Podcast
Questions and Answers
Why can't acetylcholine be administered orally?
Why can't acetylcholine be administered orally?
- It has a high affinity for butyrylcholinesterase
- It is rapidly hydrolyzed in the gastrointestinal tract (correct)
- It can't cross the blood-brain barrier
- It has poor water solubility
What is the effect of introducing a methyl group on the β-carbon of Bethanechol?
What is the effect of introducing a methyl group on the β-carbon of Bethanechol?
- Increase in selectivity to muscarinic receptor (correct)
- Increase in resistance to hydrolysis
- Steric hindrance
- Decrease in binding affinity
What is the effect of replacing the nitrogen in acetylcholine with arsenic, phosphorus, or sulfur?
What is the effect of replacing the nitrogen in acetylcholine with arsenic, phosphorus, or sulfur?
- It becomes a more potent antagonist
- It becomes a weak agonist (correct)
- It has no effect on acetylcholine's activity
- It becomes a more potent agonist
What is the importance of the positive charge on nitrogen in acetylcholine?
What is the importance of the positive charge on nitrogen in acetylcholine?
What is the difference in potency between the S-(+)-enantiomer and the R-(–)-enantiomer of methacholine?
What is the difference in potency between the S-(+)-enantiomer and the R-(–)-enantiomer of methacholine?
Which of the following is a muscarinic receptor agonist?
Which of the following is a muscarinic receptor agonist?
What is the effect of base-catalyzed epimerization at C3 in the lactone of Pilocarpine?
What is the effect of base-catalyzed epimerization at C3 in the lactone of Pilocarpine?
What happens to the S-(+)-isomer of methacholine when it interacts with acetylcholinesterase (AChE)?
What happens to the S-(+)-isomer of methacholine when it interacts with acetylcholinesterase (AChE)?
What is the effect of introducing a methyl group on the β-carbon of acetylcholine?
What is the effect of introducing a methyl group on the β-carbon of acetylcholine?
What is the effect of replacing the acetyl group of acetylcholine with a propionyl or butyryl group?
What is the effect of replacing the acetyl group of acetylcholine with a propionyl or butyryl group?
What is the reason for the greater binding affinity of S-enantiomer of Bethanechol compared to R-enantiomer?
What is the reason for the greater binding affinity of S-enantiomer of Bethanechol compared to R-enantiomer?
What is the characteristic of muscarinic agonists?
What is the characteristic of muscarinic agonists?
What is the advantage of Bethanechol over Acetylcholine?
What is the advantage of Bethanechol over Acetylcholine?
Why is carbachol more resistant to hydrolysis than acetylcholine?
Why is carbachol more resistant to hydrolysis than acetylcholine?
What is the effect of replacing the 1-methyl group with a 1-ethyl group in acetylcholine?
What is the effect of replacing the 1-methyl group with a 1-ethyl group in acetylcholine?
What is the percentage of Pilocarpine solutions that are subject to hydrolysis if not stored properly?
What is the percentage of Pilocarpine solutions that are subject to hydrolysis if not stored properly?
What is the therapeutic use of carbachol?
What is the therapeutic use of carbachol?
What is the effect of replacing the acetyl group of acetylcholine with a carbamic acid group?
What is the effect of replacing the acetyl group of acetylcholine with a carbamic acid group?
What is the only available antidote for poisoning by phosphate ester AChEIs?
What is the only available antidote for poisoning by phosphate ester AChEIs?
What is the optimum chain length for anticholinergic activity in Muscarinic Receptor Antagonists?
What is the optimum chain length for anticholinergic activity in Muscarinic Receptor Antagonists?
What is the feature of quaternary ammonium compounds that makes them exhibit most potent anticholinergic activity?
What is the feature of quaternary ammonium compounds that makes them exhibit most potent anticholinergic activity?
What is the difference between atropine and acetylcholine?
What is the difference between atropine and acetylcholine?
What is the structure of atropine?
What is the structure of atropine?
What is the type of antagonism exhibited by atropine?
What is the type of antagonism exhibited by atropine?
What is the characteristic of Atropine in terms of crossing the Blood-Brain Barrier (BBB)?
What is the characteristic of Atropine in terms of crossing the Blood-Brain Barrier (BBB)?
What is the characteristic of Tiotropium and Ipratropium?
What is the characteristic of Tiotropium and Ipratropium?
What is the mechanism of action of d-Tubocurarine?
What is the mechanism of action of d-Tubocurarine?
What is the characteristic of Succinylcholine?
What is the characteristic of Succinylcholine?
What is the consequence of the quaternary amine structure of Decamethonium?
What is the consequence of the quaternary amine structure of Decamethonium?
What is the characteristic of Tiotropium and Ipratropium in terms of their activity?
What is the characteristic of Tiotropium and Ipratropium in terms of their activity?
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Study Notes
Muscarinic Receptor Antagonists
- Pralidoxime (2-PAM) is the only available antidote for poisoning by phosphate ester AChEIs.
- Replacement of H with carboxylic, heterocyclic, aromatic ring, hydroxyl group, or hydroxymethyl group can lead to muscarinic receptor antagonists.
- Ester group provides most potent anticholinergic activity, with an optimum chain length of 2-4 C.
- Quaternary ammonium compounds exhibit most potent anticholinergic activity, and a cationic quaternary ammonium group is necessary for receptor binding.
- Atropine is a naturally occurring alkaloid, isolated from Atropa belladonna and Datura stramonium, and can cross the blood-brain barrier (BBB).
- Atropine is a tertiary amine, not ionized under physiological pH, and is the tropic acid ester of tropine.
Muscarinic Receptor Agonists
- Acetylcholine (ACh) is the natural agonist, but its duration of action is short due to rapid hydrolysis by acetylcholinesterase (AChE).
- Methacholine is a synthetic agonist, more resistant to AChE hydrolysis, and can be administered orally.
- Bethanechol is a strong agonist with a chiral center, exhibiting greater binding affinity at muscarinic receptors.
- S-enantiomer of methacholine is more potent than R-enantiomer.
Acetylcholine: Structure Activity Relationship
- Replacing acetyl group with propionyl or butyryl groups leads to weaker agonists.
- Replacing acetyl group with aromatic groups leads to antagonists.
- Replacing acetyl group with carbamic acid leads to more potent agonists.
- Introduction of a methyl group on the β-carbon increases selectivity to muscarinic receptors.
- Introduction of an amino group makes it more resistant to AChE hydrolysis.
Nicotinic Receptor Antagonists
- d-Tubocurarine is a competitive antagonist, naturally occurring alkaloid, isolated from South American plant extract.
- Decamethonium is a bis-quaternary ammonium compound, with a straight chain analogue of d-Tubocurarine.
- Succinylcholine is a bis-quaternary ammonium compound, rapidly hydrolyzed by plasma esterases.
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