Flavonols are dietary compounds widely distributed in plants and characterized by a 2-phenyl-benzo(alpha)pyrane nucleus possessing hydroxyl and ketone groups at positions 3 and 4, respectively. Kaempferol, quercetin, and myricetin are flavonols that are further mono-, di-, or trihydroxylated on the phenyl ring, respectively. To test whether these ingested flavonols might exert a direct secretory effect on intestinal epithelial cells, monolayers of the T84 colonocyte cell line were mounted in Ussing chambers and examined for ion transport response. Twenty minutes after addition of 100 microM quercetin to either the serosal or mucosal side, the short-circuit current change was maximal at 16.6 microA/cm2. Kaempferol was less potent than quercetin, while myricetin and glycosylated quercetin (rutin) did not induce secretion. The secretion induced by quercetin did not seem to be mediated by the reactive oxygen species generated by quercetin through auto-oxidation and/or redox cycling (superoxide, hydrogen peroxide, and the hydroxyl radical) because it was neither enhanced by iron, nor inhibited by desferroxamine B or catalase (alone or in combination with superoxide dismutase). Like vasoactive intestinal peptide, quercetin induced a secretory response that was inhibited by barium chloride and bumetanide, and which exhibited synergism with carbachol. Quercetin also stimulated a modest increase in intracellular cAMP levels and the phosphorylation of endogenous protein substrates for cAMP-dependent protein kinase. Thus, quercetin is a potent stimulus of colonocyte secretion that resembles secretagogues which act via a cAMP-mediated signaling pathway.