AP-2 showed no reactivity while MDP-1 bound to a new peak that was broader and anodal to the original GP IIb-IIIa peak, consistent with GP IIIa. MDP-1 inhibited ADP and thrombin induced aggregation. In addition, MDP-1 inhibited ADP induced release of ATP, but did not inhibit thrombin stimulated ATP release. Following chymotrypsin digestion, MDP-1 bound to a cleaved GP IIIa protein (nonreduced M, = 122 kDa) consistent with opening of the major disulfide loop. A second cleavage resulted in a 63 kDa species that reacted with MDP-1. Scatchard analysis revealed 22 000 molecules of MDP-1 bound per platelet, and indicated a type of binding consistent with positive cooperativity. The antibody bound equally well to stimulated and unstimulated platelets. MDP-1 binding was inhibited by a polyclonal anti-PIA1antibody, but bound to platelets from a PIA1negative individual indicating a binding site close to but not identical to the PIA1epitope. In addition, MDP-1 binding was not inhibited by Arg-Gly-Asp-Ser (RGDS) suggesting that it is not directed to the RGD binding site on GP IIIa.

ISSN:0953-7104    

DOI:10.3109/09537109609079511

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor