Wiktionary
prostacyclin
n. (context organic compound English) A prostaglandin produced in the walls of blood vessels; it acts as a vasodilator and inhibits the aggregation of platelets
Wikipedia
Prostacyclin
Prostacyclin (also called prostaglandin I2 or PGI) is a prostaglandin member of the eicosanoid family of lipid molecules. It inhibits platelet activation and is also an effective vasodilator.
When used as a drug, it is also known as epoprostenol. The terms are sometimes used interchangeably.