eLCRS - 팜 > PHARM 6: Cholinomimetics > Flashcards

PHARM 6: Cholinomimetics Flashcards

(44 cards)

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1
Q

Define cholinomimetics.

A

Cholinomimetics = drugs that mimic the action of Ach in the body

  • they are parasympathomimetic drugs
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2
Q

Describe the synthesis of Ach

A
  • Ach = synthesized from acetyl CoA + choline
  • via Choline Acetyltransferase (CAT)
  • Ach is pumped into vesicles
  • await signal
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3
Q

Describe the release of Ach

A
  • depolarization causes opening of VGCC
  • causes influx of Ca2+
  • causes exocytosis of Ach
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4
Q

What enzyme breaks down Ach?

A
  • acetylcholinesterase
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5
Q

Compare differences between muscarinic + nicotinic effects

A

Muscarinic effects:

  • can be replicated by muscarine
  • can be abolished by low doses of muscarinic antagonist ATROPINE
  • corresponds to those of parasympathetic stimulation
  • after atropine blockade, larger doses of Ach can induce effects similar to those caused by nicotine.
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6
Q

What are the three main receptor subtypes of muscarinic receptors and where are they located?

A

M1

  • CNS
  • Salivary Glands
  • stomach

M2
- Heart

M3

  • Salivary Glands
  • Bronchial/ Visceral Smooth muscle
  • sweat glands

note:
M4/5 = in CNS

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7
Q

Muscarinic Receptors are generally excitatory / inhibitory

the except is ____

A

Muscarinic Receptors are generally excitatory

the except is M2 (inhibitory)

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8
Q

All Muscarinic receptors = Type __ receptors

M1/3/5 =

M2/4 =

A

All Muscarinic receptors = Type 2 receptors
(G Protein Coupled)

M1/3/5 = Gq protein linked receptor —> stimulates PLC to increase production of IP3 + DAG

M2/4 = Gi protein linked receptor —> (inhibitory) reduces production of cAMP

odd = Gq
even = Gi
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9
Q

Nicotinic Receptors =
_______ gated ion channels

with __ subunits

There are 2 main types of nicotinic receptor
in the _____ and in the _____

A

Nicotinic Receptors =
LIGAND gated ion channels

with 5 subunits
(ALPHA, BETA, GAMMA, DELTA, EPSILON)

There are 2 main types of nicotinic receptor
in the MUSCLE and in the GANGLION

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10
Q

What are the 3 main muscarinic effects on the eye?

A
  1. contraction of the ciliary muscle
    (for near vision)
  2. Contraction of sphincter papillae
    (constricts pupil + increases drainage of intraocular fluid)
  3. Lacrimation
    (tears)
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11
Q

What is Glaucoma?

A

Glaucoma = Increase in Intraocular pressure

  • can cause damage to optic nerves + retina
  • can lead to blindness
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12
Q

What generates aqueous humour?

A
  • generated by capillaries of the ciliary body

- flows into anterior chamber of eye

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13
Q

what is the role of the aqueous humour?

A
  • to supply o2 and nutrients to lens + cornea

- as they don’t have a blood supply

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14
Q

Describe the drainage of aqueous humour

A
  • diffuses forwards across the lens
  • then across the cornea
  • drains through canals of scheme
  • back into the venous system
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15
Q

What happens in angle closure glaucoma?

A

angle between cornea + iris becomes narrowed

- this narrowing reduces drainage of intraocular fluid via the canals of schlemm

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16
Q

How would you treat angle closure glaucoma?

A
  • give these patients a muscarinic agonist (stimulates muscarinic receptors)
  • which causes contraction of the iris
  • this opens up angle increases drainage of intracocular fluid through then canal of schlemm
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17
Q

What are muscarinic effects on the heart + cardiovascular system?

Where are M2 receptors specfically found?

A
  • M2 receptors are inhibitory
  • slows down the heart rate
  • decreases cardiac output
  • causes vasodilation
  • -> causes drop in BP

M2 receptors found in atria + in both nodes.

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18
Q

What are muscarinic effects on vasculature?

Study These Flashcards
A
  • Ach acts on vascular endothelial cells –> to stimulate NO release
  • via M3 receptors
  • NO induces –> VSMC relaxation
  • causes decrease in TPR
19
Q

What are the muscarinic effect on Non vascular smooth muscle?

Study These Flashcards
A
  • Non vascular smooth muscle with parasympathetic innervation:
    (OPPOSITE TO VSMC)
    –> it contracts

so
LUNGS - bronchoconstriction
GUT - Increased motility
BLADDER - Increase bladder emptying

20
Q

What are muscarinic effects on exocrine glands?

Study These Flashcards
A
  • Salivation
  • increase bronchial secretions
  • increased GI secretions
  • Increased sweating
21
Q

What are typical agonists at muscarinic receptors? (2)

directly acting cholinomimetic drugs

Study These Flashcards
A
  1. choline esters (bethanechol)

2. alkaloids (pilocarpine)

22
Q

Describe the muscarinic agonist Pilocarpine

what is it useful for?
what are some side effects?

Study These Flashcards
A
  • non selective muscarinic agonist
  • good lipid solubility
  • half life = 3-4 hr

USES
- useful for local treatment for glaucoma

SIDE EFFECTS

  • blurred vision
  • sweating
  • GI disturbance
  • Hypotension
  • Respiratory distress
23
Q

Describe the muscarinic agonist Bethanechol

what is it useful for?
what are some side effects?

Study These Flashcards
A
  • M3 AchR
  • selective agonist
  • produced from minot modification of Ach

USES

  • assists bladder emptying
  • enhances Gastric motility

SIDE EFFECTS

  • sweating
  • impaired vision
  • bradycardia
  • hypotension
  • respiratory difficulty
24
Q

What are indirectly acting cholinomimetic drugs?

Study These Flashcards
A

drugs that increase effect of normal parasympathetic nerve stimulation

  • inhibits acetylcholinesterase
  • so therefore increases amount of Ach building up in the synapse
  • -> which increases effect of normal parasympathetic nerve stimulation
25
What are the 2 types of anticholinesterases? give examples
1. reversible Anticholinesterases - physostigmine - neostigmine - donepezil 2. Irreversible Anticholinesterases - ecothiopate - dyflos - sarin
26
what is the key function of cholinesterase enzymes?
- to metabolism Ach ---> choline + acetate
27
What are the 2 types of cholinesterase?
a) Acetylcholinesterase | b) Butyrylcholinesterase
28
Compare between Acetylcholinesterase and Butyrylcholinesterase
ACETYLCHOLINESTERASE: - Found in ALL cholinergic synapses - Very RAPID action - highly selective for Ach BUTYRYLCHOLINESTERASE: - found in PLASMA + most TISSUES but NOT in cholinergic synapses - has broad substrate specificity - it is the principal reason for low plasma acetylcholine - shows genetic variation
29
What are the effects of cholinesterase inhibitors at Low Dose: Moderate Dose: High Dose:
What are the effects of cholinesterase inhibitors at Low Dose: - enhances muscarinic activity Moderate Dose: - further enhances muscarinic activity - there is increased transmission at ALL autonomic ganglia (due to inc in Ach conc at all cholinergic synapses) High Dose: - causes Depolarising block at autonomic ganglia + neuromuscular junction - nicotinic receptors get overstimulated --> shuts down
30
How do reversible anti cholinesterase drugs work? Give examples
- they compete with Ach for active site on acetylcholinesterase - and then donates carbamyl group to the enzyme - blocks active site - prevents Ach from binding - caramel groups = removed by slow hydrolysis - INCREASES duration of Ach activity in synapse e.g physostigmine, neostigmine
31
Where does physostigmine primality act at?
- primarily acts on post ganglionic parasympathetic synapse
32
what is the half life of physostigmine?
half life = 30 mins
33
what is physostigmine used for? why?
- used in glaucoma - -> increases drainage of intraocular fluid - used in atropine poisoning - -> increases conc of Ach at synapse - -> so that Ach can outcompete the atropine
34
How do irreversible Anticholinesterase drugs work? give examples + uses
- they are organophosphate compounds - they rapidly react with the enzyme active site - leaving a large blocking group - blocking group = stable + resistant to hydrolysis e.g ecothipate (clinical) dyflos, sarin, parathion (insecticides/ nerve gas)
35
What is the use of ecothipate? why?
- ecothipate = potent inhibitor of acetylcholinesterase - used as eye drop for glaucoma treatment - it increases drainage of intraocular fluid + has a prolonged duration of action
36
What are side effects of using ecothipate?
side effects --> of parasympathetic discharge - sweating - blurred vision - GI disturbance + pain - Bradycardia - Hypotension - respiratory difficulty
37
effect of Anticholinesterase drugs on CNS at Low Dose: High Dose:
effect of Anticholinesterase drugs on CNS at Low Dose: - CNS excitation with possibility of convulsions High Dose: - Unconsciousness, respiratory depression + death
38
Non polar anticholinesterases can/cannot cross the BBB
Non polar anticholinesterases can cross the BBB
39
What 2 anticholesterase drugs are used to treat Alzheimer's disease?
- Donepezil | - Tacrine
40
How does exposure to organophosphates cause severe toxicity?
- causes increase in muscarinic activity - causes CNS excitation - resulting in depolarizing NM block
41
How would you treat exposure to organophosphate poisoning ?
TREATMENT - IV atropine - patient = put on respirator due to respiratory depression - found in first few hrs: patient given Pralidoxime (IV) --> unblocks the enzymes
42
Why do you use Atropine to treat organophosphate poisoning?
- organophosphate poisoning results in massive reduction in activity of acetylcholinesterase - which leads to increase in synaptic Ach conc - to block Ach from over stimulating the receptors --> you give muscarinic antagonist (ATROPINE)
43
Describe the removal of Ach
- Acetylcholinesterase (bound to basement memb) breaks down Ach - into choline + acetate - choline is then re uptaken and used to produce more Ach
44
list the distribution of muscarinic cholinergic target systems.
- eye - salivary glands - lungs - bladder - sweat glands - gut - heart - vasculature
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