Daidzein is absorbed by passive transport in isolated small intestine of rats

The intestinal absorption of isoflavones is an essential prerequisite for assuring biologic effects. The purpose of this study was to investigate the intestinal transport, metabolism, and tissue uptake of daidzein. To this aim, 3 different tracts of small intestine of rats (proximal, medial, and distal) were isolated, everted, and exposed to physiologic concentrations (mucosal side) of daidzein (25, 50, and 80 μmol/L); perfusion experiments were performed for 60 minutes. Concentrations of total daidzein (at 30, 45, and 60 minutes) and glucuronide daidzein (at 60 minutes) were analyzed on aliquots of serosal solutions, whereas whole intestinal tracts were analyzed to determine daidzein tissue uptake (at 60 minutes). Results show linear relationships between the amounts of aglycone absorbed and taken up by tissue and mucosal daidzein concentrations; both amounts were higher in the distal tracts than in the other intestinal tracts (P < .05). The extrapolated total daidzein intestinal absorption was about 6% and total tissue uptake was about 10%. The amounts of conjugate daidzein correspond on average to about 6% of the levels absorbed; results suggest an inverse correlation between conjugation activity and mucosal daidzein concentration. In conclusion, our study suggests that a passive, unsaturable transport is the only mechanism of daidzein absorption in the small intestine of rats, at least within the concentrations tested. Different daidzein permeability of rat intestinal tracts was also demonstrated.