ABSTRACT
<p><b>AIM</b>To study the biliary excretion of genistein and its metabolite at different doses in rats.</p><p><b>METHODS</b>Suspended in 0.5% CMC-Na solution, genistein was orally administered to rats at the dose of 6.25, 12.5 and 50 mg x kg(-1), separately. At various time intervals, the bile was collected. The bile was treated with beta-glucuronidase. The genistein in bile was extracted twice by vortexing with 2.0 mL mixture of methyl tert-tubtyl ether and pentane (8:2). The organic phase was removed into the tubes and then evaporated in ventilation cabinet. The residue was dissolved in 50 microL of methanol. Twenty microL solution was drawn and detected by high-performance liquid chromatography.</p><p><b>RESULTS</b>The accumulative biliary excretion of genistein was (42.56 +/- 6.54) , (75.17 +/- 18.87) and (126.60 +/- 34.78) microg at the dose of 6.25, 12.5 and 50 mg x kg(-1), respectively. The total drug (genistein plus glucuronidated genistein) excreted from bile was (108.46 +/- 35.23), (423.46 +/- 158.31) and ( 853.74 +/- 320. 84) microg, and the ratio of glucuronidated genistein was 60.76% , 82.25% and 85.17% at the dose of 6.25, 12.5 and 50 mg x kg(-1), respectively.</p><p><b>CONCLUSION</b>The genistein was excreted mainly in the form of glucuronidated genistein in rat bile. The genistein and glucuronidated genistein were excreted in a nonlinear dose-dependent manner.</p>