Dealkylation of pentoxyresorufin: a rapid and sensitive assay for measuring induction of cytochrome(s) P-450 by phenobarbital and other xenobiotics in the rat

Arch Biochem Biophys. 1985 Apr;238(1):43-8. doi: 10.1016/0003-9861(85)90138-9.


The O-dealkylation of pentoxyresorufin (7-pentoxyphenoxazone) by rat liver microsomes was examined. The reaction appeared highly specific for certain phenobarbital inducible forms of cytochrome P-450 and was increased 95- to 140-fold by animal pretreatment with phenobarbital (75 mg/kg/day, four ip injections) and approximately 50-fold by Aroclor 1254 (500 mg/kg, one ip injection) while animal pretreatment with 3-methylcholanthrene (50 mg/kg/day, three ip injections) resulted in less than a 2-fold increase over the rate detected in control microsomes. It was observed that this activity, in microsomes for Aroclor-pretreated rats, was dependent on O2 and was inhibited by metyrapone and SKF 525-A, indicative of cytochrome(s) P-450 mediation in the reaction. When antibodies directed against purified cytochrome(s) P-450s were employed to inhibit the pentoxyresorufin O-dealkylation reaction, antibodies to P-450PB-B greatly inhibited the reaction (greater than 90%), while antibodies to P-450PB-C or P-450PB/PCN-E had minimal effects. Assay of hepatic microsomes from rats which were pretreated with varying doses of phenobarbital (0.9-75 mg/kg/day, four ip injections) indicated that while aminopyrine-N-demethylase activity was induced only 2-fold at the maximum dose (75 mg/kg/day), pentoxyresorufin O-dealkylase activity was induced approximately 140-fold at this dose and approximately 4-fold by a dose of phenobarbital as low as 0.9 mg/kg.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aminopyrine N-Demethylase / biosynthesis
  • Animals
  • Aroclors / pharmacology
  • Chlorodiphenyl (54% Chlorine)
  • Cytochrome P-450 CYP1A1
  • Cytochrome P-450 CYP2B1
  • Cytochrome P-450 Enzyme System / biosynthesis*
  • Dealkylation
  • Enzyme Induction / drug effects
  • Male
  • Methylcholanthrene / pharmacology
  • Microsomes, Liver / enzymology*
  • Oxazines / metabolism*
  • Oxidoreductases / biosynthesis
  • Oxidoreductases, N-Demethylating / biosynthesis
  • Phenobarbital / pharmacology*
  • Rats
  • Substrate Specificity


  • Aroclors
  • Oxazines
  • Chlorodiphenyl (54% Chlorine)
  • Methylcholanthrene
  • pentoxyresorufin
  • Cytochrome P-450 Enzyme System
  • Oxidoreductases
  • Cytochrome P-450 CYP1A1
  • Cytochrome P-450 CYP2B1
  • Oxidoreductases, N-Demethylating
  • Aminopyrine N-Demethylase
  • dimethylaminoantipyrine N-demethylase
  • Phenobarbital