RHUBARB (Da Huang) Rheum palmatum
By Will Maclean and Peter Townsend
Rhubarb
(RH) is the dry root and root stock of Rheum palmatum L., Rheum tanguticum Maxim.
ex Balf. or Rheum officinale Baill. of the family Polygonaceae. The most commonly
used species is R. palmatum. Rhubarb root is one of the oldest and best-known
Chinese herbal medicines, first appearing in the Divine Husbandman's Classic of
the Materia Medica (Shen Nong Ben Cao Jing) of the latter Han dynasty.
Indications
Rhubarb
is used as a laxative, antiphlogistic, and haemostatic in the treatment of constipation,
diarrhea, jaundice, gastro-intestinal hemorrhage, menstrual disorders, conjunctivitis,
traumatic injuries, superficial suppurative sores and ulcers. It is also applied
externally for thermal burns. In TCM terms it Drains Heat and accumulations from
the Yangming level, Clears Damp Heat, Cools the Blood, Invigorates Blood, eliminates
Stagnant Blood, Clears Toxic Heat, and purges knotted Heat and stool from the
colon. In order to understand the use of "purges" in TCM it is important
to understand the concepts and principles of purgation as applied in herbal practice.
The 3 main types of purging are as follows:
1. Cold purge (heat clearing):
for symptoms such as constipation due to inflammation and paralysis of the colon
- i.e. knotted Heat.
2. Warm purge (inner warming): for acute circulatory
disturbance of the digestive tract due to consumption of cold food and drink,
and cold environment - i.e. cold accumulation or Yang deficient constipation.
3. Moistening purge (moisten dry intestine): for constipation due to dehydration
or poor nutrition resulting in dryness of the intestine (insufficient colonic
membrane secretions) - i.e. dry intestine constipation.
4. Water expulsion:
for hydrothorax, ascites, and edema.
The following formulas are included in
this category:
" Minor Rhubarb Combination (cold purge) (xiao cheng qi
tang)
" Major Rhubarb Combination (add Mirabilitum to Minor Rhubarb Combination)
(da cheng qi tang)
" Coptis & Rhubarb Combination (cold purge) (san
huang xie xin tang)
" Persica & Rhubarb Combination (cold purge)
(tao he cheng qi tang)
" Cimicifuga Combination (cold purge - mild) (yi
zi tang)
" Apricot Seed & Linum Formula (moistening purge, ma zi
ren wan) Wen Pi Tang (warm purge)
Cautions for Using Purges
1. As purging
formulas (especially cold purge and water expelling formulas) can cause digestive
disorders, they should only be used for as long as it takes to achieve the desired
action.
2. Purges should not be used during pregnancy as they may cause spontaneous
abortion.
3. If there is a surface condition with mild interior excess, first
resolve the surface then purge if necessary. If both surface and interior symptoms
are of the same severity, resolve the surface and purge the interior simultaneously.
4. As purges are mainly used to expel interior excess, if there are also deficiencies
present, tonics should be added.
5. As many cases of constipation are simply
due to lack of exercise and improper diet, these factors should always be considered
before using purging formulas.
A Note on Purging
When purging is referred
to, most of us will equate it to treatment with laxatives in the normal western
sense of the word. However, in TCM purging is not simply used to move stool out
of the bowels. Following is a summary of the type of conditions for which purging
methods are designed:
1) Anti-inflammatory
The Cheng Qi Tang formulas (Minor
Rhubarb Combination [xiao cheng qi tang], Persica & Rhubarb Combination [tao
he cheng qi tang]) etc. were not originally designed for treating constipation.
Their original application was in febrile diseases where symptoms of high fever,
delirium and convulsions occurred. The purging action was used to reduce inflammation.
Other formulas, such as Major Bupleurum Combination (da chai hu tang), are useful
in treating cholecystitis, gastroenteritis and gastric/duodenal ulcers. Rhubarb
has been found to have an inhibitory action on anaerobic bacteria, candida albicans
and several other pathogenic microorganisms (see pharmacology). The effect of
Rhubarb on anaerobic bacteria is significant in the treatment of cholecystitis
and inflammatory conditions of the bile duct, as it has been found that these
bacteria are the main aggravating factor in these conditions - especially if accompanied
with constipation.
2) Expel toxic substances from the body
Toxic substances
in the colon are expelled by purging. It is also thought that metabolized blood
from internal hemorrhaging, bruising, and inflammation may become "toxic"
(as a result of hemoglobin metabolite overload), and have an adverse effect on
the organism, giving rise to "Blood stagnation". In these cases, Blood
moving and purging herbs are used together to expel the stagnant blood. The purging
method has also been known to be effective for certain types of neuralgia and
is widely employed following traumatic injury. Formulas such as Persica &
Rhubarb Combination (tao he cheng qi tang) are very useful in the acute stages
of hematoma, contusions, sprains etc.
3) Hemostatic
Purging formulas are
especially effective for upper body hemorrhage. As well as epistaxis, hemoptysis,
and bleeding of the gums, they have also been shown to be effective for cerebrovascular
accident. Many contemporary Chinese doctors use RH formulas, particularly Major
Rhubarb Combination (da chai hu tang), in order to swiftly eliminate the accumulated
Heat and Phlegm via the "big exit". There is clinical evidence from
a number of large-scale studies that this method of removing phlegm by enforcing
the downward movement of the digestive channels is effective on a large percentage
of acute stroke patients [34].
4) Cathartic
Since Rhubarb can also cause
constipation if used on its own over a long period of time, it is often used with
Mirabilitum. Licorice is also added to prevent cramps and protect the Spleen.
In cases of "dry" constipation, such as seen in infants, the elderly
and postpartum conditions, herbs which contain oily substances such as Linum (huo
ma ren), Dang Gui, Apricot Seed (xing ren), and Persica (tao ren) are used with
cathartic agents e.g. Apricot Seed & Linum Formula (ma zi ren wan).
5)
Expel Fluids
Certain herbs in this category have a very powerful cathartic
effect - that is they cause massive evacuation of fluids and water from body cavities
and the intestines in conditions such as hydrothorax, ascites, pulmonary edema,
etc. These herbs have very severe actions and many are toxic, therefore extreme
caution should be exercised when using them.
Main Constituents
The main
constituents of RH are a series of Anthraquinone derivatives: emodin, rhein, aloe-emodin,
chrysophanol, physcion, alizarin, citreorosein, etc; Dianthrones: sennoside A~F,
sennidin A, palmidin A-C, rheidin A-C etc; Other Glycosides: stilbene, naphthalene,
chromones, phenylbutanone etc; Tannins: lindleyin, rhatannin, catechin, epicatechin,
gallic acid, cinnamic acid etc.
Pharmacology
Antibacterial & Antiviral
action
The anthraquinones, aloe emodin, emodin and rhein were found to inhibit
in vitro growth of Bacillus subtilis and Staphylococcus aureus, with rhein being
the most effective [1]. Antimicrobial activity against Escherichia coli, Micrococcus
luteus, Candida albicans, Clostridium perfringens, Fusobacterium varium and Bacteriodes
fragilis was also noted [2, 3]. The antibacterial activity appears to be the result
of mitochondrial respiratory chain inhibition. Rhein, emodin and aloe emodin specifically
interfere with NADH dehydrogenase. The water extract has been found to have an
action against Herpes [33] and Influenza virus [34].
Hemostatic effect
Significant
hemostatic effect has been demonstrated in Rheum spp, both experimentally and
clinically. RH has been found effective in treatment and prevention of experimental
gastric bleeding and ulcer formation in rats [4], and in clinical gastro-intestinal
bleeding [5, 6, 7]. RH shortened coagulation time, reduced capillary permeability,
and improved capillary fragility. It also promoted platelet formation by the bone
marrow and induced proliferation of blood capillaries [8, 9].
Antineoplastic
effect
Emodin was found to be a strong inhibitor of respiration in Ehrlich
ascites carcinoma cells [10]. This was also observed in leukemia L1210 cells [11].
Emodin strongly inhibited the oxidation and dehydrogenation of some amino acids
and intermediate metabolites of glucose in Ehrlich ascites carcinoma cells. At
50mg/ml emodin inhibited the oxidation and dehydrogenation of lactic acid in these
cells by 87 & 91% respectively. It was further reported that the anthraquinone
derivatives rhein, emodin and aloe emodin had an in vivo inhibitory effect against
P388 leukemia in mice. Their survival time was markedly increased and the ascites
volume and tumor cell number were decreased [12]. In general, it is thought that
the antineoplastic activity of RH is mainly due to the inhibition of oxidation
and dehydrogenation of the cancer cells [13].
Purgative action
The purgative
activity of RH appears to be due to rhein and the sennoside components [14]. Sennoside
content correlated highly with laxative activity, whereas the correlation between
anthraquinone content and laxative activity was low [15]. Studies on the oxidized
products of sennosides suggest that the sennosides act predominantly on large
intestine motility after their degradation by colonic microorganisms [16]. The
mechanism appears to be hydrolysis of sennosides by microbial b-glycosidase in
a stepwise fashion to sennidins A & B, which are then reduced to rheinanthrone,
the laxative principle [17, 18]. The active principles of RH seem to act by stimulating
Auerbach's plexus or the submucosal nerve plexus [19]. Other investigators found
that RH increased the water content of the large intestine, producing a watery
stool [20]. Interestingly, small doses of RH (0.05-0.3g/kg) in some patients can
be used to treat diarrhea or may increase constipation. At these dosage levels,
it is thought that the effect of the tannins in binding stool overcomes the laxative
effect. It may also be due to the differences in gut flora and consequent metabolites.
Certain species contain more tannins than others, for example R. palmatum contains
about 11% tannin, whereas other species range from 4-7%.
Psychotropic action
Rhubarb
has a suppressive action on rat ultromotivity. The ultromotive stimulant action
of methamphetamine was markedly reduced. Irritability and aggressiveness induced
in rats was markedly suppressed by the administration of RH, and, although rather
mild, conditioned evasive response was also suppressed. Also, stereotypical behavior
and circling movement induced by apomorphine was suppressed [21].
Blood Urea
Nitrogen (BUN) reducing action
Recent work in China and Japan has demonstrated
that oral or rectal administration of RH is useful in reducing Blood Urea Nitrogen
(BUN) in patients with chronic renal failure, and may prevent or delay progression
to end stage uremic syndrome. Clinical trials found that progression to renal
failure was retarded and uremic symptoms of nausea and anorexia were significantly
reduced [22, 23]. The active principles involved in this effect appear to be the
tannin fraction [24].
A common method of delivery today is via enema, usually
conducted once or twice per week. This method supplements dialysis in areas with
inadequate facilities, and enables a reduction in the need for dialysis in some
patients. It is thought the surface area of the large intestine enables enough
osmotic transfer of BUN from the blood to the intestinal lumen to significantly
reduce the load on the kidney [25]. Oral administration has also been utilized
successfully, using such formulas as Wen Pi Tang, which includes between 4 and
12 grams of RH.
Anti-inflammatory and Antipyretic action
Lindleyin, one
of the tannin fractions of rhubarb, has about the same anti-inflammatory action
as aspirin and phenylbutazone and suppresses early stage inflammation [26-28].
It also has a peripheral analgesic action which is comparable with aspirin and
phenylbutazone; its effect on joint inflammation is similar to aspirin [29]. Also,
the bound tannins have a free radical scavenging action [30]. Rabbits with fever
induced by subcutaneous inoculation of pneumococci responded with decreased body
temperature after oral administration of RH [31].
Sample clinical studies
Endometriosis
Seventy-six
women with endometriosis of the "Blood Stasis with lower abdominal masses"
type were treated in Long Hua Hospital, Shanghai, with a prescription featuring
rhubarb as the chief ingredient. Total effectiveness rate was 80.26%, with reduction
in dysmenorrhea in 88.89%, pelvic pain 66.72%, dysparenuria 72.12%, reduction
in mass size 22.15%; three cases of twenty-two infertile women fell pregnant (13.63%).
The results support the idea that rhubarb can eliminate Blood Stasis and invigorate
the circulation of Blood. Other common rhubarb based combinations used for the
treatment of endometriosis include Persica and Rhubarb Combination (tao he cheng
qi tang) and Nei Yi Wan, composed of rhubarb, amber (hu po) and tortoise shell
(bie jia).
Hypertension during pregnancy
Shanghai Medical University conducted
a double blind study with processed rhubarb (low dose of 0.75g/day) in pregnant
women at risk of pregnancy-induced hypertension (PIH). Rhubarb (140 cases) and
placebo (125 cases) was given to women at risk of PIH consecutively from the 28th
week of gestation to delivery, with another 68 pregnant women as control. In the
treated group, 5.7% of the women developed PIH, whereas in the untreated group
20.8% developed PIH. This result was statistically significant (P<0.01). The
mechanism of this apparent protection may be related to the inhibition of Plasminogen
activator inhibitor (PAI), plasma Fibronectin (Fn), and decreased damage to the
vascular endothelium [38]. Interestingly, the tannin components of RH have also
been found to have ACE-inhibiting actions [39].
Acute inflammatory diseases
RH
has Heat clearing, antipyretic and purgative action and as such is much employed
in compound prescriptions like Persica & Rhubarb Combination (tao he cheng
qi tang), Major Rhubarb Combination (da cheng qi tang), Coptis and Rhubarb Combination
(san huang xie xin tang), Major Bupleurum Combination (da chai hu tang) etc. for
acute inflammatory diseases characterized by fever, constipation, abdominal distension,
thirst and general malaise. Rhubarb prescriptions have been found effective in
such biomedically defined disorders as acute appendicitis, acute pancreatitis,
acute cholecystitis, and other acute abdominal infections [35, 36].
Pharmacokinetics
and Toxicity
RH is readily absorbed after ingestion. The serum drug concentration
peaks after two hours, and when used for purgation, the bowels generally move
after 6 - 8 hours. Habituation may be a problem in some patients with long-term
use for constipation, and thus RH generally should be phased out and other appropriate
therapeutic measures instituted or other herbs that address the "root"
of the problem added to the formula.
Generally, RH is low in toxicity, but
intoxication could result from overdosage, especially of the fresh herb. Toxic
symptoms include nausea, vomiting, dizziness, abdominal colic and jaundice. Long-term
use of the anthraquinone cathartics could lead to liver cirrhosis and hypokalemia
[32].
Use in Combination
Rhubarb and Mirabilitum (mang xiao)
The Bitter
& Cold characteristics of Rhubarb aid in the dispersal of Heat and the removal
of stagnant Damp-heat. Mirabilitum (mang xiao) is salty and cold; it moistens
dryness and softens hardness. These two substances work synergistically to resolve
stagnation and accumulation of the intestines and stomach as well as disperse
Heat. They are most commonly used together in the treatment of Heat accumulation
type constipation, resulting from knotted dryness of the stomach and intestines,
or febrile diseases due to a knotted pathogen resulting in Yang Ming type Fever,
abdominal distension and pain, and constipation with dry stool. This combination
used with Licorice (gan cao) results in the formula Regulate Stomach Cheng Qi
Tang (tiao wei cheng qi tang). Licorice, which is Sweet and Warm, counteracts
the overly Cold and strong acting actions of Rhubarb and Mirabilitum and protects
the Stomach Qi from damage.
Rhubarb and Coptis (huang lian)
A combination
of these two herbs is known as da huang huang lian xie xin tang. Both herbs are
Bitter & Cold and clear Heat. Rhubarb is superior in its descending action
while Coptis has a superior Heat clearing, Damp drying action. When the two are
combined, they are very effective in the treatment of pain and distension due
to knotted Heat pathogen. If these two herbs are also combined with Scute, which
cools Hot Blood and stops bleeding, it creates the formula Coptis and Rhubarb
Combination (san huang xie xin tang). This formula is very effective for treating
epistaxis and hemoptysis due to a Heat pathogen in the Blood causing frenetic
Blood syndrome. The combination of these three herbs is not only used for clearing
excess Heat from the Qi level (Qi Fen) but also used to purge Heat toxin from
the Blood level and resolve the various symptoms that occur due to this.
Rhubarb
and Capillaris (yin chen)
This combination of herbs is effective for the clearing
and dispersal of Damp-heat and it is very commonly used to treat jaundice. The
combination of these two herbs with Gardenia (zhi zi) is known as Capillaris Combination
(yin chen hao tang). This formula drains Heat from the Gall Bladder, with Gardenia
aiding the expulsion of Damp-heat through the urine. This is a standard combination
used to treat jaundice due to excess type Damp-heat.
Rhubarb and Cinnamon
Bark (rou gui)
Rhubarb is very Cold and disperses and descends. Cinnamon bark
is used as an adjunct herb to prevent damage to Spleen Yang. This method of treatment
is known as the Synergy of Hot and Cold and is a common treatment for habitual
constipation.
Rhubarb and Gypsum (calcined, duan shi gao)
The combination
of these two herbs powdered and made into a paste can be useful in the treatment
of burns and other excess heat skin conditions. Another external use of Rhubarb
is in a 10:2 mixture with powdered licorice for the treatment of chronic leg ulcers.
Other common combinations include Rhubarb and Moutan (mu dan pi) for the treatment
of Blood stagnation, Rhubarb and Zhi Shi for the treatment of excess stomach accumulation,
Rhubarb and Apricot Seed (xing ren) for the treatment of dry deficient type constipation,
and Rhubarb and Persica (tao ren) for the treatment of dry type constipation and/or
Blood stagnation.
Processing
When used to regulate the Blood and break up
Stagnant Blood, small quantities of RH are needed; when purging, use larger amounts
(up to 15 grams in Yangming syndrome). Unprocessed RH is a stronger purge than
processed; RH fried in wine (jiu da huang) can clear Heat from the upper body;
charred RH (da huang tan) is used to stop bleeding. When used as a purge, RH should
be added about 5 minutes before the end of cooking time (hou xia); to regulate
Blood and clear Stagnant Blood it may be cooked longer. RH (especially the raw,
unprocessed product) is generally contraindicated during pregnancy, during menstruation
and breast-feeding, post-partum, in exterior syndromes, and for Spleen and Stomach
Xu Cold conditions. Use caution in cases involving Qi, Blood and Yang Xu.
References
1.
Fuzellier MC, Mortier F, Girard T, Payen J (1981) Study of antibiotic properties
of some anthraquinones using chromatographic microplates. Ann Pharm Fr 39:313-318
2.
Matsumoto O., et al (1985) Anti-Bacteriodes fragilis component in rhubarb and
senna. Wakan Iyaku Gakkaishi 2:248-249
3. Cyong JC., et al (1987) Anti-Bacteriodes
fragilis substance from rhubarb. J Ethnopharmacol 19:279-283
4. Jiang WJ.,
et al (1985) Effects of raw and processed Da Huang on experimental gastric ulcer
in rats. Bull Chin Mater Med 10:65-67
5. Jin YC., et al (1986) Chin J Integrat
Trad West Med 6:455-457
6. Sun DA, Zhuang HQ, Deng A, Wang LZ (1986) Comparison
of the clinical effects of R. palmatum and cimetidine in upper gastro-intestinal
bleeding. Chin J Integrat Trad West Med 6:458-459
7. Zhou H, Jiao D (1990)
312 cases of gastric and duodenal ulcer bleeding treated with three kinds of alcoholic
extract rhubarb tablets. Chung Hsi I Chieh Ho Tsa Chih 10(3):150-151
8. Liang
ZJ., et al (1986) Effect of R. palmatum on the haemorheology of rabbits. Chin
J Integrat Trad West Med 6:294-296
9. Weng WL, Cui J, Chen YC, Wang JC (1986)
Effect of Da huang on platelet aggregation and thrombus formation in vitro. Chin
Trad Herb Drugs 17:507-508
10. Chen QH, Liu CY, Qiu CH (1980) Studies on Chinese
rhubarb XII. Effect of anthraquinone derivatives on the respiration and glycolysis
of Ehrlich ascites carcinoma cells. Acta Pharm Sin 15:65-70.
11. Kawai K.,
et al (1984) A comparative study on cytotoxicities and biochemical properties
of anthraquinone mycotoxins emodin and skyrin from Penicillium islandium Sopp.
Toxicol Lett 20:155-160.
12. Lu M, Chen QH (1989) Biochemical study of Chinese
rhubarb XXIX. Inhibitory effects of anthraquinone derivatives on P338 leukemia
in mice. J China Pharm Univ 20:155-157
13. Chen QH., et al (1974) J Trad Chin
Med 10(5):709
14. Xiao PG., et al (1980) Preliminary study between phylogeny,
chemical constituents and therapeutic effects of Rheum spp. Acta Pharm Sin 15:33-39
15.
Oshio H, Kawamura N (1985) Determination of the laxative components of rhubarb
by high performance liquid chromatography. Shoyakugaku Zasshi 39:139-138.
16.
Garcia-Villar R, Leng-Peschlow E, Ruckebusch Y (1980) Effect of anthraquinone
derivatives on canine and rat intestinal motility. J Pharm Pharmacology 32:323-329.
17.
Hottori M., et al (1982) Metabolism of sennosides by intestinal flora. Chem Pharm
Bull (Tokyo) 30:1338-1346
18. Kobashi K., et al (1980) Metabolism of sennosides
by human intestinal bacteria. Planta Med 40:225-236.
19. Hardcastle JD (1970)
Gut 11:1038
20. Matsuoka T (1973) Metabolism and Disease (Supplement) 10(5):
709.
21. Nokia A (1986) Gen Dai To Yo I Gaku (Mod Orient J) 7:98
22. Li
LS & Liu ZH (1991) Clinical and experimental studies of rheum on preventing
progression of chronic renal failure. Chung Hsi I Chieh Ho Tsa Chih. 11(7):392-6
23.
Zhang JH & Zhang M (1990) Clinical effects of rheum and captopril on preventing
progression of chronic renal failure. Chin Med J. 103(10):788-93
24. Yokozawa
T., et al. (1991) Effects of rhubarb tannins on uraemic toxins. Nephron 58(2):155-60
25.
Personal communication from physicians at the Red Cross Hospital, Hangzhou, PRC.
26.
Gonzares AG., et al. (1978) Pharmacol. 33:460
27. Boada JN., et al. (1980)
Planta Med. 39:297
28. Nishioka I., et al. (1981) Chen Pharm Bull. 29:2862
29.
Darias V., et al. (1978) Il Farmaco (Ed Sci) 33:460
30. Uchida M (1988) Neuroscience.
14:243
31. Guo CY, Wang BE, Zhao SY, Li ZJ (1986) Effect of Rheum palmatum
on body temperature and cerebral PGE level. Chin J Integrat Trad West Med. 6:106-107
32.
Berning H., et al. (1962) Chemical Abstracts. 56:4066b
33. May G., et al. (1978).
Arzneim-Forsch. 28:1
34. Chen QH., et al. (1974) J Trad Chin Med 5:34
35.
Jiang JM., et al. (1980) J Trad Chin Med. 1:23
36. Zheng XL (1981) J Trad Chin
Med. 1:76
37. Fruehauf H (1994) J Chin Med 44:23-36
38. Zhang ZJ, Cheng
WW, Yang YM (1994) Low dose of processed rhubarb in preventing pregnancy induced
hypertension. Chin J Obs Gyn 29(8):463-464
39. Uchida S., et al. (1987). Jpn,
J. Pharmacol. 39, 845