Thromboxane: A substance made by platelets that causes blood clotting and constriction of blood vessels. It also encourages platelet aggregation. There are two thromboxanes. Thromboxane A2 (TXA2) is active but is very unstable and has a half-life of only 30 seconds before it undergoes hydrolysis to form thromboxane B2 (TXB2) which is inactive. The thromboxanes are derived from arachidonic acid and are related to prostaglandins. Aspirin acts by inhibiting the COX enzyme from synthesizing precursors of thromboxane in platelets thereby reducing platelet aggregation.
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