Until recently the purgative activity of Rhizoma Rhei was attributed to oxyanthraquinones. However, recent research has identified sennosides A-F as being responsible constituents, and experiments on mice have added confirmation. Sennoside A is metabolized by intestinal bacteria, where it is transformed into rhein anthrone, and produces a purgative action.

The anthraquinones aloe emodin, emodin and rhein were found to inhibit in vitro the growth of Bacillus subtilis and Staphylococcus aureus, with rhein being the most effective compound.

The antimicrobial activity of rhein was also observed against Escherichia coli, Micrococcus luteus,Candida albicans, Clostridium perfringens, Fusobacterium varium and Bacteriodes fragilis, a major anaerobic microorganism in human intestinal flora.

The antibacterial activity of the anthraquinone derivatives appears to result from inhibition of the mitochondrial respiratory chain of microorganisms.

It was shown in experiments with isolated rat intestines that emodin had a strong antispasmodic action (four times stronger than papaverine) against acetylcholine induced spasm.

In Chinam the historical medical classics report the use of Rhizoma Rhei for peptic ulcers since ancient times. Chinese studies in 1966 found rhein and emodin to be effective for treating black tumor in white mice, emodin for mammary cancer in white mice and rhein for Ehrich's ascitic carcinoma. Several components of Rhizoma Rhei are under further investigation for antitumor properties.

In 1981, lindleyin was isolated from Rhizoma Rhei and shown to have the same degree of analgesic activities as aspirin and phenylbutazone, according to the Siegmund & Randall-Sellito test. It also showed the same degree of activity as aspirin in regard to anti-inflammative action and anti-arthritic action. However no antipyretic action was found.

Significant hemostatic action was exhibited by R.Rhei in both external and internal bleeding. The herb shortened the coagulation time, reduced capillary permeability and improved capillary fragility. It also promoted platelet formation by the bone marrow and induced proliferation of blood capillaries. Thus it has a facilitory effect on blood coagulation.

In addition to tannins and calcium, another important hemostatic component is chrysophanol. Chrysophanol has been used to treat menorrhagia, bleeding following therapeutic abortion, epistaxis, functional uterine bleeding and thrombocytopenia.

A study on the correlation between chemical constituents and therapeutic effects of Rheum species showed that rhenin and sennosides in R. palmatum appeared to be responsible for purgative activity. Sennoside content correlated highly with laxative activity, whereas the correlation between anthraquinone content and laxative activity was rather low. Studies on the oxidized products of sennosides suggested that sennosides act predominantly on large intestine motility after their degradation by colonic microorganisms.

In addition to laxative and antimicrobial activities it has been observed that oral administration of emodin and rhein provoked marked diuretic, naturiuretic and kaliuretic effects in rabbits.

The hemostatic activity of R. palmatum has also been demonstrated in traditional Chinese medicine experimentally and clinically.

R. palmatum was also found to be effective in treatment and prevention of experimental gastric bleeding and ulcer formation in rats.

Significant therapeutic effects of the powdered rhizome of R. palmatum were also reported in the treatment of clinical gastrointestinal bleeding.

It was reported that the anthraquinone derivatives rhein, emodin and aloe emodin had an in vivo inhibitory effect toward P388 leukaemia in mice. The survival time of the animals tested was markedly increased and the ascites volume and tumor cell number were decreased.

Except those noted, all references come from Weng Weiliang, et al., Clinical Chinese materia medica, Henan Science & Technology Press, 1998