Prostacyclin (or PGI2) is a member of the family of lipid molecules known as eicosanoids.

Prostacyclin (PGI2) chiefly prevents formation of the platelet plug involved in primary hemostasis (a part of blood clot formation). It is also an effective vasodilator.

References

Fischer S, Weber PC (1985). "Thromboxane (TX)A3 and prostaglandin (PG)I3 are formed in man after dietary eicosapentaenoic acid: identification and quantification by capillary gas chromatography-electron impact mass spectrometry". Biomed. Mass Spectrom. 12 (9): 470–6. doi:10.1002/bms.1200120905. PMID 2996649.