Lecture 11 — Cholinomimetics
Condensed source-based study notes. Consult original slides for diagrams and finer details.
Definition and Classification
• Cholinomimetics produce effects resembling acetylcholine or postganglionic parasympathetic stimulation.
• Direct-acting drugs stimulate cholinoreceptors; indirect-acting drugs inhibit enzymatic breakdown of endogenous acetylcholine.
• Direct agents can act at muscarinic receptors or nicotinic receptors.
• The source divides direct-acting cholinomimetics into choline esters and alkaloids.
Acetylcholine and Choline Esters
• Acetylcholine is released naturally from cholinergic nerve endings and rapidly hydrolyzed by acetylcholinesterase, producing a very short duration of action.
• The source states acetylcholine is used experimentally rather than as a routine therapeutic drug.
• Its quaternary ammonium group makes it permanently positively charged, hydrophilic and poorly membrane-permeable.
• The lecture discusses structural changes that can reduce rapid hydrolysis and alter membrane permeability.
Examples to Recognize
• The lecture lists acetylcholine, bethanechol, carbachol, methacholine, pilocarpine, neostigmine, physostigmine, pyridostigmine, edrophonium, donepezil, galantamine, rivastigmine and others.
• The introductory example list is marked “Don’t memorize them” in the source; follow the lecture’s specific emphasis for assessment.
Acetylcholinesterase
• The lecture illustrates ACh hydrolysis at the enzyme active center, including anionic and esteratic sites.
• Indirect cholinomimetic activity depends on preventing ACh breakdown, thereby increasing ACh effects.
