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Atropine is an alkaloid extracted from Atropa belladonna (deadly nightshade) and other plants of the family Solanaceae.

It is a drug with a wide variety of effects. All of these derive from its blocking of the muscarinic acetylcholine receptors; acetylcholine is a neurotransmitter which transmits information from nerve cells to muscles and glands. The muscarinic acetylcholine receptor is used by the parasympathetic[?] nervous system; atropine therefore lowers the activity of all muscles and glands that receive their stimulation via the parasympathetic system.

In overdoses, atropine is poisonous.

The main use of atropine is in dilating the pupil before undergoing eye exams. Atropine containing drops are directly applied to the eye; they perform their action because the muscles responsible for constricting the pupil use muscarinic acetylcholine receptors.

Injections of atropine are used in the treatment of bradycardia (to slow 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 speeds up the heart rate.

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.

By blocking the action of acetycholine, atropine also serves as an antidote for organophosphate[?] poisoning, particularly for chemical weapons such as nerve gases. Troops who are likely to be attacked with chemical weapons often carry syringes with atropine which can be quickly injected into the thigh.

Atropine is sometimes added to other potentially addictive drugs; abuse of those drugs is then prevented by the unpleasant effects of atropine overdose.

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 recreationally, though this is very dangerous.

In medicine the most common atropine compound used is atropine sulfate (C17H23NO3)2.H2SO4.H2O, the full chemical name is 1α H, 5α H-Tropan-3-α ol (±)-tropate(ester), sulfate monohydrate.

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