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)

Human umbilical vein endothelial cells were incubated with ATP, ADP, thrombin, or ionophore A23187 for as long as 600 seconds. A statistically significant rise in the prostaglandin I2 (prostacyclin; PGI2) and thromboxane A2 (TxA2) release was observed after 45 seconds. The maximum amount of cytosolic free Ca2+ was reached between 20 and 30 seconds. A statistically significant elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels was observed only in response to ATP and ADP after 120 seconds. Furthermore, adenosine, caffeine, phorbol 12-myristate 13-acetate (PMA), and adenosine 5'-(alpha, beta-methylene)triphosphate were tested alone or in combination with ATP or thrombin. PMA inhibited ATP-stimulated eicosanoid biosynthesis but had no effect on thrombin. Of the agents used to increase cytosolic free Ca2+ concentrations, only PMA failed to provoke eicosanoid release. Similarly, only PMA failed to induce a Ca2+ flux in the absence of extracellular Ca2+. The data presented show that PGI2 and TxA2 release from human umbilical cord endothelial cells is closely associated with Ca2+ mobilized from intracellular sources. Extracellular Ca2+, as well as changes in intracellular cAMP levels, has no influence on endothelial eicosanoid synthesis, at least for short-term regulation (less than or equal to 600 seconds).
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PMID:Functional implications of cAMP and Ca2+ on prostaglandin I2 and thromboxane A2 synthesis by human endothelial cells. 131 97

Substantial in vitro and animal data suggest that methylxanthines, such as caffeine and theophylline, act as adenosine receptor antagonists. To test this hypothesis in humans, we first determined if theophylline would antagonize the effects of adenosine. Intravenous administration of adenosine, 80 micrograms/kg/min, increased heart rate 28 +/- 6 bpm, systolic blood pressure 19 +/- 5 mm Hg and minute ventilation 6.1 +/- 2.2 liters/min. All these changes were significantly attenuated during theophylline administration (17 +/- 3 bpm and 1 +/- 2 mm Hg and 1.6 +/- 0.6 liters/min, respectively, P less than .05), at a dose (10 mg/kg over 1 hr, followed by 1.8 micrograms/kg/min i.v.) that produced plasma theophylline levels of 17 +/- 2 micrograms/ml (94 microM). We then determined if chronic caffeine consumption resulted in upregulation of platelet adenosine receptors in eight normal volunteers. After 7 days of caffeine abstinence, the adenosine analog 5'-N-ethylcarboxamidoadenosine produced a dose-dependent inhibition of thrombin-induced aggregation (EC50 = 69 nM). Subjects then were given caffeine, 250 mg p.o. 3 times a day for 7 days. Actual caffeine withdrawal, that is, virtual disappearance of caffeine in plasma, was apparent 60 hr after the last dose of caffeine. Caffeine withdrawal produced a significant shift to the left of 5'-N-ethylcarboxamidoadenosine inhibition of aggregation (EC50 = 49 nM, P less than .01), implying sensitization and/or upregulation of adenosine receptors as seen after chronic exposure to an antagonist. These results suggest that methylxanthines act as adenosine receptor antagonists in humans.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Caffeine and theophylline as adenosine receptor antagonists in humans. 186 59

Platelet aggregation and secretion are associated with a rise in intracellular calcium concentration ([Ca2+]i). Adenosine has been postulated as an endogenous inhibitor of platelet aggregation. The antiaggregatory effects of adenosine are related to activation of adenylate cyclase. We studied the effect of adenosine on the rise in [Ca2+]i and platelet aggregation produced by thrombin. Human platelets were obtained from dextrose/citrate-treated plasma. [Ca2+]i was determined by fluorescence-dye techniques (fura-2). Adenosine inhibited the slope of the first phase of aggregation and the rise in [Ca2+]i produced by thrombin, in a dose-dependent manner. The dose that produced 50% inhibition of both aggregation and the rise in [Ca2+]i was approximately 500 nM. The effects of adenosine on [Ca2+]i were shared by its stable analogs, 5'-N-ethylcarboxamidoadenosine being approximately 10-fold more potent than (-)N6-phenylisopropyladenosine, suggesting that these effects were mediated through adenosine A2 receptors. Furthermore, caffeine antagonized the inhibitory effects of adenosine on platelet aggregation and [Ca2+]i. The effects of adenosine on [Ca2+]i appear to be mediated through a rise in intracellular cAMP, because they were prevented by the adenylate cyclase inhibitor 2',5'-dideoxyadenosine (1 mM) and were potentiated by phosphodiesterase inhibition with papaverine (1 microM). Adenosine also inhibits the rise in [Ca2+]i produced by thrombin in a calcium-free medium, suggesting that adenosine inhibits both calcium influx and the release of calcium from intracellular stores.
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PMID:Adenosine inhibits the rise in intracellular calcium and platelet aggregation produced by thrombin: evidence that both effects are coupled to adenylate cyclase. 235 5

A ninhydrin positive compound (L2) from commercially available unfermented dry green tea (Thea sinesis) leaves is found to be a potent inhibitor of thrombin-stimulated thromboxane formation in rabbit whole blood. Its potency is compared with caffeine, a member of the methylxanthines family. Both caffeine and L2 inhibit thromboxane formation in whole blood in a dose dependent fashion. L2 inhibition when calculated as I50 by a dose response curve is found to be more than 40 fold stronger than caffeine as an inhibitor of thromboxane formation. A concentration of L2 as low as 50 microM, suppresses thromboxane formation (by 84%) whereas a concentration of 5000 microM is necessary to achieve the same inhibition with caffeine. The potent inhibitory effect of L2 on the TXB2 production maybe of benefit in the treatment of vascular disease.
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PMID:A potent inhibitor of thrombin stimulated platelet thromboxane formation from unprocessed tea. 347 9

Canatoxin is a toxic protein isolated from Canavalia ensiformis seeds. It induces death preceded by convulsions of spinal cord origin and also produces in vitro aggregation of platelets in rabbit, human and guinea-pig plasma. The aggregating effect is dose-dependent at nanomolar concentrations. Rabbit platelets pretreated with canatoxin became refractory to a second exposure to this protein or to collagen, but were still responsive to ADP, Paf-acether or arachidonic acid. [14C]-5-hydroxytryptamine was released from pre-labelled platelets on stimulation with canatoxin. Washed rabbit platelets, but not thrombin-degranulated ones, aggregated on stimulation with canatoxin provided that fibrinogen was added before the toxin. Canatoxin's pro-aggregating activity was inhibited by mepacrine, EDTA, caffeine, prostacyclin, adenosine monophosphate and also by the ADP scavenger system, creatine phosphokinase/creatine phosphate. Furthermore, 3-amino-1-[m-(trifluoromethyl)-phenyl]-2-pyrazoline (BW 755C), eicosatetraynoic acid (ETYA) and nordihydroguaiaretic acid (NDGA) were potent inhibitors of canatoxin-induced aggregation. In contrast, no inhibition was seen with indomethacin. The data indicate that canatoxin is mainly a release-reaction-promoting agent, being devoid of any direct aggregating activity. Thus the aggregation is totally dependent on the release of ADP. Furthermore, canatoxin-induced platelet activation is probably dependent on platelet phospholipase A2 and lipoxygenase activity but is not dependent on cyclo-oxygenase products or the release of Paf-acether.
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PMID:Platelet release reaction and aggregation induced by canatoxin, a convulsant protein: evidence for the involvement of the platelet lipoxygenase pathway. 391 94

Evidence which bears on the hypothesis that agents that increase platelet cyclic adenosine 3',5' monophosphate (cAMP) tend to inhibit platelet aggregation, whereas agents whose action is to induce or augment platelet aggregation are associated with a decrease in platelet content of this cyclic nucleotide is reviewed. Using radiolabeled cAMP in incubation with various agents, it was found that caffeine, colagen, thrombin, prostaglandins E1 and E2, and phosphodiesterase inhibitors are all agents that increase platelet cAMP and inhibit platelet aggregation.
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PMID:Cyclic 3',5'-adenosine monophosphate in human blood platelets. IV. Regulatory role of cyclic amp in platelet function. 434 63

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.
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PMID:Influence of the pure synthetic PAF (platelet aggregating factor) on clot retraction and platelet aggregation. 669 48

The effect of the synthetic thrombin substrate (TAME) and three compounds exerting an opposite effect on Ca-PPI and AdC (caffeine, atropine and meta-tolyl derivative of mechlorethamine (TDM)) on hormone-like and catalytic functions of thrombin was studied. It is shown that both TAME and other drugs under test block effectively the thrombin-induced platelet aggregation, as well as protect the active site of the enzyme from denaturation by dithiothreitol. The same compounds inhibit thrombin in thrombin-fibrinogen reaction and platelet 12-lipoxygenase. These data suggest identity of thrombin moieties which determine its enzymatic and hormone-like activities.
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PMID:Similarity of the effects of tosyl-L-arginine methyl ester, atropine, caffeine and antitumour alkylating agent on some biological functions of thrombin and platelet 12-lipoxygenase. 816 Feb 96

Previous studies established that thrombin stimulates phosphoinositide hydrolysis and modulates contractile function in neonatal rat ventricular myocytes. The present study further defines the signaling pathways activated by the thrombin receptor and their role in thrombin's actions in cardiac myocytes. The thrombin receptor-derived agonist peptide (TRAP, a portion of the tethered ligand created by thrombin's proteolytic activity) stimulates the rapid and transient accumulation of inositol bis- and tris-phosphates (IP2 and IP3, respectively), which is followed by the more gradual and sustained accumulation of inositol monophosphate (IP1). TRAP elicits a larger and more sustained accumulation of IP1 than does thrombin. Thrombin and TRAP also activate mitogen-activated protein kinase (MAPK) in cultured neonatal rat ventricular myocytes. Differences in the kinetics and magnitude of thrombin- and TRAP-dependent inositol phosphate (IP) accumulation are paralleled by differences in the kinetics and magnitude of thrombin- and TRAP-dependent activation of MAPK. Pretreatment with phorbol 12-myristate 13-acetate (PMA) to downregulate protein kinase C (PKC) attenuates thrombin- and TRAP-dependent activation of MAPK, although small and equivalent effects of thrombin and TRAP to stimulate MAPK persist in PMA-pretreated cells. These results support the notion that the thrombin receptor activates MAPK through PKC-dependent pathways and that the incremental activation of MAPK by TRAP over that induced by thrombin is the consequence of enhanced activation through the PKC limb of the phosphoinositide lipid pathway. TRAP also increases the beating rate of spontaneously contracting ventricular myocytes and elevates cytosolic calcium in myocytes electrically driven at a constant basic cycle length. The effects of TRAP to modulate contractile function and elevate intracellular calcium are not inhibited by tricyclodecan-9-yl-xanthogenate (D609, to block TRAP-dependent IP accumulation) or pretreatment with PMA (to downregulate PKC). The TRAP-dependent rise in intracellular calcium also is not inhibited by verapamil or removal of extracellular calcium but is markedly attenuated by depletion of sarcoplasmic reticular calcium stores by caffeine. Patch-clamp experiments demonstrate that TRAP elevates intracellular calcium in cells held at a membrane potential of -70 mV. Taken together, these results support the conclusion that the thrombin receptor modulates contractile function by mobilizing intracellular calcium through an IP3-independent mechanism and that this response does not require activation of voltage-gated ion channels.
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PMID:Thrombin receptor actions in neonatal rat ventricular myocytes. 863 12

Thrombin is a procoagulant inflammatory agonist that can disrupt the endothelium-lumen barrier in the lung by causing contraction of endothelial cells and promote pulmonary cell proliferation. Both contraction and proliferation require increases in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)). In this study, we compared the effect of thrombin on Ca(2+) signaling in human pulmonary artery smooth muscle (PASMC) and endothelial (PAEC) cells. Thrombin increased the [Ca(2+)](cyt) in both cell types; however, the transient response was significantly higher and recovered quicker in the PASMC, suggesting different mechanisms may contribute to thrombin-mediated increases in [Ca(2+)](cyt) in these cell types. Depletion of intracellular stores with cyclopiazonic acid (CPA) in the absence of extracellular Ca(2+) induced calcium transients representative of those observed in response to thrombin in both cell types. Interestingly, CPA pretreatment significantly attenuated thrombin-induced Ca(2+) release in PASMC; this attenuation was not apparent in PAEC, indicating that a PAEC-specific mechanism was targeted by thrombin. Treatment with a combination of CPA, caffeine, and ryanodine also failed to abolish the thrombin-induced Ca(2+) transient in PAEC. Notably, thrombin-induced receptor-mediated calcium influx was still observed in PASMC after CPA pretreatment in the presence of extracellular Ca(2+). Ca(2+) oscillations were triggered by thrombin in PASMC resulting from a balance of extracellular Ca(2+) influx and Ca(2+) reuptake by the sarcoplasmic reticulum. The data show that thrombin induces increases in intracellular calcium in PASMC and PAEC with a distinct CPA-, caffeine-, and ryanodine-insensitive release existing only in PAEC. Furthermore, a dynamic balance between Ca(2+) influx, intracellular Ca(2+) release, and reuptake underlie the Ca(2+) transients evoked by thrombin in some PASMC. Understanding of such mechanisms will provide an important insight into thrombin-mediated vascular injury during hypertension.
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PMID:Thrombin-mediated increases in cytosolic [Ca2+] involve different mechanisms in human pulmonary artery smooth muscle and endothelial cells. 1883 30


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