Harpagophytum
procumbens Anhang
[Ismail M. Mahomed and John A.O. Ojewole]
Harpagophytum procumbens DC [family: Pedaliaceae] is widely used in
South African traditional medicine for the treatment, management +/o. control
of a variety of human ailments. Some traditional health practitioners of South
Africa have claimed that H. procumbens secondary root is a useful obstetric
remedy for induction or acceleration of labour, as well as for expulsion of
retained placentas in pregnant women. In the present study, we have, therefore,
examined the effects of Harpagophytum procumbens secondary root aqueous extract
(HPE) on isolated uterine muscle strips taken from pregnant and non-pregnant,
young female rats. The plant’s extract (HPE, 10-800 μg/ml) induced
concentration-related, significant (P<0.05-0.001) increases in the baseline
tone (basal tension), and caused powerful spontaneous, rhythmic, myogenic contractions
of the oestrogen-dominated uterine muscle strips taken from
stilboesterol-pretreated, non-pregnant female rats. Relatively low to high
concentrations of H. procumbens secondary root aqueous extract (HPE, 10-800
μg/ml) also provoked concentration-dependent, significant
(P<0.05-0.001) increases in the baseline tone (basal tension) and contracted
uterine muscle strips taken from female rats in the early, middle and late
stages of pregnancy. Moderate to high concentrations of the plant’s extract
(HPE, 200-1000 μg/ml) always provoked powerful contractions of isolated
uterine muscle preparations of non-pregnant and pregnant rats. The results of
this in vitro study indicate that H. procumbens secondary root aqueous extract
(HPE) possesses significant contractile effect and/or uterotonic action on
mammalian uterus. This finding probably suggests that the use of Harpagophytum
procumbens secondary root preparations should be contra-indicated in pregnancy.
The contractile effect and/or uterotonic action of the plant’s extract
may be due to release of uterotonic substances or mediators. However, the
findings of the present laboratory animal study
lend pharmacological credence to the suggested folkloric, obstetric uses
of the plant’s secondary root for induction or acceleration of labour, as well
as for expulsion of retained placentas in pregnant women in some communities of
Southern Africa.
Key words: Harpagophytum procumbens, secondary root, aqueous extract,
uterotonic action.
Introduction
Harpagophytum procumbens DC [family: Pedaliaceae] is a weedy, perennial
plant with annual creeping stems spreading from a central, thick, fleshy,
tuberous tap root (Henderson and Anderson, 1966; Van Wyk et al., 2002).
The leaves are greyish-green and are usually irregularly divided into
several lobes. The tubular flowers are either yellow and violet, or uniformly
dark violet. The fruits have numerous characteristically long arms with sharp,
grapple-like hooks (thorns), as well as two straight thorns on the upper
surface (Watt and Breyer-Brandwijk, 1962; Van Wyk et al., 2002). H. procumbens
is virtually restricted to the southern part of Africa, occurring mainly in
South Africa, Namibia, Botswana and Zimbabwe. The plant is commonly referred to
as ‘Devil’s claw’, a name derived from its claw-like fruits which may cling
tenaciously to the foot and other parts of an animal’s body and, is thus
dispersed in this way (Watt and Breyer-Brandwijk, 1962; Van Wyk et al., 2002).
The thick, fleshy, tuberous secondary tap roots of Harpagophytum procumbens
are usually dried and used in South African traditional medicine. In the form
of infusions, decoctions, tinctures, powders and extracts, H. procumbens
secondary root is used for a variety of health conditions. It has an
ethnomedical reputation for efficacy in anorexia, indigestion, diabetes
mellitus, hypertension, gout, fevers, skin cancer, infectious diseases (Tb.), allergies, osteoarthritis,
fibrositis and rheumatism, being particularly effective in small joint diseases
(Van Wyk and Gericke, 2000). When taken on a regular daily basis, it has a
subtle laxative effect. Small doses of the plant’s root extract are used for
menstrual cramps, while higher doses assist in expelling retained placentas
(Watt and Breyer-Brandwijk, 1962; Van Wyk and Gericke, 2000; Van Wyk et al.,
2002). ‘Devil’s claw’ is also used post-partum as an analgesic and to keep the
uterus contracted (Watt and Breyer-Brandwijk, 1962; Van Wyk and Gericke, 2000;
Van Wyk et al., 2002). The dry, powdered tuberous root of the plant is used
directly as a wound dressing, or it is mixed with animal fat or vaseline, to
make a wound-healing or burn-healing ointment. Commercial ointments and creams
of H. procumbens are applied topically for minor muscular aches and pains, and
to painful joints
(Watt and Breyer-Brandwijk, 1962; Van Wyk and Gericke, 2000; Van Wyk et
al., 2002). Serum cholesterol and uric acid levels are also reduced by H.
procumbens products (Van Wyk and Gericke, 2000).
Previous studies in our laboratories indicate that Harpagophytum
procumbens secondary root aqueous extract stimulates and contracts the
gastro-intestinal tract and vascular smooth muscle preparations of certain
experimental animals (Mohamed and Ojewole, 2004; Mahomed et al., 2005).
Moreover, there are some anecdotal reports that H. procumbens secondary root
extracts and/or preparations possess uterotonic actions in human subjects.
In order to scientifically confirm or deny the possible oxytocic effect
of H. procumbens secondary root extracts on mammalian uterus, the present study
was undertaken to examine the plausible oxytocin-like effect of the plant’s
root aqueous extract on isolated uterine muscle strips of pregnant and
non-pregnant rats.
Materials and Methods
The experimental protocol used in this study was approved by the Ethics
Committee of the University of Durban-Westville, Durban 4000, South Africa; and
conforms with the “Guide to the care and use of animals in research and
teaching” [published by the Univerity of Durban-Westville, Durban 4000, South
Africa].
Plant Material
Fresh pieces of Harpagophytum procumbens DC secondary roots were
purchased from Upington “Muthi” Market in the Northern Cape Province of South
Africa (between November, 2002 and March, 2003). The roots were identified by
the staff of the North-West University’s Botany Department as the secondary
roots of Harpagophytum procumbens DC [family: Pedaliaceae]. Voucher specimen of
the plant’s secondary roots have been deposited in the University’s Herbarium.
Preparation of Harpagophytum
procumbens Root Aqueous Extract
One kilogramme (1 kg) of fresh secondary roots of H. procumbens were
sliced and air-dried at room temperature. The sliced, air-dried roots of the
plant were milled into fine powder in a Waring commercial blender. The powder
was Soxhlet extracted twice, on each occasion with 2.5 litres of distilled
water at room temperature for 24 hours with shaking. The combined aqueous
extracts were filtered and concentrated to dryness under reduced pressure at 30±1oC.
The resulting aqueous extract was freeze-dried, finally giving 15.56 g [i. e.,
1.556% yield] of a light-brown, powdery crude aqueous root extract of
Harpagophytum procumbens. Aliquot portions of the crude root aqueous extract
residue were weighed and dissolved in distilled water for use on each day of
our experiment.
Animal Material
Young adult, female Wistar rats (Rattus norvegicus) weighing 250-300 g
were used. The animals were kept and maintained under laboratory conditions of
temperature, humidity, and light; and were allowed free access to food
(standard pellet diet) and water ad libirum. The animals were divided into two
categories as follows:
Oestrogen-dominated, non-pregnant
rats
All the rats in this group were pretreated with stilboesterol (0.1 mg/kg
s. c.) for 20-24 hours before use (in order to induce oestrus state). Vaginal
smears were taken immediately before the animals were sacrificed in order to
ascertain that the animals were in oestrus state. Female rats in oestrus state
were used in this study.
Pregnant Rats
Mated female rats were examined daily for the presence of cervical plug.
The day on which cervical plug was first observed was taken as ‘day one’ of
pregnancy of the female rat. Early pregnancy was regarded as day 1 to day 8,
while late pregnancy was taken to be from day 16 to day 20 following cervical
plug detection.
Experimental Procedure
Each of the pregnant and stilboesterol-pretreated non-pregnant female
rats was killed by applying a sharp blow to the back of its head and bled out.
The 2 uterine horns of the animal were cleaned free from fatty and connective
tissues and trimmed. Tubular segments of approximately equal lengths (2-3 cm)
were removed from the uterine horns by cutting off both ends. The 2 tubular
uterine-horn segments (2-3 cm long) were set-up under physiological conditions
as described in detail earlier by (Ojewole, 1977). Each isolated uterine muscle
strip was separately suspended in 30-ml Ugo Basile Two-Chambered Organ Baths
(model 4050) containing de Jalon’s physiological solution (of composition, in
g/litre: NaCl, 9.0; KCl, 0.42, CaCl2, 0.06; MgCl2, 0.005; NaHCO3, 0.5; and
glucose, 0.5) maintained at 32±1oC and continuously aerated with carbogen (i.
e., 5% carbon-dioxide + 95% oxygen gas mixture). Two uterine muscle
preparations (one used as ‘control’ and the other one used as HPE- (or other
drug-) treated ‘test’ preparation) were always set-up to allow for changes in
the uterine muscle sensitivity. Each preparation was subjected to a resting
tension of 1.0 g, and allowed to equilibrate for 30-45 minutes before it was
challenged with HPE (and other drugs used). Doses of HPE (and other drugs used)
were added to the bath-fluid either cumulatively or sequentially, and washed
out three-to-five times after the maximum responses of the tissues were
attained. Distilled water (i. e., the vehicle in which HPE and other drugs used
in this study were dissolved) was used as the ‘control’ fluid for HPE and other
drugs tested. Concentrations of bath-applied HPE (and other drugs used) were
repeated where appropriate and/or possible, at regular intervals of 3-20
minutes after the last washing.
HPE- (and other drug-) induced responses of the uterine muscle
preparations were recorded isometrically by means of Ugo Basile force-displacement
transducers, Ugo Basile’s 2-Channel “Gemini” Recorder, and pen-writing
microdynamometers (model 7070).
Data Analysis
Data obtained were pooled and presented as means (+SEM). Data from
distilled water-treated ‘control’ preparations were used as baseline values.
The differences between the plant’s extract (HPE)- (and other drug-) treated
‘test’ preparations, and distilled water-treated ‘control’ preparations, were
analysed statistically by using “Paired Student’s t-test”. The level of
significance of the differences between the ‘test’ and ‘control’ group data
means was determined. Values of P ≤ 0.05 were taken to imply statistical
significance.
Results
Oestrogen-dominated, non-pregnant uterine strips
Uterine muscle strips taken from stilboesterol-pretreated, non-pregnant
female rats were found to be quiescent and devoid of spontaneous, myogenic,
rhythmic activity. However, relatively low to high concentrations of H.
procumbens secondary root aqueous extract (HPE, 10-800 μg/ml) cumulatively
applied to the bath-fluid caused concentration-related, significant (P <
0.05 - 0.001) increases in the baseline tone (basal tension), and induced
powerful spontaneous, rhythmic, myogenic contractions of the oestrogen-dominated
uterine muscle strips taken from stilboesterol-pretreated, non-pregnant female
rats. Figure 1 illustrates a typical trace obtained. Moderate to high
concentrations of the plant’s extract (HPE, 200-1000 μg/ml) sequentially
added to the bath-fluid, always provoked powerful contractions of the uterine
muscle preparations (data not shown). Sequentially applied acetylcholine (ACh,
0.1-2.0 μg/ml), physostigmine (PHY, 2.5-10.0 μg/ml), bradykinin (BKN,
1.0-10.0 ng/ml) and oxytocin (OTC, 0.05-0.5 unit/ml) also induced
concentration-dependent, significant (P<0.05-0.001) contractions of the
oestrogen-dominated uterine muscle preparations taken from the non-pregnant
rats (data not shown). The spontaneous, rhythmic, myogenic contractions of the
quiescent, oestrogen-dominted uterine muscle strips of the non-pregnant rats
induced by relatively low to high concentrations of Harpagophytum procumbens
secondary root aqueous extract (HPE, 10-1000 μg/ml) were inhibited or
abolished in a concentration-dependent manner by bath-applied indomethacin
(IDM, 0.1-5.0 μg/ml) or atropine (ATR, 0.1-5.0 μg/ml). Relatively low
to moderate concentrations of the plant’s extract (HPE, 10-800 μg/ml)
potentiated ACh-, PHY-, BKN- and OTC-induced contractions of the oestrogen-dominated
isolated uterine muscle strips in a concentration-related manner (data not
shown).
Pregnant uterine strips
Uterine muscle strips taken from pregnant rats were found to be
spontaneously active, producing rhythmic contractions on their own accord. The
effects of HPE on isolated uterine muscle strips taken from pregnant rats were
found to be qualitatively and quantitatively similar to those produced by the
plant’s extract on isolated uterine muscle strips taken from
stilboesterol-pretreated, non-pregnant female rats.
Figure 1: Effects of graded concentrations of Harpagophytum procumbens
secondary root aqueous extract (HPE) on oestrogen-dominated rat isolated
uterine muscle strip. HPE 1, 2, 3, 4 and 5 represent 25, 50, 100, 200 and 400
μg/ml of Harpagophytum procumbens secondary root aqueous extract
cumulatively added to the bath fluid at the solid points respectively. HPE was
washed out at the open, downward-pointing, right-hand-side arrow.
Relatively low to high concentrations of Harpagophytum procumbens
secondary root aqueous extract (HPE, 10-1000 μg/ml) provoked
concentration-related, significant (P < 0.05-0.001) increases in the
baseline tone (basal tension), and contracted uterine muscle strips taken from
rats in the early, middle or late stages of pregnancy (data not shown).
Discussion
The findings of the present in vitro, uterine muscle strip study are
similar to those obtained on the chick isolated, parasympathetically-innervated
oesophageal muscle preparations (Mahomed, 2004), and on some mammalian isolated
gastro-intestinal tract smooth muscles (Mahomed et al., 2005). Relatively low
to high concentrations of Harpagophytum procumbens secondary root aqueous
extract (HPE) always induced concentration-related, significant (P <
0.05-0.001), persistent and profound spontaneous, rhythmic, myogenic
contractions of, and contracted, uterine muscle strips taken from
stilboesterol-pretreated female rats. The plant’s extract produced similar
contractile effects on uterine muscle strips taken from pregnant rats. The precise
mechanism of this stimulant action of the plant’s extract on uterine muscle
strips is not fully understood at the moment. The ability of indomethacin
and/or atropine to reduce or abolish HPE-induced contractions of the uterine
muscle preparations used in this study would appear to suggest possible release
of prostaglandins and/or other uterotonic substances or mediators, including
acetylcholine, by the plant’s extract. The observation that H. procumbens
secondary root aqueous extract (HPE) possesses anticholinesterase activity
(Mahomed, 2004) would also appear to buttress the possible involvement of
cholinergic muscarinic receptor stimulation in the uterine stimulant,
uterotonic action of HPE.
Harpagophytum procumbens root has been reported to contain sugars,
flavonoids, iridoid glycosides, phenolic acids, quinones, phytosterols,
triterpenoids, acetoside esters and minerals (Watt and Breyer-Brandwijk, 1962;
Van Wyk and Gericke, 2000; Van Wyk et al., 2002). Although the exact chemical
constituent/s of H. procumbens secondary root that is/are responsible for the
observed uterine contractile effect of the plant’s aqueous extract still
remains speculative, the iridoids harpagoside (a cinnamic acid ester),
harpagide and procumbide, are speculated to probably account, at least in part,
for the uterotonic action of HPE. However, the experimental evidence obtained
in the present in vitro study indicates that aqueous secondary root extract of
H. procumbens possesses contractile, uterotonic action on mammalian uterus.
This finding also suggests that the use of Harpagophytum procumbens root should
be contra-indicated in pregnancy. The contractile effect and/or uterotonic
action of the plant’s extract (HPE) may be due to release of uterotonic
substance/s or mediator/s. However, the findings of the present laboratory
animal study lend pharmacological credence to the suggested folkloric,
obstetric uses of the plant’s secondary root extract for induction or
acceleration of labour, as well as for expulsion of retained placentas in
pregnant women in some communities of Southern Africa.