Comparison of the effects of feeding quercetin or flavone on hepatic and intestinal drug-metabolizing enzymes of the rat

The influence of dietary flavone and quercetin on the components of the drug metabolizing enzyme system was examined in the liver and small intestine of the rat. Quercetin given at a concentration of 1% in the diet for 14 days produced no significant changes on phase I or phase II enzyme activities. In contrast, 0.25% flavone caused significant increases in relative liver weight, microsomal and cytoplasmic proteins, and cytochrome P-450 content. The activities of hepatic ethoxyresorufin, pentoxyresorufin and ethoxycoumarin deethylases were significantly increased (by 20, 30 and 2.5-fold, respectively) over control levels. Hepatic UDP-glucuronyl transferase and glutathione transferase activities were increased 3–4-fold. In contrast, flavone induced no changes in these two intestinal enzyme activities. It is concluded that flavone produces an induction that shows both phenobarbital- and methylcholanthrene-type characteristics and that its effect on conjugating enzymes is tissue specific.