Prostacyclin is formed from arachidonic acid primarily by the vascular endothelium and renal cortex. It is a potent vasodilator and inhibitor of platelet aggregation. PGI2 is non-enzymatically hydrated to 6-keto PGF1α (t½ = 2-3 minutes), and then quickly converted to the major metabolite, 2,3-dinor-6-keto PGF1α (t½ = 30 minutes).