Cholinergics
Terms
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- The type of receptor at all preganglionic synapses
- Nicotinic (Nn)
- The transmitter for somatic motor systems
- Nicotinic (Nm)
- Postysynaptic and organ response receptors for parasympathetics
- Muscarinic
- Consists of 5 subunits 2alpha, beta, gamma and delta
- motor system nicotinic
- This antagonist can be used to distinguish M1 and M2 muscarinic receptors
- pirenzepine
- High affinity for pirenzepine
- M1
- Low affinity for pirenzepine
- M2
- Muscarinic found in vessels and postganlionic effector organs
- M3
- Muscarinic receptors found in the brain and sympathetic ganglion
- M1
- Muscarinic receptors found in the heart
- M2
- Muscarinic Agonists (4)
-
Methacholine
Carbachol
Bethanechol
Pilocarpine - Nicotinic Agonists (2)
-
Nicotine
Succinylcholine - Action of agonists at M2 and M3 recptors (6)
-
1. Stimulate glands
2. Stimulate smooth muscle contraction
3. Relax Sphincters
4. Vasodilation (if IV injected)
5. Cardiac slowing
6. Pupil constriction, accomodation - Used to demonstrate asthma
- Methacholine
- Used for miosis in opthalmic surgery
- Carbechol
- Minor uses for urinary retention or paralysis of GI tract
- Bethanechol (little effect on CV system and nicotinic sites)
- The actions of these drugs can exacerbate asthma, pepetic ulcer, coronary insufficiency and intestinal obstruction
- Cholinergic agonists
- The use of Pilocarpine
- Used to treate open-angle glaucoma. Miosis and accomomodation spasm for upto 1 day
- Muscarinic Antagonists (3)
-
Atropine
Scopolamine
Glycopyrrolate -
cause:
excitation or respiration
restlessness
irritability - Atropine
-
causes:
drowsiness, sleep
hallucinations
delirium - Scopolamine
- treatment of atropine poisoning
-
Physostigmine
(universal distribution, compared to neostigmine) - May cause sharp rise in intraocular pressure in those with narrow angle glaucoma
- Atropine
- Use of glycopyrolate
- prevent excessive salivation caused by inhaled anesthetics
- Used in cold preparation for symptomatic relief
- Scopolamine
- Used to treat overactive bladders
- Tolerodine
- Ipratropium Bromide
- dilates bronchial airways and less drying than atropine.
- Nictotine stimuates NMJ or ganglia better?
- Ganglia are more sensitive to nicotine than NMJ
- Cholinesterase Inhibitors (4)
-
Physostigmine
Neostigmine
Edrophonium
Pyridostigmine -
Absorbed poorly from GI tract and do not penetrate CNS
Relatively selective for the NMJ - Edrophonium, neostigmine and pyridostigmiine
- The more lipid soluble cholinesterases that are well absorbed with ubiquitous distribution
- physostigmine and isoflurophate
- actions of anti-AChE drugs
-
Miosis, spasm of accomodation
GI contraction
stimulation of skeletal muscle
stimulate glands, contraction, bradycardia and low C.O. - Because of their quaternary ammonium structure, they are poorly absorbed and large oral doses are necessary. Duration 4-6 hours
-
Anti-AChE drugs (except physostigmine)
Ipratroprium Bromide has quat ammonium - Isoflurophate
-
organophosphours anti-AChE that binds irreversibly to AChE
(clinically used drug similar to insecticides) - Use to treat intoxication with organophosphates
- Pralidoxime (reverse the irreversible binding of isofluorate and regenerates AChE)
- Pralodoxime used in the absence of DFP
- Weak anti-AChE activity
- Parlytic Illeus and Urinary Retention
- neostigmine
- Glaucoma
- physostigmine
- Myastenia Gravis
- neostigmine, pyridostigmine
- Termination of neuromuscular blocade
- neostigmine or edrophonium
- Atropine poisioning
- physostigmine
- Non Depolarizing muscle relaxers
-
Curare
Mivacurium
Rocuronium
Cisatracurium - Depolarizing muscle relaxers
- Succinylocholine
- Actions of Succinylcholine
-
depolarize muscle
no CNS effect
bradycardia and hypotension
Histamine release - Used to reverse neuromuscular blockaed by non-depolarizing antagonists
- Neostigmine and edrophonium
- Risk when using halogenated anestehtics and succinylcholine
- malignant hyperthermia (treat with dantrolene)
- Which sphincters are naturally contracted in man
-
Cardiac
Pyloric
Ileocecal - Which cholinergic agonist has action on both muscarinic and nicotinic receptors
- Carbechol
- Which cholinergic agonist is not antagonized by atropine
- Carbechol (acts on N and M receptors)
- What are the relative sensitivities to atropine
- Salivary, respiratory, cardiac and ophthalmic are more sensitivie than GI and GU
- Which effects of nicotine does tolerance develop in and which does it not
-
Tolerance to GI effects
no tolerance to cardiovascular effects - Tetracycline and Succinylcholine
- Tetra's chelate calcium (need for exocytosis) and thus potentiate NMJ blockade
- To prevent injury when performing ECT
- Succinylcholine (depolarizing NMJ blocker)