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| Identifiers | |||
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3D model (JSmol) | |||
| ChEBI | |||
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| KEGG |
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| MeSH | Thromboxane+A2 | ||
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| Properties | |||
| C20H32O5 | |||
| Molar mass | 352.471 g·mol−1 | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Thromboxane A2 (TXA2) is a type ofthromboxane that is produced by activatedplatelets duringhemostasis and has prothrombotic properties: it stimulates activation of new platelets as well as increases platelet aggregation. This is achieved by activating thethromboxane receptor, which results in platelet-shape change, inside-out activation ofintegrins, anddegranulation.[1] Circulatingfibrinogen binds these receptors on adjacent platelets, further strengthening theclot. TXA2 is also a knownvasoconstrictor[2][3][4][5] and is especially important during tissue injury and inflammation. It is also regarded as responsible forPrinzmetal's angina.[citation needed]
Receptors that mediate TXA2 actions arethromboxane 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.
Thromboxane A2 (TXA2) is generated fromprostaglandin H2 bythromboxane-A synthase in a metabolic reaction which generates approximately equal amounts of12-hydroxyheptadecatrienoic acid (12-HHT).Aspirin irreversibly inhibits plateletcyclooxygenase 1 preventing the formation of prostaglandin H2, and therefore TXA2. Contrastly, TXA2 vascular tissue synthesis is stimulated by angiotensin II which promotes cyclooxygenase I's metabolism of arachidonic acid. An angiotensin II dependent pathway also induces hypertension and interacts with TXA2 receptors.[6]
TXA2 is very unstable in aqueous solution, since it is hydrated within about 30 seconds to the biologically inactivethromboxane 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 (see12-Hydroxyheptadecatrienoic acid).[7] 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 asU46619 andI-BOP.[8] In human studies,11-dehydrothromboxane B2 levels are used to indirectly measure TXA2 production.[9][10]
