RCS 04 - Cholinergic Agonists & Antagonists 1 Flashcards
A
List and describe the types of cholinergic agonists
- Direct Acting Agents - bind to and activate muscarinic or nicotinic receptors
- Indirect Acting Agents - inhibit Ach-esterases
Are the therapeutically useful direct acting angents usually activating muscarinic or nicotinic receptors?
Muscarinic
List the direct affects of Ach on the CVS we need to know. Are these effects always seen?
M2 effect - decrease in HR, force of heart contraction, and in rate of conduction in SA and AV nodes
M3 effect - vasodilation
These effects are not always seen because homeostatic reflexes may dampen or reverse them.
List the direct effects of Ach on non-CVS tissues that we need to know.
- Sphincter Pupillae Constriction - Miosis
- Ciliary Muscle Constriction - lens accomodation for near vision
- Salivary/Sweat/Lacrimal Glands - increase in secretion
- Bronchi - constriction and increase in secretion
- GIT - increased tone, peristaltic activity, secretions, and relaxation of sphincters
- Contraction of detrusor muscles and relaxation of the urethral sphincter to facilitate urination
Important note about low and high doses of ACh.
Both low and high doses of Ach will cause a drop in MAP and PVR. However, a low dose of Ach will cause an increased HR while a high dose will cause a decreased HR.
How can you give ACh so that only the nicotinic effects are seen? What are these nicotinic effects and what is the mechanism of activation?
You can block the muscarinic effects by administering a muscarinic antagonist, like atropine, before adminstering the ACh.
Primary effects seen are both an increase in BP and vasoconstriction
These effects are due to stimulation of the sympathetic ganglia and release of E from the adrenal medulla
List the subtypes of direct acting cholinergic agonists
Choline Esters
Alkaloids
List the primary characteristic of choline esters that we need to know.
- They’re quaternary ammoniums, which means they’re charged, making them poorly absorbed and poorly distributed into the CNS
List the choline esters we need to know and comment on how resistant to cholinesterases they are.
- ACh - very rapidly hydrolyzed
- Methacholine, carbachol, and bethanechol - more resistant to hydrolysis
What are the primary uses of ACh
To obtain rapid miosis after delivery of the lens in cataract surgery and other procedures where rapid miosis is required
No systemic therapeutic applications due to its multiplicity of actions and rapid hydrolysis
What types of receptors does Bathanechol activate and what are its primary uses?
Muscarinic agonist
Primarily used to treat postoperative/postpartum urinary retention or any other type of urinary bladder atony
What types of receptors does Carbachol activate and what are its primary uses?
Activates both muscarinic and nicotinic receptors
Used to elicit miosis during surgery and reduce intraocular pressure after cataract surgery
What types of receptors does Methacholine activate and what are its primary uses?
Muscarinic agonist
Primarily used to diagnose bronchial airway hyperreactivity (asthma) in subjects who do not have clinically apparent asthma (their FEV fraction appears OK)
List the alkaloids we need to know
Pilocarpine
Nicotine