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Drugs Acting On Drugs Acting On Autonomic Nervous Autonomic Nervous System (ANS)System (ANS)
Neurotransmitters Neurotransmitters Sympathetic: noradrenaline
(norepinephrine) Parasympathetic : acetylcholine
Cholinergic receptorsCholinergic receptors
Muscarinic: M1 – M5
Activated by muscarine Nicotinic: NM, NN
Activated by nicotine
Actions of AchActions of Ach
Acetylcholine – major neurotransmitter of PNS
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
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
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
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
Actions of Ach
Characteristics NM
(muscle type)NN
(neuronal type)
Location & Function
Skeletal neuromuscular junction (NMJ) – contraction
• Autonomic ganglia– impulse transmission
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
Acetylcholine Acetylcholine No therapeutic use because i) Ultra short action: rapidly
hydrolyzed by cholinesterasesii)Widespread and nonselective
activity: act on all receptors
Drugs which mimic the actions of Ach are called as cholinergic drugs or parasympathomimetic drugs or cholinomimetic or cholinergic agonists
Classification
1. Directly actingMethacholine, bethanechol,
pilocarpine Act on muscarinic receptors
2. Indirectly acting (Anticholinesterases)
A. Reversible : Physostigmine, neostigmine, pyridostigmine, edrophoniumB. Irreversible: Organophosphates: Parathion, Malathion
Mechanism of action of Anticholinesterases
Inhibit acetylcholinesterase (AChE) enzyme
Ach ----------- Choline + acetate AChE
Accumulation of Ach Action
Neostigmine
____
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
Irreversible AChE inhibitorsIrreversible AChE inhibitors
Mainly used as insecticides and pesticides
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
Anticholinergic Anticholinergic DrugsDrugs
ClassificationNatural alkaloids : Atropine* (prototype), Scopolamine
(Hyoscine)Semisynthetic derivatives :Homatropine*, ipratropium bromide,
tiotropium bromideSynthetic compounds :i) Mydriatics – Cyclopentolate*, tropicamideii)Antiparkinsonian – Benzhexol, Biperiden,
Benztropine
iii) Antisecretory- antispasmodics –Dicyclomine PirenzepineGlycopyrrolate
Semisynthetic and synthetic anticholinergics - Atropine substitutes
Pharmacological actions of Pharmacological actions of atropineatropine
CNS :
High doses – restlessness, delirium, disorientation
CVS :Tachycardia
Eye :mydriasis : “Passive mydriasis”Photophobia, abolition of light reflex“Paralysis of accomodation or
cycloplegia”Rise in IOPDecrease in lacrimation – dry eyes
Respiratory system :Bronchodilatation Decreased secretions GIT :Reduce gastric acid secretionReduced tone and motility of gut,
constriction of sphincters – constipation
Genitourinary tract :Relaxation of ureter and urinary bladder –
urinary retentionGlands :Decreases sweat, salivary,
tracheobronchial and lacrimal secretionBody temperature :Rise in body temperature“Atropine fever”
Uses of atropine Uses of atropine Preanaesthetic medication: to
decrease secretionOraganophosphorous poisoning
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
Side effects of atropine :Dry mouthBlurred vision and photophobiaUrinary retentionConstipationDry, hot skinPrecipitation of glaucomaDecreased sweating