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LCRS Pharmacology and Therapeutics > Cholinomimetics > Flashcards

Cholinomimetics Flashcards

1
Q

What are cholinomimetics?

A

Drugs that mimic the action of acetylcholine in the body- parasympathomimetic drugs

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2
Q

How is acetylcholine synthesised?

A

From acetyl coA and choline by choline acetyltransferase (CAT)

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3
Q

What causes the exocytosis of Ach?

A

Depolarisation causes opening of voltage sensitive calcium channels and influx of calcium causes exocytosis of Ach

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4
Q

What is Ach broken down by?

A

Acetylcholinesterase

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5
Q

What is the most common muscarinic antagonist?

A

Atropine

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6
Q

What do muscarinic actions correspond to?

A

Parasympathetic stimulation

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7
Q

After atropine blockade of muscarinic actions, what do larger doses of acetylcholine induce?

A

Effects similar to those caused by nicotine

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8
Q

What are the three main muscarinic receptor subtypes?

A

M1- CNS excitation, salivary glands, stomach (release of HCl)
M2- Heart (decreases rate)
M3- Salivary glands, bronchial/visceral smooth muscle, sweat glands and eye

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9
Q

Where are M4 and M5?

A

In the CNS

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10
Q

What effect do muscarinic receptors normally have?

A

Excitatory

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11
Q

What is the exception to muscarinic receptors’ excitatory effect?

A

M2 receptors in the heart are inhibitory

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12
Q

What sort of receptors are muscarinic receptors?

A

Type 2 receptors (G protein coupled)

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13
Q

Which muscarinic receptors are Gq protein linked receptors?

A

M1, M3 and M5 (odds)

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14
Q

What sort of receptor are M2 and M4 (evens)?

A

Gi protein linked receptors

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15
Q

What do Gq protein receptors stimulate when bound to?

A

They stimulate PLC to increase production of IP3 and DAG

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16
Q

What do Gi protein receptors stimulate when bound to?

A

Inhibitory- reduces production of cAMP

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17
Q

What sort of receptor are nicotinic receptors?

A

Ligand gated ion channels

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18
Q

What are the 5 subunits the can make up the nicotinic receptor?

A

Alpha, beta, gamma, delta and epsilon

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19
Q

What do the subunits in the receptor determine?

A

Ligand binding properties of the receptor

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20
Q

What are the 2 main types of nicotinic receptor?

A

In the muscle= 2 alpha + beta + delta + epsilon

In the ganglion= 2 alpha + 3 beta

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21
Q

How does the effect of acetylcholine on nicotinic receptors compare to on muscarinic receptors?

A

Relatively weak

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22
Q

What are the three main muscarinic effects on the eye?

A

Contraction of the ciliary muscle (accommodates for near vision)
Contraction of sphincter pupillae (circular muscle of the iris)
Lacrimation

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23
Q

What does constriction of the sphincter pupillae do?

A

Constricts the pupil (mitosis) and increases drainage of intraocular fluid

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24
Q

What is glaucoma?

A

Increase in intraocular pressure

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25
Why is glaucoma harmful?
It can damage the optic nerves and retina and it can ultimately lead to blindness
26
What generates aqueous humour?
Capillaries of the ciliary body
27
Where does aqueous humour go after being generated?
Anterior chamber of the eye
28
What is the role of the aqueous humour?
Supply oxygen and nutrients to the lens and cornea because they don't have a blood supply
29
How does aqueous humour drain back into the venous system?
Through the canals of Schlemm
30
What is angle-closure glaucoma?
The angle between the cornea and the iris becomes narrowed- this reduces the drainage of the intraocular fluid via the canals of schlemm so intraocular pressure increases
31
What happens to patients with angle closure glaucoma when given a muscarinic agonist?
The iris contracts which opens up the angle and increases the drainage of intraocular fluid through the canals of Schlemm
32
How do muscarinic receptors have an inhibitory effect on the heart?
They decrease cAMP activity which leads to decreased Ca2+ entry which causes decreased cardiac output and increased K+ efflux which leads to decreased heart rate
33
Where are M2 receptors found in the heart?
In the atria and both nodes
34
What is parasympathetic control of blood vessels like?
Most blood vessels don't have parasympathetic innervation but have receptors
35
How does acetylcholine act on vasculature?
It acts on vascular endothelial cells to stimulate NO release via M3 receptors which induces vascular smooth muscle relaxation which causes a decrease in TPR
36
What is the muscarinic effect on non-vascular smooth muscle that has parasympathetic innervation?
Opposite effect to vascular smooth muscle- it contracts Lungs- constriction Gut- increased peristalsis/motility Bladder- increased bladder emptying
37
What is the muscarinic effects on exocrine glands?
Salivation Increased bronchial secretions Increased GI secretions Increased sweating
38
What are the two types of cholinomimetic?
``` Directly acting (muscarinic receptor agonists) Indirectly acting ```
39
What are the two types of muscarinic receptor agonist?
``` Choline esters (bethanechol) Alkaloids (pilocarpine) ```
40
Why is pilocarpine a non-selective muscarinic agonist?
It has a some structural similarity to acetylcholine so it can stimulate all muscarinic receptors
41
What is the half life of pilocarpine?
3-4 hours
42
What is pilocarpine often used as a treatment for?
Glaucoma (constricts sphincter pupillae)
43
What are the side effects of pilocarpine use?
``` General effects of parasympathetic discharge: Blurred vision Sweating GI disturbance and pain Hypotension Respiratory distress ```
44
What sort of agonist is bethanechol due to its structure?
Its structure is only very slightly different to acetylcholine in terms of structure so it is an M3 receptor selective agonist
45
What effect does acetylcholinesterase have on bethanechol?
None because it is highly resistant to degradation by acetylcholinesterase
46
What is the half life on bethanechol?
3-4 hours
47
What is bethanechol mainly used for?
Assist bladder emptying and enhance gastric motility
48
What are the side effects of bethanecol?
Same as pilocarpine- parasympathetic discharge
49
What do indirectly acting cholinomimetic drugs do?
They inhibit acetylcholinesterase
50
How does inhibiting acetylcholinesterase lead to a cholinomimetic effect?
It increases the amount of acetylcholine in the synapse and by doing this, they increase the effect of normal parasympathetic stimulation
51
Give some examples of reversible anticholinesterases?
Physostigmine Neostigmine Donepezil
52
Give some examples of irreversible anticholinesterases?
Ecothiopate Dyflos Sarin
53
What are the two types of cholinesterase?
Acetylcholinesterase (true cholinesterase) | Butyrylcholinesterase (pseudocholinesterase)
54
Where is acetylcholinesterase found?
All cholinergic synapses
55
How fast to act is acetylcholinesterase?
Very rapid (>10000 reactions per second)
56
Where is butyrylcholinesterase found?
In plasma and most tissues but not in cholinergic synapses
57
How does the specificity of butyrylcholinesterase compare to acetylcholinesterase?
Acetylcholinesterase is highly specific for acetylcholine but butyrylcholinesterase has a broad substrate specificity- hydrolyses other esters e.g. suxamethonium
58
What does the broad specificity of butyrylcholinesterase mean that it is the principal reason for?
Low plasma acetylcholine
59
What is the effect of cholinesterase inhibitors in low doses?
Enhanced muscarinic activity
60
What is the effect of cholinesterase inhibitors in moderate doses?
Further enhanced muscarinic activity | Increased transmission at all autonomic ganglia- Ach conc will increase at all
61
What is the effect of cholinesterase inhibitors in high doses?
There is a depolarising block at the autonomic ganglia and neuromuscular junction- nicotinic receptors get overstimulated so shut down
62
How do reversible anti cholinesterase drugs like physostigmine and neostigmine work?
They compete with acetylcholine for the active site on acetylcholinesterase- they donate a carbamyl group to the enzyme blocking the active site
63
How are carbamyl groups removed from the active sites?
Slow hydrolysis which takes minutes and this increases duration of acetylcholine activity in synapse
64
Where does physostigmine primarily act?
Postganglionic parasympathetic synapse
65
What is the half life of physostigmine?
30 mins
66
What is physostigmine used to treat?
Glaucoma- increases drainage of intraocular fluid | Atropine poisoning
67
How is physostigmine treat atropine poisoning?
Atropine is a competitive muscarinic antagonist meaning that it is surmountable, physostigmine increases the concentration of Ach at the synapse so that it can outcompete atropine
68
What sort of compounds are irreversible anticholinesterase drugs?
Organophosphate compounds
69
How do irreversible anti cholinesterase drugs work?
They rapidly react with the enzyme active site, leaving a large blocking group which is stable and resistant to hydrolysis so recovery requires production of new enzymes which takes days/weeks
70
What is the only irreversible anti-cholinesterase drug in clinical use?
Ecothiopate
71
What is ecothiopate used to treat?
Glaucoma
72
How can anticholinesterase drugs reach the CNS to have an effect?
If they are non-polar they can cross the blood brain barrier
73
If low doses of anticholinesterase drugs reach the CNS, what effect do they have?
CNS excitation with possibility of convulsions
74
If high doses of anticholinesterase drugs reach the CNS, what effect do they have?
Unconsciousness, respiratory depression and death
75
What anticholinesterases are used to treat Alzheimer's?
Donepezil and tacrine
76
What brain functions is acetylcholine important in?
Learning and memory
77
Why are organophosphates poisonous?
They cause an increase in muscarinic activity which leads to CNS excitation which leads to depolarising NM block
78
How do you treat organophosphate poisoning?
IV atropine Respirator If found in first few hours give pralidoxime (IV)

LCRS Pharmacology and Therapeutics (33 decks)

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