Daidzein (4',7-dihydroxylisoflavone), a water-insoluble isoflavone, is mainly present in leguminous plants. This study was aimed at investigating the absorption characteristics of daidzein across the intestinal membranes. Borneol has been used to enhance the intestinal absorption and bioavailability of daidzein. We chose an in vitro diffusion chamber system using isolated rat intestinal membranes as a model. A sensitive, accurate and reliable LC method was developed and validated to determine daidzein in rat plasma. A linear relationship for daidzein was found in the range of 20–800 ng mL-1. The mean absolute recoveries of daidzein determined over three concentrations were 89.8 ± 4.8, 91.3 ± 2.8 and 95.4 ± 1.7%. The coefficients of variation for inter-day and intra-day assay were found to be less than 6.1%. The plasma concentration of daidzin following oral administration was significantly increased by coadministration of borneol in rats, and a 1.5-fold enhancement of relative bioavailability of daidzein was observed as compared to daidzein administered alone.
