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Y2 LCRS Pharmacology and Therapeutics > sympathetic nervous system > Flashcards

sympathetic nervous system Flashcards

adrenoceptor agonists: list the clinical uses, principal pharmacological features, mechanism of action and unwanted effects of selective and non-selective α and β adrenoceptor agonists

1
Q

where are a1, a2, B1 and B2 (also B3) adrenoceptors located

A

SNS: post-ganglionic neurone to effector organ, adrenal medulla to effector organ

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2
Q

what do adrenoceptor agonists do

A

mimic actions of noradrenaline or adrenaline by binding to and stimulating adrenoceptors

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3
Q

what type of receptor are adrenoceptors

A

type 2 (G-protein coupled receptor)

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4
Q

secondary messengers of a1

A

PLC, IP3, DAG

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5
Q

secondary messengers of a2

A

downregulate cAMP so Gi (negative feedback receptor)

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6
Q

secondary messengers of B1

A

upregulate cAMP

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7
Q

secondary messengers of B2

A

upregulate cAMP

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8
Q

where are adrenoceptor agonists used principally

A

CVS, eyes, lungs

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9
Q

eye: adrenoceptor, importance and effect

A

a1, important, dilation; B, vaguely important, aqueous humour production by ciliary body

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10
Q

trachea and bronchioles: adrenoceptor, importance and effect

A

B2, vaguely important, dilation

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11
Q

liver: adrenoceptor, importance and effect

A

a1 and B2, very important, glycogenolysis and gluconeogenesis

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12
Q

adipose: adrenoceptor, importance and effect

A

a1 and B1, important, lipolysis

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13
Q

kidney: adrenoceptor, importance and effect

A

B1, important, increased renin secretion

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14
Q

ureters and bladder: adrenoceptor, importance and effect

A

B2, vaguely important, detrusor relaxation; a1, important, trigone and sphincter contraction

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15
Q

salivary glands: adrenoceptor and effect

A

a/B, thick and viscous secretions

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16
Q

skin: adrenoceptor, importance and effect

A

a1, very important, piloerection; increased sweating (cholinergic)

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17
Q

heart: adrenoceptor, importance and effect

A

B1, important, increased rate and contractility

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18
Q

GI: adrenoceptor and effect

A

a/B, decreased motility and tone, sphincter contraction

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19
Q

blood vessels to skeletal muscle: adrenoceptor, importance and effect

A

B2, important, dilation

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20
Q

blood vessels to skin, mucous membranes and splanchnic area: adrenoceptor, importance and effect

A

a1, very important, constriction

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21
Q

what endogenous agonists can activate all adrenoceptors

A

noradrenaline and adrenaline

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22
Q

relative selectivity for noradrenaline of adrenoceptors

A

a1 = a2 > B1 = B2; still selective to both

23
Q

relative selectivity for adrenaline of adrenoceptors

A

B1 = B2 > a1 = a2; still selective to both

24
Q

noradrenaline metabolism, release and uptake

A

tyrosine -> noradrenaline by enzymatic steps (incl. in vesicle) -> action potential promotes exocytosis -> has effect -> removed from synpase by transport proteins into tissue (a2 is presynpatic receptor and inhibits noradrenaline release, suppressing SNS) or nerve

25
Q

5 directly acting SNS adrenoceptor agonsists and relevant adrenoceptor

A

adrenaline (non-selective), phenylephrine (a1), clonidine (a2), dobutamine (B1), salbutamol (B2)

26
Q

why is adrenaline used in anaphylaxis treatment and relevant adrenoceptors

A

opens airways (B2 - bronchodilation); causes vasoconstriction (a1) and so increases TPR and blood pressure (as histamine acts as vasodilator); increases heart rate (B1 - tachycardia); suppresses mediator release from mast cells (B receptors present); stomach cramps prevented as SNS effect relaxes gut motility etc.

27
Q

5 other clinical uses of adrenaline and relevant adrenoceptors

A

in asthma (B2: IM, SC; bronchodilation and mediator release); acute bronchospasm associated with chronic bronchitis or emphysema (B2); cardiogenic shock - sudden inability of heart to pump sufficient oxygen-rich blood (B1); spinal anaesthesia (a1: maintains blood pressure by vasoconstriction); local anaesthesia (a1: vasoconstricts - prolongs action to stop it getting into systemic circulation)

28
Q

5 locations of unwanted actions of adrenaline (non-selective)

A

secretions, CNS (minimal), CVS, GIT (minimal), skeletal muscle

29
Q

unwanted actions of adrenaline (non-selective) on secretions

A

reduced, thickened mucous

30
Q

unwanted actions of adrenaline (non-selective) on CVS, including if overdose

A

tachycardia, palpitations, arrhythmias; cold extremities (vasoconstriction), hypertension; overdose - cerebral haemorrhage, pulmonary oedema

31
Q

unwanted action of adrenaline (non-selective) on skeletal muscle

A

tremor (typically due to noradrenaline)

32
Q

example of a selective a1 adrenoceptor agonist, and relevant adrenoceptor selectivity

A

phenylephrine: a1»a2»>B1/B2; chemically related to adrenaline

33
Q

clinical uses of phenylephrine

A

nasal decongestant, vasoconstriction, mydriatic (pupil dilation)

34
Q

why mght phenylephrine be used as a decongestant

A

vasoconstriction, so less white cell invasion and oedema into sinus (which is mucous)

35
Q

phenylephrine relative duration in peripheral vs central

A

more resistant to COMT (peripheral enzyme) not MAO (central enzyme), so longer lasting in peripheral tissue

36
Q

example of a selective a2 adrenoceptor agonist, and relevant adrenoceptor selectivity

A

clonidine: a2»a1»>B1/B2

37
Q

how does clonidine work

A

a2 agonist so negative feedback, preventing noradrenaline release, looking like SNS antagonism

38
Q

sympathomimetics treating glaucoma: cause and consequence

A

caused by increase in intraocular pressure due to poor drainage of aqueous humour produced by cilliary body by blocked venous drainage channels; if untreated, permanently damages optic nerve, causing blindness

39
Q

sympathomimetics: which 2 areas are targeted by sympathomimetics to cause decreased glaucoma risk

A

in cilliary body, agonise a1 to cause vasoconstriction (restricts blood flow and thus aqueous humour production by limiting fluid loss), and agonise a2 to cause decreased humour formation; don’t activate B1 with agonist as this stimulates aqueous humour production

40
Q

3 clinical uses of clonidine

A

treat glaucoma; treat hypertension and migraine (possible link); reduce sympathetic tone

41
Q

how does clonidine reduce sympathetic tone and therefore blood pressure

A

stimulates a2 adrenoceptor of presynpatic neurone, inhibiting noradrenaline release; central action in brainstem within baroreceptor pathway to reduce symapthetic outflow

42
Q

example of a selective B adrenoceptor agonist, and relevant adrenoceptor selectivity

A

isoprenaline: B1=B2»»a1/a2; chemically related to adrenaline

43
Q

isoprenaline resistance to degradation and uptake and relevant location

A

more resistant to MAO and uptake 1 so used in brain not peripherally

44
Q

clinical uses of isoprenaline

A

cardiogenic shock, acute heart failure, myocardial infarction

45
Q

why might B2 receptor stimulation be a problem using isoprenaline

A

stimulates vasodilation in vascular smooth muscle in skeletal muscle, resulting in fall in venous blood pressure, triggering tachycardia via baroreceptor stimulation (reflex tachycardia)

46
Q

example of a selective B1 adrenoceptor agonist, and relevant adrenoceptor selectivity

A

dobutamine: B1»B1»>a1/a2

47
Q

clinical use of dobutamine

A

cardiogenic shock

48
Q

why is dobutamine used to treat cardiogenic shock

A

lacks isoprenaline’s reflex tachycardia, and has a plasma half life of 2 minutes as rapidly metabolised by COMT so acute effect

49
Q

example of a selective B2 adrenoceptor agonist, and relevant adrenoceptor selectivity

A

salbutamol (ventolin): B2»B1»>a1/a2

50
Q

salbutamol resistance to degradation

A

synthetic catecholamine derivative with relative resistance to MAO and COMT

51
Q

2 clinical uses of salbutamol

A

treatment of asthma, treatment of threatened premature labour

52
Q

how does salbutamol treat asthma

A

B2 relaxation of bronchial smooth muscle; upregulates cAMP, leading to hyperpolarisation as K+ efflux so harder for action potential to be triggered, causing muscle relaxation; inhibition of release of bronchoconstritor substances from mast cells

53
Q

how does salbutamol treat threatened premature labour

A

B2 relaxation of uterine smooth muscle

54
Q

side effects of salbutamol use

A

reflex tachycardia, tremor, blood sugar dysregulation

Y2 LCRS Pharmacology and Therapeutics (68 decks)

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