Cholinoreceptor antagonists Flashcards
What is the relationship between agonists, antagonists and affinity
agonists and antagonists possess affinity
What is the relationship between agonists, antagonists and efficacy
Only agonists possess efficacy
activate the receptor to generate a response
What are nicotinic receptor antagonists
ganglion blocking drugs
Blocks ligand-dating ion channels or receptors
Give 2 examples of nicotinic receptor antagonists and what are their clinical uses
hexamethonium - 1st anti-hypertensive (nictonic receptor)
trimetaphan - hypotension during surgery (LG-ion channel)
Why do ganglion blocking drugs cause hypotension
Blocks the sympathetic system which increases renin secretion in the kidney and causes constriction in the blood vessels -> hypotension
What are the overall effects of ganglion blocking drugs
Hypotension (CVS)
Overall relaxation (pupil dilation, decrease GI tone, bladder dysfunction, bronchodilation Exocrine secretions decrease
What is a natural nicotinic receptor anrtagonist
alpha-bungarotoxin from the common krait snake which strongly covalently bonds to nicotinic receptor (affects somatic nervous system -> skeletal muscle affected)
Give 2 examples of muscarinic receptor antagonists
Atropa belladone -> atropine
Hyoscymus niger -> Hyoscine
What are the effects of atropine on the CNS
Normal dose - little effect
toxic - mild restelessness, agitation
What are the effects of hycosine on the CNS
normal dose - sedation, amnesia
Toxic dose - CNS depression or paradoxical CNS excitation (associated with pain)
Which drug permeates into the CNS greater: atropine or hycosine
Hycosine
Give an example of a msucarinic receptor antagonists used clinically for the eye
Tropicamide
Examination of the retina
Blocks the muscarinic receptor, paralysing the ciliary muscle and pupil causing dilation to widen the view of the retina
What are the effects of the muscarinic receptor antagonists that are useful for anaesthetic premedication
Blocks constriction of trachea and bronchioles
Blocks copious watery secretion from the salivary glands
Blocks and decreases heart rate and contractility
Sedation
How are muscarinic receptor antagonists used neurologically
Hycosine patch
Motion sickness
How are muscarinic receptor antagonists used in Parkinson’s disease
cholinergic/dopaminergic balance in basal ganglia
How are muscarinic receptors antagonists used in respiratory diseases
Asthma/obstructive airway disease
e.g. ipratropium bromide (+atropine)
How are muscarinic receptor antagonists used in GI diseases
Irritable bowel syndrome
M3 receptor antagonists to reduce side effects
What are the unwanted effects of muscarinic receptor antagonists
Hot - decreased sweating and thermoregulation
Dry - Decrease secretions
Blind - cyclopegia
Mad - CNS disturbance
Describe LG-ion channels
No affinity
Use-dependent
Incomplete blocking/antagonism
What are the kinds of effects you can achieve from a ganglion blocking drug
Increased heart rate
Bronchodilation
How do ganglia blocking drugs cause hypotension
Dilation of blood vessels (reduced TPR)
Stops renin secretion (less aldosterone, less reabsorption)
What are the clinical uses of hexamethonium and trimetaphan
Hexamethonium -> 1st Anti-hypertensive
Trimetaphan-> Hypotension during surgery (short acting)
Which physiological responses are influenced by muscarinic receptor antagonists
Pupil and ciliary muscle contraction
Bronchiole constriction
Saliva production
Increased GI motility, tone and secretion
Contraction of depressor, relaxation of trigone and sphincter
Sweating
Why is ipratropium used clinically despite its structure being similar to atropine
Charged group added so therefore more polar
Less likely to diffuse through lipid membranes and hence the lungs
Which drugs could you administer to treat an atropine overdose
Bethanechol
Physostigmine
*ecothiopate would work but is irreversible and would be dangerous
Why is physostigmine used to treat atropine overdose
Is an anti-acetylcholinesterase and therefore increases acetylcholine conc. in the synapse, making it a better competitive substrate for the receptor
What is the botulinum toxin
Parasympatholytics
Prevents acetylcholine exocytosis
