OBJECTIVE Senna and rhubarb are classified as stimulative laxatives, and known to have similar effec?tive constituents, the anthraquinones. Being protected by theβ-glucoside bond, the anthraquinones can reach the intes?tines where they are degraded into complex metabolites by enzymes secreted from the intestinal microbiome. It is these complex metabolites that produce the laxative effects. Then the similarities and differences of action between the anthra?quinones require further elucidation. METHODS Here, we studied metabolites of senna anthraquinones (SAQ), rhubarb anthraquinones (RAQ) and their chemical marker, sennoside A (SA), in a rat diarrhea model. In the in vitro biotransfor?mation experiments, SAQ, RAQ and SA were incubated with rat fecal flora solution and the metabolites produced were analyzed using HPLC. In the in vivo studies, the same compounds were investigated for purgation induction, with mea?surement of histopathology and multiple aquaporins (Aqps) gene expression in six organs. RESULTS SAQ and RAQ had similar principal constituents but could be degraded into different metabolites. A similar profile of Aqps down-regula?tion for all compounds was seen in the colon, suggesting a similar mechanism of action for purgation. However, in the kidneys and livers of the diarrhea-rats, down-regulation of Aqps was found in the RAQ-rats whereas up-regulation of Aqps was seen in the SAQ-rats. Furthermore, the RAQ-rats showed lower aquaporin 2 (Aqp2) protein expression in the kidneys, whilst the SA-rats and SAQ-rats had higher Aqp2 protein expression in the kidneys. This may have implications for side effects of SAQ or RAQ in patients with chronic kidney or liver diseases. CONCLUSION SAQ and RAQ showed similar laxative actions with a similar mechanism, they could display different actions in rat kidneys and livers. We suggest that the clinical usage of senna or rhubarb products should be clarified for patients having chronic kidney or liver diseases.