We compared levels of (+)-catechin, (-)-epicatechin, and their metabolites in rat plasma and urine after oral administration. Rats were divided into four groups and given (+)-catechin (CA group), (-)-epicatechin (EC group), a mixture of the two (MIX group) or deionized water. Blood samples were collected before administration and at designated time intervals thereafter. Urine samples were collected 0-24 h postadministration. (+)-Catechin, (-)-epicatechin and their metabolites in plasma and urine were analyzed by HPLC-mass spectrometry after treatment with β-glucuronidase and/or sulfatase. After administration, absorbed (+)-catechin and (-)-epicatechin were mainly present in plasma as metabolites, such as nonmethylated or 3′-O-methylated conjugates. In the CA and MIX groups, the primary metabolite of (+)-catechin in plasma was glucuronide in the nonmethylated form. In the EC and MIX groups, in contrast, the primary metabolites of (-)-epicatechin in plasma were glucuronide and sulfoglucuronide in nonmethylated forms, and sulfate in the 3′-O-methylated forms. Urinary excretion of the total amount of (-)-epicatechin metabolites in the EC group was significantly higher than the amount of (+)-catechin metabolites in the CA group. The sum of (+)-catechin metabolites in the urine was significantly lower in the MIX group than in the CA group, and the sum of (-)-epicatechin metabolites in the MIX group was also significantly lower than in the EC group. These results suggest that the bioavailability of (-)-epicatechin is higher than that of (+)-catechin in rats, and that, in combination, (+)-catechin and (-)-epicatechin might be absorbed competitively in the gastrointestinal tract of rats.
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