8-iso PGF2α-d4 is intended for use as an internal standard for the quantification of 8-iso PGF2α by GC- or LC-mass spectrometry. 8-iso Prostaglandin F2α (8-iso PGF2α) is an isoprostane produced by the non-enzymatic peroxidation of arachidonic acid in membrane phospholipids.^1,2,3 It circulates in human plasma in two distinct forms - esterified in LDL phospholipids and as the free acid. The ratio of these two forms is approximately 2:1, with a total plasma 8-iso PGF2α level of about 150 pg/ml in normal volunteers. In normal human urine, 8-iso PGF2α levels are about 180-200 pg/mg of creatinine.^1,2 8-iso PGF2α is a weak TP receptor agonist in vascular smooth muscle.⁴ Conversely, 8-iso PGF2α inhibits platelet aggregation induced by U-46619 (10−6 M) and I-BOP (3 x 10−7 M) with IC50 values of 1.6 x 10−6 M and 1.8 x 10−6 M, respectively.³