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- Atropine (belladonna) causes a reversible blockade of the action of acetylcholine at muscarinic receptors (blockade may be overcome by more acetylcholine);Atropine is also used to treat organophosphate poisoning
- Remember: In the autonomic nervous system, muscarinic receptors are at the postganglionic end organ parasympathetic receptors in the heart, smooth muscle, and glands (nicotinic receptors are preganglionic); in the parasympathetic system both nicotinic and muscarinic receptors bind Acetylcholine
- In the sympathetic system acetylchline is the preganglionic neurotransmitter at the nicotinic receptors
- At the end organ, the post-ganglionic receptors are beta-1 in the heart (inhibition), alpha-1 in the smooth muscle (excitation), and beta-2 (inhibition) in the smooth muscle and glands
- All of these receptors bind with norepinepherine EXCEPT for the eccrine sweat glands which use acetylcholine; apocrine sweat glands of the axilla and anus, however, are innervated by adrenergic fibers and sweat in response to mental stress
- In the somatic nervous system, acetylcholine acts on nicotinic receptors at the skeletal muscle level – See Figure 10
- Muscarinic Effects: (1) dry mouth, (2) difficulty talking and swallowing, (3) blurred vision, (4) photophobia, (5) tachycardia, (6) dry/flushed skin, (7) rash on face, neck, upper chest. (8) increased temperature (secondary to inhibition of sweating--"atropine fever"), and (9) increased minute ventilation
- Nicotinic Effects: (1) skeletal muscle weakness, (2) orthostatic hypotension.
- Anticholinergic syndrome: Most commonly occurs with scopolamine but can be seen with high dose atropine. Symptoms consist of delirium, restlessness, confusion, and obtundation. Elderly patients are particularly susceptible. CNS toxic effects may be potentiated by inhalational anesthetics.
- Treatment: Physostigmine 15-60 ug/kg IV. Repeated doses may be needed secondary to rapid metabolism.