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the 1st letter of the Roman alphabet (同)a
the blood group whose red cells carry the A antigen (同)type_A, group A

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answer / ampere

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/01/24 23:11:30」(JST)

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Thromboxane A2 (TXA2) is a type of thromboxane that is produced by activated platelets and has prothrombotic properties: it stimulates activation of new platelets as well as increases platelet aggregation. This is achieved by increasing expression of the glycoprotein complex GPIIb/IIIa on the cell membrane of platelets. The same effect^{[improper synthesis?]} is also achieved by ADP in platelet stimulation, which is blocked by clopidogrel. Circulating fibrinogen binds these receptors on adjacent platelets, further strengthening the clot. Thromboxane A2 is also a known vasoconstrictor and is especially important during tissue injury and inflammation. It is also regarded as responsible for Prinzmetal's angina.

Receptors that mediate TXA2 actions are thromboxane A2 receptors. The human TXA2 receptor (TP) is a typical G protein-coupled receptor (GPCR) with seven transmembrane segments. In humans, two TP receptor splice variants - TPα and TPβ - have so far been cloned.

Synthesis and breakdown

TXA2 is generated from prostaglandin H2 by thromboxane-A synthase in a metabolic reaction which generates approximately equal amounts of 12-Hydroxyheptadecatrienoic acid (12-HHT). Aspirin irreversibly inhibits platelet cyclooxygenase 1 preventing the formation of prostaglandin H2, and therefore thromboxane A2.

TXA2 is very unstable in aqueous solution, since it is hydrolyzed within about 30 seconds to the biologically inactive thromboxane B2. 12-HHT, while once thought to be an inactive byproduct of TXA2 synthesis, has recently been shown to have a range of potentially important actions, some of which relate to the actions of TXA2 (see 12-Hydroxyheptadecatrienoic acid).^[1] Due to its very short half life, TXA2 primarily functions as an autocrine or paracrine mediator in the nearby tissues surrounding its site of production. Most work in the field of TXA2 is done instead with synthetic analogs such as U46619 and I-BOP.^[2] In human studies, 11-dehydrothromboxane B2 levels are used to indirectly measure TXA2 production.^[3]^[4]

Eicosanoid synthesis.

References

^ J Biochem. 2015 Feb;157(2):65-71. doi: 10.1093/jb/mvu078
^ Michael P. Walsh; et al. "Thromboxane A2-induced contraction of rat caudal arterial smooth muscle involves activation of Ca2+ entry and Ca2+sensitization: Rho-associated kinase-mediated phosphorylation of MYPT1 at Thr-855 but not Thr-697" (PDF).
^ Catella F, Healy D, Lawson JA, FitzGerald GA (1986). "11-Dehydrothromboxane B2: a quantitative index of thromboxane A2 formation in the human circulation". PNAS. 83 (16): 5861–5865. doi:10.1073/pnas.83.16.5861. PMC 386396. PMID 3461463.
^ Lordkipanidzé M, Pharand C, Schampaert E, Turgeon J, Palisaitis DA, Diodati JG (2007). "A comparison of six major platelet function tests to determine the prevalence of aspirin resistance in patients with stable coronary artery disease". Eur Heart J. 28 (14): 1702–1708. doi:10.1093/eurheartj/ehm226. PMID 17569678.

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1. 止血の概要 overview of hemostasis
2. 血小板生物学 platelet biology
3. アスピリン：リウマチ性疾患における作用機序、主な毒性、および使用 aspirin mechanism of action major toxicities and use in rheumatic diseases
4. 下肢末梢動脈疾患の症状を治療するための試験的治療 investigational therapies for treating symptoms of lower extremity peripheral artery disease
5. 冠動脈疾患における血小板の役割 the role of platelets in coronary heart disease

English Journal

Endothelin-1 shifts the mediator of bradykinin-induced relaxation from NO to H2 O2 in resistance arteries from patients with cardiovascular disease.

Leurgans TM1, Bloksgaard M1, Brewer JR2, Bagatolli LA2, Fredgart MH1, Rosenstand K1, Hansen ML3, Rasmussen LM3,4, Irmukhamedov A4,5, De Mey JG1,4,5,6.
British journal of pharmacology.Br J Pharmacol.2016 Feb 23. doi: 10.1111/bph.13467. [Epub ahead of print]
BACKGROUND AND PURPOSE: We tested the hypothesis that in resistance arteries from cardiovascular disease patients, effects of an endothelium-dependent vasodilator depend on the contractile stimulus.EXPERIMENTAL APPROACH: Arteries dissected from parietal pericardium of cardiothoracic surgery patients
PMID 26914408

Endometriosis-Derived Stromal Cells Secrete Thrombin and Thromboxane A2, Inducing Platelet Activation.

Guo SW1, Du Y2, Liu X3.
Reproductive sciences (Thousand Oaks, Calif.).Reprod Sci.2016 Feb 22. pii: 1933719116630428. [Epub ahead of print]
Platelets have been recently revealed to play important roles in the development of endometriosis. However, it is unclear whether endometriotic lesions can secrete any platelet inducers outside the menstruation window. Hence, this study was undertaken to see whether endometriosis-derived stromal cel
PMID 26902428

Apelin: an antithrombotic factor that inhibits platelet function.

Adam F1, Khatib AM2, Lopez JJ1, Vatier C3, Turpin S1, Muscat A3, Soulet F2, Aries A1, Jardin I4, Bobe R1, Stepanian A5, de Prost D6, Dray C7, Rosado JA4, Valet P7, Feve B8, Siegfried G2.
Blood.Blood.2016 Feb 18;127(7):908-20. doi: 10.1182/blood-2014-05-578781. Epub 2015 Dec 3.
Apelin peptide and its receptor APJ are directly implicated in various physiological processes ranging from cardiovascular homeostasis to immune signaling. Here, we show that apelin is a key player in hemostasis with an ability to inhibit thrombin- and collagen-mediated platelet activation. Mice lac
PMID 26634301

Japanese Journal

ONO-1301, a Sustained-Release Prostacyclin Analog, Ameliorates the Renal Alterations in a Mouse Type 2 Diabetes Model Possibly Through Its Protective Effects on Mesangial Cells

Acta Medica Okayama 69(1), 1-15, 2015-02
NAID 120005549937

Salvia Miltiorrhiza Bge.f.alba Ameliorates the Progression of Monocrotaline-Induced Pulmonary Hypertension by Protecting Endothelial Injury in Rats

The Tohoku Journal of Experimental Medicine 236(2), 155-162, 2015
NAID 130005075698

Methods for Preclinical Assessment of Antipruritic Agents and Itch Mechanisms Independent of Mast-Cell Histamine

Biological and Pharmaceutical Bulletin 38(5), 635-644, 2015
NAID 130005068087

Related Pictures

Platelet thromboxane (11-dehydro-Thromboxane B2) and aspirin response in patients with Platelet Aggregation Stock Illustrations, Images & Vectors | Shutterstock miracle drug | emilysevolution About Thromboxane - Assignment Point Kevin Ahern's Biochemistry Course (BB 350) at Oregon State University Anti-Thromboxane A2 receptor 抗体 [EPR7336] (ab134959)

★リンクテーブル★

リンク元	「トロンボキサンA2」「TXA2」
拡張検索	「prostaglandin H2-thromboxane A2 receptor」「thromboxane A2 receptor」
関連記事	「A」

「トロンボキサンA2」

Thromboxane A2
Identifiers
CAS Number	57576-52-0
3D model (Jmol)	Interactive image
ChEBI	CHEBI:15627
ChemSpider	4444137
IUPHAR/BPS	4482
KEGG	C02198
MeSH	Thromboxane+A2
PubChem	5280497
	InChI InChI=1S/C20H32O5/c1-2-3-6-9-15(21)12-13-17-16(18-14-20(24-17)25-18)10-7-4-5-8-11-19(22)23/h4,7,12-13,15-18,20-21H,2-3,5-6,8-11,14H2,1H3,(H,22,23)/b7-4-,13-12+/t15-,16+,17+,18-,20+/m0/s1 Key: DSNBHJFQCNUKMA-SCKDECHMSA-N ;
	SMILES CCCCC[C@@H](/C=C/[C@@H]1[C@H]([C@@H]2C[C@@H](O2)O1)C/C=C\CCCC(=O)O)O ;
Properties
Chemical formula	C20H32O5
Molar mass	352.465 g/mol
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references