Investigation of the absorption mechanisms of baicalin and baicalein in rats.

To characterize and compare the absorption mechanisms of baicalin (BG) and baicalein (B), either of them was perfused in situ in rats with ligation of the bile duct as well as without it. Two RP-HPLC methods were developed to determine the drugs' concentrations in the gastric and intestinal perfusates, respectively. The result showed that BG was moderately absorbed in stomach but poorly in small intestine and colon, while B was well absorbed in stomach and small intestine but relatively less in colon. It also indicated that bile could excrete BG and significantly promote the absorption of B. When BG or B was perfused alone in the small intestine after ligation of the bile duct, there came out to be increasing B or BG in the perfusate, respectively. In addition, when B was intravenously administered to rats after ligation of the bile duct, there came out to be BG in the intestinal perfusate. In conclusion, B was more suitable to be administered orally than BG, which was absorbed as B and then restored to BG in the body. Part of the BG formed from the absorbed or intravenously administered B could be excreted back into the gut.