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Year 2 LCRS > Pharmacology 6 - Cholinomimetics > Flashcards

Pharmacology 6 - Cholinomimetics Flashcards

1
Q

What are the two classes of cholinomimetic drugs?

A
  • Directly acting (choline esters and alkaloids)

- Indirectly acting

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2
Q

Why is acetylcholine of no therapeutic use?

A
  • It doesn’t differentiate between nicotinic and muscarinic receptors
  • It is rapidly degraded
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3
Q

What does muscarine cause?

A

Mushroom poisoning

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4
Q

Give an example of a choline ester

A
  • Bethanechol
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5
Q

Give examples of alkaloids

A
  • Pilocarpine (of pilocarpus)
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6
Q

What are the uses of bethanechol?

A
  • A modified acetylcholine resistant to degradation - limited acess to brain, orally active
  • Selective for muscarinic M3 receptors
  • Used to assist bladder emptying and stimulate gastrointestinal motility
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7
Q

What is the use of pilocarpine?

A
  • Selective for muscarinic receptors (not selective between the subtypes of receptors)
  • Given locally to treat glaucoma (causes pupil constriction and fluid drainage)
  • Applied topically (eye drops)
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8
Q

What drugs are indirectly acting cholinomimetics?

A

Anticholinesterase drugs

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9
Q

What is the mode of action of anticholinesterase drugs?

A
  • Produces pharmacological actions by inhibiting acetylcholinesterase and preventing breakdown of acetylcholine
  • Potential to increase cholinergic activity at all cholinergic synapses
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10
Q

What are the two types of cholinesterases and where are they found?

A
  • Acetylcholinesterase (true) is found in all cholinergic synapses in the PNS and CNS
  • Butyrylcholinesterase (pseudocholinesterase) is found in tissues and plasma
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11
Q

How does butyrylcholinesterase differ from acetylcholinesterase?

A
  • Butyrylcholinesterase has a broader substrate specificity and hydrolyses other esters such as suxamethonium
  • Shows genetic variance, which influences the duration of action of drugs it normally metabolises
  • Acetylcholinesterase has a rapid hydrolysis action and is highly selective
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12
Q

Describe the mechanism of hydrolysis by acetylcholinesterase

A
  • Acetylcholine + enzyme
  • Choline + acetylated enzyme
  • Acetate + free enzyme
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13
Q

How are anticholinesterase drugs classified?

A
  • Reversible

- Irreversible

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14
Q

Give examples of reversible anticholinesterase drugs

A

Alkaloids (physostigmine - postganglionic parasympathetic synapse - and neostigmine)

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15
Q

What is the mechanism of reversible antichonesterase drugs?

A
  • Carbamyl esters (physostigmine and neostigmine) inactivate the enzyme by transferring their carbamyl group and blocking the active site
  • Carbamyl group removed by slow hydrolysis (minutes)
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16
Q

Give examples of irreversible anticholinesterase drugs

A

Organophosphate compounds (eg. ecothiopate)

17
Q

How do irreversible anticholinesterase drugs work?

A
  • They inactivate the enzyme by leaving a large blocking group
  • The inactive phosphorylated enzyme is stable (recovery depends upon synthesis of a new enzyme - could take weeks)
18
Q

List the effects of anticholinesterase drugs on the autonomic nervous system

A
  • Low dose results in enhanced muscarinic activity
  • Moderate dose results in enhancement of muscarinic activity and enhanced transmission at all autonomic ganglia
  • High doses cause sepolarising block at ganglia
19
Q

What is physostigmine used to treat?

A
  • Glaucoma (eye drops)

- Atropine poisoning (I.V)

20
Q

What is ecothiopate used to treat?

A
  • Glaucoma (eye drops)
21
Q

How does organophosphorous poisoning occur?

A
  • Compounds used in agriculture/horticulture
  • Nerve agents
  • Highly lipid soluble so readily absorbed through the nasal mucosa, skin and lungs
22
Q

What are the signs and symptoms of organophosphorus poisoning?

A
  • Increased muscarinic activity (seizures)
  • CNS excitation
  • NM block
  • Cessation of respiration
23
Q

What are the potential treatments of organophosphorous poisoning?

A
  • Atropine IV
  • Artificial respiration
  • Pralidoxime
24
Q

Define cholinomimetic drug

A

A drug that mimics acetylcholine

25
Q

What is the characteristic of muscarinic receptor structure?

A

7 transmembrane components

26
Q

What are the second messengers of M1, M2, M3, M4 and M5

A

M1, M3, M5 Gq protein - increases IP3 and DAG

M2 and M4 Gi protein - reduces cAMP

27
Q

List the subunits of nicotinic receptors, and compare composition of the muscle and ganglion type

A

5 subunits - alpha beta gamma delta and epsilon

  • Muscle type 2alpha, beta, delta, epsilon
  • Ganglion type 2alpha, 3beta
28
Q

What are the main effects of the muscarinic receptors in the eye?

A
  • Contraction of the ciliary muscle (convex, allows near vision)
  • Contraction of the spincter pupillae (constricts pupil and improves drainage of intraocular fluid)
  • Lacrimation (tears)
29
Q

How does intraocular drainage occur following contraction of sphincter pupillae?

A
  • Opens the pathway for the aqueous humour, produced by the ciliary body
  • This drains via the canals of schlemm
  • Reduces intra-ocular pressure
30
Q

Describe how muscarinic receptors affect the heart

A
  • M2 AChR in atria and nodes cause decreased cAMP

- This deacreases Ca2+ entry (decreased CO) and increases K+ efflux (decreased HR)

31
Q

How does ACh affect vascular endothelial cells?

A
  • Binds to M3 in endothelial cells stimulating NO release

- This induces smooth muscle relaxation, decreasing TPR

32
Q

List the side effects of pilocarpine

A
  • Blurred vision
  • Sweating
  • Gastro-intestinal disturbance and pain
  • Hypotension
  • Respiratory distress
33
Q

List the side effects of bethanechol

A
  • Sweating
  • Impaired vision
  • Bradycardia
  • Hypotension
  • Respiratory difficulty
34
Q

What is the principal reason for low plasma acetylcholine?

A

Butyrylcholinesterase

Year 2 LCRS (128 decks)

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