4.cholinergic and anticholinergics
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Transcript of 4.cholinergic and anticholinergics
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Drugs Acting On Drugs Acting On Autonomic Nervous Autonomic Nervous System (ANS)System (ANS)
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Neurotransmitters Neurotransmitters Sympathetic: noradrenaline
(norepinephrine) Parasympathetic : acetylcholine
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Cholinergic receptorsCholinergic receptors
Muscarinic: M1 – M5
Activated by muscarine Nicotinic: NM, NN
Activated by nicotine
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Actions of AchActions of Ach
Acetylcholine – major neurotransmitter of PNS
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Actions of Ach
Characteristics
M1 (neuronal)
M2
(cardiac)M3 (glandular)
Location & Function
• Ganglia – impulse transmission
• SA node -Decreased rate of impulse generation • AV node –decreased conduction velocity • Atrium, ventricle-decreased contractility
• Exocrine glands-secretion
• Visceral smooth Muscle – contraction
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Actions of Ach
Characteristics
M1 (neuronal)
M2
(cardiac)M3 (glandular)
Location & Function
• Ganglia – impulse transmission
• SA node -Decreased rate of impulse generation • AV node –decreased conduction velocity • Atrium, ventricle-decreased contractility
• Exocrine glands-secretion
• Visceral smooth Muscle – contraction
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Actions of Ach
Characteristics
M1 (neuronal)
M2
(cardiac)M3 (glandular)
Location & Function
• Ganglia – impulse transmission
• SA node -Decreased rate of impulse generation • AV node –decreased conduction velocity • Atrium, ventricle-decreased contractility
• Exocrine glands-secretion
• Visceral smooth Muscle – contraction
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Actions of Ach
Characteristics
M1 (neuronal)
M2
(cardiac)M3 (glandular)
Location & Function
• Ganglia – impulse transmission
• SA node -Decreased rate of impulse generation • AV node –decreased conduction velocity • Atrium, ventricle-decreased contractility
• Exocrine glands (salivary, sweat) -secretion
• Visceral smooth Muscle (bronchus, bladder, GIT) – contraction
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Actions of Ach
Characteristics NM
(muscle type)NN
(neuronal type)
Location & Function
Skeletal neuromuscular junction (NMJ) – contraction
• Autonomic ganglia– impulse transmission
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Actions of ACh on eye
Muscarinic:Eye: -Circular muscle of iris (M3)- contraction-
miosis-Ciliary muscle (M3) – contraction- eye’s
focus is accomodated for near vision – spasm of accomodation
-Better drainage of aqueous humor – reduced intraocular pressure
-Lacrimal glands (M3) - lacrimation
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Acetylcholine Acetylcholine No therapeutic use because i) Ultra short action: rapidly
hydrolyzed by cholinesterasesii)Widespread and nonselective
activity: act on all receptors
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Drugs which mimic the actions of Ach are called as cholinergic drugs or parasympathomimetic drugs or cholinomimetic or cholinergic agonists
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Classification
1. Directly actingMethacholine, bethanechol,
pilocarpine Act on muscarinic receptors
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2. Indirectly acting (Anticholinesterases)
A. Reversible : Physostigmine, neostigmine, pyridostigmine, edrophoniumB. Irreversible: Organophosphates: Parathion, Malathion
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Mechanism of action of Anticholinesterases
Inhibit acetylcholinesterase (AChE) enzyme
Ach ----------- Choline + acetate AChE
Accumulation of Ach Action
Neostigmine
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Therapeutic uses
Ophthalmic use : i) Glaucoma ii)To counteract the effects of mydriatics iii) To break adhesions between the iris
and lens or iris and corneaMyasthenia gravis : neostigmineBelladona (Atropine) poisoning : Physostigmine – specific antidote
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Irreversible AChE inhibitorsIrreversible AChE inhibitors
Mainly used as insecticides and pesticides
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Adverse effects of Adverse effects of anticholinesterases anticholinesterases Diarrhea, urination,
bronchoconstriction, lacrimation, salivation, sweating, bradycardia, fasciculation of skeletal muscle
Organophosphorus poisoning: treated with an anticholinergic, atropine
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Anticholinergic Anticholinergic DrugsDrugs
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ClassificationNatural alkaloids : Atropine* (prototype), Scopolamine
(Hyoscine)Semisynthetic derivatives :Homatropine*, ipratropium bromide,
tiotropium bromideSynthetic compounds :i) Mydriatics – Cyclopentolate*, tropicamideii)Antiparkinsonian – Benzhexol, Biperiden,
Benztropine
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iii) Antisecretory- antispasmodics –Dicyclomine PirenzepineGlycopyrrolate
Semisynthetic and synthetic anticholinergics - Atropine substitutes
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Pharmacological actions of Pharmacological actions of atropineatropine
CNS :
High doses – restlessness, delirium, disorientation
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CVS :Tachycardia
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Eye :mydriasis : “Passive mydriasis”Photophobia, abolition of light reflex“Paralysis of accomodation or
cycloplegia”Rise in IOPDecrease in lacrimation – dry eyes
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Respiratory system :Bronchodilatation Decreased secretions GIT :Reduce gastric acid secretionReduced tone and motility of gut,
constriction of sphincters – constipation
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Genitourinary tract :Relaxation of ureter and urinary bladder –
urinary retentionGlands :Decreases sweat, salivary,
tracheobronchial and lacrimal secretionBody temperature :Rise in body temperature“Atropine fever”
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Uses of atropine Uses of atropine Preanaesthetic medication: to
decrease secretionOraganophosphorous poisoning
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Therapeutic uses Therapeutic uses Motion sickness : Scopolamine Parkinson’s disease :benzhexol,
benztropine etc.Bronchial asthma : ipratropium and
tiotropium bromidePreanaesthetic medication :
glycopyrrolate , As mydriatic during fundoscopy and
testing of refractive error – Tropicamide, cyclopentolate
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Side effects of atropine :Dry mouthBlurred vision and photophobiaUrinary retentionConstipationDry, hot skinPrecipitation of glaucomaDecreased sweating