Digitalis Leaves

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Chapter: Pharmacognosy and Phytochemistry : Drugs Containing Glycosides

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

 

 



                               Digitalis purpurea 


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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