cholinergic drugs

25,309 views

Published on

4 Comments
80 Likes
Statistics
Notes
No Downloads
Views
Total views
25,309
On SlideShare
0
From Embeds
0
Number of Embeds
77
Actions
Shares
0
Downloads
0
Comments
4
Likes
80
Embeds 0
No embeds

No notes for slide

cholinergic drugs

  1. 1. Cholinergic (CholinoceptorActivating) Drugs-1 Dept. of Pharmacology Faculty of Medicine & Health Sciences AIMST
  2. 2. Cholinergic Drugs-1-LectureOutline  Cholinoceptors(Review)  Types  Muscarinic  Nicotinic  Characteristics  Typical Locations  Cholinergic Drugs  Classification  Direct Acting  Choline Esters  Cholinomimetic Alkaloids
  3. 3. Cholinergic Drugs-1-LectureOutline(contd.)  Cholinergic Drugs (contd.)  Indirect Acting (Anticholinesterase Agents)  Reversible  Irreversible  ACh-Pharmacological Actions  Choline Esters  Properties  Therapeutic Uses  Cholinomimetic Alkaloids  Cholinomimetic Drugs  Contraindications
  4. 4. Cholinergic Receptors(Cholinoceptors)-Types & Characteristics Acetylcholine Receptors (Cholinoceptors)  Main subdivision is into muscarinic (mAChR) and nicotinic (nAChR) subtypes  In smooth muscle, cardiac muscle and glands the cholinergic receptors are of the muscarinic (mAChR) type (i.e. stimulated by muscarine, an alkaloid from Amanita muscaria mushrooms)
  5. 5. Cholinergic Receptors(Cholinoceptors)-Types & Characteristics Acetylcholine Receptors (Cholinoceptors)  In striated (skeletal) muscle and autonomic ganglia (sympathetic and parasympathetic) the cholinergic receptors are nicotinic (nAChR) (i.e. stimulated by nicotine)  mAChR’s are G-protein coupled receptors, causing:  Activation of phospholipase C  Inhibition of adenylate cyclase  Activation of potassium channels  Inhibition of calcium channels
  6. 6. Cholinergic Receptors(Cholinoceptors)-Types & Characteristics Muscarinic Acetylcholine Receptors(mAChR’s)  Five types occur, viz.:  M1-receptors (neural)- Selectively blocked by pirenzepine  M2-receptors (cardiac)- Decrease cardiac contractility and heart rate; selectively blocked by gallamine  M3-receptors (glandular)- causing secretion, visceral smooth muscle contraction, vascular relaxation  M4-receptors & M5-receptors- largely confined to CNS; functional role not well understood
  7. 7. Autonomic Nervous System(ANS)-Cholinergic Receptors M1-receptors -  M1, M3 and M5 receptor subtypes have stimulatory effect on the target tissue  M2 and M4 subtypes are inhibitory
  8. 8. Cholinergic Muscarinic Receptors
  9. 9. Cholinergic Receptors(Cholinoceptors)-Types & Characteristics Nicotinic Acetylcholine Receptors(nAChR’s)  Two types occur, viz.:  NM receptors (muscle type)- located at skeletal muscle neuromuscular junction, Na+, K+ depolarizing ion channel, blocked by d-tubocurarine  NG receptors (neuronal type)- located at postganglionic cell body, Na+, K+ depolarizing ion channel, blocked by hexamethonium
  10. 10. Cholinergic (Cholinoceptor Activating)Drugs Cholinergic Drugs(Cholinomimetics/ Parasympathomimetics)  Drugs producing actions similar to that of Acetylcholine (ACh) Two modes of action:  May directly interact with cholinergic receptors  Increase availability of ACh at receptor sites
  11. 11. Cholinergic (Cholinoceptor Activating)Drugs-Classification Cholinergic Drugs  Direct-acting drugs (bind to & activate muscarinic or nicotinic receptors)  Choline esters  Acetylcholine  Bethanechol  Carbachol  Methacholine  Cholinomimetic Alkaloids  Pilocarpine  Muscarine  Nicotine  Lobeline  Arecoline  Oxotremorine
  12. 12. Cholinergic (Cholinoceptor Activating)Drugs-Classification Cholinergic Drugs (contd.)  Indirect-acting drugs (↑ ACh/Cholinesterase inhibitors/Anticholinesterases)  Reversible (water soluble)  Edrophonium  Physostigmine  Neostigmine  Pyridostigmine  Ambenonium  Demecarium  Eptastigmine  Rivastigmine  Donepezil
  13. 13. Cholinergic (Cholinoceptor Activating)Drugs-Classification Cholinergic Drugs (contd.)  Indirect-acting drugs (↑ ACh/ Cholinesterase inhibitors)  Irreversible (lipid soluble)  Organophosphates (e.g., Echothiophate, Diisopropylfluorophosphate, Malathion, Parathion, Diazinon, Soman, Sarin, Tabun, etc.)  Carbamates (e.g., Carbaryl, Propoxur)
  14. 14. Acetylcholine (ACh)- Actions Muscarinic  Heart  SA Node  Hyperpolarization of SA nodal cells  Decreased rate of impulse generation (Bradycardia, negative chronotropy)  Atria  Decrease in contractile strength(negative inotropy)  Atrioventricular Node  Decrease in conduction velocity (negative dromotropy)  Ventricles  Small decrease in contractile strength
  15. 15. Acetylcholine (ACh)- Actions Muscarinic  Blood vessels  Very few blood vessels receive cholinergic innervation  Muscarinic receptors present on vascular endothelial cells  Arteries  Dilation (via EDRF(NO))  Veins  Dilation (via EDRF(NO))
  16. 16. Acetylcholine (ACh)- Actions Muscarinic  Lung  Bronchial muscle  Contraction (Bronchoconstriction)  Bronchial glands  Stimulation of secretion  Gastrointestinal tract (evacuation of bowel)  Motility  Increase  Sphincters  Relaxation  Secretion  Stimulation
  17. 17. Acetylcholine (ACh)- Actions Muscarinic  Urinary bladder (voiding of bladder)  Detrusor  Contraction  Trigone & sphincter  Relaxation  Ureter  Increased peristalsis  Glands  Sweat/salivary/lacrimal/nasopharyngeal  Increased secretions
  18. 18. Acetylcholine (ACh)- Actions Muscarinic  Eye  Sphincter (circular) muscle of iris  Contraction (miosis)  Ciliary muscle  Contraction for near vision  Spasm of accomodation  Increased aqueous outflow  Reduction in intraocular tension
  19. 19. Acetylcholine (ACh)- Actions Nicotinic  Autonomic ganglia  Both parasympathetic & sympathetic ganglia stimulated  High dose ACh after atropine administration leads to  Tachycardia  Rise in BP  Skeletal muscles  Iontophoretic application of ACh to motor endplate leads to skeletal muscle contraction
  20. 20. Choline Esters-PropertiesCholine Ester Susceptibility Muscarinic Nicotinic to Action Action Cholinesteras eAcetylcholine ++++ +++ +++chlorideMethacholine + ++++ NonechlorideCarbachol Negligible ++ +++chlorideBethanechol Negligible ++ Nonechloride
  21. 21. Choline Esters-Properties Bethanechol  Not destroyed by cholinesterase (both true & pseudo)  Has mainly muscarinic actions (well antagonized by atropine)  Negligible CVS effects  Acts chiefly on the bladder & bowels  Preferable to carbachol because of this partial selectivity Carbachol  Not destroyed by cholinesterase (both true & pseudo)  More potent than bethanechol & methacholine  Muscarinic effects not adequately antagonized by atropine
  22. 22. Choline Esters-Properties Carbachol(contd.)  Stimulates autonomic ganglia & skeletal muscles  Actions are most pronounced on the bladder & bowels  Used to stimulate bladder & intestines after surgery Methacholine  Effective orally (though its absorption upon oral administration is variable)  3 times more resistant to hydrolysis by true cholinesterase w.r.t. ACh  Totally resistant to hydrolysis by pseudocholinesterase  Longer duration of action than ACh
  23. 23. Choline Esters- Uses Acetylcholine not used because of its transient & non- selective action Others rarely used nowadays Bethanechol has been used in  Postoperative paralytic ileus & gastric atony  Postoperative/postpartum nonobstructive urinary retention  Neurogenic bladder atony  Congenital megacolon, and  Gastroesophageal reflux Methacholine was occasionally used to terminate paroxysmal supraventricular tachycardia (PSVT)
  24. 24. Cholinomimetic Alkaloids Pilocarpine(Tertiary amine)  Obtained from leaves of Pilocarpus microphyllus  Prominent muscarinic actions  Causes marked sweating, salivation & increases other secretions  Applied to the eye, it penetrates cornea and promptly causes miosis, ciliary muscle contraction and fall in intraocular tension  Initial therapy (pilocarpine + physostigmine) in acute angle-closure glaucoma  Used as 0.5-4% drops to treat chronic simple glaucoma
  25. 25. Cholinomimetic Alkaloids Muscarine  Occurs in poisonous mushrooms (Amanita muscaria & Inocybe spp.)  Quaternary amine  Has only muscarinic actions  Not used therapeutically Nicotine  Derived from the plant Nicotiana tabacum  Tertiary amine  Has only nicotinic actions Lobeline  Plant derivative similar to nicotine
  26. 26. Cholinomimetic Drugs-Contraindications Bronchial Asthma  Cholinergic drugs can precipitate an asthmatic attack in susceptible individuals as they can cause bronchoconstriction Peptic Ulcer  Enhance gastric acid production and hence can aggravate symptoms of acid peptic disease
  27. 27. Cholinergic Drugs-1(Summary) Two types of cholinergic receptors (muscarinic & nicotinic) Muscarinic receptors-smooth muscles/cardiac muscle/glands/CNS Nicotinic receptors-skeletal muscles/ganglia/ CNS Cholinergic Drugs(Direct & Indirect-acting) ACh actions on various organ systems Choline esters & cholinomimetic alkaloids
  28. 28. THANK YOU !

×