中文摘要：

目的研究甘草次酸18位差向异构体即18α-甘草次酸、18β-甘草次酸对Caco-2细胞上β-糖蛋白功能和表达的影响，方法建立Caco-2细胞模型，采用罗丹明-123摄取法评价β-糖蛋白的功能；使用荧光定量PCR检测MDRlmRNA；Western blot分析Caco-2细胞膜上β-糖蛋白的表达。结果中、高浓度（1，10μmol·L^-1）的18α-甘草次酸和高浓度（10μmol·L^-1）的18β-甘草次酸使细胞内罗丹明-123摄取减少。高浓度（10μmol·L^-1）的18α-甘草次酸在转录水平上调MDRImRNA的表达；实验浓度的18β-甘草次酸未影响MDRImRNA的表达；高浓度（10μmol·L^-1）18α-甘草次酸对P-糖蛋白有诱导作用，实验浓度的18β-甘草次酸没有影响β-糖蛋白表达，结论18β-甘草次酸对P-糖蛋白功能和表达的影响均表现为诱导作用，而18β-甘草次酸只对P-糖蛋白功能表现出一定的诱导作用。

英文摘要：

OBJECTIVE The aim of our work wasto study the effects of C-18 epimers of glycyrrhetinic acid, 18α-glycyrrbetinie acid （α-GA） and 18/3-glycyrrhetinic acid （β-GA） on the function and expression of P-gp in Caco-2 cell monolayers. METHODS Caco-2 cells were cultured, the effects of P-gp tunction were analyzed by means of rhodamine accumulation test, real-time PCR was used to measure the expression of MDRi mRNA and wesfern blot was used to analysis P-gp expression in Caco-2 cell. RESULTS In the rhodamine accumulation test, middle and high concentrations （1 and 10 μmol·L^-1） α-GA and high concentration （ 10 μmol·L^-1 ） β-GA decreased the cellular rhodamine concentration. At high concentrations （ 10μmol·L^-1）, α-GA up-regulated the expres- sion of MDR1 mRNA while 19-GA has no effect on the expression of MDR1 mRNA at three test concentrations, α-GA up-regulated the expression of P-gp protein at high concentrations （10 μmol·L^-1） while ,8-GA has no effect on the expression of P-gp protein at three test concentrations. CONCLUSION Our findings provide experimental evidence that α-GA up-regulated both function and expression of P-gp while β-GA only up-regulate the function of P-gp.