Prostaglandin E2-d4 -PGE2-d4) contains four deuterium atoms at the 3, 3 , 4, and 4 positions. It is intended for use as an internal standard for the quantification of PGE2 by GC- or LC-mass spectrometry. PGE2 is one of the primary cyclooxygenase products of arachidonic acid and one of the most widely investigated prostaglandins. Its activity influences inflammation, fertility and parturition, gastric mucosal integrity, and immune