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PubMed1995

Interspecies comparison of platelet aggregation, LIBS expression and clot retraction: observed differences in GPIIb-IIIa functional activity.

We examined interspecies differences in the function of the platelet fibrinogen receptor, GPIIb-IIIa, by comparing platelet aggregation responses to adenosine diphosphate (ADP) added alone or in combination with a GPIIIa specific monoclonal antibody (mAb), D3. D3 can activate the GPIIb-IIIa receptor in the absence of platelet activation, and it preferentially binds to a region on the GPIIIa subunit after the GPIIb-IIIa complex is occupied by ligand. Using human, monkey, dog, rabbit and pig platelets, we examined whether all species' platelets bound the D3 mAb similarly, and if the binding of Arg-Gly-Asp-Ser (RGDS) peptides induced the exposure of the anti-LIBS (D3) epitope as previously described for human platelets. We also evaluated how blocking of this neoantigenic region by the D3 mAb affected clot retraction, a process that requires linkage of GPIIb-IIIa with fibrin(ogen) and the platelet cytoskeleton. We found that all species tested bound the D3 mAb. Only in human and monkey platelets did D3 cause aggregation as well as inhibit clot retraction. However, in all species tested, except for pig, D3 prevented disaggregation of platelets typically observed when platelets are treated with low dose ADP. With the exception of pig platelets, there was increased D3 binding to platelets in the presence of RGDS peptides. We propose that this region of GPIIIa is important in the conformational changes that GPIIb-IIIa undergoes during the binding of ligand in most species tested. Our studies suggest 1) there are measurable inter-species differences in GPIIb-IIIa mediated platelet aggregation and clot retraction, 2) LIBS expression due to receptor occupancy is a common but not all-inclusive response and 3) interspecies comparisons may be useful in understanding structural and functional aspects of platelet GPIIb-IIIa.

Adenosine Diphosphate↗
PubMedDate not supplied

[Effect of dibazol, euphylline, No-Spa and galidor on thrombocyte osmotic resistance and blood clot retraction].

The osmotic resistance of thrombocytes and the blood clot retraction are shown to diminish in the presence of nospanum and holidor in the plasma and blood. A double logarithmic relationship between the values characterizing the action on the osmotic resistance of thrombocytes and the blood clot refraction, on the one hand, and concentrations of some of the study substances, on the other, was revealed. With parenteral introduction the fall of the osmotic resistance of thrombocytes and an increase in the amount of the retracted serum were noted to occur with a protracted subcutaneous injection of dibasol (5 mg/kg), whereas euphylline (24 mg/kg) caused only a smaller degree of retraction.

Aminophylline↗
PubMedDate not supplied

[Method of recording isotonic blood clot retraction].

The method and the device for photometric registration of blood clot isotonic retraction when the preset constant force is applied to the blood clot are described. The mathematic model enabling one to derive kinetic and energy parameters of the considered process is built. These parameters include: a velocity constant, a half-period of fibrinosis, a latent period, phase durations of contraction and tension, a specific working capacity, velocity constants of clot retraction and relaxation. The method may be useful in clinical diagnostic practice and in research work to evaluate hemocoagulation process and functional properties of blood cells.

Clot Retraction↗
PubMed1994

Acute intracranial hemorrhage secondary to thrombocytopenia: CT appearances unaffected by absence of clot retraction.

PURPOSE: To describe the in vivo CT appearance of acute intracerebral blood clots formed from anemic platelet-depleted blood. METHODS: Three patients with intracerebral hemorrhage secondary only to thrombocytopenia were examined with CT within 2 1/2 hours after the onset of clinical symptoms. RESULTS: There were no unusual CT features found in the intracerebral hemorrhages of patients with only thrombocytopenia. Specifically, a hyperdense zone(s) surrounded by areas of decreased density was identified. CONCLUSION: Clot retraction (which cannot occur in patients with severe thrombocytopenia) is not necessary for the CT appearance of acute intracerebral hemorrhage.

Adult↗
PubMed1976

Reptilase clot retraction induced by electrical stimulation.

Retraction of platelet rich plasma clotted by reptilase is induced by electrical stimulation. Optimal retraction is obtained by stimuli, applied for more than 4 min, with the following characteristics: intensity = 150 volts, duration = 50 msec each, frequency = 10/sec. Electrically induced reptilase clot retraction is shown to be inhibited by EDTA, EGTA, methyl-xanthines, PGE1, acetylsalicylic acid, indomethacin, but not by apyrase or by phosphoenolpyruvate-pyruvate kinase and MgCl2. The results indicate that electrical stimulation induces retraction of PRP clotted by reptilase by triggering off an increased availability of Ca2+ in the intracellular space.

Apyrase↗
PubMed1983

Comparison of fibrin clot retraction with other transformation parameters after hydridization of normal and established cell lines.

The expression of transformation parameters (inhibition of cell division during cell crowding, anchorage dependence, loss of fibrin clot retractile activity and secretion of plasminogen activator) was studied in a heterospecific cellular hybrid, made between established L(TK-) cells and the normal human MRC-5 cells. The hybrid nature of the cross was confirmed by the ability to incorporate [3H]-thymidine, by growth in selective HAT medium, by the identification of human chromosomes and by the expression on the surface of 100% of hybrid cells of a human glycoprotein, which is recognized by the 4F2 monoclonal antibody. The hybrid cultures showed cell cycle inhibition which became less stringent with increasing population doublings and the loss of human chromosomes. Fibrin clot retraction and anchorage dependence were absent in spite of the presence of many human chromosomes. The two properties were present or lost simultaneously in the normal parent cells and in the transformed parent or hybrid cells respectively. The human type of plasminogen activator was secreted even with very little human genetic material left, and a complete dissociation between fibrin clot retraction and production of plasminogen activator was observed. The data strengthen the hypothesis that transformation is a multistep process that involves complex genetic control and where cells progressively express different phenotypes and escape growth control.

Animals↗
PubMed2002

A naturally occurring Tyr143His alpha IIb mutation abolishes alpha IIb beta 3 function for soluble ligands but retains its ability for mediating cell adhesion and clot retraction: comparison with other mutations causing ligand-binding defects.

The molecular basis for the interaction between a prototypic non-I-domain integrin, alpha(IIb)beta(3), and its ligands remains to be determined. In this study, we have characterized a novel missense mutation (Tyr143His) in alpha(IIb) associated with a variant of Glanzmann thrombasthenia. Osaka-12 platelets expressed a substantial amount of alpha(IIb)beta(3) (36%-41% of control) but failed to bind soluble ligands, including a high-affinity alpha(IIb)beta(3)-specific peptidomimetic antagonist. Sequence analysis revealed that Osaka-12 is a compound heterozygote for a single (521)T>C substitution leading to a Tyr143His substitution in alpha(IIb) and for the null expression of alpha(IIb) mRNA from the maternal allele. Given that Tyr143 is located in the W3 4-1 loop of the beta-propeller domain of alpha(IIb), we examined the effects of Tyr143His or Tyr143Ala substitution on the expression and function of alpha(IIb)beta(3) and compared them with KO (Arg-Thr insertion between 160 and 161 residues of alpha(IIb)) and with the Asp163Ala mutation located in the same loop by using 293 cells. Each of them abolished the binding function of alpha(IIb)beta(3) for soluble ligands without disturbing alpha(IIb)beta(3) expression. Because immobilized fibrinogen and fibrin are higher affinity/avidity ligands for alpha(IIb)beta(3), we performed cell adhesion and clot retraction assays. In sharp contrast to KO mutation and Asp163Ala alpha(IIb)beta(3), Tyr143His alpha(IIb)beta(3)-expressing cells still had some ability for cell adhesion and clot retraction. Thus, the functional defect induced by Tyr143His alpha(IIb) is likely caused by its allosteric effect rather than by a defect in the ligand-binding site itself. These detailed structure-function analyses provide better understanding of the ligand-binding sites in integrins.

Adult↗
PubMed1952

CLOT retraction.

Explore the source record for details and available documents.

Blood Coagulation↗
PubMed1996

Heparin ablates force development during platelet mediated clot retraction.

Although snake venom enzymes such as reptilase do not cause viscous metamorphosis, platelet secretion or clot retraction; when batroxobin and calcium are added to citrated blood significant platelet force development occurs. When this batroxobin-calcium system was applied to the study of platelet function during cardiopulmonary bypass (CPB), force development was found to be completely inhibited. After heparin reversal by protamine sulfate, significant recovery of force occurred. The present investigation was performed to evaluate the role of heparin in reducing force development during CPB. At concentrations above 0.10 U/ml, heparin totally suppressed force development in normal plasma. Addition of protamine sulfate to heparinized plasma caused complete recovery of force development. These concentrations of heparin had little effect on platelet aggregation by ADP or collagen. Possible direct effects of heparin on fibrin assembly and structure were studied by adding varying amounts of heparin to plasma and then inducing clot formation with batroxobin. At 1 U/ml, heparin reduced the size of fibrin fibers by 33%. Higher heparin concentrations had no additional effect. These results indicate that heparin may be responsible for a significant component of the decreased platelet force noted during cardiopulmonary bypass. To test whether heparin's effect could be due to suppression of thrombin activity, the effects of the antithrombin hirudin on force development were measured. Hirudin also inhibited force development in a concentration dependent manner. Thus, heparin's reduction of platelet force development may be due, at least in part, to suppression of thrombin activity.

Batroxobin↗
PubMed1982

Impaired clot retraction in thrombocytopenia due to methyldopa.

We have described a case of thrombocytopenic purpura caused by methyldopa. A methyldopa-dependent antiplatelet antibody as the mechanism of the patient's thrombopenia was suggested by a positive clot retraction inhibition test. This simple in vitro test should be done more often in suspected cases of drug-induced thrombocytopenia.

Clot Retraction↗
PubMed1975

Reptilase clot retraction test. (Its cofactors and relation to other platelet functions).

C-PRP clotted by reptilase does not retract due to the lack of activation of platelets. In order to support retraction, the platelets must undergo membrane changes resulting in contractile system activation. Only in the presence of aggregating agents capable of eliciting these membrane changes in vitro (e.g. ADP, adrenaline and collagen but not bovine fibrinogen or ristocetin), strong reptilase clot retraction (RCR) occurs. During RCR an aggregating activity, platelet factor 4, and retraction stimulating factor (RSF) were released, but acid phosphatase was not available. Not only inhibitors of platelet adhesion-aggregation reaction (PAAR) but also specific blockers of release are capable of inhibiting RCR. In coagulation disorders RCR was normal in most cases, but in thrombopathies different abnormalities of RCR were found. The RCR defect may be associated not only with a defect in the initial stages of PAAR, but in some instances also with a specific defect in release reaction. Besides inducer--"activated" platelets and their adhesion to polymerizing fibrin, the presence of divalent cations and free thrombocytar--SH groups is necessary for the retraction of reptilase clots.

Adenosine Diphosphate↗
PubMed1984

Influence of the pure synthetic PAF (platelet aggregating factor) on clot retraction and platelet aggregation.

Pure synthetic platelet aggregating factor (PAF) (1-O-Hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine) induces a dose-dependent platelet aggregation in platelet-rich plasma (PRP) and in gel-filtered platelets. Irreversible platelet aggregation was observed at final concentrations of PAF higher than 2 X 10-(7) mol/l, while reversible or two-wave aggregation was obtained with lower final concentrations. The second wave was inhibited by acetylsalicylic acid, indomethacin, dipyridamole, EDTA, EGTA, theophylline, caffeine, PGE1 and verapamil. PAF does not induce reptilase clot retraction (RCR); however, it does not inhibit RCR induced by ADP or thrombin. Since all substances known to activate platelets also induce RCR, the lack of this activity by PAF would support the existence of a third pathway in platelets.

Animals↗
PubMed2000

Platelet secretion during clot retraction.

The precise route serving as the pathway for extrusion of products contained in platelet storage organelles following cell activation has been controversial for many years. Some workers believe that the granules and dense bodies fuse together to form secretion vacuoles that move to the exposed cell surface, fuse with it and extrude contained products to the outside. Others suggest that the organelles fuse with channels of the open canalicular system (OCS) and deposit their contents which are subsequently secreted to the exterior. The controversy has been difficult to resolve because nearly all workers have used platelets in suspension to arrive at diverse conclusions. The present study has used ethylenediamine tetracetic acid (EDTA)-treated platelets and isometric clot retraction as a model system, and either polylysine or tannic acid to define the pathway used for secretion. Results indicate that secretion takes place in EDTA platelets under isometric tension by fusion of granules to OCS channels and passage of products through these conduits to the cell exterior. There is no evidence to suggest the organelles form secretion vacuoles or extrude their products by fusion with the inside of the exposed surface membrane.

Blood Coagulation↗
PubMed1994

Antibodies to GPIIb alpha (300-312) inhibit Fg binding, clot retraction, and platelet adhesion to multiple ligands.

We previously reported that a peptide with the sequence Gly-Ala-Pro-Leu (GAPL) found as residues 309-312 in glycoprotein IIb alpha (GPIIb) comprises at least part of a Fg binding site on GPIIb (1). Subsequent studies demonstrated that a peptide corresponding to residues 300-312 of GPIIb alpha can bind to Fg and Vn, and is a potent inhibitor of platelet aggregation and the adhesion of activated platelets to at least four adhesive ligands: Fg, Fn, Vn, and vWf (2). Here, the production and initial characterization of polyclonal antibodies against this peptide are described. ELISAs and dot-blot assays reveal the specificity of the antibodies for the peptide immunogen. In immunoblots, the antibodies recognize GPIIb under reducing conditions. The binding of Fg to immobilized GPIIb/IIIa, the rate of clot retraction and the adhesion of stimulated platelets to Fg, fibronectin (Fn), vitronectin (Vn), and von Willebrand factor (vWf) were inhibited by these antibodies, but not by a control IgG. These results together with our earlier published data indicate that GPIIb alpha (300-312) comprises at least part of a common ligand binding site within the integrin alpha IIb subunit.

Amino Acid Sequence↗
PubMed2003

Thrombin binding to GPIbalpha induces platelet aggregation and fibrin clot retraction supported by resting alphaIIbbeta3 interaction with polymerized fibrin.

We have investigated the mechanisms leading to platelet aggregation following thrombin interaction with the glycoprotein (GP) Ib-IX-V complex. We show that platelets desensitized for the two thrombin receptors, PAR-1 and PAR-4, are still able to aggregate in response to thrombin and that this aggregation can be inhibited by a monoclonal antibody (VM16d) that blocks thrombin binding to GPIbalpha, or by pretreatment of platelets with Mocarhagin, a protease that specifically cleaves GPIbalpha. The thrombin/GPIbalpha-initiated signaling cascade induces platelet shape change through activation of the Rho kinase p160ROCK, independent of calcium mobilization, transient MEK-1 phosphorylation as well as the cleavage of talin through a calcium-independent mechanism. This signaling cascade does not induce the exposure of high affinity alphaIIbbeta3 integrin receptors, nor does it lead to micro -calpain cleavage of filamin or the integrin cytoplasmic tail. In contrast, we provide evidence that binding of thrombin to GPIbalpha induces fibrin binding to resting alphaIIbbeta3 leading to fibrin-dependent platelet aggregation and clot retraction, that can be selectively inhibited by alphaIIbbeta3 antagonists such as RGDS, the dodecapeptide or lamifiban, as well as by the fibrin polymerization inhibitor GPRP-amide.

Biopolymers↗
PubMed1977

Ammonia production during clot retraction and its use in assay of fibrinoligase.

Clotting of recalcified plasma is followed by an increase in its ammonia content that lasts 4 to 6 h. This ammonia production closely parallels the increase in acid-insoluble fibrin, which is evidence that the ammonia results from the action of fibrinoligase. If the clot is removed, ammonia production stops. The initial velocity of ammonia production is directly proportional to the fibrinogen concentration in plasma. Thus the rate-limiting factor in normal shed blood is the fibrinogen concentration. A maximum of 6.4 +/- 1.5 (SD) molecules of ammonia are produced per molecule of fibrinogen. Determination of the total ammonia produced is the fastest direct method of estimating the extent of frbrin cross-linkage in whole plasma. A method is proposed for assaying fibrinoligase, based on the rate of ammonia production in the presence of casein as substrate. Normal values are 7.6 +/- 2.9 (SD) mumol/min per liter of plasma.

Adult↗