Physiologically active compounds found in many organs of the body. They are formed in vivo from the prostaglandin endoperoxides and cause platelet aggregation, contraction of arteries, and other biological effects. Thromboxanes are important mediators of the actions of polyunsaturated fatty acids transformed by cyclooxygenase.
Thromboxane is a member of the family of lipids known as eicosanoids. It is produced in platelets by thromboxane synthetase, which is produced from the endoperoxides by the cyclooxygenase (COX) enzyme from arachidonic acid.
Thromboxane is a vasoconstrictor and a potent hypertensive agent, and it facilitates the clumping of platelets. It is in homeostatic balance in the circulatory system with prostacyclin, a related compound. The widely used drug aspirin acts by inhibiting the ability of the COX enzyme to synthesize the precursors of thromboxane within platelets.
Thromboxane is named for its role in clot formation (thrombosis). Thromboxane A2 (TXA2), produced by activated platelets, has prothrombotic properties, stimulating activiation of new platelets as well as increasing platelet aggregation. Platelet aggregation is achieved by mediating expression of the glycoprotein complex GP IIb/IIIa in the cell membrane of platelets. Circulating fibrinogen binds these receptors on adjacent platelets, further strengthening the clot.
It is believed that the vasoconstriction caused by thromboxanes plays a role in Prinzmetal's angina.