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Cholinergics- Muscarinics Flashcards

1
Q

Cholinergics

A

Agents that bind nicotinic and/or muscarinic receptors and mimic effects of ACh, can be both excitatory and inhibitory

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2
Q

Giving exogenous ACh

A

M3 release endothelial nitric oxide to vasodilate, M2 reduce heart rate

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3
Q

Atropine with cholinergics

A

Blocks muscarinic receptors, ACh can only bind to nicotinic receptors, release of NE, NE acts on alpha-receptors to vasoconstrict

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4
Q

Direct-acting muscarinic cholinergics

A

Agonists- Cholinomimetics

Antagonists- Antimuscarinics

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5
Q

Direct-acting nicontinic cholinergics

A

Agonists- Cholinomimetics

Antagonists

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6
Q

Indirect-acting cholinomimetics

A

Choline esterase inhibitors (ChEI)

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7
Q

Muscarinics

A

Compounds that selectively bind and activate/inactivate muscarinic receptors, actions similar to alkaloid muscarine

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8
Q

Muscarinic actions

A

Correpond to parasympathetic stimulation through release of ACh at parasympathetic postganglionic sites

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9
Q

Exceptions to muscarinic actions

A

ACh vasodilate blood vessels but no parasympathetic innervation to blood vessels, ACh released at sweat glands by sympathetic innervation

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10
Q

Muscarinic receptors

A

G-protein coupled receptors, Gq, Gi, G0

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11
Q

Gq activation

A

Activated by M1, M3, M5

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12
Q

Gi activation

A

Activated by M2, M4

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13
Q

Action of G0

A

Increases opening probability of G-protein modified inwardly rectifying K channels, mediated by M2, M4, hyperpolarizes the cell, metabotropic

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14
Q

Alkaloids

A

Natural compounds, muscarine, pilocarpine

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15
Q

Muscarine

A

No clinical use, found in certain mushrooms, used as investigational tool to differentiate between agents with muscarinic or nicotinic activity

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16
Q

Pilocarpine

A

Tertiary cholinomimetic alkaloid, well absorbed, partial agonist

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17
Q

Choline esters

A

Agents with modified ACh structure for more muscarinic receptor selectivity and less susceptibility to cholinesterase inactivation, charged, little CNS penetration

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18
Q

Methyl group of choline esters

A

Makes drug more selective for muscarinic receptors

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19
Q

Acetyl to carbamol substitution on choline esters

A

Confers resistance to cholinesterase hydrolysis

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20
Q

Muscarinic effects on eye

A

Muscarinic agonists contract both iris sphincters and ciliary muscles through M3, iris pulled away from anterior chamber, trabecular meshwork at base of ciliary muscle opened, both facilitate aqueous humor outflow into canal of Schlemm

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21
Q

Cardiovascular effects of muscarinics

A

M2 mediates an increase in K current in cardiac cells to cause hyperpolarization, reduce action potential duration, decrease contractility of the heart

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22
Q

Cardiovascular effects of low concentrations of muscarinics

A

Activation of M3 on endothelial cells release NO, diffuses to adjacent vascular smooth muscle to activate guanylyl cyclase, increase cGMP, causes vasodilation, will stimulate reflex to return blood pressure to normal

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23
Q

Cardiovascular effects of high concentrations of muscarinics

A

Activation of M3 on vascular smooth muscle stimulates IP3 production, releases intracellular calcium, causes vasoconstriction

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24
Q

Muscarinic effects on lungs

A

M3, contraction of bronchial muscle (bronchoconstriction), stimulation of bronchial glands

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25
Muscarinic effects on GI
M3, increase motility, relax sphincters, stimulates secretion
26
Muscarinic effects on bladder
M2, M3, contraction of detrusor, relaxation of trigone and sphincter
27
Muscarinic effects on glands
M3, stimulates sweat, salivary, lacrimal, nasopharyngeal secretion
28
Muscarinic effects in CNS
M1 expressed in areas involving cognition, M2 mediates tremor, hypothermia, antincociception, M3 in hypothalamus, reduces appetitie and dimishes body fat mass
29
Clinical uses of acetylcholine
Direct-acting choline ester, miosis induction for eye surgery
30
Clinical uses of metacholine
Direct-acting choline ester, asthma diagnosis
31
Clinical uses of carbachol
Direct-acting choline ester, miosis induction for eye surgery, glaucoma
32
Clinical uses of bethanechol
Direct-acting choline ester, urinary retention, agent of choice for post-op, postpartum, and drug-related urinary retention, used to increase tone of the lower esophageal sphincter in patients with reflux esophagitis
33
Clinical uses of pilocarpine
Direct-acting alkaloid, glaucoma, Sjogren's syndrome (xerostomia)- systemic autoimmune disease where immune cells destroy exocrine glands
34
Clinical uses of cevimeline
Direct-acting muscarinic agonist for treatment of dry mouth associated with Sjogren's syndrome
35
Side effects of muscarinics
Diarrhea, urination, miosis/muscle weakness, bronchospasm, bradycardia, excitation, lacrimation, salivation/sweating/seizures (DUMBBELS)
36
Contraindications of muscarinics
Coronary insufficiency (reduced blood pressure exacerbates decrease in coronary blood flow), hyperthyroidism (reduces AV conduction with increased heart rate- arrhythmia), asthma (bronchoconstriction), peptic ulcer disease (increased gastric acid secretion)
37
Muscarinic antagonists
Sometimes called parasympatholytics- do not lyse parasympathetic neurons, exert effects not predictable from block of parasympathetic nervous system, better called antimuscarinics
38
Classes of muscarinic antagonists
Naturally occuring alkaloids- atropine, scopolamine Semisynthetic derivatives of alkaloids- ipratropium, tiotropium Synthetic congeners with selectivity for muscarinic receptor subtypes- tolterodine
39
Atropine
Alkaloid, used to dilate pupils
40
Scopolamine
Alkaloid, used for prophylactic treatment of motion sickness
41
Ipratropium, tiotropium
Quaternary compounds, do not cross the blood brain barrier, used for bronchial asthma and COPD
42
Tolterodine
Treatment of urinary incontinence
43
Pharmacokinetics of alkaloid and tertiary antimuscarinic
Well absorbed from the gut and conjunctival membranes, can get into CNS, scopolamine is rapidly distributed into the CNS, has greater effects than other antimuscarinics
44
Pharmacokinetics of quaternary antimuscarinics
Only 10-30% of the drug is absorbed and are poorly taken up by the brain, less CNS effect, exhibit greater nicotinic blocking activity and more likely to interfere with ganglionic or neuromuscular transmission
45
Pharmacodynamics of atropine
Reversible inhibitor of muscarinic receptors, receptors are active, most drugs that block actions of ACh are inverse agonists, atropine binds nicotinic receptors with low potency
46
CNS effects of scopolamine
Low doses- produces CNS depression, drowsiness, amnesia | High doses- can cause excitement, agitation, hallucinations, delirium, coma
47
CNS effects of atropine
Low doses- causes mild vagal excitement | High doses- can cause excitement, agitation, hallucinations, delirium, coma
48
Effects of antimuscarinics on the eye
Cause unopposed sympathetic dilator activity and mydraisis, Weaken contraction of ciliary muscle, cycloplegia, which results in loss of accomodation and focus for near vision, may cause acute glaucoma
49
Effects of antimuscarinics in the heart
Low doses- reduction in heart rate due to blockade of presynaptic M1 receptors (normally limit ACh release) High dose- tachycardia
50
Respiratory effects of antimuscarinics
Can cause bronchodilation and reduce secretion, not useful in asthma treatment, limited effectiveness in COPD due to blockade of parasympathetic postganglionic presynaptic M2 autoreceptors, frequently used before inhalant anesthetics to reduce secretions
51
GI effects of antimuscarinics
Impaired tone and motility, prolonged gastric emptying time, induced intestinal paralysis is temporary
52
Effects of antimuscarinics on urinary tract
Relaxes smooth muscle of ureters and bladder and slows voiding, may precipitate urinary retention in men with prostatic hyperplasia
53
Effects of antimuscarinics on glands
Inhibit secretion of most glands, leading to dry mouth and dry skin
54
Clinical uses of antimuscarinics
Inhibit effects of parasympathetic nervous system activity, have undesired side effects that are usually not serious, local administration to minimize systemic absorption
55
Side effects of 0.5 mg atropine
Depress salivary and bronchial secretion and sweating
56
Side effects of 1 mg atropine
Pupils dilate, accomodation of lens to near vision inhibited, vagal effects on heart are blocked (increases heart rate)
57
Side effects of 2 mg atropine
Inhibit parasympathetic control of urinary bladder and GI tract, inhibit micturition and decrease tone and motility of the gut
58
Side effects of 5 mg atropine
Gastric secretion and motility inhibited
59
Side effects of >10 mg atropine
Excitement, hallucination, delirium, coma
60
Contraindications of antimuscarinics
Patients with glaucoma, elderly men (increased incidence for prostatic hyperplasia), increase symptoms in patients with gastric ulcer

Pharmacology (15 decks)

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