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Clinical pharmacy 2024/2025 Level 3 Pharm D Pharmacology 1 (PO 502)

Cholinergic nervous system

Ach ➔ chemical transmitter in the following sites:
1. Somatic N.S. at the neuromuscular junction.

2. Sympathetic & parasympathetic ganglia.
3. Parasympathetic postganglionic nerve ending.
4. Sympathetic postsynaptic (postganglionic) fiber to sweat gland & medulla.

➢ In 1914 Dale distinguished 2 types of receptors:
Muscarinic actions on smooth muscle, cardiac muscle and glands ➔

 Muscarinic receptors (has 6 subtypes)
M1 (Neuronal) M2 (Cardiac) M3 (glandular/smooth muscle)

➢ In CNS, peripheral ➢ On peripheral ➢ On exocrine glands &
neurons & gastric neurons & heart. smooth muscles.
parietal cells (gastric ➢ Selective M2 ➢ Atropine competitively

acid secretion). antagonist ➔ blocks all types of
➢ Selective M1 antagonist gallamine. muscarinic receptors
➔ pirenzepine. (muscarinic blocker).

 Nicotinic receptors

Nn Nm
➢ In brain neurons & all ganglia ➢ In skeletal muscle (Neuromuscular
➢ blocked by hexamethonium & junction)

conc. Nicotine ➢ blocked by d-tubocurarine  paralysis

Acetylcholine

 Distribution: distributed in nervous tissues, motor fibers, ganglia and also in brain
 Two types of acetylcholine esterase:

True cholinesterase found in nerve ending, neuromuscular junction and RBCs.

Specific, very slow turnover, non-specific found in plasma,
Pseudocholinesterase
intestine, liver and skin.

 There are cholinesterase inhibitors   Ach  can be used therapeutically (as in

Alzheimer disease)
 Hemicholinium ➔ inhibits biosynthesis of Ach by competitively inhibiting the
transport of choline into nerve ending.
 Ach is not used therapeutically:

➢ Unstable ➔ Hydrolyzed rapidly by cholinesterase.
➢ Have diverse actions (Ganglionic stimulation, skeletal muscle stimulation,
parasympathetic effects and adrenal stimulation).

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