Cholinoceptor Antagonists Flashcards
Where are nicotinic receptors found
All autonomic ganglia
What part of the ANS can nicotinic receptor ant/agonists interfere with
The whole ANS
What type of receptor is a nicotinic receptor
Type 1 ion channel
What 2 ways can a nicotinic receptor antagonist work
Can block the receptor or block the ion channel
what does use dependent blocking mean
drugs work most effectively when the ion channels are open. Thus, the more agonist that is present at the receptor, the more opportunity for the antagonist to block the channel, therefore, the more useful and effective these drugs can be
What makes a use dependent blocker more potent
If there is more agonist to open the ion channel
what is incomplete blocking
Ion channel blockers, they don’t completely block they slow it down considerably but not fully stop the functioning
Difference between normal receptor blockade and ion channel blockade regarding use dependency
When have a normal receptor blockade, then less agonist makes it more effective. Opposite is true for ion channel blockers
why do nicotinic receptor antagonists cause hypotension (2)
The SNS is dominant in blood vessels and the dominant effect is to constrict. This increases TPR and in turn, increases BP. The drugs take out the dominant sympathetic effect so the vessel will dilate. The TPR would decrease and so the BP would decrease.
Drugs might also interfere with the Renin secretion reduced aldosterone would be produced which means less water and Na is reabsorbed so less renin produced and thus, less ACE produced (see below).
Sympathetic dominated organ? (5)
Liver, kidney, adipose tissue, skin, blood vessels
PS dominated organ? (5)
Eyes, lungs, bladder/ureters/GIT
predominant method of action of trimetaphan
Receptor antagonism (but also ion channel blockade)
predominant method of action of hexamethonium
Ion channel blockade (but also receptor antagonism)
Use of trimetaphan?
IV for hypotension presurgery
other name for nicotinic receptor antagonist?
Ganglion blocking drugs
difference between receptor blockade antagonists and ganglion blocking drugs targets?
ganglion blocking drugs only target ANS nicotinic receptors, RBA can also target somatic NS
difference between receptor blockade antagonists and ganglion blocking drugs binding?
Ganglion blocking drugs are usually reversible RBA usually covalently bind and are irreversible
Another name for ganglion blocking drugs
Nicotinic receptor anatagonists
What part of the NS do muscarinic receptor antagonists target?
The PSNS
2 examples of muscarinic receptor antagonists?
Atropine, hyoscine
Where are muscarinic receptors predominantly found? Exception is?
In the PSNS effector organs, exception is the sweat glands
Atropine effects, normal and high dose?
Normal, does not do much.
High dose causes restlessness and CNS agitation
Hyoscine effects, normal and high dose?
Sedative/amnesia at normal dose, high dose causes CNS depression and paradoxical CNS excitation
Difference between hyoscine and atropine? What does this mean for its use
Hyoscine is more lipid soluble and so can penetrate the brain.
Other theory is that it is more M1 selective and so targets brain better.
What is tropicamide used for? Its drug class? effect? Use?
Muscarinic receptor antagonist for the eye. Inhibits PS pupillary constriction and so causes dilation. used in eye exams
What drugs are used as anaesthetic premeds?
Muscarinic receptor antagonists
What is used for optical exams to dilate eyes
Tropicamide
What effects do you want anaesthetic premeds to do? (3+1 for hyoscine)
Reduce secretions, reduce bronchoconstrictions, increase heart rate. Hyoscine also induces a little sedation
What drug is used to stop motion sickness
Hyoscine patches
How does hyoscine work to stop motion sickness?
Blocks muscarinic receptors in the vomiting centre
Which neurons are important for fine control of movement
Nigrostriatal dopamine neurons
What are nigrostriatal dopamine neurons important for
Fine movement
What (name) neurons are lost in parkinsons
Nigrostriatal dopamine neurons
Nigrostriatal dopamine neurons are lost in what disease
Parkinson’s
What system is inhibitory to the dopaminergic system
Cholinergic
How do muscarinic receptor antagonists help with parkinsons
Remove the inhibition caused by cholinergic (M4) neurons on the dopaminergic (D1) neurons
What type of neurone is lost in parkinsons
D1 dopaminergic
What drug is used to treat COPD and Asthma
Muscarinic receptor antagonist - ipratropium bromide
How do muscarinic receptor antagonists help COPD and asthma
These block the PS constriction of the lungs so bronchodilation occurs.
Why is ipratropium bromide especially good for asthma and COPD
Because it is a large polar molecule so cannot cross into the blood when inhaled and then cause muscarinic side effects
How can muscarinic receptor antagonists help with irritable bowel syndrome
Block M3 mediated GI tone and motility, as well as secretions
What are the main uses for muscarinic receptor antagonists (7)
Eye examination, anaesthetic premed, motion sickness, Parkinsons, COPD/asthma and irritable bowel syndrome
4 sentences to help remember side effects of muscarinic receptor antagonists
Hot as hell
Dry as a bone
Blind as a bat
Mad as a hatter
What are the side effects of muscarinic receptor antagonists (4)
Decreased sweating and thermoregulation, reduced secretions, ability to focus on nearby objects, CNS disturbance
What is an inability to focus on nearby objects called
Cyclopegia
What would be used for atropine/muscarinic receptor antagonists overdose? (3)
Bethanechol, ecothiopate or physostigmine
How does botulinum toxin work
prevents the ACh from being exocytosed and getting to the synapse
therapeutic use of botulinum toxin
Get rid of wrinkles or stop people sweating
Effects of nicotinic receptor antagonists? (6)
Hypotension sympathetic causes vasoconstriction and increased renin secretion Pupil dilation Bronchodilation Bladder Dysfunction Decrease GI tone Decrease in secretions
