Synopsis

Acetylcholine is a widespread chemotransmitter in the body, mediating a broad range of physiological effects.There are two distinct classes of receptor for acetylcholine defined on the basis of their preferential activation by the alkaloids, nicotine (from tobacco) and muscarine (from a fungus, Amanita muscaria).

Cholinergic drugs (acetylcholine agonists) mimic acetylcholine at all sites although the balance of nicotinic and muscarinic effects is variable.

Acetylcholine antagonists (blockers) that block the nicotine-like effects (neuromuscular blockers and autonomic ganglion blockers) are described elsewhere (see Ch. 18).

Acetylcholine antagonists that block the muscarine-like effects, e.g. atropine, are often imprecisely called anticholinergics.The more precise term antimuscarinic is preferred here.

• Cholinergic drugs

— Classification

— Pharmacology

— Choline esters

— Alkaloids with cholinergic effects

— Anticholinesterases; organophosphate poisoning

— Disorders of neuromuscular transmission: myasthenia gravis

• Drugs which oppose acetylcholine

— Antimuscarinic drugs

Cholinergic drugs (cholinomimetics)

These drugs act on postsynaptic acetylcholine receptors (cholinoceptors) at all the sites in the body where acetylcholine is the effective neurotransmitter. They initially stimulate and usually later block transmission. In addition, like acetylcholine, they act on the noninnervated receptors that relax vascular smooth muscle in peripheral blood vessels.

• For myasthenia gravis, both to diagnose (edrophonium) and to treat (neostigmine, pyridostigmine, distigmine)

• To stimulate the bladder and bowel after surgery (bethanechol, carbachoi. distigmine)

• To lower intraocular pressure in chronic simple glaucoma (pilocarpine)

• To bronchodilate patients with airflow obstruction (ipratropium, oxitropium)

• To improve cognitive function in Alzheimer's disease (rivastigmine, donepezil)

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