Cascara is the dried bark of Rhamnus purshiana DC., belong-ing to family Rhamnaceae. It is collected at least one year before use.
CASCARA BARK
Synonyms
Californian Buckthorn, Cascara Buckthorn, Cascara Sagrada, Kaskara
Sakrada, Kasukarasakurada, Pursh’s Buckthorn, Sacred Bark, Chittem Bark.
Biological Source
Cascara is the dried bark of Rhamnus purshiana DC., belong-ing to family Rhamnaceae. It is
collected at least one year before use.
Geographical Source
It is indigenous to North America, British Columbia, Canada
and Kenya.
Cultivation and Collection
It is an evergreen tree growing to 6–12 m in height. The
plant prefers sandy, loamy and clay soils. The plant prefers acid, neutral and
basic soils. It can grow in semishade or no shade. It requires moist soil. It
is cultivated using different techniques like sowing seeds, cuttings and
layering. Seeds are sown in the autumn in a cold frame. Stored seed will
require 1–2 months cold stratification at about 5°C and should be sown as early
in the year as possible in a cold frame or outdoor seed bed. Seedlings are
transferred to the pots and then they are transplanted in late spring or early
summer of the following year. Cuttings are carried out using half-ripe wood,
July/August. Layering can be done in early spring.
Earlier the barks were collected by felling technique and
then by making longitudinal incisions on the trees. To save the destruction of
this species nowadays it is collected by coppicing method. So the stump
remaining above the soil produces new shoots, which bear leaves, flowers and
fruits and seed dispersal takes place and new plants grow. Bark is collected
from 9 to 15 years old trees having minimum 10 cm diameter in dry weather after
rains in May to August by making suitable transverse and longitudinal
incisions. During drying the outer bark is protected from moisture and rains
and inner bark is protected from direct sunlight. Moisture leads to mould due
to the sunlight bark becomes black colour. After complete drying the bark is
made in to small pieces that form squill. It should be harvested in the autumn
or spring at least 12 months before it is used medicinally, in order to allow
the more violent purgative effect to be modified with age.
Characteristics
The drug mostly occurs in quilled, channelled or incurved of
varying lengths and sizes, usually 20 cm long and 1–4 mm thick, smooth or
nearly so externally, covered with a greyish-white layer, which is usually
easily removed, and frequently marked with spots or patches of adherent
lichens. Beneath the surface it is violet-brown, reddish-brown or brownish, and
internally a pale yellowish-brown and nearly smooth. Fracture is short and
granular in the outer part and fibrous in the phloem. It has no marked odour,
but a nauseous, bitter taste. It is frequently also imported in flattened
packets, consisting of small pieces of the bark compressed into a more or less
compact mass.
Microscopy
The cork consists of numerous layers of small, thin walled
flattened, polygonal prisms, arranged in radial rows and having yellowish brown
contents. Next to cork few layers of collenchyma cells are present. Groups of
irregular thick walled lignified stone cells are in the cortex and 1–5 celled
wide phloem rays and tangentially elongated lignified fibres in the phloem. The
fibres are crystal fibres and surrounded by parenchyma containing calcium
oxalate prisms. Crystal fibres are of diagnostic importance in identification
of the powdered drug.
Chemical Constituents
Cascara bark contains 80–90% of C-glycosides and 10–20%
O-glycosides. The C-glycosides present in cascara are aloin or barbaloin and
11-deoxyaloin or chrysaloin. Cascarosides A and B are the primary glycosides of
aloin and cascarosides C and D are primary glycosides of chrysaloin. Cascara
also contains chrysaloin and barbaloins, dianthrones of emodin, aloe-emodin,
chrysophanol; heterodianthrones like Palmidins A, B and C, free emodin,
aloe-emodin and a bitter lactone. Apart from glycosides it also contains fat,
starch, glucose, volatile odorous oil, malic and tannic acids.
Fresh cascara bark contains anthranol derivatives which have
griping; and emetic properties and after storage for one year, anthranol
derivatives are oxidized to anthraquinone derivatives and bark loses irritant
properties.
Chemical Test
It gives red colour with 5% potassium hydroxide solution.
Uses
Cascara sagrada is widely used as a gentle laxative that
restores tone to the bowel muscles and thus makes repeated doses unnecessary.
It is considered suitable for delicate and elderly persons and is very useful
in cases of chronic constipation. The bark also has tonic properties,
promot-ing gastric digestion and appetite. As well as its uses as a laxative,
it is taken internally in the treatment of digestive complaints, haemorrhoids,
liver problems and jaundice.
Substitutes
These include R.
alnifolia, which is too rare to be a likely substitute; R. crocea, whose bark bears little
resemblance to the official drug. R.
californica is very closely related to R.
purshiana. It has a more uniform coat
of lichens and wider medullary rays than the official species, but resembles
the latter in having sclerenchymatous cells. The bark of R.fallax has been recorded as a cascara substitute.
Marketed Products
It is one of the ingredients of the preparations known as
Herbal Laxative (Trophic Canada Ltd.).
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