Involvement of CYP3A‐derived arachidonic acid metabolite(s) in responses to endothelium‐derived K + channel opening substance in monkey lingual artery

In monkey lingual artery strips partially contracted with prostaglandin F 2α , acetylcholine‐induced, concentration‐related relaxations were abolished by removal of the endothelium. The response was not significantly influenced by indomethacin but attenuated by N G ‐nitro‐ L ‐arginine ( L ‐NOARG); the effect of the nitric oxide (NO) synthase inhibitor was reversed by L ‐arginine. The response to acetylcholine resistant to L ‐NOARG was suppressed in the strips exposed to high K + media. Charybdotoxin partially inhibited the relaxation, and the remaining relaxation was abolished by additional treatment with apamin, whereas glibenclamide, iberiotoxin or apamin alone was without effect. Relaxations induced by sodium nitroprusside were not influenced by charybdotoxin. The L ‐NOARG‐resistant acetylcholine‐induced relaxation was inhibited by metyrapone, proadifen and 17‐octadecynoic acid, non‐selective cytochrome P450 mono‐oxygenase (CYP) inhibitors, and progesterone and ketoconazole, inhibitors selective to CYP3A. The inhibitors did not affect the nitroprusside‐induced relaxation. Selective inhibitors of other CYP isoforms, such as debrisoquine and lauric acid, did not reduce the response to acetylcholine. Reaction mixture containing human liver microsome rich in CYPs, arachidonic acid and NADPH incubated at 37°C and filtrated relaxed endothelium‐denuded monkey lingual artery strips, used as bioassay tissues. This response was abolished in the strips exposed to high K + media. The response was also suppressed by combined treatment of the assay tissue with charybdotoxin plus apamin, but was not affected by treatment with iberiotoxin. The reaction mixture co‐incubated with ketoconazole failed to relax the strips. It is concluded that the monkey lingual arterial relaxation dependent on the endothelium is mediated by NO and also by a charybdotoxin plus apamin‐sensitive but iberiotoxin‐insensitive Ca 2+ ‐activated K + channel opening substance(s) that may be a CYP3A‐derived arachidonic acid metabolite(s).British Journal of Pharmacology (1999) 128 , 802–808; doi: 10.1038/sj.bjp.0702843