Cholinoceptor (PNS) antagonists

Question 1

What sort of function is affected by a muscarinic receptor antagonist?

Answer 1

Parasympathetic

Question 2

Give 2 examples of muscarinic receptor antagonists

Answer 2

Atropine, hyoscine

Question 3

Recall the effects on the CNS of atropine and hyoscine

Answer 3

At normal dose - atropine = no effect, hyoscine = sedative

At toxic dose - atropine = mild agitation, hyoscine = CNS suppression

Question 4

Why do atropine and hyoscine have different effects on the CNS?

Answer 4

1. Hyoscine slightly more M1 selective, shich is more prevalent in the cerebral cortex
2. Hyoscine is slightly more lipid soluble and so penetrates brain further

Question 5

Recall the 6 main clinical uses for muscarinic receptor antagonists

Answer 5

1. Parkinson’s treatment
2. Asthma
3. IBS
4. eye examination
5. Anaesthetic premedication
6. Motion sickness

Question 6

How do muscarinic receptor antagonists enhance eye examination?

Answer 6

Block PNS, cause pupil dilation

Question 7

Give 3 ways that muscarinic receptor antagonists are useful for anaesthetic premedication

Answer 7

1. Airway dilation
2. Dries up secretions to prevent aspiration of fluids
3. Increases HR to counteract effects of anaesthetic

Question 8

Why are muscarinic receptor agonists effective for motion sickness?

Answer 8

Prevent SNS response to labyrinthe/ eye sensory info mismatch, prevents vomiting centre activation by hippocampus

Question 9

Why are muscarinic receptor antagonists used to treat Parkinson’s?

Answer 9

M4 receptor impairs D1 receptor function
D1 function required for fine movement activation and control
D1 receptor decreased in Parkinson’s
MRA reduces D1 inhibition by blocking M4

Question 10

Describe the chemical composition of the muscarinic receptor antagonist used in asthma treatment, and the reason for this

Answer 10

Modified atropine to have high positive charge - limits the drug to lung tissue

Question 11

What muscarinic receptor antagonist is used to target IBS and why?

Answer 11

M3 receptor antagonist - slows down gut motility and secretions to counteract hyperactive gut in IBS

Question 12

Recall the 4 unwanted effects of muscarinic receptor antagonists

Answer 12

Hot as hell
Dry as a bone
Mad as a hatter
Blind as a bat

Question 13

What drug would be used to treat atropine poisoning?

Answer 13

Reversible anti - Ach Esterase

Question 14

How does the botulinum toxic act?

Answer 14

Inhibits SNARE complex in pre-synaptic bouton

Question 15

Where are nicotinic receptors found?

Answer 15

All autonomic ganglia

Question 16

Describe the 2 types of nicotinic receptor blockade

Answer 16

1. Binding to receptor itself

2. Blocking the ion channel associated with the receptor

Question 17

Describe the different response of use-dependent and use-independent drugs to addition of true-agonist to the system?

Answer 17

1. Use-independent - addition of agonist competes for active site, decreases efficacy of drug
2. Use-dependent - addition of agonist opens channel further and increases efficacy of drug

Question 18

Name 2 nicotinic-receptor antagonists and recall their clinical use

Answer 18

1. Hexamethonium - too many side effects

2. Trimetaphan - short-acting anti-hypertensive used during surgery

Question 19

Which arm of the ANS is knocked out by ganglion-blocking drugs?

Answer 19

Whichever is dominant - usually PNS

Question 20

Since ganglion-blocking drugs reduce the parasympathetic influence on heart rate, why do these drugs cause hyoptension? (3 reasons)

Answer 20

1. Vasodilation –> decrease in TPR
2. Decrease in renin production –> decrease in aldosterone –> decreased volume
3. Decreased renin –> decreased AngII

Question 21

Recall 4 unwanted side effects of cholinoceptor agonists (ganglion-blocking drugs)

Answer 21

1. Pupil overdilation
2. SMC interference –> GIT, urinary and lung dysfunction
3. impaired sweating capacity
4. Reduced gut secretion