OXYGENATION OF 5,8,11-EICOSATRIENOIC ACID BY PROSTAGLANDIN-H SYNTHASE-2 OF OVINE PLACENTAL COTYLEDONS - ISOLATION OF 13-HYDROXY-5,8,11-EICOSATRIENOIC AND 11-HYDROXY-5,8,12-EICOSATRIENOIC ACIDS

Prostaglandin H synthase-1 of ram vesicular glands metabolises 5,8,11- eicosatrienoic (Mead) acid to 13R-hydroxy-5,8,11-eicosatrienoic and to 11R-hydroxy-5,8,12-eicosatrienoic in a 5:1 ratio. We wanted to determ ine the metabolism of this fatty acid by prostaglandin H synthase-2. W estern blot showed that microsomes of sheep and rabbit placental cotyl edons contained prostaglandin H synthase-2, while prostaglandin H synt hase-1 could not be detected. Microsomes of sheep cotyledons metabolis ed [1-C-14]5,8,11-eicosatrienoic acid to many polar metabolites and di clofenac (0.05 mM) inhibited the biosynthesis. The two major metabolit es were identified as 13-hydroxy-5,8,11-eicosatrienoic and 11-hydroxy- 5,8,12-eicosatrienoic acids. They were formed in a ratio of 3:2, which was not changed by aspirin (2 mM). 5,8,11 -Eicosatrienoic acid is lik ely oxygenated by removal of the pro-S hydrogen at C-13 and insertion of molecular oxygen at either C-13 or C-11, which is followed by reduc tion of the peroxy derivatives to 13-hydroxy-5,8,11-eicosatrienoic and 11-hydroxy-5,8,12-eicosatrienoic acids, respectively. Prostaglandin H synthase-1 and -2 oxygenate 5,8,11-eicosatrienoic acid only slowly co mpared with arachidonic acid.