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

Biochem Pharmacol. 1983 May 15;32(10):1573-80. doi: 10.1016/0006-2952(83)90330-1.

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

  • Animals
  • Benzoflavones / pharmacology*
  • Chromatography, High Pressure Liquid
  • Coumarins / metabolism*
  • Cytochrome P-450 Enzyme System / metabolism
  • Flavonoids / pharmacology*
  • Humans
  • Intestinal Mucosa / drug effects
  • Intestinal Mucosa / metabolism*
  • Kinetics
  • Male
  • Methylcholanthrene / pharmacology*
  • Mice
  • Microsomes / drug effects
  • Microsomes / metabolism*
  • Phenacetin / metabolism*
  • Rats
  • Rats, Inbred Strains

Substances

  • Benzoflavones
  • Coumarins
  • Flavonoids
  • 7-ethoxycoumarin
  • Methylcholanthrene
  • alpha-naphthoflavone
  • Cytochrome P-450 Enzyme System
  • Phenacetin