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14 Cards in this Set
- Front
- Back
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What are the three important places we find the cholinergic neuron in the ANS?
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The preganglionic fibers terminating in the adrenal medulla, the autonomic ganglia (both parasympathetic and sympathetic), and the post-ganglionic fibers of the parasympathic division of the ANS.
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What enzyme catalyzes the reaction of choline with acetyl CoA to form acetylcholine in the cytosol?
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Choline acetyltransferase (CAT)
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What can degrade ACh at the synaptic cleft?
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acetylcholinesterase, cleaves ACh to choline and acetate or butylcholinesterase (less specific)
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How is choline recycled? What drug can inhibit this?
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Recaptured by a sodium-coupled high affinity uptake system that transports it back into neuron, where it is acetylated and stored until next AP. Hemicholinium inhibits re-uptake.
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Why would ACh itself be of no use therapeutically?
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(1) Multiplicity of actions - ACh agonists can target distinct muscarinic & nicotinic receptors and (2) rapid inactivation by AChEsterase
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What are cholinergic agonists?
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Synthetic esters of choline or naturally occuring alkaloids that mimic the effects of ACh. They are more specific and less labile than ACh. Methacholine, carbachol, and bethanechol are most prominent esters.
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What does stimulation of ACh receptors in blood vessels do?
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Causes vasodilation, reducing blood pressure.
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What does stimulation of Ach receptors at SA node do?
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Decreases rate of firing, causing a decrease in cardiac rate and stroke volume, therefore lowing cardiac output, but NOT contractile force.
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What does atropine do?
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Blocks muscarinic receptors and prevents ACh from producing vasodilation - it's a ACh ANTAGONIST
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In general, what do the cholinergic agonists (choline esters) do?
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Cardiovascular vasodilation, negative chronotropic & inotropic effects, countered by baroreceptor reflex (exc. bethanechol has little cardiovascular effect), increased GI tone & mobility, contraction of detrusor muscle of bladder, and pupillary constriction (miosis)
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What does bethanechol do? (what is its therapeutic value)
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A choline ester, it activates muscarinic receptors - major actions are on smooth musculature of the bladder and GI tract, causing increased GI motility and tone, and stimulating the detrusor muscle of bladder & expulsion of urine
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What are the two naturally occuring alkaloid cholinergic agonists?
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Pilocarpine & arecoline - pilocarpine is a muscarinic agonistused for reduction of intraocular pressure in glaucome & for xerostomia (dry moouth)
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What are the effects of nicotinic agonists, ie nicotine?
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Complicated actions - at both sympa & parasympa ganglia, skeletal muscles, and even CNS - cause release of epinephrine from adrenal medulla with resulting cardiovascular effects, directly sT chemoreceptors in carotid and aortic bodies, eventually causing transmission block - desensitization of receptor sets in wherein receptor becomes unresponsive
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What compounds INDIRECTLY provide a cholinergic action by prolonging the lifetime of acetylcholine, resulting in more ACh in the synaptic space? (and they eventually get desensitization blockade at nicotinic junctions, accounting for lethality of drugs)
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Anticholinesterase, like edrophonium, physostigmines, neostigmine, and DFP
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