Tissue distribution of quercetin in pigs after long-term dietary supplementation.

Although the flavonol quercetin is intensively investigated, our knowledge about its bioavailability and possible target organs is far from being complete. The aim of this study was to check the potential of quercetin to accumulate in various tissues after long-term dietary treatment compared with a single treatment with flavonol. Pigs ingested either a single dose of quercetin aglycone (25 mg/kg body weight; Expt. 1) or received the flavonol twice a day at the same dose mixed into their regular meals (i.e 50 mg.kg(-1).d(-1)) for 4 wk (Expt. 2). In both experiments, we took plasma and tissue samples 90 min after the final meal and analyzed them using HPLC. Additionally, the specific activity of the enzyme beta-glucuronidase was measured in selected tissues. Higher flavonol concentrations than in plasma were found in only the liver (Expt. 1) or the intestinal wall and kidneys (Expt. 2). All tissues except blood plasma contained a variable amount of deconjugated quercetin in the range of 30-100% of total flavonols. However, the specific beta-glucuronidase activity was not correlated with the proportions of deconjugated flavonols in the various tissues. Long-term dietary intake of the flavonol did not lead to a greater accumulation in any tissue compared with the single treatment. Flavonol concentrations only exceeded the plasma concentration within organs involved in its metabolism and excretion, including liver, small intestine, and kidneys.