Absorption, distribution, and secretion of epicatechin and quercetin in the rat

Flavanols and flavonols are thought to be the most important monomeric flavonoids in the human diet. In this study, we compared the apparent absorption, blood concentrations, tissue distribution, and excretion of the flavanol epicatechin and flavonol quercetin, including all metabolites thereof, in the rat. For this, ileostomized rats and rats equipped with a permanent cannula in the portal vein were administered either 3H-labeled epicatechin or 14C-labeled quercetin through a tube in the esophagus. Digesta and blood plasma samples were collected at various time points from the ileostomy and cannula, respectively, and analyzed for radioactivity. In addition, 24-hour feces and urine samples were collected and analyzed for radioactive content. Finally, at the termination of the study, tissue samples from various parts of the body were taken to determine the amount of accumulated radioactive label. Maximum plasma concentrations and time to maximum were similar for epicatechin and quercetin equivalents. Radioactivity from epicatechin was rapidly cleared from the circulation, but increased again from 6 hours after administration onward. The amount of radioactivity reaching the end of the ileum during 3 to 7 hours after ingestion, which presents in the different gastrointestinal segments at 24 hours after ingestion, as well as the amount of radioactivity excreted in feces during 24 hours after ingestion, was similar for epicatechin and quercetin. The 24-hour urinary excretion showed that more radioactivity from epicatechin is excreted during the first 12 hours after ingestion than from quercetin. Epicatechin and quercetin had not accumulated in tested organs and tissues at 24 hours after ingestion, except for the gastrointestinal segments. In conclusion, tissue accumulation in 24 hours and fecal secretion rates of epicatechin and quercetin appeared to be similar, but differences were observed with respect to the urinary excretion of these flavonoids and their metabolites.