Atropine
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'''Atropine''' is a tropane alkaloid extracted from the deadly nightshade (''Atropa belladonna'') and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a hard drug|drug with a wide variety of effects. Being potentially deadly, it derives its name from Atropos, one of the three Fates who, according to Greek mythology, chose how a person was to die.
Physiological effects and uses
Generally, atropine lowers the "rest and digest" activity of all muscles and glands regulated by the parasympathetic nervous system. This occurs because atropine is a competitive inhibitor of the acetylcholine receptor|muscarinic acetylcholine receptors. (Acetylcholine is the neurotransmitter used by the parasympathetic nervous system.) Therefore, it causes swallowing difficulties.
Ophthalmic use
Topical atropine is used as a cycloplegic, to temporarily paralyze accommodation reflex|accommodation, and as a mydriatic, to dilate the pupils. Atropine degrades slowly, typically wearing off in 2 to 3 days, so tropicamide is generally preferred as a mydriatic. In atropine-induced mydriasis, the mechanism of action involves blocking the contraction of the circular pupillary sphincter muscle (which is normally stimulated by acetylcholine release), thereby allowing the radial pupillary dilator muscle to contract and dilate the pupil. Atropine is contraindicated in patients predisposed to narrow angle glaucoma.
Resuscitation
Injections of atropine are used in the treatment of bradycardia (an extremely low heart rate) and pulseless electrical activity (PEA) in cardiac arrest. This works because the main action of the vagus nerve of the parasympathetic system on the heart is to slow it down. Atropine blocks that action and therefore may speed up the heart rate.
The main action of parasympathetic nervous system is to stimulate the M2 muscarinic receptor in the heart, but atropine inhibits this action.
Secretions and brochoconstriction
Atropine reduces bronchial and salivary secretion (which are also directed by the parasympathetic system); a dry mouth and increased heart rate are usually among the first effects of the drug. As stated above, atropine inhibits "activity of all muscles and glands regulated by the parasympathetic nervous system," such as the salivary and sweat glands. Because of this effect which inhibits overall sweat gland function, it has (along with other anticholinergics, i.e. Glycopyrrolate) been used to a minimal extent by physicians in the treatment of Hyperhidrosis (uncontrollable, excessive, sweating) even though it has not been officially indicated for this purpose. This is most likely attributed to a lack of other treatments, or if an individual does not respond to available treatments.
An article on eMedicine (http://www.emedicine.com/derm/topic893.htm) reports:
"Systemic agents used to treat hyperhidrosis include anticholinergic medications. Anticholinergics such as propantheline bromide, glycopyrrolate, oxybutynin, and benztropine are effective because the preglandular neurotransmitter for sweat secretion is acetylcholine (although the sympathetic nervous system innervates the eccrine sweat glands). The use of anticholinergics may be unappealing because their adverse effect profile includes mydriasis, blurry vision, dry mouth and eyes, difficulty with micturition, and constipation."
Antidote for organophosphate poisoning
By blocking the action of acetylcholine, atropine also serves as an antidote for poisoning by organophosphate insecticides and nerve gases. Troops who are likely to be attacked with chemical weapons often carry autoinjectors with atropine and obidoxime which can be quickly injected into the thigh.
Some of the nerve gases attack and destroy acetylcholinesterase, so the action of acetylcholine becomes prolonged. Therefore, atropine can be used to reduce the effect of ACh.
Side effects and overdoses
Adverse reactions to atropine include ventricular fibrillation, supraventricular or ventricular tachycardia, giddiness, nausea, blurred vision, loss of balance, dilated pupils, photophobia, and possibly, notably in the elderly, confusion, hallucinations and excitation. These latter effects are due to the fact that atropine is able to cross the blood-brain barrier. Because of the hallucinogenic properties, some have used the drug recreational drugs|recreationally, though this is very dangerous.
In overdoses, atropine is poisonous. Atropine is sometimes added to other potentially addictive drugs; abuse of those drugs is then prevented by the unpleasant effects of atropine overdose.
The antidote to atropine itself is physostigmine or pilocarpine.
Chemistry and pharmacology
Atropine is a racemic mixture of D-hyoscyamine and L-hyoscyamine, with most of its physiological effects due to L-hyoscyamine.
The most common atropine compound used in medicine is atropine sulfate (carbon|C17hydrogen|H23Nitrogen|NOxygen|O3)2. sulfate|H2SO4 . water|H2O, the full chemical name is 1α H, 5α H-Tropan-3-α ol (±)-tropate(ester), sulfate monohydrate.
History
Atropine extracts from the Egyptian henbane were used by Cleopatra in the last century B.C. to dilate her pupils, in the hope that she would appear more alluring.
In the Renaissance, women used the juice of the berries of ''Atropa belladonna'' to enlarge the pupils of their eyes, for cosmetic reasons; "belladonna" is Italian for "beautiful lady".
Atropine and its mydriatic effects were discovered in 1833 by the Germany|German chemistry|chemist Friedrich Ferdinand Runge (1795-1867).
Natural sources
Atropine is found in several members of the Solanaceae family. The most commonly found sources are ''Atropa belladonna'', ''Datura innoxia'', ''Datura metel|D. metel'', and ''Datura stramonium|D. stramonium''. Other sources include members of the ''Brugmansia'' and ''Hyoscyamus'' genera. The ''Nicotiana'' genus (including the tobacco plant, ''Nicotiana tabacum|N. tabacum'') is also found in the Solanaceae family, but these plants do not contain atropine or other tropane alkaloids.
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