Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Extensive aggregation of human platelets can be induced by ADP without secondaryaggregation or release of granule contents. This occurs with washed platelets in Tyrode solution containing 0.35% albumin, human fibrinogen, and apyrase, and in platelet-rich, heparin- or hirudin-plasma. Conditions that caused release during ADP-inducedaggregation were-citrate as the anticoagulant in platelet-rich plasma; addition of citrate (11-15 mM) to a suspension of washed platelets, or to hirudin-plasma or heparin-plasma; suspension of platelets in a medium containing magnesium but no calcium;and the presence of trace amounts of thrombin or aggregated gamma globulin in the platelet suspensions. Acetylsalicylic acid, phenylbutazone, or sulfinpyrazone inhibited secondary aggregation and release in all these circumstances. Heparin or hirudin inhibited ADP-INDUCED SECONDARY AGGREGATION AND RELEASE PROMOTED BY TRACES OF THROMBIN. Although fibrinogen is required for ADP-induced primary aggregation, it does not support secondary aggregation and release, provided that it has no clot-promoting activity. The main agent responsible for ADP-induced secondary aggregation and release in human, citrated, platelet-rich plasma appears to be sodium citrate. Suspending washed human platelets in a medium without calcium mimics the effect of citrate.
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PMID:Factors responsible for ADP-induced release reaction of human platelets. 5 Jul 44

We have shown previously that washed human platelets resuspended in Tyrode solution containing albumin and apyrase maintain their disc shape and their ability to aggregate upon the addition of low concentration of ADP, providing fibrinogen is added to the suspending medium. We have now examined their responses to other aggregating and release-inducing agents. Collagen, arachidonate, thrombin, immune serum globulin, the ionophore A23, 187 and phytohaemagglutinin from Phaseolus vulgaris caused aggregation and release of granule contents. The response to adrenaline was variable. Serotonin caused the platelets to change shape but no aggregation or release occurred. Addition of a small amount of plasma was necessary for ristocetin-induced aggregation. Polylysine caused immediate platelet-to-platelet adherence with little or no release of granule contents. Responses to collagen or thrombin were greater in a modified medium containing magnesium but no calcium; in this medium, aggregation caused by ADP or polylysine was followed by the release of granule contents whereas these agents caused aggregation without release in a medium with both calcium and magnesium. When protein was omitted from the suspending medium, platelet aggregation in response to ADP was variable. In this medium, collagen and thrombin caused more extensive release than in the albumin-containing medium. Aggregation by polylysine was accompanied by release and extensive lysis in the protein-free medium. Thus, the composition of the final resuspending medium has a major effect on the responses of washed human platelets to aggregating agents.
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PMID:Properties of washed human platelets. 32 7

The minimal concentration of the platelet aggregation principle (Platelet Aggregoserpentin, PAS) necessary to induce platelet aggregation was 10 ng/ml, about one-hundredth of that of the crude venom. PAS induced the release of platelet factors 3 and 4 from platelets, but the released platelet factor 3 was easily inactivated by the anti-phospholipid effect of PAS. Pretreatment of platelets with neuraminidase potentiated PAS-induced platelet aggregation. PAS-induced platelet aggregation was independent on released ADP; it could occur in the ADP-removing systems, such as apyrase or a combination of phosphoenolpyruvate and pyruvate kinase. However, PAS-induced platelet aggregation could be inhibited by adenine nucleotides and adenosine. PAS-induced platelet aggregation was inhibited by some anti-inflammatory agents, antimalarial drugs, local anesthetics, antihistamine and smooth muscle relaxants. After deaggregation of PAS-treated platelets, thrombin and sodium arachidonate could further induce platelet aggregation, but ADP and second dose of PAS could not. It is concluded that PAS-induced platelet aggregation is due to prostaglandin synthesis. Recent literatures on the mechanism of platelet aggregation were surveyed and the actions of PAS were discussed.
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PMID:The action mechanism of the purified platelet aggregation principle of Trimeresurus mucrosquamatus venom. 46 15

Endothelial cells in culture can modulate platelet aggregation and vascular tone, in part by producing prostacyclin (PGI2), a powerful vasodilator and inhibitor of platelet aggregation, but also by their ecto-ADPase activity, which initiates the conversion of pro-aggregating ADP to adenosine, a potent vasodilator and platelet inhibitor. We have now demonstrated that cultured aortic endothelial cells exposed to trypsin, thrombin or other stimuli can liberate a high proportion of their adenine nucleotides without substantial loss of lactate dehydrogenase. ADP rapidly accumulates extracellularly, reaching biologically active concentrations before there is further breakdown to adenosine. Whether this selective release of nucleotides is a response to damage, or whether it represents a specific secretory mechanism remains to be resolved. Cultured aortic smooth muscle cells can secrete adenine nucleotides in a similar manner, but extracellular conversion to adenosine occurs much faster.
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PMID:Vascular endothelial and smooth muscle cells in culture selectively release adenine nucleotides. 48 3

Separation of platelets from plasma is achieved by adding ADP (final concentration 10-5 M) to platelet-rich plasma and allowing aggregates to form. Aggregates are removed quickly by brief, gentle centrifugation, washed two to three times with 0.9% NaCl (saline), and then incubated for 10 minutes in the presence of apyrase, albumin and calcium. Platelet aggregates deaggregate completely during this incubation period. The platelet suspension is then subjected to 1100g for 12 minutes, gently resuspended in a small volume of saline, and finally diluted with an appropriate medium to the desired concentration. The entire separation procedure requires approximately 30 minutes. Platelets obtained by this procedure are a) comparable in aggregability to the platelet preparations obtained by gel filtration, b) have normal intracellular amounts of ATP and ADP, and c) except for slight dilatation of the surface-connected canalicular system, have normal ultrastructural appearance. When suspended in an appropriate medium, these separated platelets take up serotonin 14-C and subsequently release it in nearly normal quantities when exposed to thrombin, collagen or ADP.
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PMID:Characterization of human platelets separated from blood by ADP-induced aggregation. 112

A number of investigators have implicated sialic acid on the surface of platelets in platelet function. In this study we have quantitated the amount of sialic acid removed by purified neuraminidase from the surface of washed platelets of man, rabbit, or pig and examined the effects of this removal. Purified neuraminidase did not induce the release of platelet granule contents. Platelets were pre-labeled with 14C-serotonin for measurement of the release reaction or with 51Cr for determination of adherence to a collagen-coated surface or damaged aortic surface, and for in vivo platelet survival studies. Washed, neuraminidase-treated platelets were resuspended in Tyrode's solution containing 0.35 per cent albumin or in citrated platelet-free plasma from the same species. Both resuspending fluids contained apyrase. Aggregating agents tested were ADP, acid-soluble collagen, thrombin, ristocetin (with human platelets), polylysine, and serotonin (with rabbit platelets). With all of these agents except polylysine, aggregation of neuraminidase-treated human or rabbit platelets was slightly enhanced compared with control platelets; aggregation of pig platelets was unchanged. When release-inducing agents were used, neuraminidase-treated platelets released more of their 14C-serotonin than control platelets. The extent to which rabbit platelets adhered to a collagen-coated surface or to the damaged surface of everted rabbit aorta was unchanged by pretreatment of platelets with neuraminidase. Therefore it seems unlikely that sialic acid is involved in platelet adherence to collagen. When more than 15 per cent of total sialic acid had been removed from rabbit platelets, they were completely cleared from the circulation within 1 hour of their injection into rabbits. When 8 to 10 per cent of total sialic acid had been removed, the platelets were not cleared immediately from the circulation but were cleared more quickly than control platelets. Thus, although removal of up to 65 per cent of platelet sialic acid has only a slightly enhancing effect on platelet aggregation and release in vitro, removal of as little as 8 to 10 per cent results in the recognition of platelets as "foreign" in vivo.
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PMID:Effects on platelet function of removal of platelet sialic acid by neuraminidase. 112 70

Clots formed upon the addition of thrombin to human platelet-rich plasma (PRP) retracted readily but the clotting enzyme from Bothrops atrox venom did not cause retraction in PRP unless ADP, collagen, epinephrine, or low concentrations of thrombin (0.1 U) were added. The latter type of retraction was inhibited by apyrase and creatine phosphate kinase in the presence of creatine phosphate, but that induced with higher concentration of thrombin (2 U) was not. In a system composed of washed human platelets and purified fibrinogen, Bothrops marajoensis (BM) thrombinlike enzyme (highly purified preparations of viper venom) did not cause clot retraction. Addition of ADP to the platelet-fibrinogen mixture prior to BM enzyme resulted in stimulation of clot retraction that could be dissociated from the release of platelet constituents. Addition of low concentrations of thrombin (0.1 U/ml) caused retraction associated with a considerable release of adenine nucleotides that was inhibited by potato apyrase. Electron micrographs showed platelet-fibrin aggregates in all types of retracted clots. Nonretracted clots formed in the presence of potato apyrase contained discoidal platelets that were not in close association with fibrin. It has been postulated that platelet-dependent fibrin clot retraction induced by collagen, epinephrine, and low concentration of thrombin is mediated by ADP. High concentrations of thormbin may possibly promote clot retraction independently of ADP.
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PMID:ADP, thrombin, and Bothrops atrox thrombinlike enzyme in platelet-dependent fibrin retraction. 121 67

The role of platelets in the maintenance of endothelial barrier is examined in an in vitro model of the microvasculature. Human platelets (6,000/microliters) perfused through a cell column of endothelial-covered microcarriers decrease paracellular permeability of sodium fluorescein (mol wt 342) to 63% of baseline values. This effect is reversible and a second application and removal of platelets produces a similar response. This effect occurs within 5 min and reverses within 10 min after platelet removal. The reduction in permeability is not due to mechanical obstruction of endothelial junctions, since the number of recirculating platelets is not reduced and releasate from unstimulated 2-h platelet incubations also decreases permeability. Releasate from platelets stimulated with 0.1 U/ml of thrombin for 15 min have the same permeability reducing effect. In this system, the platelet factors serotonin (10(-3) M) and ADP (10(-4) M) have no effect on permeability. However, the platelet factors adenosine (10(-4) M), ATP (10(-5) M), and beta-agonists decrease permeability. None of these appear to account for platelet permeability activity, since activity is not blocked by agents directed against these mediators (adenosine deaminase, apyrase, 8-phenyltheophylline, or propranolol). The active factor(s) is stable at -20 degrees C, heat stable, sensitive to trypsin, and has an apparent molecular weight > 100. We conclude that unstimulated platelets release a factor(s) that enhances endothelial barrier in vitro and may be important in maintenance of the normal in vivo barrier.
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PMID:Platelets and a platelet-released factor enhance endothelial barrier. 147 5

Although DDAVP has been shown to be haemostatically efficacious in patients with various congenital or acquired platelet disorders, no reasonable explanation has been found for this effect. We have previously shown DDAVP to increase platelet adhesiveness as measured with a platelet retention test. The aim of the present study was to investigate the mechanism of action responsible for the increased platelet retention in response to DDAVP. Patients with vWD type III and type Ia, severe haemophilia and severe thrombasthenia, as well as healthy controls, were included in the study. The effect of different concentrations of vWF in plasma and platelets was explored, as was the effect on platelet function of apyrase and monoclonal antibodies against GP IIb/IIIa and GP Ib. We found the effect of DDAVP on platelet retention to be unaffected by changes in the plasma concentration of vWF. The enhanced platelet retention after DDAVP is apparently dependent on the presence of platelet-vWF and on a normal function of the GP IIb/IIIa. The effect is not mediated via ADP or thrombin. The platelet-stimulating effect of DDAVP may be one explanation for the positive haemostatic effect in patients with certain platelet disorders.
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PMID:DDAVP-induced enhancement of platelet retention: its dependence on platelet-von Willebrand factor and the platelet receptor GP IIb/IIIa. 149 98

Triflavin, an Arg-Gly-Asp (RGD)-containing peptide, purified from snake venom of Trimeresurus flavoviridis, inhibits human platelet aggregation through the blockade of fibrinogen binding to fibrinogen receptors associated with glycoprotein IIb/IIIa complex. In this report, we examined the effect of triflavin on tumor cells (human hepatoma J-5)-induced platelet aggregation (TCIPA) of heparinized platelet-rich plasma (PRP). ADP-scavenger agents, apyrase (10 U/ml) and creatine phosphate (5 mM)/creatine phosphokinase (5 U/ml) did not inhibit TCIPA while hirudin (5 U/ml) completely inhibited it. J-5 cells initially induced platelet aggregation, then blood coagulation occurred. J-5 cells concentration-dependently shortened the recalcification time of normal as well as Factor VIII, IX-deficient human plasmas, while it was inactive at shortening the recalcification time of Factor VII-deficient plasma, suggesting J-5 cells induced platelet aggregation through activation of extrinsic pathway, leading to thrombin formation as evidenced by the amidolytic activity on s-2238 by expressing tissue factor-like activity. Triflavin inhibited TCIPA in a dose-dependent manner (IC50, 0.02 microM). When compared on molar ratio, triflavin was approximately 30,000 times more potent than GRGDS (IC50, 0.58 mM). On the other hand, GRGES showed no significant effect on TCIPA, even its concentration was raised to 4 mM. Additionally, the monoclonal antibodies, raised against glycoprotein IIb/IIIa complex (i.e., 7E3 and 10 E5) inhibited J-5 TCIPA. In conclusion, we suggest the inhibitory effect of triflavin on J-5 TCIPA may be chiefly mediated by the binding of triflavin to the fibrinogen receptor associated with glycoprotein IIb/IIIa complex on platelet surface membrane.
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PMID:Triflavin, an Arg-Gly-Asp containing snake venom peptide, inhibits aggregation of human platelets induced by human hepatoma cell line. 151 27


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