is an alkaloid derived from the solanaceous plants Atropa belladonna
), Hyoscyamus niger
(black henbane), and Datura stramonium
(thornapple). These plants contain a mixture of two closely related alkaloids, hyoscyamine
; atropine is a mixture of two isomers of hyoscyamine. In 1867, von Bezold found that atropine blocked the slowing of the heart caused by vagal stimulation. We now know that atropine blocks the action of the neurotransmitter acetylcholine
at all the nerve endings where the membrane receptors
are of the so-called muscarinic
type. This includes those of the parasympathetic nervous system
in the heart, glandular tissue, and smooth muscle
. Thus atropine causes a rise in heart rate and inhibits secretions (for example of saliva, causing a dry mouth, and of the digestive enzymes). It also relaxes smooth muscle
in the gastrointestinal tract, the urinary bladder, and the bronchial trees, by preventing the effects of the normal background discharge of parasympathetic neurons to these organs.
The central nervous system
also contains muscarinic receptors
. Blockade of these by atropine leads to restlessness and mental excitement, and can improve the rigidity and tremor characteristic of Parkinson's disease. Large doses of atropine can cause hallucination.
Long-lasting pupillary dilation results if atropine drops are placed in the eye. The iris has both circular and radial muscles, and the balance between the tonic activities of these two muscle groups controls the pupil diameter. The circular muscle is under parasympathetic control, so when the transmitter, acetylcholine, is blocked with atropine, the pupil will dilate. It is told that Spanish ladies put atropine drops in their eyes for the allure given by large, black pupils: hence the name belladonna
— ‘fine lady’.
Alan W. Cuthbert
See also autonomic nervous system
; membrane receptors
atropine (ăt´rəpēn, –pĬn), alkaloid drug derived from belladonna and other plants of the family Solanaceae (nightshade family). Available either as the tincture or extract of belladonna, or as the pure substance atropine sulfate, it is a depressant of the parasympathetic nervous system. It has some chemical similarity to the body substance acetylcholine and interferes with nerve impulses transmitted by that substance. Atropine produces rapid heart rate, dilated pupils, dry skin, and anesthetizes the nerve endings in the skin. Because it relaxes smooth muscle and suppresses gland and mucous secretions, it has been used to treat peptic ulcer by reducing the production of stomach acid. Atropine is given before general anesthesia to keep the air passages clear and is an ingredient in various preparations for symptomatic relief of colds and asthma. It also acts as an antidote in poisoning from such agents as mushrooms, morphine, prussic acid, and nerve gas, but overdosage causes delirium, convulsions, and coma. A related alkaloid, scopolamine, is used mainly as a sedative.
alkaloid poison from deadly nightshade
. XIX. f. modL. atropa deadly nightshade
, fem. f. Gr. Átropos
(‘Inflexible’) name of one of the Fates
, f. A-4
turn; see TROPE
N) obtained from certain plants such as Atropa belladonna (deadly nightshade
). Atropine is used medicinally to regularize the heartbeat during anaesthesia, to dilate the pupil of the eye and to treat motion sickness
atropine (at-rŏ-peen) n.
an antimuscarinic drug extracted from belladonna. Atropine is used as a mydriatic (see cycloplegia
). It is also used in surgery (as premedication and to reverse the action of muscle relaxants) and occasionally to relieve gut spasms. Trade names: Isopto Atropine
, Minims Atropine Sulphate
a poisonous alkaloid compound, C17N23NO3, found in deadly nightshade and related plants, and used in medicine.
A poisonous crystalline alkaloid, C17
. It can be extracted from deadly nightshade
and other solanaceous plants and is used in medicine to treat colic, to reduce secretions, and to dilate the pupil of the eye.
A substance that, by competing with acetylcholine
for post-synaptic membrane receptor sites, inhibits the passage of nerve impulses across a synapse