Thromboxane A2

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 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 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.