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Pharmacology 3 > L10: the Sympathetic Nervous System > Flashcards

L10: the Sympathetic Nervous System Flashcards

1
Q

What are the main differences in anatomy of parasympathetic and sympathetic systems neurons?

A
  • pre-ganglionic neurone is shorter in sympathetic than parasympathetic
  • post-ganglionic neurone is longer in sympathetic than parasympathetic
  • sympathetic post-ganglionic synapse neurotransmitter is noradrenaline which acts on adrenoreceptors on effector organs, while in parasympathetic it’s ACh acting on muscarinic ACh receptors

SEE L10, slide 4 for diagram

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2
Q

What is the difference between adrenaline and noradrenaline?

A

Noradrenaline is released from most post-ganglionic neurons, while adrenaline is released as a consequence of sympathetic nervous system. Adrenaline is predominantly synthesised in the adrenal medulla.

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3
Q

What are the exceptions in sympathetic neurotransmitters and neurones anatomy of sympathetic system?

A
  • there is NO post-ganglionic neurone in adrenal medulla, only pre-ganglionic which releases ACh, which acts on nicotinic ACh receptors on adrenal medulla
  • neurotransmitter in sweat glands post-ganglionic synapse is ACh, which acts on muscarinic ACh receptors, and NOT noradrenaline

SEE L10, slide 6

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4
Q

What are the drugs inhibiting noradrenaline synthesis, storage and release?

A
  • Ganglion Block: Hexamethonium
  • Synthesis: α-Methyl-tyrosine (hypertension in pregnancy), Methyl-dopa, Carbidopa (Parkinson’s)
  • Storage: Reserpine
  • Release: Guanethidine.
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5
Q

What are the classes of adrenoreceptors? What are their differences?

A
  • Alpha (more noradrenaline potent)
  • beta (more adrenaline potent)
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6
Q

What are the subclasses of adrenoreceptors?

A
  • alpha-1, alpha-2
  • beta-1, beta-2, beta-3
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7
Q

Where are alpha-2 adrenoreceptors found?

A

alpha-2 receptors are found pre-synaptically

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8
Q

Where are alpha-1, beta-1, beta-2 adrenoreceptors found?

A

alpha-1, beta-1, beta-2 adrenoreceptors are found post-synaptically

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9
Q

Which class do adrenoreceptors belong to?

A

GPCRs

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10
Q

In which tissue or organ are alpha-1 adrenoreceptors found?

A

Smooth muscle and heart

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11
Q

What is the G protein associated with alpha-1 adrenoreceptor?

A

Gq/11

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12
Q

In which tissue or organ are alpha-2 adrenoreceptors found?

A

Smooth muscle

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13
Q

What is the G protein associated with alpha-2 adrenoreceptor?

A

Gi

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14
Q

In which tissue or organ are beta-1 adrenoreceptors found?

A

Heart muscle

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15
Q

What is the G protein associated with beta-1 adrenoreceptor?

A

Gs

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16
Q

In which tissue or organ are beta-2 adrenoreceptors found?

A

Smooth muscle

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17
Q

What is the G protein associated with beta-2 adrenoreceptor?

A

Gs

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18
Q

In which tissue or organ are beta-3 receptors found?

A

Fat cells

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19
Q

What is the G protein associated with beta-3 adrenoreceptor?

A

Gs

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20
Q

What is the G protein for alpha-1 adrenoreceptor? What is its mechanism?

A

Gq/11
They work on Phospholipase C-beta (PLC-beta), which catalyses PIP2 conversion to IP3, which triggers calcium release and smooth muscle contraction. BUT they cause relaxation of smooth muscle in the GI tract.
CHECK L10, slide 9

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21
Q

What is the G protein for alpha-2 adrenoreceptor? What is its mechanism?

A

Gi
- Inhibits AC, which normally catalyses ATP conversion to cAMP,
- which then inhibits calcium release leading to inhibition of Transmitter Release.
- also PKi is not converted to PKa, which usually phosphorylates MLKC, leading to smooth muscle relaxation
- because of this, smooth muscle contracts
CHECK L10, slide 9

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22
Q

What is the G protein for beta-1 adrenoreceptors? What is its mechanism?

A

Gs
- Acts on adenylate cyclase (AC), which catalyses ATP conversion to cAMP
- leads to heart muscle contraction, stimulation increases heart rate and force of contraction.
CHECK L10, slide 9

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23
Q

What is the G protein for beta-2 adrenoreceptors? What is its mechanism?

A

Gs
Found in smooth muscle, causes relaxation and blood vessel dilation, promotes cAMP conversion, which then acts on converting PKi to PKa, PKa then phosphorylates MLCK, phosphorylated MLCK becomes inactivated and causes relaxation.
CHECK L10, slide 9

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24
Q

What is the G protein for beta-3 adrenoreceptors? What is its mechanism?

A

Gs
Found on fat cells (adipocytes) and stimulate lipolysis.
CHECK L10, slide 9

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25
Q

What is the adrenoreceptor in bronchioles and what is its effect upon activation?

A

beta-2, dilation

26
Q

What is the adrenoreceptor in GI tract and what is its effect upon activation?

A

alpha and beta-2, lower motility

27
Q

What is the adrenoreceptor in uterus (pregnant and non-pregnant) and what is its effect upon activation?

A

pregnant: alpha, contraction
non-pregnant: beta, dilation

28
Q

What is the adrenoreceptor in penis and what is its effect upon activation?

A

alpha, impotence and ejaculation

29
Q

What is the adrenoreceptor in eye (pupil and ciliary muscle) and what is its effect upon activation?

A

Pupil: alpha, dilation
Ciliary muscle: beta, relaxation

30
Q

What is the adrenoreceptor in salivary glands and what is its effect upon activation?

A

alpha and beta, secretion

31
Q

What is the adrenoreceptor in kidney and what is its effect upon activation?

A

beta, renin secretion

32
Q

What is the adrenoreceptor in liver and what is its effect upon activation?

A

alpha and beta-2, higher glucose levels

33
Q

What is the adrenoreceptor in fat and what is its effect upon activation?

A

beta-3, lipolysis

34
Q

What are the effects of alpha adrenoreceptors antagonists?

A
  • vasodilator effects in CV indications
  • treatment of benign prostatic hyperplasia (enlarged prostate gland, not cancerous)
35
Q

What are the effects of beta-2 adrenoreceptors agonists?

A

smooth muscle relaxants (airways)

36
Q

What are the effects of beta-1 adrenoreceptors antagonists?

A

cardio-depressant effects (decrease heart rate)

37
Q

What are the endogenous agonists on adrenoreceptors? What are their targets, actions and clinical use?

A
  • noradrenaline, target: alpha-1, alpha-2, beta-1, increases BP, not selective so not much use, sepsis
  • adrenaline, target: alpha-1, alpha-2 receptors, action: bronchodilation, used in emergencies of asthma
  • adrenaline, target: beta-1, beta-2, increases BP used in anaphylaxis or increases HR causing cardiac arrest
  • Phenylephrine, methoxamine, target alpha-1 receptors to cause vasoconstriction. Used as nasal decongestant, and in an emergency to increase the blood pressure.
  • Clonidine, target alpha-2 receptors, thus reduces noradrenaline release from nerve endings. May be given to lower blood pressure by acting in the brain, but is little used now
38
Q

Which drugs inhibit synthesis of noradrenaline? Where are they used?

A
  • alpha-methyl-tyrosine used in Phaeochromocytoma (tumour of adrenal gland)
  • carbidopa blocks production of dopamine used in Parkinson’s disease
  • methyldopa used in hypertension in pregnancy (occasional)
39
Q

Which drug inhibits storage of noradrenaline? Where is it used?

A

reserpine, former antihypertensive

40
Q

Which drug inhibits release of noradrenaline? Where is it used?

A

guanethidine, former antihypertensive (lower BP), complicated use because of high number of different activities

41
Q

What is the action of hexamethonium in sympathetic nervous system?

A

hexamethonium acts on nAChRs by blocking the receptor and sympathetic signalling, used as former antihypertensive. Side effects: parasympathetic block - constipation, long-sighted

42
Q

What are the side effects of inhibitors of NA synthesis, storage and release?

A
  • hypotension (postural) (low blood pressure after standing up)
  • drowsiness
  • diarrhoea
  • impotence
  • depression
43
Q

What are the mechanisms of noradrenaline re-uptake and metabolism?

A
  • Neuronal uptake 1: taken back to the pre-ganglionic neurone, recycled back into the vesicles (75% NA is recycled back) or converted to inactive metabolites by monoamine oxidase (MAO)
  • Extra-neuronal uptake 2: limits the spread of NA, taken by post-ganglionic neurone and converted to inactive metabolites by Catechol-O-methyl transferase (COMT)
44
Q

What are the indirect sympathomimetic drugs? What’s their mechanism of action?

A

Indirect sympathomimetic drugs increase SN activity and circulating NA.

  • cocaine, tricyclic antidepressants, NaSSRI inhibit uptake 1
  • amphetamines, phenelzine, selegiline (used for early stages of Parkinson’s) inhibit MAO, no conversion to inactive metabolites
  • entacapone inhibit COMT in uptake 2
  • tyramine, structurally related to NA, transported to synaptic vesicles by Uptake 1 and exchanged for NA, NA escapes via uptake 1 and acts on adrenergic receptors.
    CHECK L10, slide 17
45
Q

What’s the mechanism of action of cocaine, tricyclic antidepressants, NaSSRI as indirect sympathomimetic drugs?

A

Inhibit uptake 1

46
Q

What’s the mechanism of action of amphetamines, selegiline, phenelzine as indirect sympathomimetic drugs?

A

used for early stages of Parkinson’s inhibit MAO, no conversion to inactive metabolites

47
Q

What’s the mechanism of action of entacapone as indirect sympathomimetic drugs?

A

Inhibit COMT in uptake 2

48
Q

What’s the mechanism of action of tyramine as indirect sympathomimetic drugs?

A

transported to synaptic vesicles by Uptake 1 and exchanged for NA, NA escapes via uptake 1 and acts on adrenergic receptors.

49
Q

What are the main uses of indirect sympathomimetic drugs?

A

Stimulants, antidepressants (ephedrine - nasal decongestant); limited therapeutic actions; significant abuse potential

50
Q

What are the unwanted effects of indirect sympathomimetic drugs?

A
  • hypertension
  • convulsions
  • dependence
  • “cheese reaction” (MAOI only)
51
Q

How do indirect sympathomimetic drugs cause hypertension?

A

sympathomimetic action (increased NA) –> vasoconstriction, increased heart rate –> hypertension

52
Q

Which systems are affected by alpha-1A, alpha-1B and alpha-1D adrenoreceptors?

A

Cardiovascular system and lower urinary tract, mediates smooth muscle contraction

53
Q

What are the alpha adrenoreceptors agonists, their target and their action?

A
  • methoxamine targets alpha-1 and alpha-2 receptors, causes vasoconstriction, decongestant
  • phenylephrine targets alpha-1 receptors, causes vasoconstriction, decongestant, haemorrhoids, mydriasis, priapism
54
Q

How can noradrenaline release be modulated via alpha-2 receptors?

A

Presynaptic/prejunctional alpha-2 receptors - negative feedback. Likely to involve G protein-mediated inhibition of pre-synaptic VGCC. Inhibits further NA release.
CHECK L10, slide 25

55
Q

What is the partial agonist of alpha-2 adrenoreceptor? What is its action?

A

clonidine, former antihypertensive, migraine

56
Q

What is the alpha-2 receptor antagonist? What is its action?

A

yohimbine, idazoxan, aphrodisiac?

57
Q

What is the agonist of beta-1 adrenoreceptor, what is its action?

A

Dobutamine, causes positive inotropy, used in cardiogenic shock

58
Q

What is the effect of triggering beta-1 adrenoreceptor?

A

In cardiac myocyte causes higher levels of cAMP, thus contraction

59
Q

What is the effect of triggering beta-2 adrenoreceptor?

A

In smooth muscle cells causes rise in levels of cAMP and dilation. (vein, skeletal muscle artery or bronchiole)

60
Q

What is the agonist of beta-2 adrenoreceptor, what is its action?

A

Isoprenaline or salbutamol, used in asthma, side effects: peripheral vasodilation, tremor dysrhythmias

61
Q

What are the beta adrenoreceptor antagonists (sympatholytics)? What is their action?

A
  • propanolol targets beta-1/2, causes reduced inotropy (contractility)
  • metoprolol targets beta-1, causes reduced inotropy
    both used in angina, hypertension, cardiac dysrhythmia, anxiety, tremor, glaucoma
  • nebivolol targets beta-1, reduces inotropy, vasodilation, used for hypertension

Pharmacology 3 (21 decks)

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