8-iso PGF2β is an isomer of PGF2α with a non-enzymatic, non-cyclooxygenase origin. It is one of 64 possible isomers of PGF2α which can be produced by free radical peroxidation of arachidonic acid. 8-iso PGF2β exhibits very weak contraction of human umbilical vein artery{11143} and does not promote aggregation of human whole blood.{11143,11145} However, 8-iso PGF2β moderately contracts both the canine and porcine pulmonary vein, although the effect is much weaker than that exhibited by other isoprostanes such as 8-iso PGE1, 8-iso PGE2, or 8-iso PGF2α{11144,11146}