Comparison of the intestinal absorption of quercetin, phloretin and their glucosides in rats

Absorption and metabolism of quercetin and isoquercitrin (quercetin 3-O-glu cose) were investigated in rats after in situ perfusion of jejunum plus ile um (15 nmol/min) for 30 min and compared with those of phloretin and phlori dzin (phloretin 2'-O-glucose). After perfusion of the glucosides, the corre sponding aglycone forms and conjugated derivatives appeared in the lumen. T he conjugated metabolites were similar to those recovered after intestinal perfusion of the aglycone forms. Regardless of the aglycone or glucoside pe rfused, only conjugated forms were present in the mesenteric vein blood dra ining the perfused segment showing the importance of intestinal conjugation . The hydrolysis of glucosides was a prerequisite step before their conjuga tion by intestinal enzymes and their transport towards the mucosal and sero sal sides. In contrast to phloridzin, lactase phloridzin hydrolase activity did not seem to be an essential pathway for isoquercitrin hydrolysis. The 3-O-glucosylation of quercetin improved the net absorption of the aglycone (P < 0.05), whereas phloretin absorption decreased when present as 2'-O-glu coside (P < 0.05). Whatever the perfused compound, the efficiency of the ab sorption seemed to be linked to the intestinal conjugation process and to t he luminal secretion of metabolites.