Objective To investigate the effects of total anthraquinone in rheum on aquaporin 2 and aquaporin 4 expression in rat kidney and explore its diuresis mechanism.Methods Thirty-two SD rats were randomly divided into control group,low dose group,medium dose group and high dose group.Total anthraquinone in rheum was administered to rats at different doses.Urinary volume of 24 h,Na+ concentration and osmolality were detected.Rats were sacrificed 5 days later.Blood samples were taken from the abdominal aorta to detect blood biochemical indicators. Kidneys of rats were removed to detect AQP2, AQP4 expression through immunohistochemistry,Western blot,and RT-PCR. Results Compared with control group,there were significantly increased 24 h urine output of rats in medium and high dose group[(16.21±1.96),(18.16±1.8) ml vs(13.85±1.25)ml,P＜0.05].24 h urine output in low-dose group did not change significantly.AQP2 protein and mRNA expression were significantly decreased in rats'kidneys of medium and high dose group (P＜0.01),The AQP4 protein and mRNA expression was significantly down-regulated in high dose group (P＜0.01).In medium does group,the AQP4 protein expression was down-regulated (P＜0.01),without significant decrease in the mRNA expression.Protein and mRNA expression of AQP2 and AQP4 did not significantly change in low dose group.Conclusion Total anthraquinone in rheum can reduce the expression level of AQP2 and AQP4 in rat kidney,which is probably one mechanism of diuresis caused by rheum.