CHARACTERIZATION OF CYTOCHROME P-450-DEPENDENT ARACHIDONIC-ACID METABOLISM IN RABBIT INTESTINE

We characterized cytochrome P-450-dependent arachidonate (P-450 AA) me tabolism throughout the intestinal tract, since some metabolites deriv ed via this pathway modify epithelial ion transport and regional blood flow. Microsomes (0.3 mg/ml) were prepared from each region of the in testines of anesthetized New-Zealand White male rabbits and incubated with [C-14]AA (7 muM) for 30 min at 37-degrees-C. In the presence of N ADPH (1 mM) ileal microsomes exhibited the greatest P-450-AA metabolis m, whereas duodenal microsomes exhibited little or no activity. For je junal, ileal, and cecal microsomes, AA metabolism was reduced in the a bsence of NADPH and by boiling microsomes, was unaffected by indometha cin (10 muM) and BW-755C (50 muM), but was significantly attenuated by the P-450 enzyme inhibitors, 7-ethoxyresorufin (1 muM) and SKF-525A ( 100 muM). However, colonic (ascending, transverse, and descending) mic rosomal activity was inhibited by both P-450 and lipoxygenase inhibito rs. Analysis of ileal AA metabolites by high-pressure liquid chromatog raphy and negative ion chemical ionization gas chromatography-mass spe ctrometry revealed products corresponding to monohydroxyeicosatetraeno ic acids (HETEs). Semiquantitative analysis showed that 20-, 19-, 18-, 17-, and 16-HETEs were present in a ratio of 6.2:3.3:0.3:0.1:0.1, res pectively. Furthermore, ileal P-450-HETEs dilated the isolated perfuse d mesenteric bed, as did 20-HETE, the predominant ileal AA metabolite. Because 20-HETE was also shown to affect epithelial ion transport, we suggest that P-450-AA metabolites may make important contributions to intestinal function.