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Fundamentals of Pharmacology > Cholinergic Pharmacology > Flashcards

Cholinergic Pharmacology Flashcards

1
Q

What are cholinergic nerves?

A

Nerves that release acetylcholine and are found in all divisions of the nervous system

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2
Q

What divisions of the nervous system release acetylcholine?

A 
Somatic motor nerves
parasympathetic pre and post ganglionic neurones 
sympathetic preganglionic neurones 
Enteric 
CNS
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3
Q

What is a major pathway to drug discovery?

A

Toxins!!
Berries of deadly nightshade - dilate pupils
Calabar bean - Potentiates the effects of the parasympathetic stimulation.

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4
Q

What is muscarine?

A

Active compound that mimicked the activation of the parasympathetic nervous system found in poisonous fungi (fly agaric)

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5
Q

What is cholinergic transmission?

A

Nerves which use acetylcholine as a neurotransmitter

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6
Q

how is acetylcholine supplied?

A

Choline comes from the diet and liver since nerves cannot make enough choline.
Uptake into nerve endings via high affinity carrier Na dependent transport proteins.

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7
Q

What is Hemicholinum?

A

A competitive inhibitor of the choline carrier.

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8
Q

How is acetylcholine synthesised?

A

Choline + acetylCoA catalysed by choline acetyltransferase (ChAT)
This occurs in the nerve cytoplasm
ChAT inhibitors are not used clinically.

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9
Q

How is acetylcholine stored?

A

Store is maintained by energy dependent pumps into synaptic vesicles.

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10
Q

What happens when there is inhibition of pumps storing ACh?

A

Drugs such as Vesamicol leads to the depletion of stores by inhibiting the pumps

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11
Q

What is Acetyltriethylcholine?

A

Formed from triethylcholine by ChAT, which can also be taken up and stored.
Then it can be released as a false neurotransmitter.
(has weak effect on the postsynaptic receptors)

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12
Q

How is acetylcholine released?

A

Always requires Ca entry into nerve endings.

Occurs by exocytosis where the vesicle membrane fuses with the cell membrane

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13
Q

What drugs affect the release of acetylcholine?

A

Massive release and depletion of vesicle evoked by alpha-latrotoxin (black widow spider venom)

Release can be blocked by the botulinum toxin.

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14
Q

How is ACh removed from the synaptic cleft and inactivated?

A

Diffusion is not important unless cholinesterase is inhibited.

Hydrolysis of ACh by AChE in a non-reversible reaction

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15
Q

what is Sarin?

A

A neurotoxin developed as a chemical weapon in the 1950s

An acetylcholinesterase inhibitor which hence blocks skeletal neuromuscular transmission and augments parasympathetic effects

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16
Q

How is acetylcholine fedback?

A

Cholinergic nerves have presynaptic or prejunctional receptors:

  • ACh(muscarinic) inhibits release of ACh (enteric)
  • ACh (nicotinic) increases the release of ACh probably less functionally important)
  • ATP is converted to adenosinewhich inhibits release (A1 receptors)
  • Morphine (opioids)inhibit release (µ-receptors), leading to constipation
  • Noradrenalineinhibits release (a2-adrenoceptors); ‘sympathetic cross-inhibition’ in tissues
17
Q

What are the main receptors for ACh?

A

Nicotinic receptors

Muscarinic receptors

18
Q

How are receptors classified?

A

Anatomical
Chemical/pharmacological
Molecular

19
Q

How can we determine between pharmacological or molecular receptors?

A

Pharmaxological - Potency series of agonists or specific antagonists

Molecular - Well suited to knockout and expression systems

20
Q

Where are nicotinic receptors found?

A

Skeletal muscle

```
Autonomic ganglia
Not the same type of nicotinic receptor though
~~~

21
Q

What are nicotinic receptor agonists?

A

Nicotine

Transiently stimulate ganglia and motor end-plate if given briefly at very high concentrations.

22
Q

What are some nicotinic receptor antagonists?

A

Selectively antagonised by autonomic ganglia (and CNS)
Hexamethonium

Non-specific antagonist - d-tubicurarine

23
Q

What is Hexamethonium and what is it used to treat?

A

Nicotinic antagonist which blocks the autonomic ganglia.

Used to treat high blood pressure.

24
Q

What is the mechanism of action of hexamethonium?

A

Blocks the ion channel

25
Q

What is the unusual mechanism of action of galantamine?

A
  • Found in the Snowdrop (Galanthus sp.)
  • Act on nicotinic receptors to increase their activity (allosteric potentiating ligand or ‘positive allosteric modulator)
  • Also has anticholinesterase activity
  • Used for the treatment of Alzheimer’s disease (central action)
  • Peripheral side effects include an changes in gut motility.
26
Q

What are muscarinic cholinoceptors?

A

a relative potency seriesfor agonists (when cholinesterase is inhibited): methacholine, muscarine > carbachol&raquo_space;> nicotine

27
Q

What are some muscarinic antagonists?

A

M1 (Pirenzepine) - stomach, salivary glands
M2 (Gallamine) - cardiac muscle
M3 - smooth muscle

Less specific antagonists - atropine, hyoscine, cyclopentolate

28
Q

What are some clinical uses of antimuscarinic drugs?

A
  • Asthma (ipratropium)
  • To treat bradycardia (atropine)
  • To decrease gut motility; decrease secretions (pirenzapine)
  • During operations: decrease secretions, decrease AChEI side-effects (atropine)
  • To dilate pupils (tropicamide)
  • Urinary incontinence (oxybutynin)
  • Motion sickness (hyoscine)
29
Q

What are some muscarinic agonists?

A

Parasympathomimetics

ACh
Carbachol
Muscarine
Pilocarpine

30
Q

What are the effects of parasympathomimetics?

A

Cardiovascular - decreased heart rate, cardiac output

Smooth muscle -contracts, vascular dilates via endothelium (EDRF = NO)

Exocrine glands -secrete -sweating, lacrimation, salivation, bronchial secretion

31
Q

What are some uses of parasympathomimetics?

A

Rarely used to widespread side effects

May be used for the treatment of glaucoma

32
Q

What are the nicotinic Cholinoceptors agonists?

A 
Nicotine
Carbachol
DMPP
Methacholine 
Muscarine
33
Q

What are the relative potency series of nicotinic cholinoceptor agonists at skeletal muscle?

A

Nicotine > Carbachol&raquo_space;DMPP»>methacholine/muscarine

34
Q

What are the relative potency series of nicotinic cholinoceptor agonists at autonomic ganglia and CNS?

A

Nicotine, DMPP > Carbachol&raquo_space;>methacholine/muscarine

35
Q

What are the problems with hexamethonium?

A 
Poorly absorbed (requires Injection)
Blocks both sympathetic and parasympathetic ganglia so unpredictable side effects
36
Q

What are the muscarinic Cholinoceptor agonists?

A

Methacholine
Muscarine
Carbachol
Nicotine

37
Q

What is the relative potency series of muscarinic chonlinoceptor agonists (when cholinesterase is inhibited)

A

Methacholine, Muscarine > Carbachol&raquo_space;> Nicotine

Fundamentals of Pharmacology (19 decks)

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