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Y2 Pharm (LCRS1) > Cholinomimetics > Flashcards

Cholinomimetics Flashcards

1
Q

Describe the synthesis of acetylcholine.

A

Acetylcholine is synthesised from Acetyl CoA and choline via choline acetyltransferase (CAT)

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2
Q

Why are the receptors described as nicotinic and muscarinic?

A

Muscarinic effects are those that can be replicated by muscarine Nicotinic effects are those that an be replicated by nicotine Comes from amanita muscaria and nicotiana tabacum

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3
Q

What can be given to abolish muscarinic effects?

A

Atropine (competitive muscarinic antagonist)

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4
Q

State where you would find the different types of muscarinic receptor.

A

M1 – salivary glands, CNS, stomach M2 – heart M3 – salivary glands, bronchial/visceral smooth muscle, eyes, and sweat glands M4 and M5 are found in the CNS NOTE: muscarinic receptors are generally excitatory except for on the heart

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5
Q

What type of receptor are all muscarinic receptors?

A

G-protein coupled receptors

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6
Q

What is the difference in the G-protein receptors of M1, M3 and M5 compared to M2 and M4?

A

M1, M3 and M5 = Gq protein linked receptors – they stimulate PLC which increases IP3 and DAG M2 and M4 = Gi protein linked receptors (inhibitory) – they decrease the production of cAMP

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7
Q

Describe the structure of nicotinic receptors. What determines its ligand binding properties?

A

Nicotinic receptors consist of 5 subunits (alpha, beta, gamma, delta or epsilon) The combination of subunits determines its ligand binding properties.

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8
Q

What are the two main types of nicotinic receptor? Describe their subunit composition.

A

Muscle and Ganglion Muscle = 2 alpha + beta + delta + epsilon Ganglion = 2 alpha + 3 beta

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9
Q

How do the effects of acetylcholine on nicotinic receptors compare to its effects on muscarinic receptors?

A

The effects of acetylcholine are relatively weak on nicotinic compared to muscarinic

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10
Q

What three effects does muscarinic stimulation have on the eye?

A

Contraction of the ciliary muscle (accommodate for near vision) Constriction of sphincter pupillae (circular muscle of the eye) – this constricts the pupil and increases drainage of intraocular fluid Lacrimation

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11
Q

What is glaucoma?

A

Sustained raised intraocular pressure – this can cause damage to the optic nerves and retina and can lead to blindness

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12
Q

Where is aqueous humour produced? Describe its passage through the eye.

A

The capillaries in the ciliary body produce aqueous humour Aqueous humour passes anteriorly into the anterior chamber and is then drained through the canals of Schlemm into the venous system

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13
Q

What is the role of aqueous humour?

A

Provides oxygen and nutrients to the cornea and lens because they don’t have a blood supply

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14
Q

What happens in Angle-closure glaucoma?

A

The angle between the cornea and the iris is narrowed which decreases the drainage of intraocular fluid through the canals of Schlemm

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15
Q

What are the effects of giving a muscarinic agonist to people with Angle-closure glaucoma?

A

This causes constriction of sphincter pupillae and opens up the angle to increase the drainage of intraocular fluid

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16
Q

Describe, in detail (including the mechanism), the muscarinic effects on the heart.

A

Binding of acetylcholine to the M2 receptors (Gi protein linked receptor) causes a decrease in cAMP production This triggers a decrease in Ca2+ influx, which leads to a decrease incardiac output It also triggers an increase in K+ efflux, which leads to a decrease in heart rate

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17
Q

Describe the muscarinic effects on the vasculature.

A

There is no direct parasympathetic innervation of blood vessels However, there are muscarinic receptors on the endothelial cells When stimulated, it triggers the production of nitric oxide (NO) from the endothelial cells, which causes vasodilation and a decrease in TPR

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18
Q

Summarise the muscarinic effects on the cardiovascular system.

A

Decrease in heart rate Decrease in cardiac output (due to decreased atrial contraction) Decrease in total peripheral resistance (due to vasodilation) Decrease in blood pressure

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19
Q

Describe the muscarinic effects on non-vascular smooth muscle.

A

It is the opposite of muscarinic effects on vascular smooth muscle It causes CONTRACTION of non-vascular smooth muscle Lungs – bronchoconstriction GI tract – increased motility Bladder – increased bladder emptying

20
Q

Describe the muscarinic effects on exocrine glands.

A
  • Salivation
  • Increased bronchial secretions
  • Increased GI secretions (including gastric HCl production)
  • Increased sweating (sympathetic-mediated)
21
Q

What are the two types of cholinomimetic drug?

A

Directly Acting – muscarinic agonists Indirectly Acting – acetylcholinesterase inhibitors -> increase the synaptic concentration of acetylcholine

22
Q

State two types of muscarinic receptor agonists and give an example of each.

A

Choline Esters – Bethanechol Alkaloids - Pilocarpine

23
Q

Describe the selectivity of pilocarpine.

A

Non-selective muscarinic receptor agonist It stimulates ALL muscarinic receptors

24
Q

What is pilocarpine used to treat?

A

Glaucoma

25
Q

State some side-effects of pilocarpine.

A
  • Blurred vision
  • Hypotension
  • Sweating
  • Respiratory difficulty
  • GI disturbance and pain
26
Q

Describe the selectivity of bethanechol.

A

M3 selective agonist

27
Q

What are the effects of bethanechol?

A

Assist bladder emptying Enhanced gastric motility

28
Q

State some side-effects of bethanechol.

A
  • sweating
  • impaired vision
  • bradycardia
  • hypotension
  • respiratory difficulty
29
Q

What is the half-life of pilocarpine and bethanechol?

A

3-4 hours

30
Q

What are the two types of anticholinesterase? Give examples of each.

A

Reversible – physostigmine, neostigmine, donepezil Irreversible – ecothiopate, dyflos, sarin

31
Q

What are the two types of cholinesterase?

A

Acetylcholinesterase Butyrylcholinesterase

32
Q

Where is acetylcholinesterase found? Describe its properties.

A

It is found in ALL cholinergic synapses It has very RAPID action and it is HIGHLY SELECTIVE for acetylcholine

33
Q

Where is butyrylcholinesterase found? Describe its properties

A

Butyrylcholinesterase is found in plasma and most tissues but NOT in cholinergic synapses It has a broad substrate specificity – it hydrolyses other esters e.g. suxamethonium It shows genetic variation

34
Q

State the effects of low, moderate and high doses of cholinesterase inhibitors.

A

LOW – enhances muscarinic effects MODERATE – further enhances muscarinic effects + increases transmission at ALL autonomic ganglia (nicotinic receptors) HIGH – depolarising block at autonomic ganglia and NMJ (the nicotinic receptors get overstimulated so they shut down)

35
Q

Describe the mechanism of action of reversible anticholinesterases.

A

Reversible anticholinesterases donate a CARBAMYL group, which blocks the active site of the acetylcholinesterase Carbamyl groups are removed by slow hydrolysis (takes mins rather than miliseconds)

36
Q

Which synapses does pilocarpine primarily act on?

A

Postganglionic parasympathetic synapses

37
Q

What is physostigmine used to treat?

A

Glaucoma

38
Q

What is the half-life of physostigmine?

A

30 mins

39
Q

What type of poisoning is physostigmine used to treat?

A

Atropine poisoning (because it increases the synaptic concentration of acetylcholine so it can outcompete the atropine)

40
Q

What type of compound are irreversible anticholinesterases?

A

Organophosphates

41
Q

Describe the mechanism of action of irreversible anticholinesterases.

A

They rapidly react with the enzyme active site, leaving a large blocking group The blocking group is stable and resistant to hydrolysis so recovery requires the production of new enzymes

42
Q

What is ecothiopate used to treat?

A

Glaucoma

43
Q

State some side-effects of ecothiopate.

A
  • Blurred vision
  • Sweating
  • Respiratory difficulty
  • Hypotension
  • GI disturbance and pain
  • Bradycardia
44
Q

What type of anticholinesterases can cross the blood-brain barrier?

A

Non-polar

45
Q

Describe the effects of low and high doses of anticholinesterase drugs on CNS activity.

A

Low – CNS excitation with the possibility of convulsions High – unconsciousness, respiratory depression and death

46
Q

State two anticholinesterases that are used to treat Alzheimer’s disease

A

Donepezil Tacrine

47
Q

Describe the treatment of organophosphate poisoning.

A

IV atropine – this blocks the muscarinic receptors thus reducing the effect of the raised synaptic acetylcholine concentration Patient is put on a respiratory because of the respiratory depression caused by the excess acetylcholine at the synapse (causing a depolarising block) If found within the first few hours, the patient should be given IV PRALIDOXIME, which can unblock the enzymes

Y2 Pharm (LCRS1) (34 decks)

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