| Foxglove | |
|---|---|
| Digitalis purpurea (Common Foxglove) | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Asterids |
| Order: | Lamiales |
| Family: | Plantaginaceae[1] |
| Genus: | Digitalis L. |
| Species | |
|
Over 20 species, including: |
|
Digitalis ( /ˌdɪdʒɨˈteɪlɨs/[2] or /ˌdɪdʒɨˈtælɨs/[3]) is a genus of about 20 species of herbaceous perennials, shrubs, and biennials that are commonly called foxgloves. This genus was traditionally placed in the figwort family Scrophulariaceae, but recent reviews of phylogenetic research have placed it in the much enlarged family Plantaginaceae.[1] This genus is native to western and south western Europe,[4] western and central Asia, and northwestern Africa. The scientific name means "finger-like" and refers to the ease with which a flower of Digitalis purpurea can be fitted over a human fingertip. 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. This is a biennial plant which is often grown as an ornamental plant due to its vivid flowers. These range in colour from various purple tints through various shades of light gray, and to purely white. The flowers can also possess various marks and spottings.
The first year of growth of the Common Foxglove produces only the stem with its long, basal leaves. During the second year of the plant's life, a long leafy stem from 50 to 255 centimeters tall grows atop the roots of healthy plants.[5][6]
The larvae of the insect the "Foxglove pug" consume the flowers of the Common Foxglove for food. Other species of Lepidoptera eat the leaves of the Common Foxglove, including Lesser Yellow Underwing.
The term digitalis is also used for drug preparations that contain cardiac glycosides, particularly one called digoxin, that are extracted from various plants of this genus.
Contents |
There have been many suggestions for the derivation of the name "foxglove". According to the 19th century book, English Botany, Or, Coloured Figures of British Plants:
Dr. Prior, whose authority is great in the origin of popular names, says "It seems probably that the name was in the first place, foxes' glew, or music, in reference to the favourite instrument of an earlier time, a ring of bells hung on an arched support, the tintinnabulum"... we cannot quite agree with Dr. Prior for it seems quite probable that the shape of the flowers suggested the idea of a glove, and that associated with the name of the botanist Fuchs, who first gave it a botanical name, may have been easily corrupted into foxglove. It happens, moreover, the name foxglove is a very ancient one and exists in a list of plants as old as the time of Edward III. The "folks" of our ancestors were the fairies and nothing is more likely than that the pretty coloured bells of the plant would be designated "folksgloves," afterwards, "foxglove." In Wales it is declared to be a favourite lurking-place of the fairies, who are said to occasion a snapping sound when children, holding one end of the digitalis bell, suddenly strike the other on the hand to hear the clap of fairy thunder, with which the indignant fairy makes her escape from her injured retreat. In south of Scotland it is called "bloody fingers" more northward, "deadman's bells" whilst in Wales it is known as "fairy-folks-fingers" or "lambs-tongue-leaves".[7]
Digitalis thrives in acidic soils, in partial sunlight to deep shade, in a range of habitats including open woods, woodland clearings, moorland, and heath margins, sea-cliffs, rocky mountain slopes and hedge banks.[4][8] It is commonly found on sites where the ground has been disturbed, such as recently cleared woodland, or where the vegetation has been burnt.[9]
A group of medicines extracted from foxglove plants are called Digitalin. The use of Digitalis purpurea extract containing cardiac glycosides for the treatment of heart conditions was first described in the English speaking medical literature by William Withering, in 1785,[10] which is considered the beginning of modern therapeutics.[11][12] It is used to increase 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. Digitalis is hence often prescribed for patients in atrial fibrillation, especially if they have been diagnosed with congestive heart failure. Digoxin was approved for heart failure in 1998 under current regulations by the Food and Drug Administration on the basis of prospective randomized study and clinical trials. It was also approved for the control of ventricular response rate for patients with atrial fibrillation. Recent American College of Cardiology/American Heart Association guidelines recommend digoxin for symptomatic chronic heart failure for patients with reduced systolic function, preservation of systolic function, and/or rate control for atrial fibrillation with a rapid ventricular response. Recent Heart Failure Society of America guidelines for heart failure provide similar recommendations. Despite its relatively recent approval by the Food and Drug Administration and the guideline recommendations, digoxin use is decreasing in patients with heart failure. This is likely the result of several factors. Digoxin has not been promoted by the pharmaceutical industry and has received little attention at national and international meetings, possibly the result of the development and promotion of other, newly patented therapies for heart failure. Also, safety concerns about digoxin therapy–increased mortality in women also may have contributed to this decrease in its use.
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 Crystodigin and Lanoxin, respectively. The two drugs differ in that Digoxin has an additional hydroxyl group at the C-3 position on the B-ring (adjacent to the pentane). Both molecules include a lactone and a triple-repeating sugar called a glycoside.
Digitalis works by inhibiting sodium-potassium ATPase. This results in an increased intracellular concentration of sodium ion and thus a decreased concentration gradient across the cell membrane. This increase in intracellular sodium activates a sodium/calcium exchange pump that brings calcium ions into the cell while extruding sodium in order to restore its gradient across the membrane. The increased cytosolic calcium ion concentration results in increased calcium ion storage in the sarcoplasmic reticulum. Upon action potential (cardiac contraction) more calcium is released from the sarcoplasmic reticulum and this gives a positive inotropic effect (higher contractility). Digitalis 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 used the drug as a weight loss aid.
Digitalis is an example of a drug that is derived from a plant that was 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 the human pulse was understood, it was employed for a variety of purposes, including the treatment of epilepsy and other seizure disorders, which are now considered to be inappropriate treatments.
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 names: 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, diarrhoea, 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 colour 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.[13]
There have been instances of people confusing digitalis with the relatively harmless Symphytum (comfrey) 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 and poultry, as well as felines and canines.
Digitalis poisoning can cause heart block and either bradycardia (decreased heart rate) or tachycardia (increased heart rate), depending on the dose and the condition of one's heart. It should however be noted, that electric cardioversion (to "shock" the heart) is generally not indicated in ventricular fibrillation in digitalis toxicity, as it can increase the dysrhythmia in digitalis toxicity. Also, the classic drug of choice for VF (ventricular fibrillation) in emergency setting,[14] amiodarone, can worsen the dysrhythmia caused by digitalis, therefore, the second-choice drug Lidocaine is more commonly used.
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 labelled 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.