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Biochem Pharmacol. 1983 May 15;32(10):1573-80.

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.

PMID:
6860345
DOI:
10.1016/0006-2952(83)90330-1
[Indexed for MEDLINE]

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