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Year 2 LCRS Pharmacology > 6: Cholinomimetics > Flashcards

6: Cholinomimetics Flashcards

1
Q

What kind of drug is Atropine?

A

It is a kompetitive Muscarinic receptor antagonist

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2
Q

What does muscarine do?

A

Agonist of the Muscarinic receptor

–> Stimmulation (not broken down by Ach-esterase)

  • tears
  • saliva
  • miosis
  • sweating etc.
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3
Q

Where are the M1 muscarenic achetylcholine receptors loacted?

Which secound messenger system do they activatie?

A

•M1:

  • Salivary glands
  • Stomach
  • CNS

Activate Gq-Protein: exitory

  • IP3 + DAG (–> increases Ca2+ influx)
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4
Q

Where are the M2 muscarenic achetylcholine receptors loacted?

Which secound messenger system do they activatie?

A

•M2: Heart

  • are inhibitory

Activate Gi-protein

  • downregulation of cAMP
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5
Q

Where are the M3 muscarenic achetylcholine receptors loacted?

Which secound messenger system do they activatie?

A

M3:

  • Salivary glands
  • Bronchial/visceral SM
  • Sweat glands
  • Eye

Are exitory: Activate Gq protein

  • increase in IP3 and DAG
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6
Q

What are the structural features of the Muscarinic receptor?

A

Has 7 transmembrane regions

connencted to loop + G-protein in the inside

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7
Q

Explain the structure of a nicotinic receptor

A
  • Ionotropic receptor
  • Has 5 subunites (alpha-epsylon)
  • Binding property is determines by the combination of Subunits
  • •Effects of ACh relatively weak
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8
Q

What are the effects of muscarinic exitation in the eye?

A

Contraction of the ciliary muscle: accommodation for near vision

Contraction of the sphincter pupillae (circular muscle of the iris): Constricts pupil (miosis) and improves drainage of intraocular fluid

Lacrimation (tears)

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9
Q

What is the effect of contraction of the spincter puppilare?

How can this be used in glaucoma treatment?

A

Contraction of sphincter pupillae opens pathway for aqueous humour, allowing drainage

–> reducing intra-ocular pressure

–> in some form of glaucoma, iris is deformed, blocking fluid drainage and hence increasing intraoccular pressure

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10
Q

What are the effects of muscarinic stimmulation on the heart?

A
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11
Q

Which effect does Ach has on the vasculature?

A

No direct PNS innervation but has M3 receptors:

  • stimmulation causing endothelial NO release
  • SM relaxation
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12
Q

Which effect does parasympathetic innervation has on the non-vascular smooth muscle?

A

–> Constriction:

  • Lung: Bronchoconstriction
  • Gut: Increased peristalsis (motility)
  • Bladder: Increased bladder emptying
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13
Q

Which effect does stimmulation of muscarinic Ach receptor have on excretions?

A

Exitory:

  • Salivation
  • •Increased bronchial secretions
  • •Increased gastro-intestinal secretions (including gastric HCl production)
  • •Increased sweating (SNS-mediated)
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14
Q

What directly acting cholinomimetic drugs are there?

A
  1. Alkaloids (Pilocarpine)
  2. Choline esters (Bethanechol)
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15
Q

What are the characteristics of Pilocarpine?

What kind of drug is it?

A

It is a non-selective muscarenic agonist

–> good lipid solubility

–> half life around 3-4h

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16
Q

What is the clinical use of pilocarpine?

A

Mostly used for local treatment of glaucoma

(non-selective muscarenic agonist)

17
Q

What are possible side effects of pilocarpine? Why?

A
  • Blurred vision (–> PNS stimmulation of eye)
  • sweating (SNS stimmulation)
  • gastro-intestinal disturbance and pain
  • hypotension
  • respiratory distress

–> all others: PNS stimmulation

18
Q

What kind of drug is Bethanechol?

What are its characteristics?

A

M3 Acetylcholinereceptor selective agonist

  • no degradation
  • orally active (can be orally given)
  • half life: 3-4h
19
Q

What is the clinical use of Bethanechol?

A

To assist bladder emptying and enhance gastric motility

20
Q

What are the side effects of Bethanechol administration?

A
  • Sweating
  • imparied vision
  • bradycardia
  • hypotension
  • respiratory distress
21
Q

What is the function of Acetylcholinesterase?

Where is it found?

A

Break down ACh to acetate and choline

  • found in all cholinergic synapses
  • very fast and highly selective
22
Q

What is the function of Butyrylcholinesterase?

Where is it found?

What are its characteristics?

A
  • Break down ACH
  • found in plasma and most tissues, not in synapse –> reason for low ACh plasma levels
  • •Broad substrate specificity - hydrolyses other esters e.g. suxamethonium
  • Genetic variation
23
Q

What happens at a low, medium and high dose of cholinesterase inhibitors?

A

Low dose

  • Enhanced muscarinic activity (see above)

Moderate dose

  • Further enhancement of muscarinic activity
  • Increased transmission at ALL autonomic ganglia (nAChRs)

High dose (toxic)

  • Depolarising block at autonomic ganglia & NMJ (see PT9 NMJ lecture) –> too much fiering –> receptors shout down –> paralysis
24
Q

Which drug is a reversibel Anticholinesterase drug?

Why is it reversible?

A

Physostigmine and Neostigmine

  • competitive inhibitor –> binds to active side
  • Donates Carbamyl group that blocks the receptor
  • Carbamyl group removed by slow hydrolysis (mins rather than msecs)
25
Q

What is physiostigme?

What are its characteristics?

A

A reversibele indirectly cholinomimetic drug

  • reversibly blocks Cholinesterase (get freed again after minutes)
  • Primarily acts on postganglionic parasympathetic synapse
  • Half life about 30m
26
Q

What is the clinical use of physiosigme?

A

Clinical use:

  • Glaucoma treatment
  • To treat atropine poisoning (particularly in children)
27
Q

What kind of drugs are irreversibel Anticholinesterase Drugs?

How do they act?

A
  1. ecothiopate (only one with clinical use)
  2. dyflos, parathion and sarin used as pestisides or chemical weapons

React with enzyme active side

  • Make a stable block, resistant to hydrolysis
  • –> recovery may require production of new enzymes
28
Q

What is Ecothiopate?

A

Potent inhibitor of acetylcholinesterase

–> Slow reactivation of the enzyme by hydrolysis takes several days

29
Q

What is the clinical use of Ecothiopate?

A

Irreversible anticholinesterase inhibitor

Used in treatment of glaucoma

  • prolonged effect in fluid drainage
30
Q

What are the side effect of Ecothiopate?

A
  • Sweating
  • blurred vision
  • GI pain
  • bradycardia
  • hypotension
  • Respiratory problems

–> PNS stimmulation

31
Q

What are the effect of Anicholinestases in the CNS?

A

Non-polar Anticholinesterases can cross BBB

Low doses

  • exitation with possibility of convulsions (Krämpfe)

High dose:

Unconsciousness, respiratory depression, death

32
Q

What are possible treatments for Organophosphate Poisonings?

A

Organophsphate = irreversible anticholinesterase

Can be treated via

  • Atropine (Muscarenic antagonist)
  • Parlidoxime within first hours –> displaces the bound organophsphate from enzyme

Year 2 LCRS Pharmacology (38 decks)

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