title: Kinetics of in vitro O-deethylation of phenacetin and 7-ethoxycoumarin by rat intestinal mucosal cells and microsomes. The effect of induction with 3-methylcholanthrene and inhibition with alpha-naphthoflavone.
abstract: A novel, sensitive (0.5 ng) assay for acetaminophen, using HPLC with selective electro-chemical detection, enabled us to study rat small intestinal O-deethylation of phenacetin and compare it with corresponding 7-ethoxycoumarin-O-deethylation. Two in vitro systems, i.e. isolated intestinal mucosal cells and microsomal fractions thereof, were used to study kinetics for the O-deethylation of both substrates. Kapp m- and Vmax-values are similar for 7-ethoxycoumarin- and phenacetin-O-deethylation. Apparent Km-values varied between 50 and 70 microM in control rats and decreased after 3-methylcholanthrene pretreatment to 20-45 microM. Vmax-values were increased by 3-methylcholanthrene pretreatment. O-Deethylation was inhibited equally in cells and microsomes by alpha-naphthoflavone, but is inhibited more markedly in intestinal preparations after pretreatment with 3-methylcholanthrene. It is suggested that 7-ethoxycoumarin and phenacetin are O-deethylated by different forms of cytochrome P-450 with almost identical Kapp m and that these enzymes have a different distribution along the villus.
mesh_terms: D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D003374:Coumarins / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology*; D051379:Mice; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D010615:Phenacetin / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001571:Benzoflavones; D003374:Coumarins; D005419:Flavonoids; C017299:7-ethoxycoumarin; D008748:Methylcholanthrene; C011512:alpha-naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D010615:Phenacetin