SNS agonists Flashcards
What is the mechanism by which adrenoceptor agonists work
Mimics the actions of catecholamines by binding to and stimulating adrenoceptors
They are used principally for their actions in the CVS, eyes and lungs
What are alpha adrenoceptors involved in
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
What are beta adrenoceptors involved in
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
Compare the selectivity of adrenoceptors for noradrenaline
a1 = a2 > b1 = b2
Compare the selectivity of adrenoceptors for adrenaline
b1 = b2 > a1 = a2
Describe the metabolism of noradrenaline
- Tyrosine enters the nerve
- Tyrosine converted to DOPA by tyrosine hydroxylase
- DOPA converted to dopamine by DOPA decarboxylase
- dopamine enters a vesicle
- Dopamine is converted to NA by dopamine hydroxyls
- NA exocytosis due to AP
Give examples of directly acting SNS agonists
Adrenaline (non-selective) Phenylephrine (a1) Clonidine (a2) Dobutamine (b1) Salbutamol (b2)
What is adrenaline used for clinically
Allergic reactions and anaphylactic shock
Acute bronchospasm associate with chronic bronchitis or emphysema
Cardiogenic shock
Spinal and local anaesthesia
Why is adrenaline used in the treatment of anaphylaxis
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
Why can adrenaline be used for asthma and acute bronchospasm
Activates beta2 receptors to cause airway mediator release
Why can adrenaline be used for cariogenic shock
beta1 receptors - inotropic effects
Why can adrenaline be used for spinal and local anaesthesia
alpha1 - maintains BP and and vasoconstrictor to prolong anaesthesia action
What are the unwanted actions of adrenaline
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
Give an example of a alpha receptor specific adrenergic agonist and describe
Phenylephrine
a1>a2>b1/b2
Chemically related to adrenaline but more resistant to COMT (not MAO)
Lasts longer and affects the peripheral system more
What are the clinical uses of phenylephrine
Vasoconstrictions Mydriatic Nasal decongestant (causes vasoconstriction, less white cells, less fluid)
What is clonidine and what is it used for
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)
What are sympathomimetics used for
Used for glaucoma
What is glaucoma
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
What is isoprenaline
b1>b2>a1/2
Chemically related to adrenaline but more resistant to MAO and uptake 1
What are the clinical sues of isoprenaline
Cariogenic shock
Acute heart failure
Myocardial infarction
Why may beta2 receptor stimulation be a problem
b2 in vascular smooth muscle in skeletal muscle results in fall in venous blood pressure which triggers a reflex tachycardia via the stimulation baroreceptors
What is dobutamine and what is used
b1>b2>a1/2
Lacks isoprenaline’s reflex tachycardia (no b2 effect)
Plasma half life of 2 minutes (rapidy metabolised by COMT)
Cardiogenic shock
What is salbutamol
Synthetic catecholamine derivative with relative resistance to MAO and COMT
b2>b1>a1/2
What are the clinical uses of salbutamol
Treatment of asthma
Treatment of threatened premature labour
