Explain in detail the role of prostacyclin and thromboxane on platelet aggregation

Prostacyclin and thromboxane are two opposing eicosanoids (locally-acting hormones) that play a critical role in platelet aggregation. These 2 Local hormones are produced in the Arachidonic Acid Metabolism Pathway.

Role of TXA2 on platelet Aggregation:

  • Thromboxane A2 is produced from Prostaglandin H2 by the Enzyme Thromboxane A synthase.
  • Mature platelets express only COX-1 and releases TxA2.
  • This TxA2 then binds with TP receptor and induces platelet Aggregation by Protein Kinase C Dependent pathways. (increased Stickiness)
  • PGI2 also binds with TP receptor of Vascular smooth muscle inhibiting PKC pathway causing increased cAMP level causing Vasoconstriction.  

The role of TXA2 in platelet aggregation is so important that aspirin, which inhibits TXA2 production by blocking the cyclooxygenase-1 (COX-1) enzyme, is one of the most widely used antiplatelet drugs in the world. Aspirin is used to prevent heart attack and stroke in people at high risk for these conditions.

Role of Prostacyclin (PGI2) on platelet Aggregation

  • PGI2 binds with IP receptor of Platelet and Inhibits the PKC inhibiting IP3 and DAG production which are the main mediators of the calcium dependent translocation of Platelet adhesion molecules. inhibiting platelet aggregation.
  • PGI2 also binds with IP receptor of Vascular smooth muscle inhibiting Adenylyl cyclase pathway causing Vasodilation. 



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