cholinergic drugs_ans
TRANSCRIPT
CHOLINERGIC DRUGSDr Indrajit BanerjeeAssistant ProfessorMBBS, M.DDepartment of PharmacologyDr. D Y Patil Medical CollegeMauritius
Learning Objectives
• Neurotransmitters of Cholinergic system
• Sites of acetylcholine release, synthesis and fate of acetylcholine
• Cholinergic receptors, agonist and antagonists
• Physiological actions of acetylcholine
• Classification of directly acting cholinergic drugs, uses, adverse effects of acetylcholine and acetylcholine substitutes
• Mushroom poisoning
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•Acetylcholine [Ach] an choline
ester, is a neurotransmitter of
parasympathetic system. Nerves
which synthesize, stores &
release Ach are known as
‘Cholinergic”
CHOLINERGIC SYSTEM
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•GANGLIA- All pre-ganglionic fibers of ANS.[Both in sympathetic & parasympathetic ganglia.]•POST GANGLIONIC PARASYMPATHETHIC nerve endings
SITES OF ACTYLCHOLINE RELEASE:
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•SWEAT GLANDS: Sympathetic
postganglionic nerve endings
supplying sweat glands
•SKELETAL MUSCLES- Somatic
nerve endings supplying skeletal
muscles
SITES OF ACTYLCHOLINE RELEASE:
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•ADRENAL MEDULLA
•CNS- brain & spinal cord.
SITES OF ACTYLCHOLINE RELEASE:
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ACETYLCHOLINE (Ach)
• Is major neurotransmitter autonomic & somatic site
• Hemicholinium block choline uptake in axoplasm
• Transport of Ach into synaptic vesicle is blocked vesamicol
• Botulinum toxin inhibit Ach release relieve spasm in spastic disorder, facial wrinkles
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Termination of action of Ach
• A specific Acetylcholineesterase present in all cholinergic sites hydrolyses ester bond choline in µs (very fast)
• Location: All cholinergic sites, RBC, Gray matter
• Nonspecific Butrylcholinesterase (Pseudo) present in plasma hydrolyses Ach slowly
• Location: Plasma, Liver, Intestine, White matter
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Cholinergic receptor
• Muscarine alkaloid mimic the effect of parasympathetic nerve discharge but not in autonomic ganglia
• Nicotinic alkaloid stimulate autonomic ganglia, neuromuscular junction but not other autonomic effector cells
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Muscarinic receptor sub types
Receptor/ Location
Transducer mechanism
Agonist Antagonist
M1-CNS,nerves, Gastric parietal cells
IP3/DAG- cytosolic Ca++
Oxotremorine Pirenzepine
M2-Heart cAMP-k+ channel regulation
Methacholine Tripitamine
M3-gland,smooth muscle,endothelium
IP3/DAG- cytosolic Ca++
Bethanechol Darifenacin
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Nicotinic sub types
NM
Neuromuscular junction
Opening of cation (Na+ K+) channels
Agonist-
PTMA
Antagonist-
Tubocurarine
NN
Autonomic ganglia
Opening of cation (Na+ K+) channels
DMPP Trimethaphan
PTMA-Phenyltrimethylammonium
DMPP-Dimethylphenylpiperazinium
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Cholinergic Drugs
Choline esters
•Acetylcholine
•Bethanechol
•Carbachol
•Methacholine
Alkaloid
•Muscarine
•Arecoline
•Pilocarpine
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Acetylcholine (Prototype)
• Orally destroyed, given iv destroyed by pseudocholinesterase in plasma & at the site of action by cholinesterase
• Nonspecific in action
• Not used therapeutically
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Physiology of Ach & action in vitro
preparation
Eye-(M3)
• Sphincter muscle of iris-contraction(miosis)
• Ciliary muscle-contraction for near vision
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Heart M2
• SA node-Hyperpolarization rate of impulse generation (-ve chronotropic)
• Atria –K+channel open(hyperpolrization),cAMP, refractory period (-ve inotropic)Contractility
• AV node- conduction velocity(-ve dromotropic)
• Ventricle-small decrease in contractile strength
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Blood vessels (M3)• Vasodilatation is primarily mediated through
endothelium derived relaxing factor(EDRF) which is nitric oxide
• In vivo parasympathetic stimulation effects appears as fall in BP and flushing esp in blush area of face which has cholinergic innervation
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Smooth muscle (M3)• Tone and peristalsis in GI tract-
• Sphincters relax – abdominal cramps & evacuation of bowels
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Bronchial smooth constrict-
bronchoconstriction
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Detrusor muscle contract while bladder
trigone & sphincter relax-Voiding of urine
urinary bladder.htm
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Glands
•Glands- sweating, salivation, lacrimation
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Skeletal muscle(NM)
• Ach to muscle end plate causes contraction of fibre
• High dose can cause twitching & fasciculations
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Ach substitute
• Effective orally, more selective in their action
• Methacholine –
Less susceptible to acetylcholinesterase, totally resistant to pseudocholinesterase
• Carbachol, Bethanechol resistant to hydrolysis of both true and pseudocholinesterase
• Bethanechol(M3)have negligible effects on CVS (M2), no nicotinic action
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Adverse effects
• Extension of pharmacological action
• Flushing, salivation, sweating, bradycardia, bronchospasm, hypotension
Uses• Post-operative paralytic ileus, Urinary
retention, abdominal distension
• Bethanechol is preferred drug due to specific action & wider margin of safety
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Cholinomimetic AlkaloidPilocarpine-
• Alkaloid obtained from the leaves of Pilocarpusmicrophyllus
• Systemic administration produce toxic effects, it can be given orally (5-10 mg)
USES:
• Topical preparation for eye-0.5-4%,uses as miotic in reversing angle closure glaucoma(contraction of circular muscle of iris),break the adhesions of iris with lens or cornea by alternating use with mydriatics
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Cont…..• T/t for open angle glaucoma-contraction of
ciliary muscle of iris increases outflow facility• ADR-
• Painful spasm of accommodation & brow pain frequent side effects
• Systemic effects-nausea, diarrhoea, sweating & bronchospasm
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ARECOLINE
• Found in Betal nut
• Areca catechu
• Has Muscarinic & Nicotinic action
• Tried in dementia
• Not used therapeutically
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Muscarine
• Not used therapeutically
• Can cause Mushroom Poisoning
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MUSHROOM POISONING
• Amanita muscaria, Inocybe, A.phalloides
• TYPES:• Muscarine Type-(Early Mushroom
Poisoning)• Inocybe species• Nausea, Vomiting , Diarrhoea, Bradycardia,
Salivation, Sweating, Bronchospasm, hypotension
• Treated by Atropine IV
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• Hallucinogenic Type:
• Caused by Amanita muscaria
• Due to muscimol and other isoxazolecompounds.
• Produces central effects
• Activates aminoacid receptor in Brain
• Block muscarinic receptor
• No specific tratment
• Atropine is C/I
Another type Psilocybe mexicana whose active
psilocybine is a tryptaminergic
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CONT…
• LATE MUSHROOM POISONING:
• A. phalloides
• Occurs due to pepide toxins
• Causes inhibition of RNA & Protein synthesis
• Causes gastrointestinal, hepatic & renal damage
• Treated with thioctic acid
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