8-iso Prostaglandin E2-d4 (8-iso PGE2-d4) contains four deuterium atoms at the hydroxyethyl 3, 3',4, and 4' positions. It is intended for use as an internal standard for the quantification of 8-iso PGE2 by GC- or LC-mass spectrometry. 8-iso PGE2 is one of several isoprostanes produced from arachidonic acid during lipid peroxidation.{1943} It is a potent renal vasoconstrictor in the rat.{1943,5157} 8-iso PGE2 inhibits U-46619 or I-BOP-induced platelet aggregation with IC50 values of 0.5 and 5 µM, respectively.{1258} When infused into the renal artery of the rat at a concentration of 4 mg/kg/min, 8-iso PGE2 decreases the GFR and renal plasma flow by 80% without affecting blood pressure.{1943}