Flavonoids as antagonists at A1 adenosine receptors

This study aimed to investigate the potential for flavonoid action at A(1) adenosine receptors in vitro. In a radioligand binding assay for A(1) adenosine receptor occupancy in particulate preparations from guinea-pig cerebral cortex, Havonoids competed in concentration-dependent manners with Hill slopes typically not different from unity. Of the flavonoids tested, quercetin showed highest affinity (pK(i) value of 5.33). At a concentration of 28 mu m, quercetin evoked a rightward shift in the N-6-cyclopentyladenosine-induced inhibition of electrically evoked contractions of the guinea-pig isolated ileum, allowing the calculation of a pK(i) value of 4.71. These data suggest, therefore, that flavonoids represent an additional dietary source of A(1) adenosine receptor antagonists (beyond the methylxanthines, caffeine and theophylline). Copyright (c) 2006 John Wiley & Sons, Ltd.