Digitalis consists of dried leaves of Digitalis purpurea Linn., belonging to family Scrophulariaceae.
DIGITALIS LEAVES
Synonyms
Digitalis, purple foxglove, finger flower, lady’s glove,
Fox-glove Leaves, Folia Digitalis.
Biological Sources
Digitalis consists of dried leaves of Digitalis purpurea Linn., belonging to family Scrophulariaceae.
Geographical Sources
It is mainly found in England, Germany, France, North
America, India, Iraq, Japan, Kurdistan, Mexico, Nepal, Spain, Turkey.
Cultivation and Collection
Digitalis is a biennial herb growing wild but good quality
of the drug is obtained especially from cultivated plant. The plant will
flourish best in well drained loose soil, prefer-ably of siliceous origin, with
some slight shade. The plants growing in sunny situations possess the active
qualities of the herb in a much greater degree than those shaded by trees, and
it has been proved that those grown on a hot, sunny bank, protected by a wood,
give the best results.
It grows best when allowed to seed itself, if it is desired
to raise it by sown seed, 2 lb of seed to the acre are required. For
cultivation special strains of the seeds are selected which would produce
disease-resistant plants with maximum activity. Attention is specially paid to
the structure of the soil in seed beds. As the seeds are so small and light,
they should be mixed with fine sand in order to ensure even distribution.
Before sowing soil is sterilized. They should be thinly covered with soil. The
seeds are uncertain in germination, but the seedlings may be readily and safely
transplanted in damp weather, and should be pricked out to 6–9 inches apart.
Sown in spring, the plant will not blossom till the following year. Seeds must
be gathered as soon as ripe. In dry season sufficient water is supplied to the
plant. In the first year, a long stalk with rosette of leaves is produced. The
flowers of the true medicinal type must be pure, dull pink or magenta, not
pale-coloured, white or spotted externally.
Collection of these leaves is carried out from Septeber to
November by hand and thus other organic matter and discoloured leaves are
avoided. After collection the leaves should be dried as soon as possible at
60°C. By quick drying characteristic green colour of the leaves is maintained.
Drying is carried out till moisture is not more than 5%. Leaves are packed under
pressure in airtight containers.
Morphology
Microscopy
Digitalis has dorsiventral leaf structure. It has plenty of
simple covering and glandular trichomes on both the surfaces. The covering
trichomes are uniseriate, usually three to four cells long, having collapsed
cells, acute apex and finely warty cuticle. The glandular trichomes have a
short, unicellular stalk and bicellular or rarely unicellular head. It has
anomocytic or ranunculaceous type of stomata. Trichomes and stomata are more in
lower surface. The pericycle is parenchymatous above and collenchymatous below.
Calcium oxalate crystals are absent.
T .S. (schematic) of Digitalis leaf
Transverse section of Digitalis leaf
Chemical Constituents
Digitalis leaves contains 0.2–0.45% of both primary and
secondary glycosides. Purpurea glycosides A and B and glucogitoloxin are
primary glycosides. Because of greater stability of secondary glycosides, and
lesser absorption of primary glycosides a higher content of primary glycosides
are not considered ideal and secondary glycosides are used. Purpurea glycosides
A and B are present in fresh leaves and by their hydrolysis digitoxin and
glucose or gitoxin and glucose are obtained respectively. Hydrolysis of purpurea
glycosides can take place by digipuridase (enzyme) present in the leaves.
Digitoxin yields on hydrolysis digitoxigenin and three digitoxose. By
hydrolysis of verodoxin, gitaloxi-genin and digitalose are obtained. Digitalis
leaves also con-tains glycosides like odoroside-H, gitaloxin, verodoxin and
glucoverodoxin.
Verodoxin was found to potentiate the activity of digi-toxin
by synergism. Digitoxose and digitalose are desoxy sugars found only in cardiac
glycosides and answers Keller– Killiani test. The important saponins include
digitonin, tigonin and gitonin, and luteolin, a flavone responsible for the
colour of the drug are also present in the leaves.
Chemical Tests
Digitalis glycosides having five membered lactone ring
answers positive for the following tests which are due to the intact lactone.
1. Baljet
Test: To a thick
section of the leaf sodium picrate reagent
is added. Yellow to orange colour indicates the presence of glycoside.
2. Legal
Test: Glycoside is
dissolved in pyridine and sodium
nitroprusside solution is added to it and made alkaline. Pink to red colour is
produced.
3. Keller–Killiani
Test: The isolated
glycoside is dissolved in glacial
acetic acid and a drop of ferric chloride solu-tion is added followed by the
addition of sulphuric acid which forms the lower layer. A reddish-brown colour
is seen in between two liquids and the upper layer becomes bluish green.
If the powdered leaves are used, 1 gm of the powdered leaves
is extracted with 10 ml of 70% alcohol for couple of minutes, filtered and to 5
ml of filtrate 10 ml of water and 0.5 ml of strong solution of lead acetate is
added and filtered and the filtrate is shaken with 5 ml of chloroform.
Chloroform layer is separated in a porcelain dish and the test is carried out
as mentioned above.
Uses
The foxglove is a widely used herbal medicine with a
rec-ognized stimulatory effect upon the heart. It is also used in allopathic
medicine in the treatment of heart complaints. It has a profound tonic effect
upon a diseased heart, enabling the heart to beat more slowly, powerfully and
regularly without requiring more oxygen. At the same time it stimulates the
flow of urine which lowers the volume of the blood and lessens the load on the
heart. It has also been employed in the treatment of internal haemorrhage, in
inflammatory diseases, in delirium tremens, in epilepsy, in acute mania and
various other diseases. Digitalis has a cumulative effect in the body, so the
dose has to be decided very carefully.
Adulterants
Verbascum thapsus also known as Mullelin leaves. These leaves are covered with large woolly
branched candelabra trichomes.
Primula vulgaris (Primrose leaves) can be detected by
the presence of long eight- to
nine-celled covering trichomes in them.
Symphytum officinale (Comfrey leaves), this leaves
contains multicellular trichomes
forming hook at the top.
Inula conyza (Ploughman’s Spikenard), may be
distinguished by their greater
roughness, the less-divided margins, the teeth of which have horny points and
odour when rubbed.
Marketed Products
It is one of the ingredients of the preparation known as
Lanoxin tablets (Glaxo Smith Kline).
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