ISSN:0953-7104    

DOI:10.3109/09537109609023586

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Extracellular adenine nucleotides interact with P2 purinergic receptors to regulate a broad range of physiological processes among which platelet aggregation P2 purinoceptors were divided into two main groups: the G-protein coupled receptor or 'metabotropic' superfamily termed P2Y and the ligand-gated ion channel or 'ionotropic receptor' superfamily termed P2X. Platelet aggregation by ADP plays a key role in the development and extension of arterial thrombosis. At present, despite a great deal of investigation aimed at assessing the central role of ADP in haemostasis, the platelet ADP receptor or so-called P2Tpurinoceptor remains basically unknown. Attempts to achieve its cloning have to date been unsuccessful and in addition more than one purinoceptor would appear to be involved in the multiple effects of ADP on platelets. The aim of this review is to try to begin to find an initial answer to the questions of how do platelets respond to ADP and what receptors are involved in these processes. A model of at least two receptors, one responsible for rapid Ca2+entry which could be a P2×1receptor and one responsible for aggregation and inhibition of adenylyl cyclase which could be a P2Y1receptor is proposed.

ISSN:0953-7104    

DOI:10.3109/09537109609023587

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The aim of the present study was to determine whether dietary intake of monounsaturated or long chain n-3 fatty acids could be effective in lowering platelet responsiveness through modulation of platelet phospholipid composition. Rats were fed diets containing 20% fat with equal cholesterol and 13a-tocopherol contents. These diets were supplemented with saturated, oleic or n-3 fatty acids, n-3 polyunsaturated fatty acids being added either pure, as eicosapentaenoic and docosahexaenoic ethyl esters, or as MaxEPA oil. Dietary n-3 fatty acids did not affect the oxidation status of plasma lipids. Oleic acid- and saturated fatty acid-rich diets led to similar enrichment of platelet phospholipids in arachidonic acid and to comparable thromboxane A2generation on stimulation with collagen or thrombin. Platelets of n-3-fed groups were differently enriched in eicosapentaenoic and docosahexaenoic acids at the expense of arachidonic acid. These groups displayed similar thromboxane A2production, although levels were lower than those for groups fed with oleic- or saturated fatty acid-rich diets. Only the MaxEPA diet led to a reduction in platelet reactivity, measurable as a small decrease in the aggregation induced by collagen. This diet was also responsible for a high cholesteroUphospholipid ratio and low a-tocopherol content in platelets. Overall results indicated that (i) only MaxEPA reduced platelet reactivity and (ii) this effect was moderate and apparently unrelated to platelet arachidonic acid content, membrane cholesterol to phospholipid ratio or thromboxane A2production.

ISSN:0953-7104    

DOI:10.3109/09537109609023588

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

We treated red cells and platelet sepatatelyin vitrowith aspirin or indomethacin to inhibit platelet function. The excess of drug was removed by profuse washing prior to blood reconstitution. We examined the influence of such treatments on platelet interaction with vascular subendothelium employing a perfusion system. Treatment of red cells or platelets with aspirin showed a similar pattern of platelet deposition onto subendothelium. However, platelet adhesion was significantly increased in treated red cells (21.7±2.7% vs 13.7±1.9% in controls;P<0.05) whereas thrombus was significantly decreased in treated platelets (6.2±1.62% vs 13.8±1.7% in controls;P<0.05). Treatment of red cells or platelets with indomethacin strongly inhibited platelet interaction. Thrombus and covered surface were decreased in experiments with treated red cells (2.3±0.73% and 14.9±2.3%, respectively;P<0.05). Adhesion, thrombus and covered surface were decreased in experiments with treated platelets (4.3±0.7%, 2.3±0.9%, 9.2±1.5%, respectively;P<0.05). Platelet aggregation experiments performed with aspirin-treated red cells showed a progressive inhibition of platelet function. Testing levels of drug in plasma samples from the perfusates showed that levels of drug were very similar to those obtained if treated red blood cells were not washed after treatment. All these results suggest that red cells retained some quantities of drug. Our data highlight the potential effect of red cells interfering with platelet function inhibitors.

ISSN:0953-7104    

DOI:10.3109/09537109609023589

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

To prevent r-hirudin induced excess bleeding an animal model was established in pigs for the investigation of an anti-bleeding strategy. We used the Simplate®device to monitor skin bleeding time (SBT) at the inner site of the ear. r-Hirudin infused in a dose of 0.3 mag per h induced a prominent increase of SBT. The aim of our studies was to reverse r-hirudin induced bleeding by enhancing platelet adhesion to the endothelium via the administration of von Willebrand Factor (vWF). Pigs were treated with vWF containing solutions (Haemate®and a vWF-concentrate) at 3h after the start of the r-hirudin infusion. Both compounds suppressed SBT 1h after administration and significantly prevented bleeding until the termination of the experiment. SBT values (given in times of baseline) in the placebo group were 3.32±0.9, 1.51±0.14 in the Haemate®and 1.85±0.42 in the vWF concentrate group (P= 0.008 or 0.032, in a two-sided Kruskall-Wallis-test). Coagulation parameters (aPTT, PT) were unaltered by the treatment, as were the r-hirudin plasma levels suggesting that vWF is not an antidote in its strict sense. It is concluded that vWF reverses bleeding without altering the anticoagulant effect of r-hirudin. Addition of 20 mg/kg per h aspirin resulted in a further increase of SBT. Aspirin, moreover, suppressed platelet aggregation but did not alter platelet counts. In a further study, bleeding induced by r-hirudin and aspirin was antagonized by Haemate®(66 Ukg i.v. bolus + 187 Ukg per h for 2 h infusion) and a significant reduction of bleeding time occurred.

ISSN:0953-7104    

DOI:10.3109/09537109609023590

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The involvement of glycoprotein (GP) IV (CD36) in arachidonic acid uptake by human platelets was investigated using an anti-CD36 monoclonal antibody (MAB). The binding of [14C]arachidonic acid to MAB-treated platelets was significantly reduced compared with untreated platelets. The MAB also inhibited arachidonic acid-induced platelet aggregation and thromboxane A2synthesis in a dose-dependent manner. Pre-incubation of gel-filtered platelets with the MAB (10mg/I) inhibited arachidonic acid-induced platelet aggregation by 50% and collagen-induced platelet aggregation by 7-8% and the lag time was increased by 200%. Although the mechanism of platelet aggregation is not fully understood yet, the inhibition of arachidonic acid-induced platelet aggregation by the MAB could be the result of a reduced uptake of exogeneously added arachidonic acid by the MAB-treated platelets. Our data clearly indicate that arachidonic acid uptake by platelets is mediated, at least in part, by CD36.

ISSN:0953-7104    

DOI:10.3109/09537109609023591

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

P-selectin is an alpha granule membrane associated glycoprotein in platelets (P1) expressed on the surface following exposure to secretagogues in suspension. It is not clear, whether P-selectin is transported from granule membranes to the P1 surface, or released by surface-activation (SfA). In the present study washed P1 were allowed to interact with grids for different periods of time (5-20 min), fixed briefly and exposed to a monoclonal antibody to P-selectin. Grids were washed and exposed to goat anti-mouse IgG antibody coupled to 10 nm gold particles. Examination in the electron microscope revealed a differential distribution of the gold probe on SfA P1. Discoid P1 did not express P-selectin. Early dendritic P1 revealed a few gold probes for P-selectin near the central zone. Late dendritic P1 expressed P-selectin on P1 bodies and some on pseudopods. On fully spread P1 P-selectin probes were evenly distributed, but more concentrated on the peripheral margin than the central zone. Results demonstrate that P-selectin is released from SfA P1. Its initial expression in the central zone suggests it reaches the surface through channels of the open canalicular system. The centrifugal movement of P-selectin is opposite in direction to translocation of mobile receptor-ligand complexes.

ISSN:0953-7104    

DOI:10.3109/09537109609023592

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

CD9 is a well-defined component of the platelet plasma membrane and has a copy number almost equivalent to that of glycoprotein (GP) IIb-IIIa complexes, the aggregation receptor on platelets. It has an apparent molecular mass of 24 kD and is otherwise known as p24. Stimulation of p24 by monoclonal antibodies (MAb) induces platelet aggregation and granule release, involves FcγRII, and is mainly mediated through the stimulation of phospholipase C. In accordance with a signalling function, p24 has been reported to associate with small GTP-binding proteins and to GP IIb-IIIa complexes upon activation. We now report further evidence of a strong relationship between p24 and GP IIb-IIIa in platelets. Using the MAIPA (monoclonal antibody immobilization of platelet antigens) assay in the screening of human antibodies to platelet glycoproteins, we found that GP IIb-IIIa-antibody complexes were almost invariably associated with p24 in the harvested detergent-soluble fraction of platelet lysates. Thus, associated human antibodies were detected following the targeting of either GP IIb-IIIa or p24 by monospecific murine monoclonal antibodies (MAbs). This is a point to bear in mind when assessing for antibodies to p24 or GP IIb-IIIa in immune thrombocytopenias.

ISSN:0953-7104    

DOI:10.3109/09537109609023593

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

Platelets contain three types of secretory granules, dense granules,α-granules and lysosomes, which are characterized by their different contents. Dense granule andα-granule secretion appear to be similar in responsiveness to dose and types of agonists, whereas lysosomal secretion is observed only with higher doses of strong agonists such as thrombin. Recently, with the advent of flow cytometry, surface expression of membrane granule proteins, which are claimed to be specific for granule type, has come into use as a monitor for secretion. Expression of CD62 (PADGEM) in particular has become synonymous withα-granule secretion, based on comparisons with measurements ofβ-thromboglobulin release by a method in which secretion is not stopped by fixation. We have now developed an immunoassay for fibrinogen that tolerates fixation stopping and have compared the release of dense andα-granule markers in the same platelet supernatants with the expression of CD62 and CD63 in gel-filtered platelets. At thrombin concentrations less than 0.04 U/ml, secretion ofα-granule fibrinogen was both more rapid and quantitatively greater than that of dense granule serotonin, ATP and ADP. Comparison of the secretion of granule markers (contents) with the expression of granule membrane markers on the platelet surface showed that surface expression of CD62 (P-selectin, PADGEM) corresponded to fibrinogen secretion, and CD63 correlated reasonably well with the release of dense granule contents. Pretreatment of platelets with acetylsalicylic acid (ASA) before gel-filtration moderately inhibited thrombin-induced dense andα-granule release in GFP at a concentration range of 0.01-0.03 U/ml. The agonist effect of a thrombin receptor agonist peptide (TRAP) was comparable to that of thrombin with respect to all measured markers except forβ-hexosaminidase release, which was significantly less with TRAP.

ISSN:0953-7104    

DOI:10.3109/09537109609023594

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

The present study has used washed human platelets combined with ethylene diamine tetracetic acid (EDTA) to determine the influence of calcium ions on thrombin-induced down-regulation of glycoprotein (GP) Ib/IX, the platelet surface receptor for von Willebrand factor (vWF). Bovine plasma vWF (BvWF) does not require the antibiotic, ristocetin, or calcium ions to cause agglutination of platelets. Thus, EDTA platelets agglutinate as well with BvWF as platelets in the absence of the chelating agent. Thrombin treatment of EDTA platelets prevented subsequent agglutination by BvWF. However, the addition of calcium ions to the sample restores sensitivity of the six PIb/IX receptors, and irreversible agglutination occurs when BvWF is added. Monoclonal antibodies to GPIb/IX and GPIIb/IIIa demonstrated that restoration of refractory platelet sensitivity to BvWF was related to GPIb/IX, not to GPIIb/IIIa. Experimental results suggest that GPIb/IX receptors on thrombin-treated EDTA platelets can be down-regulated by thrombin, but are not cleared from the surface to internal membranes.

ISSN:0953-7104    

DOI:10.3109/09537109609023595

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor