SNS Agonists

Question 1

What do SNS agonists do?

Answer 1

Mimic the actions of NA/A by binding to and stimulating adrenoceptors (GPCRs)

Question 2

What are SNS agonists used principally for?

Answer 2

Their actions in the CVS, eyes and lungs

Question 3

What type of adrenoceptor is noradrenaline more selective for?

Answer 3

a1=a2 > b1=b2.

Question 4

What type of adrenoceptor is adrenaline more selective for?

Answer 4

b1=b2 > a1=a2

Question 5

Where is noradrenaline made?

Answer 5

In nerve terminals

Question 6

Where is adrenaline made?

Answer 6

In adrenal medulla

Question 7

What is the noradrenaline metabolism?

Answer 7

Tyr -> DOPA -> DA -> NE

Question 8

What effect does norepinephrine have on a2 adrenoceptors?

Answer 8

NE binding to prejunctional a2 adrenoceptors negatively feedbacks on NE exocytosis

Question 9

What adrenoceptor is adrenaline selective for?

Answer 9

Adrenaline is non selective

Question 10

What adrenoceptor is phenylephrine selective for?

Answer 10

a1»a2»>b1/b2

Question 11

What adrenoceptor is clonidine selective for?

Answer 11

a2»a1»>b1/b2

Question 12

What adrenoceptor is isoprenaline selective for?

Answer 12

b1=b2»»a1/a2

Question 13

What adrenoceptor is dobutamine selective for?

Answer 13

b1»b2»>a1/a2

Question 14

What adrenoceptor is salbutamol selective for?

Answer 14

b2»b1»>a1/a2

Question 15

How is adrenaline used to treat anaphylaxis?

Answer 15

It is non selective - and therefore is used in the management of airways - b2, tachycardia - b1, peripheral vasodilation - a1, suppression of mediator release

Question 16

How is adrenaline used to treat COPD?

Answer 16

Used in asthma - emergencies via I.M or S.C in the management of airway - b2 and suppression of mediator release but a selective b2 agonist is preferable

Question 17

How is adrenaline used to treat glaucoma?

Answer 17

Vasoconstriction of ocular blood vessels restricts blood flow and therefore decrease production of aqueous humour - production being derived from blood flow therefore management of IOP - a1

Question 18

What are other uses of adrenaline as a treatment (not glaucoma, copd or anaphylaxis)

Answer 18

Cardiogenic shock
Spinal anaesthesia
Local anaesthesia - prolong duration of action using a1 action to reduce blood flow thus removal of anaethesia drug

Question 19

What are unwanted actions of adrenaline as an SNS agonist

Answer 19

Because so non- selective there are lots of unwanted actions eg.
Secretions - reduced and thickened
CVS - tachycardia, palpitations, arrhythmia, hypertension/cold extremities, overdose, cerebral haemorrhage and pulmonary oedema
Skeletal muscle - tremor
CVS issues usually occur if already have underlying heart issue

Question 20

What are the similarities and differences between adrenaline and phenylephrine

Answer 20

Molecularly similar to adrenaline but resistant to COMT (but not MAO)

Question 21

What are the clinical uses of phenylephrine?

Answer 21

Vasoconstriction
Mydriasis (dilation)
Nasal decongestant via vasoconstriction

Question 22

What receptor does clonidine mainly act on and what is the result?

Answer 22

Mainly acts on prejunctional neuronal a2 receptor to inhibit NA release

Question 23

What are the clinical uses of clonidine?

Answer 23

Treat hypertension and migrane
Reduce sympathetic tone - a2 mediated presynaptic inhibition of NA release
Central brainstem action within baroreceptor pathway to reduce sympathetic outflow

Question 24

What are the similarities and differences between adrenaline and isoprenaline

Answer 24

Molecularly similar but isoprenaline less susceptible to uptake 1 and MAO breakdown

Question 25

What are clinical uses of isoprenaline?

Answer 25

Cardiogenic shock
Acute heart failure
MI

Question 26

Why may b2 receptor stimulation be a problem?

Answer 26

b2 stimulation in VSM in skeletal muscle triggers a fall in venous BP triggering a reflex tachycardia via stimulation of BR

Question 27

How is dobutamine administered and what is the half life? What metabolises it?

Answer 27

Administered by IV infusion with very short half life of 2 minutes - rapidly metabolised by COMT

Question 28

What are the clinical uses of dobutamine?

Answer 28

Treat cardiogenic shock as lacks isoprenaline’s reflex tachycardia

Question 29

What is salbutamol (with reference to catecholamines)

Answer 29

Synthetic catecholamine derivative with resistance to COMT and MAO

Question 30

What are the clinical uses of salbutamol?

Answer 30

Treat asthma - by b2 relaxation of sm and inhibition of release of bronchoconstriction substances
Treatment of threatened premature labour by b2 relaxation of SM

Question 31

What are the side effects of salbutamol?

Answer 31

reflex tachycardia, tremor, blood sugar dystregulation

Question 32

How does cocaine work as an indirectly acting SNS agonist?

Answer 32

It is an uptake 1 blocker

Question 33

What are the SNS effects of cocaine on CNS in low doses?

Answer 33

Euphoria, excitement, increased motor activity

Question 34

What are the SNS effects of cocaine on CNS in high doses?

Answer 34

Activation of CTZ, CNS depression, resp failure, convulsions and death

Question 35

What are the effects of cocaine on the CVS in low doses?

Answer 35

Tachycardia, vasoconstriction, raised BP

Question 36

What is tyramine also known as?

Answer 36

cheese reaction

Question 37

How does tyramine act?

Answer 37

As a false neurotransmitter -

1. Weak action at the receptors for NA.
2. Weak inhibitory effect on the uptake 1.
3. Displaces NA from the vesicles.
4. Competes for MAO breakdown so less breakdown of NA.
5. Leakage of NA out of the vesicles.

Question 38

What happens if you use tyramine and a MAO inhibitor?

Answer 38

Tyramine can compete with any MAO left and can lead to a massive hypertensive crisis when NA build up is more than usual

Question 39

When are MAO inhibitors prescribed?

Answer 39

As antidepressants