PHARMACOLOGICAL EFFECTS OF SELECTED FLAVONOIDS ON RAT ISOLATED ILEUM - STRUCTURE-ACTIVITY RELATIONSHIP

1. Eleven selected flavonoids were studied to evaluate their effects o n the rat isolated ileum and to determine their structure-activity rel ationships. 2. The flavonoids rutin and 3',5,7-trihydroxy-4' methoxyfl avone-7-rutinoside, which have a sugar moiety (O-rha-glu), had no sign ificant effect on the ileum, indicating that the presence of sugar sub stitution reduces the biological activity of the flavonoids. 3. Nine o ther flavonoids caused inhibition of tonic and phasic contractions of the ileum with the following order of potency from highest to lowest: galangin, quercetin, chrysin, xanthomicrol, flavone, naringenin, fiset in, morin, and flavanone. 4. Flavones were more potent than flavanones , indicating that the double bond at carbon 2-3 increases the potency of the flavonoid. 5. Galangin, quercetin, chrysin, and xanthomicrol, w hich have hydroxyl substituents on carbon 3 and/or 5, showed higher po tency than flavone, indicating that such hydroxyl groups are essential for the activity. 6. Galangin was more potent than quercetin, morin, and fisetin, suggesting that the hydroxyl substituents on ring B atten uate the potency. 7. Quercetin caused more potent relaxation of the il eum than morin, suggesting that the presence of a hydroxyl group at C- 2' of ring B attenuates the myolytic activity. (C) 1997 Elsevier Scien ce Inc.