Objective. Anthraquinones are bioactive constiuents which mainly present as glycosides in rhubarb. Most of flavonoid glycosides are usually absorbed only after being hydrolyzed to their corresponding aglycones by enterobacterial enzymes. In the present study, we investigated the presystemic metabolism of four anthraquinones, aloe-emodin, rhein, emodin, and chrysophanol as well as their glycosides in rhubarb decoction and in rat feces. Methods. Anthraquinone aglycones and their glycosides in rhubarb decoction and rat feces suspension were determined by HPLC methods developed in this study. The presystemic metabolisms of these anthraquinones by enteral microflora were investigated by separately incubating rhubarb decoction and anthraquinone aglycones with rat feces suspension under anaerobic conditions. Results. The contents of four anthraquinone aglycones in rhubarb decoction were significantly increased immediately after mixing with feces suspension indicating the hydrolysis of their glycosides by the enterobacteria. The order for the increment of each aglycone was opposed to that of aglycone contents in the original decoction. Thereafter, the rapid decrease of all anthraquinones demonstrated the extensive degradation by the enterobacteria. Conclusions. The presystemic metabolism would reflect the oral absorption of anthraquinones of Rhubarb. More concern should be paid on the intestinal transformation of anthraquinones in the clinical therapy except their contents in Rhubarb and herbs containing them.?
