Cholinoceptor antagonists Flashcards
Where can nicotinic receptors have its effect?
- they are always present on autonomic ganglia
- therefore they have the ability to interfere with the whole ANS
Where can drugs targeting muscarinic receptors have their effect?
- they are present within the effector organs of the PNS and sweat glands innervated by the SNS
- drugs effecting muscarinic receptors will be much more specific
What else are nicotinic receptor antagonists called and why?
- ganglion blocking drug
- they block the action of nicotinic receptors that lie at the ganglion
WHat 2 ways can you interfere with an ion-channel linked receptor?
- blocking the receptor
- blocking the ion channel
What are 2 clinical examples of nicotinic receptor antagonists?
- hexamethonium (better at blocking the channel pore)
- trimetaphan (better at blocking the channel receptor)
What determines the effect of the drug on the body?
- they are tissue specific, it depends which branch of the ANS predominates in a particular tissue
e. g if sympathetic predominates those effects will be lost and vise versa
Which tissues are sympathetically dominated?
- kidneys
- blood vessels
Which tissues are parasympathetically dominated?
- eyes
- lungs
- bladder, ureter, GI tract
What types of secretions will cholinoceptor blockade also stop?
-exocrine (cannot sweat and issues producing saliva)
what was hexamethonium used for?
-anti-hypertensive
why was hexamethonium suspended?
- wide side effect profile
e. .g loss of bladder control, pupil dilation, loss of GI motility
What is trimetaphan used for?
- surgery when controlled hypotension is needed
- very short acting
Where are receptor blockade antagonists mostly found?
- toxins and venoms
- irreversible they lead to a total loss of autonomic function
Why are muscarinic receptor antagonists more useful?
- more specific
- target parasympathetic effector organs and sweat glands vs everything
List 3 different muscarinic receptor antagonists
- atropine
- hyoscine
- tropicamide
What is tropicamide used for?
- paralyses smooth muscle of the eye responsible for contraction
- pupil can then fully dilate for examination
How are muscarinic receptor antagonists used in anaesthetic premedication?
- dilates the airway
- production of copious watery secretions is blocked
How does a hyosciene patch work for motion sickness?
- blocks muscarinic receptors at the vomiting centre preventing nausea
How do muscarinic receptor antagonists treat Parkinsons disease?
- block the M4 receptor so the inhibitory effect to dopamine is blocked
- creating a bigger response to dopamine and decreasing parkinson’s
How is asthma treated?
-ipratropium bromide or atropine are used to block the constriction pathway
How is IBS treated?
M3 receptor antagonists reduce side effects, block parasympathetic activity of a hyperactive gut
What are the unwanted side effects of muscarinic receptor antagonists?
- hot as hell (decreased sweating, lack of thermoregulation)
- dry as a bone (lack of secretions)
- blind as a bat (cyclopegia)
- mad as a hatter (CNS disturbance)
How do you teat atropine poisoning?
- bethanechol (stable version of acetylcholine and will outcompete atropine)
- physostigmine (blocks acetylcholinesterase enzyme , it allows acetylcholine to build up in the synapse and out compete atropine)
How is the botulinum toxin toxic?
- blocked SNARE protein complex involved with exocytosis of acetylcholine- cannot have an effect on the muscle and is therefore paralysed
- used in botox- paralyses skeletal muscle in the skin but has to be tightly regulated as it is extremely toxic
