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1. Pallidifloside D, a saponin glycoside constituent from the total saponins of Smilax riparia, had been proved to be very effective in hyperuricemic control. But it is poorly bioavailable after oral administration. Here, we determined the role of P-glycoprotein (P-gp) in the intestinal absorption of Pallidifloside D. 2. We found that Pallidifloside D significantly stimulated P-gp ATPase activity in vitro ATPase assay with a small EC value of 0.46 μM. 3. In the single-pass perfused mouse intestine model, the absorption of Pallidifloside D was not favored in the small intestine (duodenum, jejunum and ileum) with a P* value of 0.35-0.78. By contrast, this compound was well-absorbed in the colon with a P* value of 1.23. The P-gp inhibitors cyclosporine significantly enhanced Pallidifloside D absorption in all four intestinal segments (duodenum, jejunum, ileum and colon) and the fold change ranged from 5.5 to 15.3. Pharmacokinetic study revealed that cyclosporine increased the systemic exposure of Pallidifloside D by a 2.5-fold after oral administration. 4. These results suggest that P-gp-mediated efflux is a limiting factor for intestinal absorption of Pallidifloside D in mice.

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