Barbaloin
Barbaloin is an anthraglycoside, and is the glucoside of aloe emodin. Like aloe emodin, barbaloin is cathartic; however, unlike aloe emodin which acts by irritating the intestines, barbaloin is absorbed into the bloodstream and stimulates the appropriate nerves near the bowels to cause the cathartic action.
References
Leung, Albert Y. 1980. Encyclopedia of Common Natural Ingredient used in Food, Drugs and Cosmetics. John Wiley and Sons, N Y. 409 pp.
Weiner, Michael and A. Janet Weiner. 1980. Weiner's Herbal The Guide to Herb Medicine. Stein and Day, New York. 224 pp.