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Pharmacology > Drugs and the parasympathetic nervous system > Flashcards

Drugs and the parasympathetic nervous system Flashcards

1
Q

List the poisoning symptoms of amanita muscaria (mushroom)

A

Increased salivation, excessive sweating, lacrimation, bronchial secretions, bronchoconstriction, bradycardia, hypotension, miosis (papillary constriction), blurred vision, abdominal cramping, diarrhoea, tremor, convulsions, hypothermia

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2
Q

List the poisoning symptoms of atropa belladonna

A

Dr mouth, dry eyes, reduced bronchial secretions, tachycardia, dilated pupils, blurred vison, diarrhoea, stupor, delirium, hallucinations

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3
Q

What is muscarine?

A

Found in the mushrooms

Direct-acting acetylcholine receptor agonist

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4
Q

How is the acetylcholine receptor family split up?

A 
Class nicotinic (ligand-gated ion channels)= Skeletal NMJ, Ganglionic, Neuronal CNS
Class Muscarinic (selective)= G protein coupled
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5
Q

Describe the anatomy of the PNS

A 
Cranial outflow (3, 7, 9, 10) from medullary to eye/ lacrimal gland/ salivary glands/ heart, lungs, upper GI tract
Sacral outflow to lower GI tract, bladder, genitalia
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6
Q

Contrast sympathetic and parasympathetic neuron pathways

A
  • Sympathetic= short pre-ganglionic, nicotinic ACh synapse at sympathetic chain ganglion, long post-ganglionic, noradrenaline and adrenoreceptors
  • Para= long pre-ganglionic, Nicotinic ACh receptors ganglion, short post-ganglionic, ACh at muscarinic ACh
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7
Q

What are the names and characteristics of the sub types of muscarinic receptors?

A

M1= neural (slow EPSP in ganglia)- mediate slow excitation
M2- Cardiac- regulate heart rate and force of contraction
M3- glandular secretion, contraction of visceral smooth muscle, vascular relaxation
M4, M5

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8
Q

What are the cellular signalling pathways linked to muscarinic receptor activation?

A
  • Activate Phospholipase C leading to the production of IP3 (releasing intracellular Ca2, contraction of muscle) and diacyl glycerol (DAG) (activator of Protein Kinase C= phosphorylation)- M1,3,5
  • Inhibit adenylate cyclase causing decrease in cAMP levels- M2,4
  • Open/ activate K+ channels, PNS and heart, M2
  • Inhibit Ca2 channels, M2
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9
Q

What does parasympathomimetic/ cholinomimetic mean?

A

Drugs that mimic the effect of parasympathetic nerve stimulation, particularly by activation of responses mediated by muscarinic cholinergic receptors

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10
Q

Describe the effect of drugs affecting the synthesis and release of ACh

A
  • ACh transporter blocked by vesamicol, no vesicles
  • Exocytosis Ca2 dependent blocked by botulinum toxin
  • Acetylcholinesterase inhibited to prolong lifetime in cleft (breakdown into Acetate and choline inhibited)
  • Choline transporter into presynaptic terminal blocked by hemicholinium
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11
Q

What are the types of direct acting agonists?

A 
Choline esters (all quaternary ammonium esters)
Natural plant compounds
(similar structures to acetylcholine)
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12
Q

What are the types of choline esters?

A
  • Acetylcholine- too unstable in plasma to be effective, muscarinic and nicotinic effects, not used
  • Bethanechol- not hydrolysed by cholinesterase, weak nicotinic agonist, selective muscarinic agonist
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13
Q

What are the natural plant compounds?

A
  • Muscarine
  • Pilocarpine
    Neither selective for subtypes
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14
Q

What are the types in indirect acting agonists?

A

Reversible/ irreversible inhibitors of acetylcholinesterase

Increase concentration of ACh and prolong lifetime in synapse/ junction

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15
Q

What are the types of reversible inhibitors?

A
  • Physostigmine= tertiary plant alkaloid
  • Neostigmine= synthetic quaternary compound
    (Insecticide= synthetic tertiary compound)
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16
Q

What are the types of irreversible inhibitors?

A 
Organophosphates
- Insecticides (accidental poisoning)
- Ecothiopate (open angle glaucoma)
- Military nerve gases (poisoning)
- Novichok
Extremely lipophilic- cross all barriers including blood-brain barrier
17
Q

What are the pharmacological actions of direct acting agonists?

A

Mainly muscarinic effects at end effectors
Most synthetic direct acting compounds do not have CNS effects but plant alkaloids muscarine and pilocarpine can enter CNS

18
Q

What are the pharmacological actions of indirect acting agonists?

A

Potentiate transmission at all cholinergic junctions- muscarinic, ganglionic and skeletal muscle effects
Have CNS effects in permeable to blood-brain barrier

19
Q

How are symptoms bradycardia and hypotension caused?

A

M2 receptors in heart at SAN, AVN and atrial muscle= bradycardia (dec. rate, force, conduction velocity)
No effect on ventricular muscle
ACh dilates blood vessels, lower bp- hypotension
generally no PNS nerves in tissues except erectile tissue and salivary glands- M3 mediates dilation

20
Q

How does signal transduction in the heart affecting by M2 receptors lead to bradycardia?

A

ACh binding to M2 receptors= K+ channels opening (direct action of G protein beta gamma subunits)
Elicits hyperpolarisation of cardiac muscle membrane potential- shortens duration of cardiac action potential, increases interval between potentials
Reduced contraction= inhibited Ca2 channels

21
Q

How are symptoms abdominal cramping, increased gastric acid secretion and diarrhoea caused?

A

M3 receptors in GI tract causes increased motility of smooth muscle (contraction= spasms), dilation of sphincter, secretion of glands
Gastric acid secretion= M1

22
Q

What are the therapeutic uses for cholinomimetics in intestinal atony and urinary bladder atony?

A

Bethanechol (direct), neostigmine (indirect)- build up ACh
- Increase peristalsis by activation of muscarinic receptor
- Stimulate micturition by activating muscarinic receptors on bladder detrusor muscle
Useful in postpartum or postoperative non-obstructive urinary retention

23
Q

How are symptoms pupillary constriction and blurred vision caused?

A

M3 receptors in pupils= constriction

M3 receptors in ciliary muscles= contraction (width of lens to focus affected)

24
Q

What are the therapeutic uses of cholinomimetics for glaucoma?

A

Glaucoma= build up of aqueous humour, obstruction where normally drained, optic nerve damage (pressure)
Pilocarpine= direct, lipid soluble so rapidly diffuses locally, eye drops
Ecothiopate= indirect, longer acting, CNS effects so local administration
Relax lens, open Canal of Schlemm

25
Q

What are the therapeutic uses of cholinomimetics for Alzheimer’s?

A

Muscarinic receptors involved in transmission in hippocampus- Donepezil/ Aricept, mild anticholinesterase acting on specific forms of the enzyme in the brain, beneficial effects for cognitive symptoms in early stages

26
Q

What are the types of anticholinergic drugs?

A

Atropine= tertiary amine, prototypical muscarinic receptor antagonist
Hyoscine/ scopolamine= tertiary amine, lipophilic so absorbed by gut/ patch, readily crosses into CNS
All functions mediated by muscarinic receptors blocked
Little effect on nicotinic- selective

27
Q

What are the pharmacological effects of muscarinic antagonists in the heart?

A

SAN, AVN, atrial muscle= inc. rate, force, conduction velocity so tachycardia
Ventricular muscle no effect
Atropine blocks effects of vagus nerve stimulation

28
Q

What are the pharmacological effects of muscarinic antagonists in the eye and glands?

A
  • Eye- pupil dilation (mydriasis), ciliary muscle relaxation= paralysis of accommodation (inability to focus)
  • Salivary and lacrimal glands= inhibition of secretion (dry)
29
Q

What are the pharmacological effects of muscarinic antagonists in the viscera?

A
  • Bronchi smooth muscle dilation
  • Bladder smooth muscle relaxation
  • Reduced motility of smooth muscle in GI tract, constriction of sphincter, moderate inhibition of glands and inhibition of gastric acid secretion
30
Q

List the therapeutic uses of antimuscarinics

A

Pre-anaesthetic medication
Ophthalmological uses
Gastrointestinal antispasmodic agents
Treatment of poisoning by cholinomimetics

31
Q

How are antimuscarinics used in pre-anaesthetic medication?

A

Hyoscine, Atropine

Reduction of salivary and bronchial secretions minimises postoperative pulmonary complications

32
Q

How are antimuscarinics used in ophthalmology?

A

Atropine, shorter lasting derivatives topically (tropicamide)
Muscarinic receptor blockade on concentric muscle of iris causes pupil dilation and paralysis of accommodation - eye surgery

33
Q

How are antimuscarinics used as GI antispasmodic agents?

A

Atropine derivatives- dicycloverine

Relaxes smooth muscle to facilitate endoscopy

34
Q

How are antimuscarinics used in treatment of poisoning?

A

Atropine derivatives

Antagonise lethal effects of high level muscarinic activation in periphery and CNS

Pharmacology (12 decks)

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