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Digitalis

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For the medication sometimes called "Digitalis", see Digoxin.

iDigitalis

Image:Digitalis purpurea2.jpg

Digitalis purpurea (Common Foxglove)

Scientific classification

Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Lamiales
Family:	Plantaginaceae
Genus:	Digitalis L.

Species

About 20 species, including:
Digitalis cariensis
Digitalis ciliata
Digitalis davisiana
Digitalis dubia
Digitalis ferruginea
Digitalis grandiflora
Digitalis laevigata
Digitalis lanata
Digitalis leucophaea
Digitalis lutea
Digitalis obscura
Digitalis parviflora
Digitalis purpurea
Digitalis thapsi
Digitalis trojana
Digitalis viridiflora

Digitalis is a genus of about 20 species of herbaceous biennials, perennials and shrubs that was traditionally placed in the figwort family Scrophulariaceae. Due to new genetic research, it has now been placed in the much enlarged family Plantaginaceae. The genus is native to Europe, western and central Asia and northwestern Africa.

The term digitalis is also used for preparations containing cardiac glycosides, particularly digoxin, extracted from plants of this genus.

The members of this genus are known in English as foxgloves. The scientific name means "finger-like", and refers to the ease which a flower of Digitalis purpurea can be fitted over a human fingertip. "Foxglove" has a similar origin, seen as a suitable glove for a fairy, the word being a corruption of "folk's glove", referring to the fairy folk.

The flowers are produced on a tall spike, are tubular, and vary in colour with species, from purple to pink, white and yellow.

The best-known species is the Common Foxglove, Digitalis purpurea. It is a biennial, often grown as an ornamental plant due to its violet flowers. The first year of growth produces only the long, basal leaves, while in the second year the erect leafy stem 0.5-2.5 m tall develops.

The larvae of the Foxglove Pug feed on the flowers of Digitalis purpurea. Other Lepidoptera species feed on the leaves including Lesser Yellow Underwing.

1 Medicinal use
2 Toxicity
3 Molecular Biology Use: Digoxigenin
4 Gallery
5 References and external links

[edit] Medicinal use

The use of Digitalis purpurea extract containing cardiac glycosides for the treatment of heart conditions was first described by William Withering. In contemporary medicine, a purer form of digitalis (usually digoxin) is obtained from Digitalis lanata.<ref name=Hollman>Digoxin comes from Digitalis lanata. Hollman A. BMJ 1996;312:912. online version accessed 18 Oct 2006 [1]</ref> It is used to strengthen cardiac contractility (it is a positive inotrope) and as an antiarrhythmic agent to control the heart rate, particularly in the irregular (and often fast) atrial fibrillation. It is therefore often prescribed for patients in atrial fibrillation, especially if they are in heart failure.

A group of pharmacologically active compounds are extracted mostly from the leaves of the second year's growth, and in pure form are referred to by common chemical names such as digitoxin or digoxin, or by brand names such as Lanoxin, or Purgoxin.

Digitalis works by inhibiting sodium-potassium ATPase, which increases intracellular calcium. The increased intracellular calcium gives a positive inotropic effect. It also has a vagal effect on the parasympathetic nervous system, and as such is used in reentrant cardiac arrhythmias and to slow the ventricular rate during atrial fibrillation. The dependence on the vagal effect means that digitalis is not effective when a patient has a high sympathetic nervous system drive, which is the case with acutely ill persons, and also during exercise.

Digitalis toxicity (Digitalis intoxication) results from an overdose of digitalis and causes anorexia, nausea, vomiting and diarrhoea, as well as sometimes resulting in xanthopsia (jaundiced or yellow vision) and the appearance of blurred outlines (halos). Bradycardia also occurs. Because a frequent side effect of digitalis is reduction of appetite, some individuals have abused the drug as a weight loss aid.

Digitalis is a classic example of a drug derived from a plant formerly used by folklorists and herbalists: herbalists have largely abandoned its use because of its narrow therapeutic index and the difficulty of determining the amount of active drug in herbal preparations. Once the usefulness of digitalis in regulating pulse was understood, it was employed for a variety of purposes, including the treatment of epilepsy and other seizure disorders, now considered inappropriate.

[edit] Toxicity

Depending on the species, the digitalis plant may contain several deadly physiological and chemically related cardiac and steroidal glycosides. Thus, the digitalis has earned several more sinister monikers: "Dead Man’s Bells", and "Witches’ Gloves".

The entire plant is toxic (including the roots and seeds), although the leaves of the upper stem are particularly potent, with just a nibble being enough to potentially cause death. Early symptoms of ingestion include nausea, vomiting, anorexia, diarrhea, abdominal pain, wild hallucinations, delirium, and severe headache. Depending on the severity of the toxicosis the victim may later suffer irregular and slow pulse, tremors, various cerebral disturbances, especially of a visual nature (unusual color visions with objects appearing yellowish to green, and blue halos around lights), convulsions, and deadly disturbances of the heart. For a case description, see the paper by Lacassie.<ref name=Lacassie>A non-fatal case of intoxication with foxglove, documented by means of liquid chromatography-electrospray-mass spectrometry. Lacassie E et al, J Forensic Sci. 2000 Sep;45(5):1154-8. Abstract accessed online 19 Sep 2006. [2]</ref>

There have been instances of people confusing digitalis with the harmless Symphytum (comphrey) plant (which is often brewed into a tea) with fatal consequences. Other fatal accidents involve children drinking the water in a vase containing digitalis plants. Drying does not reduce the toxicity of the plant. The plant is toxic to animals including all classes of livestock, as well as cats and dogs.

[edit] Molecular Biology Use: Digoxigenin

Digoxigenin (DIG) is a steroid found exclusively in the flowers and leaves of the plants Digitalis purpurea and Digitalis lanata. It is used as a molecular probe to detect DNA or RNA. It can easily be attached to nucleotides by chemical modifications. DIG molecules are often linked to uridine nucleotides; DIG labeled uridine (DIG-U) can then be incorporated into RNA probes via in vitro transcription. Once hybridisation occurs in situ, RNA probes with the incorporated DIG-U can be detected with anti-DIG antibodies that are conjugated to alkaline phosphatase. To reveal the hybridised transcripts, alkaline phosphatase can be reacted with a chromogen to produce a colour precipitate.

[edit] Gallery

Digitalis ciliata	Digitalis grandiflora	Digitalis lutea	Digitalis purpurea drawings by Franz Köhler
Digitalis purpurea	Digitalis purpurea	Digitalis purpurea	Digitalis purpurea var. alba
A wild Digitalis sp. flower spike beside a Norwegian fjord	Digitalis purpurea (Foxglove)