Metabolism of arachidonic acid by isolated rat hepatocytes, renal cells and by some rabbit tissues. Detection of vicinal diols by mass fragmentography.

Purified cytochromes P-450 (LM2 and PB-B2) in a reconstituted system and epoxide hydrolase were recently found to metabolize arachidonic (eicosatetraenoic) acid to four vicinal dihydroxyeicosatrienoic acids. These metabolites were chemically synthetized from octadeuterated arachidonic acid and employed as internal standards for mass fragmentography. Isolated rat hepatocytes and renal cells were incubated with arachidonic acid (0.1 mM; 37 degrees C, 15 min) and, following extractive isolation and reversed-phase HPLC, formation of 11,12-dihydroxy-5,8,14-eicosatrienoic acid and 14,15-dihydroxy-5,8,11-eicosatrienoic acid was demonstrated by mass fragmentography using a capillary GC column. Furthermore, these diols were also detected in rabbit liver and renal cortex and they therefore appear to be formed endogenously. Formation of vicinal diols was also studied in cell free systems. Rabbit liver and renal cortical microsomes were incubated with NADPH (1 mM) and arachidonic acid (0.15 mM) for 15 min at 37 degree C and, besides 11,12-dihydroxy- and 14,15-dihydroxyeicosatrienoic acid, small amounts of 8,9-dihydroxy- and 5,6-dihydroxyeicosatrienoic acid could be detected by mass fragmentography. Renal as wall as hepatic monooxygenases can thus epoxidize each of the four double bonds of arachidonic acid. In contrast, rabbit lung microsomes and NADPH metabolized arachidonic acid mainly to prostaglandins and 19-hydroxy- and 20-hydroxyarachidonic acid, while only small amounts of 11,12-dihydroxyeicosatrienoic acid could be found. Monooxygenase metabolism of arachidonic acid by epoxidation might therefore be a significant pathway for the metabolism of this essential fatty acid in isolated rat renal cells and hepatocytes but presumably not in the lung.