SNS agonists

Question 1

What is the mechanism by which adrenoceptor agonists work

Answer 1

Mimics the actions of catecholamines by binding to and stimulating adrenoceptors
They are used principally for their actions in the CVS, eyes and lungs

Question 2

What are alpha adrenoceptors involved in

Answer 2

Saliva secretion
Glycogenolysis
Lipolysis
Decrease motility and tone, sphincter contraction

Constriction of trigone and sphincter
Pupil dilation

Piloerection in skin
Constriction of blood vessels in the skin, mucous membranes and splanchnic area

Question 3

What are beta adrenoceptors involved in

Answer 3

Thick, viscous secretion
Aqueous homer production by the ciliary body in the eye
Dilation of the trachea and bronchioles
Relaxes dextrusor
Decrease motility and tone, sphincter contraction

Lipolysis
Increased renin secretion from the kidney
Increased rate and contractility in the heart
Dilation of blood vessels

Question 4

Compare the selectivity of adrenoceptors for noradrenaline

Answer 4

a1 = a2 > b1 = b2

Question 5

Compare the selectivity of adrenoceptors for adrenaline

Answer 5

b1 = b2 > a1 = a2

Question 6

Describe the metabolism of noradrenaline

Answer 6

1. Tyrosine enters the nerve
2. Tyrosine converted to DOPA by tyrosine hydroxylase
3. DOPA converted to dopamine by DOPA decarboxylase
4. dopamine enters a vesicle
5. Dopamine is converted to NA by dopamine hydroxyls
6. NA exocytosis due to AP

Question 7

Give examples of directly acting SNS agonists

Answer 7

Adrenaline (non-selective)
Phenylephrine (a1)
Clonidine (a2)
Dobutamine (b1)
Salbutamol (b2)

Question 8

What is adrenaline used for clinically

Answer 8

Allergic reactions and anaphylactic shock
Acute bronchospasm associate with chronic bronchitis or emphysema
Cardiogenic shock
Spinal and local anaesthesia

Question 9

Why is adrenaline used in the treatment of anaphylaxis

Answer 9

alpha1 - vasoconstriction
beta1 - tachycardia
beta2- bronchodilation

Beta receptors on mast cells -> suppresses release of mediators form mast cells to reduce inflammation
Slowing of the gut to reduce stomach pain

Question 10

Why can adrenaline be used for asthma and acute bronchospasm

Answer 10

Activates beta2 receptors to cause airway mediator release

Question 11

Why can adrenaline be used for cariogenic shock

Answer 11

beta1 receptors - inotropic effects

Question 12

Why can adrenaline be used for spinal and local anaesthesia

Answer 12

alpha1 - maintains BP and and vasoconstrictor to prolong anaesthesia action

Question 13

What are the unwanted actions of adrenaline

Answer 13

Reduced and thickened mucous secretions
Tachycardia, palpitations arrhythmiasm, cold extremities, hypertension
Tremor in the skeletal muscle
(minimal CNS and GIT)
overdose - cerebral haemorrhage, pulmonary oedema

Question 14

Give an example of a alpha receptor specific adrenergic agonist and describe

Answer 14

Phenylephrine
a1>a2>b1/b2

Chemically related to adrenaline but more resistant to COMT (not MAO)
Lasts longer and affects the peripheral system more

Question 15

What are the clinical uses of phenylephrine

Answer 15

Vasoconstrictions 
Mydriatic 
Nasal decongestant (causes vasoconstriction, less white cells, less fluid)

Question 16

What is clonidine and what is it used for

Answer 16

a2>a1>b1/2
As it binds to the alpha2 receptor the effect is antagonist-like
Treatment of hypertension and migraine
Reduces sympathetic tone (a2 mediated inhibition of NA release, central action in brainstem within baroreceptor pathway, reducing sympathetic outflow)

Question 17

What are sympathomimetics used for

Answer 17

Used for glaucoma

Question 18

What is glaucoma

Answer 18

Characterised by an increase in intraocular pressure
Caused by poor drainage of the aqueous humour
If untreated, it will permanently damage the optic nerve leading to blindness

Question 19

What is isoprenaline

Answer 19

b1>b2>a1/2

Chemically related to adrenaline but more resistant to MAO and uptake 1

Question 20

What are the clinical sues of isoprenaline

Answer 20

Cariogenic shock
Acute heart failure
Myocardial infarction

Question 21

Why may beta2 receptor stimulation be a problem

Answer 21

b2 in vascular smooth muscle in skeletal muscle results in fall in venous blood pressure which triggers a reflex tachycardia via the stimulation baroreceptors

Question 22

What is dobutamine and what is used

Answer 22

b1>b2>a1/2
Lacks isoprenaline’s reflex tachycardia (no b2 effect)
Plasma half life of 2 minutes (rapidy metabolised by COMT)

Cardiogenic shock

Question 23

What is salbutamol

Answer 23

Synthetic catecholamine derivative with relative resistance to MAO and COMT
b2>b1>a1/2

Question 24

What are the clinical uses of salbutamol

Answer 24

Treatment of asthma

Treatment of threatened premature labour

Question 25

How does salbutamol aid in asthma treatment

Answer 25

b2-relaxation of bronchial smooth muscle

Inhibition of release of bronchoconstrictor substances form mast cells

Question 26

How does salbutamol aid in treatment of threatened premature labour

Answer 26

b2 relaxation of uterine smooth muscle

Question 27

What are the side effects of salbutamol

Answer 27

Reflex tachycardia
Tremor
Blood sugar dysregulation

Question 28

What is the role of the alpha2 receptor

Answer 28

Acts as a negative feedback receptor

More NA in the synapse -> binds to alpha2 which acts to suppress the sympathetic nervous system as it slows NA secretion

Question 29

Which muscarinic receptors can be targeted for glaucoma treatment

Answer 29

A1 - causes vasoconstriction to decrease the fluid

A2 - Negative feedback, directly decreases intra-ocular fluid formation