Prostanoids are a series of arachidonic acid metabolites produced by the action of cyclooxygenase and further modified by isomerases and synthases. Cells rapidly secrete prostanoids after synthesis, whereupon the prostanoids bind to a family of 8 GPCRs to exert their biological effects. The prostaglandin PGE2 causes pain, vasodilation, immunosuppression of T cells, bone remodeling and promotion of carcinogenesis. Four related GPCRs: EP1, EP2, EP3 and EP4, each bind to PGE2, but the different G protein coupling status of each receptor leads to distinct biological effects. EP4 couples primarily to Gs to increase intracellular cAMP levels. During neonatal development, EP4 participates in closure of the ductus arteriosus, a process required for switching circulation from the placenta to the lungs. In addition, EP4 mediates PGE2-induced bone formation by promoting osteoblastogenesis, and selective EP4 agonists are being evaluated as potential treatments for osteoporosis.