ISSN:0953-7104    

DOI:10.3109/09537109509013263

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Human platelet cholesteryl ester hydrolytic (CEH) activity was determined toward high density lipoprotein (HDL) labelled with cholesteryl [1-14C] oleate resulting in esterilkation of [l-14C] oleate to platelet phospholipid. The observed CEH activity was enhanced by 100 nM prostacyclin (PGI2), inhibited by 500μM 2′, 3′dideoxyadenosine (DDA), but unaffected by 100 mM chloroquine diphosphate. The CEH activity may represent a mechanism for delivery of other unsaturated fatty acids from HDL to platelets with subsequent modification of the fatty acid composition of platelet phospholipids and potential modification of platelet reactivity.

ISSN:0953-7104    

DOI:10.3109/09537109509013264

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Platelets from dogs with Basset hound hereditary thrombopathy (BHT) change shape but do not aggregate in response to most physiologic agonists [adenosine diphosphate (ADP), platelet-activating factor (PAF), collagen, thromboxane mimetic U46619 plus epinephrine and low concentrations of thrombin]. Aggregation in response to higher concentrations of thrombin is slow, but irreversible. The responses of normal canine and affected BHT platelets to the nonphysiologic agonist phorbol myristate acetate (PMA) were investigated. Aggregation of normal canine and affected platelets by PMA was irreversible and associated with dense granule adenosine triphosphate (ATP) secretion. The addition of PMA to [3H]-arachidonic acid-labelled normal and affected canine platelets had no significant effect on the production of 1,2-diacylglycerol (1,2-DAG). Activation of [32P]-labelled platelets by PMA was associated with rapid phosphorylation of the 47 kDa substrate of protein kinase C and slow phosphorylation of the 20 kDa myosin light chain in both groups. In affected platelets, there was reduced phosphorylation of a band of approximately 65 kDa. The identity and functional significance of this band is not known. This study provides evidence that direct activation of protein kinase C by PMA in BHT circumvents the dysfunction characteristic of Basset hound hereditary thrombopathy and that the defect must exist somewhere at a point in signal transduction prior to activation of protein base C. We also conclude that normal and affected canine platelets possess protein kinase C and a 47 kDa substrate function that is similar to human platelets.

ISSN:0953-7104    

DOI:10.3109/09537109509013265

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Adhesion of platelets to collagen, exposed on the subendothelium as a result of vessel wall injury, is a vital step in the formation of a haemostatic plug. Glycoprotein CD36, also known as GPIIIb/GPIV, is one of the platelet glycoproteins known to interact with collagen. The aim of this work was to identify structural/functional sites on CD36 interacting with collagen. Eight peptides, corresponding to sites presumed to be hydrophylic, were synthesized by Fmoc (Fluorenylmethoxycarbonyl) chemistry. Peptides were tested for their ability to inhibit platelet aggregation induced by type I collagen. Peptide E5 (WLNETGTIGDEKA; 415-427), but not the other peptides, inhibited aggregation and secretion of washed platelets induced by collagen but had no effect on thrombin or ADP induced aggregation. Moreover, peptide E5 was shown to interfere with the binding of125I-labelled CD36 to collagen. Peptide E5 had little or no effect on collagen-induced platelet aggregation performed in platelet rich plasma (PRP), as previously described in the cases of monoclonal antibodies directed againstα2orβ1. These results indicate that peptide E5 represents a site on CD36 that interacts with collagen and is involved in platelet functions.

ISSN:0953-7104    

DOI:10.3109/09537109509013266

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

It is important that, at the time of transfusion, platelets prepared by different techniques are effective in vivo and meet acceptable criteria. A paired study was undertaken in 8 volunteer donors to compare apheresis platelets collected on the COBE Spectra with platelets derived from the buffy coat of whole blood donations after 5 days storage. In vivo recovery, survival and biodistribution were determined following indium-111 labelling of the platelets and autologous infusion into volunteers together with the in vitro evaluation of platelet function and biochemistry.The in vivo and in vitro characteristics of both types of platelet concentrate were not significantly different. Both products were equally viable after 5 d storage and both were of an acceptable quality as judged by currently used platelet products. Mean platelet survival (multiple hit) was 5.4 d for the apheresis platelets and 6.9 d for the buffy coat derived platelets and maximum recovery in circulation was 28.1% and 34.8%, respectively. There was a significantly higher platelet yield, as expected, from apheresis and a 1.5 log lower level of white cell contamination. This would be advantageous for patients in need of prolonged or recurrent transfusions as the number of donor exposures and the risk of alloimmunisation or viral transmission would be reduced.

ISSN:0953-7104    

DOI:10.3109/09537109509013267

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Evaluation of platelet aggregation in vitro has generally been performed by the turbidometric method. This technique is largely insensitive to early events of aggregation which, are best evaluated by following the decrease in number of free-platelets after agonist addition. In this study the kinetics of free-platelet decrease after adenosine-5-diphosphate (ADP) addition was analyzed in platelet rich plasma and in whole blood samples obtained from 29 normal donors and 5 thrombocytopenic subjects. Analysis of experimental data using a single exponential decay equation allowed us to compute the maximal velocity and the rate constant of the reaction as well as the number of un-reactive platelets. The velocity of aggregation was positively correlated with platelet number and was markedly increased by the presence of red blood cells. The process was unaffected by platelet cyclooxygenase inhibition and was also independent of thrombospondin or von Willebrand factor binding to GpIIb-IIIa. Fibrinogen receptor blockade by either anti-GpIIb-IIIa monoclonal antibody or by the RGDS analogue, MK-852, reduced, in a dose dependent manner, the aggregation velocity. Simple decay estimations based on the difference between counts made before and 15 s after ADP addition, were used to evaluate the anti-aggregating effect of MK-852. Compared to turbidometry, the method provided a more accurate dose-response curve and gave, in addition, a significantly higher IC, value (0.21±0.05 vs 0.11±0.04 pmol/l p<0.01, means±SD). We conclude that the kinetics of free-platelet decay allows characterization of early events of the platelet response to ADP by quantitative parameters. In addition, this technique may represent a significant improvement over turbidometry in the laboratory monitoring of the anti-aggregating effect of fibrinogen binding inhibitors.

ISSN:0953-7104    

DOI:10.3109/09537109509013268

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

We have investigated interactions between human blood platelets and the vitronectin-containing fluid-phase terminal complement complex, the SC5b-9, which is a non-cytolytic variant of the membrane attack complex C%9(m). SC5b-9 affinity for the platelet membrane glycoprotein IIb/IIIa (GPIIb/IIIa) complex was demonstrated by crossed radio-immunoelectrophoresis of solubilized, washed platelets followed by incubation of the immunoplates with125I-labelled SC5b-9 and exposure to X-ray films. Platelet adhesion to surfaces of polystyrene coated with the SC5b-9 complex was studied under static conditions in an enzyme immunoassay (EIA). Thrombin-stimulated platelets but not non-stimulated platelets adhered to the SCSb-9coated surface, and platelet adherence was inhibited in a dose-dependent manner by the tetrapeptide RGDS (Arg-Gly-Asp-Ser). This indicates an interaction between platelet GPIIb/IIIa and an RGD sequence in SC5b-9, possibly in its vitronectin moiety. The effect of the SC5b-9 complex on platelet aggregation was examined in a dual-channel aggregometer. Here the SC5b-9 complex inhibited both ADP-and thrombin-induced platelet aggregation in a dose-dependent manner. These results were confirmed by electron microscopical examination of the contents of the aggregometer cuvettes. Platelets which had been thrombin-stimulated in the presence of SC5b-9 appeared activated and had undergone secretion, but showed no aggregation. By contrast, platelets from the control experiments which had been thrombin-stimulated in the absence of SC5b-9 were aggregated. To the best of our knowledge, this is the 6rst report on a biological role of the SC5b-9 complex in platelet function.

ISSN:0953-7104    

DOI:10.3109/09537109509013269

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

In a previous study the volume of blood obtained from bleeding time incisions was measured every 30 s from normal subjects (n = 15), patients with thrombasthenia (TSA, n=4), idiopathic thrombocytopenic purpura (ITP, n=4), von Willebrand's disease (vWD, n=3), Bernard-Soulier syndrome (BSS, n = 2), andδandαδ-storage pool deficiencies (SPD, n=4 and 5, respectively) and the experimental results analyzed by empirical curve-fitting of the data. In the present investigation, a mathematical model based on blood flow physiology was developed to describe the rate of blood loss over time from these same patients as a function of two parameters,α, which describes the magnitude of vessel contraction following transection, andβ, the rate of vessel dilation to its nominal diameter. For the normal controls a third parameter,δ, was used to describe the rate of vessel closure due to the formation of a hemostatic plug. Optimal values for these parameters for the normal subjects and each patient group were determined by least-squared fitting of the experimental bleeding time data. For all subjects, values for the magnitude of vessel contraction were similar (α=0.65±0.02). However, values forβwere reduced in both TSA (β=0.22±0.04) andvWD (β= 0.30±0.03) and were increased relative to normal controls (β=0.39±0.03) in BSS (β=0.50±0.01) and bothδSPD (β=0.50±0.07) andαδSPD (β=0.50±0.05). The initial rate of blood loss was also significantly greater in patients with BSS, ITP,δ-SPD, andαδSPD than in the normal subjects, as determined by a one-way analysis of variance. These results suggest that: (1) the initial contraction of severed blood vessels does not appear to be mediated by any plasma or platelet compounds absent in the various bleeding disorders considered in this study; and (2) the increased initial bleeding observed in SPD may reflect the absence of vasoactive agents, such as ADP or serotonin, released from platelet dense granules following platelet activation. These conclusions are consistent with those reported previously on the same patients and indicate that mathematical modeling of bleeding time measurements, based on assumptions of vascular and platelet reactivity, can provide insights into the complex series of events occurring at sites of vessel injury.

ISSN:0953-7104    

DOI:10.3109/09537109509013270

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

The effects of the anti-platelet agent dipyridamole on vascular endothelial cells were assessed by measurement of the injury index induced by oxygen stress. Vascular endothelial cell injury was assayed by measuring51Cr release from labeled vascular endothelial cells. Leukocytes activated by phorbol 12-myristate 13-acetate (PMA) were used to induce the injury of endothelial cells. In this system, dipyridamole suppressed endothelial cell injury in a dose dependent manner (0.1-10 4mUM) while it had no effect on production of superoxide anion in PMA-activated leukocytes. Treatment of endothelial cells with hydrogen peroxide also induced endothelial cell injury in a dose dependent manner (50-150μM). Dipyridamole also prevented the endothelial cell injury induced by hydrogen peroxide with a dose dependent fashion (1-10μM). There were no significant changes in the activities of catalyzing enzymes such as catalase and glutathione peroxidase in the endothelial cells following dipyridamole treatment. In contrast, dipyridamole significantly increased the cyclic GMP content of endothelial cells in a dose dependent manner (1-10μM). Addition of 8-bromo-cyclic GMP (1 mM) to the culture also protected endothelial cells from injury induced by hydrogen peroxide, but 8-bromo-cyclic AMP did not. These data suggest that the protective effect of dipyridamole against oxygen stress is correlated with the increase in the cyclic GMP content of the endothelial cells.

ISSN:0953-7104    

DOI:10.3109/09537109509013271

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Mechanisms of Platelet Activation and Control (Vol 344 Advances in Medicine and Biology) Kalwant S. Authi, Steve P. Watson and Vijay V. Kakkar (eds). Plenum Press, New York, 1993.272 pages. Price $95

ISSN:0953-7104    

DOI:10.3109/09537109509013272

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor