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PHARMACOLOGY > Cholinergic Pharmacology II > Flashcards

Cholinergic Pharmacology II Flashcards

1
Q

Describe the actions of Nicotine as the dose increases.

A

At small doses, the actions of nicotine are central. Larger doses stimulate ganglia.

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2
Q

What are the 4 effects of nicotine on autonomic ganglia?

A

It causes increased PNS and SNS activity.

  • rise in BP
  • tachycardia
  • inhibition of gastric motility
  • increased salivation and bronchial secretion
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3
Q

Name a ganglionic blocking drug of the nACh receptor

A

Hexamethonium

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4
Q

What are the effects of Hexamethonium on the Cardiovascular System?

A

Effects are mainly due to inhibition of the SNS.

  • Skin vasodilation
  • Loss of cardiovascular reflexes
  • Loss in BP
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5
Q

What are the effects of Hexamethonium on the Gastrointestinal system?

A

Effects are mainly due to inhibition of the PNS.

- reduction of secretion and motility of the GI tract leading to constipation

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6
Q

What are the effects of Hexamthonium on the Genito-Urinary System?

A
  • Block of PNS leads to erection failure
  • Block of SNS leads to inhibition of ejaculation
    Net result is impotence in men
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7
Q

What are the effects of Hexamethonium on the Eye?

A

Effects are mainly due to inhibition of the PNS.

  • Loss of accommodation as iris sphincter muscles and ciliary muscles no longer contract
  • Loss of pupillary reflex causes photophobia
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8
Q

State three uses of neuromuscular junction blocking drugs

A
  • muscle paralysis for intubation
  • muscle relaxation in abdominal surgery
  • assist ventilation in intensive care
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9
Q

What are the two classes of NMJ blockers?

A

Competitive blockers and Depolarizing Blockers

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10
Q

What are the features of Competitive block?

A
  • causes relaxation of muscle without preliminary excitation
  • the block can be reversed by anticholinesterases
  • Myasthenia Gravis sufferers are more sensitive to this
    block
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11
Q

Give an example of a Competitive Blocker

A

Tubocurarine

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12
Q

What are the features of Depolarizing Blockers?

A
  • they are agonists of nACh receptors
  • they cause initial fasciculation of the muscle fibres
  • block is enhanced by anticholinesterases
  • Myasthenia Gravis patients are insensitive to the block
  • can cause hyperkalaemia
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13
Q

Give an example of a Depolarizing Blocker

A

Suxamethonium

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14
Q

How is Suxamethonium metabolised in the body?

A

By plasma cholinesterase

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15
Q

Name three other drugs that are neither Competitive or Depolarizing blockers that affect the transmission of an ACh mediated synapse.

A

Botulinum Toxin - blocks the release of ACh
Hemicholinium - competitively inhibits uptake of choline
Streptomyocin - blocks Ca2+ so prevents ACh release

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16
Q

What are the two main types of cholinesterase?

A

Acetylcholinesterase and Butyrylcholinesterase

17
Q

What are the features of Butyrylcholinesterase?

A
  • it is soluble and found in plasma

- it’s unspecific but will hydrolyse butyrylcholine like substances faster than Ach

18
Q

What is the Dibucaine Screening Test?

A

A blood test to asses the sensitivity of the enzyme Butyrylcholinesterase to its inhibitor Dibucaine.

19
Q

Describe the two binding sites on Acetylcholinesterase

A

The catalytic site contains a reactive serine OH group

The anionic site binds the cationic ammonium group of ACh

20
Q

What are the three stages involved in the hydrolysis of ACh by AChE?

A

1) The ACh binds to the two sites on AChE
2) The acetyl group on ACh transfers onto the OH serine
3) The choline dissociates followed by spontaneous hydrolysis of the acetylated serine OH releasing acetic acid

21
Q

Name the three classes of Anticholinesterases and their mechanism of action

A

Short acting - e.g Edrophonium. bind only to the anionic site forming ionic bonds
Medium acting - e.g. Neostigmine. bind to both sites and form an ester bond with the OH serine
Long acting - e.g. DFP. Irreversibly bind to the OH serine due to phosphorylation

22
Q

What are the main effects of anticholinesterases on autonomic ganglia?

A

Effects mainly on the PNS

  • increased secretions (salivation, sweating)
  • increased GI motility results in vomiting and diarrhoea
  • decrease in intraocular pressure (due to increased contraction of eye muscles)
  • bronchoconstriction
23
Q

What are the main effects of anticholinesterases on the neuromuscular junction?

A

Initial facilitation of transmission followed by depolarizing neuromuscular block (due to excess ACh)

24
Q

What are the clinical uses of anticholinesterases?

A
  • treatment of glaucoma
  • treatment and diagnosis of Myasthenia Gravis
  • reversal of competitive neuromuscular block
25
Q

What is the danger involved with organophosphates and how can their effect be reversed?

A
  • they can cause demyelination due to inactivating the enzyme involved in myelination
  • cholinesterase can be reactivated by oxime compunds

PHARMACOLOGY (8 decks)

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