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Year 2 - Pharmacology and Therapeutics > Cholinomimetics > Flashcards

Cholinomimetics Flashcards

1
Q

Cholinomimetics?

A

Drugs that mimics the action of Ach

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2
Q

Muscarine, atropine and nicotine?

A

Muscarinic effects can be replicated by muscarine and abolished by the antagonist atropine

After atropine blockade, larger doses of Ach can induce effects similar to those caused by nicotine

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3
Q

3 main muscarinic receptors?

A

M1, M2 and M3

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4
Q

Where do the 3 muscarinic receptors work

A

M1 - salivary glands, stomach and CNS

M2 - heart

M3 - salivary glands, bronchial/visceral SM, sweat glands, eye

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5
Q

Are muscarinic receptors generally exciatory or inhibitory?

A

Generally exciatory EXCEPT M2 as it slows down HR and reduces contractility

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6
Q

G-proteins & messengers associated w the muscarinic receptors

A

M1, M3 & M5
Gq protein - stimulatory which INCREASES formation of IP3 + DAG from PIP2

M2 & M4 - Gi protein - inhibitory which REDUCES cAMP formation

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7
Q

Nicotinic receptors?

A

Type 1 - 5 sub-units (alpha, beta, gamma, delta and epsilon)

Effects of Ach relatively weak on these so need higher doses

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8
Q

Subunit combination effect on nicotinic receptors?

A

Determines ligand-binding properties of the receptors

Muscle - 2alpha, beta, delta and epsilon
Ganglion - 2alpha & 3beta

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9
Q

Muscarinic target systems?

A

Eye, sweat glands, lungs, heart, gut, bladder and vasculature

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10
Q

Muscarinic effects on: EYE

A

x Ciliary muscle contraction - near vision (lens bulges = convex)
x Sphincter pupillae contraction - miosis (constrict pupil) & drainage of intra-ocular fluid
x Lacrimation - tears

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11
Q

What bathes the lens/cornea?

A

Ciliary body produces aqueous humour which bathes the lens and cornea as does not have own blood supply

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12
Q

Glaucoma

A

Contraction of sphincter pupillae opens pathway for aq. humour, draining via canals of Schlemm and REDUCING intra-ocular pressure

In glaucome this is impeded - so given drugs to stimulate muscarinic receptors in ciliary muscle to open pathway again

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13
Q

Muscarinic effects on: HEART

A

M2 AchR located in atria and nodes

REDUCES cAMP = reduced Ca2+ entry / increased K+ efflux = decreased CO / HR

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14
Q

Muscarinic effects on: VASCULATURE

A

Most blood vessels do NOT have PSN innervation

Ach works on endothelial cells to stimulate NO = vasodilator (decreases TPR)

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15
Q

Muscarinic effects on: CVS

A

HYPOtensive response - drop in BP

Decreased HR, CO
Vasodilation

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16
Q

Muscarinic effects on: NON-VASCULAR SM

A

SM that DOES have PSN innervation responds in OPP way to vascular muscle i.e. CONTRACTS

Lungs - bronchoconstriction
Gut - increases peristalsis
Bladder - increased bladder emptying

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17
Q

Muscarinic effects on: EXOCRINE GLANDS

A

x Salivation
x Increasd bronchial/GI secretions
x Increased sweating (SNS-mediated)

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18
Q

Muscarinic effects SUMMARY

A 
	Decreased HR and BP.
	Increased sweating, salivation and lacrimation. 
	Difficulty breathing.
	Bladder contraction.
	GI pain.
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19
Q

2 types of cholinomimetic drugs?

A

Directly and Indirectly acting

20
Q

2 examples of directly acting cholinomimetic drugs (muscarinic)?

A

These are Agonists!!

Choline esters (bethanechol)

Alkaloids (pilocarpine)

21
Q

Pilocarpine and what is it used to treat?

A

Directly acting muscarinic agonist - alkaloid
Non-selective & good lipid-solubility!

Used to treat glaucoma

22
Q

Side effects of pilocarpine?

A

Blurred vision, sweating, GI pain, hypotension, respiratory distress

Lower incidence of last 2 as given as eye-drops so more local

23
Q

Bethanechol and what is it used to treat?

A

M3 AChR selective agonist (choline esters)

Used to assist bladder emptying and enhance gastric motility (e.g. used post-op to stimulate this)

24
Q

Advantage of bethanechol?

A

Resistant to degradation so not broken down by cholinesterases like ACh

ALSO orally active & limited access to the brain

25
Q

Side-effects of bethanechol?

A

sweating, impaired, bradycardia, hypotension, respiratory difficulty

Higher incidence of last 3 as given orally so enters systemic circulation

26
Q

How do indirectly acting cholinomimetic drugs work?

A

Increase the effect of NORMAL PS nerve stimulation

Target is therefore acetylcholinesterases = increases endogenous Ach

27
Q

2 types of indirectly acting cholinomimetic drugs?

A

Reversible anticholinesterases e.g. physostigmine

Irreversible anticholinesterases e.g. ecothiopate

28
Q

2 types of cholinesterase enzymes?

A

Acetylcholinesterase (specific to Ach)

Butrylcholinesterase (pseudocholinesterase)

29
Q

How do cholinesterase enzymes work?

A

Metabolise Ach to choline and acetate

30
Q

True or specific cholinesterase?

A

Acetylcholinesterase

Found at ALL cholinergic synpases
Rapid action
Highly selective for Ach

31
Q

Pseudocholinesterase?

A

NOT FOUND at cholinergic synpases but plasma and most tissues

Broad substrate specifity - also hydrolyses other esters

Main reason for LOW PLASMA Ach

Shows genetic variation

32
Q

Effects of cholinesterase inhibitors at low dose?

A

ENHANCED muscarinic activity

33
Q

Effects of cholinesterase inhibitors at moderate dose?

A

Further enhancement of muscarinic activity

Increased transmission at ALL ANS ganglia - nAchRs

34
Q

Effects of cholinesterase inhibitors at high dose?

A

‘Depolarising’ block at ANS ganglia & NMJ (LECTURE 9)

35
Q

Reversible anticholinesterase drug- how does it work?

A

Competes w Ach for active site -

donates a CARBAMYL group to the enzyme, blocking the active site

carbamyl group then removed by slow hydrolysis - increases duration of Ach activity in synpase

36
Q

Physostigmine?

A

Reversible anticholinesterase drug - tertiary amine

Acts at PS postganglionic synapse - used to treat glaucoma and atropine poisoning

37
Q

Irreversible anticholinesterase drug- how does it work?

A

Rapidly react w enzyme active site - leaves a large blocking group

Stable and resistant to hydrolysis - recovery may require production of new enzymes (days/weeks)

38
Q

Ecothiopate?

A

Irreversible anticholinesterase drug - only drug used clinically (rest are insecticides)

Long-acting drug - slow reactiviation of enzyme by hydrolysis

Used to treat glaucoma - eye drops

Side-effects as before!

39
Q

Anticholinesterase drugs & the CNS?

A

Non-polar anticholinesterases can cross the BBB

40
Q

Anticholinesterase drugs that can cross the BBB?

A

Physostigmine

Nerve agents

41
Q

Low dose Anticholinesterase drugs on CNS?

A

Excitations - possibility of convulsions

42
Q

High doses of Anticholinesterase drugs on CNS?

A

Unconsciousness, respiratory depression, DEATH

43
Q

Organophosphate poisoning?

A

Found in insecticides and nerve agents

Causes severe toxicity

44
Q

How does organophosphate poisoning cause severe toxicity?

A

Increase in muscarinic activity, increasing CNS excitation and leading to a depolarising NM block (nicotinic receptors)

45
Q

Treatment for organophosphate poisoning?

A

Atropine (iv) - directly works on muscarinic receptors

Artificial respiration

Pralidoxime - works on nicotinic receptors as well, reversing the block (unbinding anticholinesterases) BUT needs to be given in the first couple of hours

Year 2 - Pharmacology and Therapeutics (9 decks)

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