PTGIR is a member of the G protein-coupled receptor family 1 and has been shown to be a receptor for prostacyclin (prostaglandin I2 or PGI2). Isoprenylation does not influence ligand binding but is required for efficient coupling to the effectors adenylyl cyclase and phospholipase C. Prostacyclin, the major product of cyclooxygenase in macrovascular endothelium, elicits a potent vasodilation and inhibition of platelet aggregation through binding to PTGIR.