Pharmacology Notes First Semester

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  • Topic: Acetylcholine, Adrenergic receptor, Norepinephrine
  • Pages : 20 (4098 words )
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  • Published : April 20, 2013
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14. CHOLINERGIC AGONISTS AND CHOLINESTERASE INHIBITORS CHOLINERGIC AGONISTS
Overview
“muscarinic receptor agonists” cholinergic agonists are drugs that act on acetylcholine receptors, thus causing excitation of the parasympathetic autonomic nervous system there are 2 types of acetylcholine receptors 1) NICOTINIC RECEPTORS - are receptor-mediated ion channels - 3 types RECEPTOR TYPE MUSCLE TYPE GANGLION TYPE LOCATION - neuromuscular junction - sympathetic autonomic ganglia - parasympathetic autonomic ganglia - CNS

CNS TYPE

-

agonists of nicotinic receptors are discussed later (“depolarizing neuromuscular blocking agents”, see 16)

2) MUSCARINIC RECEPTORS - are g-protein coupled receptors - 3 types RECEPTOR TYPE M1 LOCATION - CNS - exocrine glands (gastric. bronchial-, salivary-, lacrimal-, and sweat glands) - CNS - GI tract smooth muscle - atria of the heart - exocrine glands - GI tract smooth muscle - 37 -

M2

M3

- genito-urinary tract smooth muscle - bronchial smooth muscle - smooth muscle of the eye - endothelium of blood vessels

General Effects
8 types ORGAN CNS EFFECT - increased skeletal muscle tension - tremor - hypothermia - improved cognition (improved learning) - decreased heart rate (“bradycardia”) - decreased force of contraction - decreased blood pressure (due to vasodilation) - myosis (due to contraction of the pupilary sphincter) - accomodation to near vision (due to contraction of the ciliary muscle) - decreased intraoccular pressure (due to opening of the schlemm canal) - GI tract emptying (due to increased peristalsis) - urinary bladder emptying (due to contraction of the detrusor muscle) - bronchoconstriction (due to contraction of bronchial smooth muscle) - increased gastric secretion - increased bronchial secretion - increased salivation - increased lacrimation - increased sweating

HEART

BLOOD VESSELS EYE

GI TRACT GENITO-URINARY TRACT

BRONCHI

EXOCRINE GLANDS

Relevant Drugs
3 types - 38 -

DRUG NAME ACETYLCHOLINE

DESCRIPTION General information - acetylcholine itself - non-selective acetylcholine receptor agonist (acts on both nicotinic- and muscarinic receptors) - not used clinically General information - selective muscarinic receptor agonist (acts only on muscarinic receptors) - selective to the eye and exocrine glands Clinical uses - treatment of glaucoma (by reduction of intraoccular pressure)

PILOCARPINE

MUSCARINE

General information - same as pilocarpine (see above) - found naturally in toadstool - the causative agent of mushroom poisoning - not used clinically

CHOLINESTERASE INHIBITORS
Overview
there are 2 types of cholinesterase enzymes

ENZYME NAME PLASMACHOLINESTERASE

DESCRIPTION - “butyrylcholinesterase” - located in the blood - responsible for the breakdown of acetylcholine in the blood stream - not discussed further here - located in the cholinergic synapses - responsible for the breakdown of acetylcholine in the cholinergic synapses

ACETYLCHOLINESTERASE

-

cholinesterase inhibitors ("anticholinesterases") inhibit the degradation of acetylcholine by acetylcholinesterase at the nicotinic cholinergic synapses, thus prolonging it's effect

- 39 -

General Effects
2 types ORGAN PARASYMPATHETIC POSTGANGLIONIC SYNAPSES EFFECT - increased parasympathetic effects (see above) - large doses may lead to decreased parasympathetic effects (due to depolarization block in autonomic ganglia caused by continuous acetylcholine action) - increased skeletal muscle tension - large doses may lead to paralysis (depolarization block)

NEUROMUSCULAR JUNCTION

Relevant Drugs
2 categories 1) REVERSIBLE - 3 types DRUG NAME NEOSTIGMINE DESCRIPTION Clinical uses - treatment of myasthenia gravis Clinical uses - same as neostigmine (see above) General information - may cross the blood-brain barrier Clinical uses - treatment of glaucoma Side effects - coma and respiratory failure (due to initial...
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