Cholinoceptor (PNS) antagonists Flashcards
What sort of function is affected by a muscarinic receptor antagonist?
Parasympathetic
Give 2 examples of muscarinic receptor antagonists
Atropine, hyoscine
Recall the effects on the CNS of atropine and hyoscine
At normal dose - atropine = no effect, hyoscine = sedative
At toxic dose - atropine = mild agitation, hyoscine = CNS suppression
Why do atropine and hyoscine have different effects on the CNS?
- Hyoscine slightly more M1 selective, shich is more prevalent in the cerebral cortex
- Hyoscine is slightly more lipid soluble and so penetrates brain further
Recall the 6 main clinical uses for muscarinic receptor antagonists
- Parkinson’s treatment
- Asthma
- IBS
- eye examination
- Anaesthetic premedication
- Motion sickness
How do muscarinic receptor antagonists enhance eye examination?
Block PNS, cause pupil dilation
Give 3 ways that muscarinic receptor antagonists are useful for anaesthetic premedication
- Airway dilation
- Dries up secretions to prevent aspiration of fluids
- Increases HR to counteract effects of anaesthetic
Why are muscarinic receptor agonists effective for motion sickness?
Prevent SNS response to labyrinthe/ eye sensory info mismatch, prevents vomiting centre activation by hippocampus
Why are muscarinic receptor antagonists used to treat Parkinson’s?
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
Describe the chemical composition of the muscarinic receptor antagonist used in asthma treatment, and the reason for this
Modified atropine to have high positive charge - limits the drug to lung tissue
What muscarinic receptor antagonist is used to target IBS and why?
M3 receptor antagonist - slows down gut motility and secretions to counteract hyperactive gut in IBS
Recall the 4 unwanted effects of muscarinic receptor antagonists
Hot as hell
Dry as a bone
Mad as a hatter
Blind as a bat
What drug would be used to treat atropine poisoning?
Reversible anti - Ach Esterase
How does the botulinum toxic act?
Inhibits SNARE complex in pre-synaptic bouton
Where are nicotinic receptors found?
All autonomic ganglia
Describe the 2 types of nicotinic receptor blockade
- Binding to receptor itself
2. Blocking the ion channel associated with the receptor
Describe the different response of use-dependent and use-independent drugs to addition of true-agonist to the system?
- Use-independent - addition of agonist competes for active site, decreases efficacy of drug
- Use-dependent - addition of agonist opens channel further and increases efficacy of drug
Name 2 nicotinic-receptor antagonists and recall their clinical use
- Hexamethonium - too many side effects
2. Trimetaphan - short-acting anti-hypertensive used during surgery
Which arm of the ANS is knocked out by ganglion-blocking drugs?
Whichever is dominant - usually PNS
Since ganglion-blocking drugs reduce the parasympathetic influence on heart rate, why do these drugs cause hyoptension? (3 reasons)
- Vasodilation –> decrease in TPR
- Decrease in renin production –> decrease in aldosterone –> decreased volume
- Decreased renin –> decreased AngII
Recall 4 unwanted side effects of cholinoceptor agonists (ganglion-blocking drugs)
- Pupil overdilation
- SMC interference –> GIT, urinary and lung dysfunction
- impaired sweating capacity
- Reduced gut secretion