Endogenous epoxyeicosatrienoic acids. Cytochrome P-450 controlled stereoselectivity of the hepatic arachidonic acid epoxygenase.

Chiral analysis of the endogenous rat liver epoxyeicosatrienoic acids shows the biosynthesis of 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids in a 4:1, 2:1, and 3:1 ratio of antipodes, respectively. Animal treatment with phenobarbital results in a 3.7-fold increase in microsomal cytochrome P-450 concentration and a concomitant, regioselective 6.8- and 3.4-fold increase in the liver concentration of 8,9- and 14,15-epoxyeicosatrienoic acids, respectively. Phenobarbital induces the in vivo synthesis of both regioisomers as nearly optically pure enantiomers. These results demonstrate the enzymatic origin of the epoxyeicosatrienoic acids present in rat liver and document a novel metabolic function for cytochrome P-450 in the regio- and enatioselective epoxygenation of endogenous pools of arachidonic acid.