Cholinergic Agonists & Antagonists Flashcards
To which receptors does ACh bind?
Both nicotinic and muscarinic
To which receptors does methacholine bind?
Primarily muscarinic
To which receptors does carbachol bind?
Both nicotinic and muscarinic
To which receptors does bethanechol bind?
Primarily muscarinic
Describe the mechanism of indirectly-acting cholinergic agonists.
They inhibit AChE, so they don’t actually bind the receptor, but they effectively increase the amount of ACh present in the synapse and enhance its effects.
Name a tertiary amine muscarinic agonist
Pilocarpine
What differentiates pilocarpine from the quaternary amines?
It is able to cross the blood-brain barrier, so it has appreciable CNS effects
To which receptors does pilocarpine bind?
Muscarinic only
For what is methacholine used?
To test for asthma
For what is carbachol used?
As a miotic agent; reduces intraocular pressure
For what is bethanechol used?
Stimulates GI motility and bladder control
For what is pilocarpine used?
To treat lack of sweat/lacrimation/salivation
Three reversible cholinesterase inhibitors discussed in class
Neostigmine
Edrophonium
Physostigmine
What does neostigmine do, and what is it used for?
Blocks ACh binding AChE for >1 hour; used to treat myesthenia gravis and reverse the neuromuscular blockade
What does edrophonium used for clinically?
Used to test myasthenia gravis progression vs. ACh poisoning; preferential due to its short half-life
What does physostigmine do clinically?
Crosses the blood brain barrier and counteracts delirium from anticholinergic activation, such as atropine poisoning
What does pralidoxime (2PAM) do?
Helps to treat organophosphate poisoning by restoring function to AChE
Muscarinic antagonists
Atropine
Scopalamine
Glycopyrrolate
What happens at a high enough concentration of atropine?
Nicotinic cholinergic receptors at the autonomic ganglia will also be blocked
Symptoms of atropine poisoning
Dilated pupils Blurred vision Dry mouth Thirst Dysphagia Tachycardia Hypertension Urinary retention Respiratory collapse Hallucinations Psychosis
For what are atropinic agents used?
Bladder problems, nausea/vomiting, overstimulation of the gut
What side effects will atropinic agents cause?
Increase in heart rate and mydriasis