Comparison of the effects of various flavonoids on ethoxycoumarin deethylase activity of rat intestinal and hepatic microsomes.

Fifteen flavonoids were examined for their effects on the activity of 7-ethoxycoumarin O-deethylase in rat hepatic and intestinal microsomes. The effect depended on both the chemical structure of the flavonoid and the origin of the microsomes. Polyhydroxylated flavonoids with a C2-C3 double bond (flavones and flavonols) were more effective inhibitors of the enzyme in both hepatic and intestinal microsomes than were the reduced homologues (flavanonols, flavanones and flavan-3-ols). In contrast, flavones lacking hydroxyl substituents (e.g. 5,6-benzoflavone, 7,8-benzoflavone and flavone) increased ethoxycoumarin deethylase activity in liver microsomes although they had an inhibitory effect in intestinal microsomes.