Prostaglandin I-2 (PGI-2 or Prostacyclin) (Last Updated - 2/26/2005)

-a natural (endogenous) anti-coagulant synthesized by vascular endothelial cells
-inhibits thrombosis in intact vessels via inhibition of platelet aggregation & secretion

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References:

Goodman & Gilman's: The Pharmacologic Basis Of Therapeutics - 10th Edition - 2001. Chapter 55.