13,14-dihydro-15-keto Prostaglandin E2 (13,14-dihydro-15-keto PGE2) is the primary metabolite of PGE2 in plasma.[1] Endogenous or infused PGE2 is rapidly metabolized by the enzymes 15-hydroxy PGDH and 15-oxo-PG δ13-reductase to form 13,14-dihydro-15-keto PGE2. 13,14-dihydro-15-keto PGE2 accumulates to detectable levels; plasma levels in humans are between 10-100 pg/ml.[1][2] It undergoes further metabolism and chemical decomposition, giving it a relatively short half-life. In dogs, the plasma half-life of 13,14-dihydro-15-keto PGE2 is about 9 minutes.[3] In humans the metabolite has a similar short half-life, making it a poor choice of analytes for assays designed to measure total PGE2 biosynthesis. [4][5]
Reference：
[1]. Hamberg, M., and Samuelsson, B. On the metabolism of prostaglandins E1 and E2 in man. J. Biol. Chem. 246(22), 6713-6721 (1971).
[2]. Fitzpatrick, F.A., Aguirre, R., Pike, J.E., et al. The stability of 13,14-dihydro-15 keto-PGE2. Prostaglandins 19(6), 917-931 (1980).
[3]. Bothwell, W., Verburg, M., Wynalda, M., et al. A radioimmunoassay for the unstable pulmonary metabolites of prostaglandin E1 and E2: An indirect index of their in vivo disposition and pharmacokinetics. J. Pharmacol. Exp. Ther. 220(2), 229-235 (1982).
[4]. Leonhardt, A., Krauss, M., Gieler, U., et al. In vivo formation of prostaglandin E1 and prostaglandin E2 in atopic dermatitis. Br. J. Dermatol. 136(3), 337-340 (1997).
[5]. Granström, E., Hamberg, M., Hansson, G., et al. Chemical instability of 15-keto-13,14-dihydro-PGE2: The reason for low assay reliability. Prostaglandins 19(6), 933-945 (1980).