11β-Prostaglandin F2α (11β-PGF2α) is the primary metabolite of PGD2 .¹ It is formed from PGD2 via the NADPH-dependent aldo-keto reductase PGF synthase (PGFS) in the liver or lung.² 11β-PGF2α induces contraction of isolated cat iris sphincter, which endogenously expresses high levels of PGF2α (FP) receptors, with an EC50 value of 0.045 µM.¹ It also induces contraction of isolated human bronchial smooth muscle when used at concentrations ranging from 0.1 to 30 µM.³ 11β-PGF2α (0.1 and 1 µM) induces phosphorylation of ERK and CREB, as well as increases the viability of MCF-7 breast cancer cells stably expressing the FP receptor when used at concentrations of 0.1 and 1 µM.⁴