Bioavailability of dietary doses of 3H-labelled tea antioxidants (+)-catechin and (-)-epicatechin in rat

1. The bioavailability and pharmacokinetic characteristics of the tea antioxidants (+)-catechin and (-)-epicatechin were investigated in the rat following intake of dietary doses. 2. To achieve this objective, tritiated derivatives (tritium was incorporated at the 3-position of the heterocyclic ring) of these compounds were administered to rats orally and intravenously at dose levels equivalent to human dietary levels of intake. 3. Following intravenous administration of both compounds, about one-third of the dose was excreted in the urine and two-thirds in the faeces, indicating extensive biliary excretion. When the same doses were administered orally, only about 5% of the dose of each compound was recovered in the urine. 4. Comparison of the areas under the curve following oral and intravenous administration revealed that the bioavailability of both compounds was less than 5%. 5. Exchange of tritium with water in the blood occurred 3 h after oral, but not after intravenous, administration of the flavanols to rat. This is believed to represent microbial degradation of the compounds by the gut flora. 6. It was established that the bioavailability of the tea antioxidants (+)-catechin and (-)-epicatechin in the rat following intake of dietary doses was poor.