Sympathetic nervous system agonists Flashcards
What are adrenergic receptors?
Receptors found in the SNS that use NA/A neurotransmitters.
They are principally used for their actions in CVS, eyes and lungs.
What are the different subtypes of adrenoreceptors?
Alpha 1
Alpha 2
Beta 1
Beta 2
What adrenoreceptors are found on the heart?
Beta 1
What adrenoreceptors are found on the lungs?
Beta 2
Which adrenoreceptors are found on the blood vessels?
Mostly alpha 1 but with some beta 2
Which beta receptors are found on the…
- eye
- trachea and bronchioles
- liver
- adipose tissue
- kidney
- ureter and bladder
- Blood vessels (skin)
- Blood vessels (skeletal muscle)
- GI
- Heart
- Skin
- Salivary glands
…?
How is Noradrenaline metabolised?
NA is made in nerve terminals whereas adrenaline is synthesised in the adrenal medulla.
- Tyrosine –> DOPA (via tyrosine hydroxylase)
- DOPA –> dopamine ( via DOPA decarboxylase)
- Dopamine –> NA (via dopamine ß-hydroxylase, inside the vesicle)
- Vesicle fuses with membrane and exocytosis of NA occurs
What is the role of the alpha 2 adrenoreceptor with NA release?
There is an alpha 2 receptor present on the pre-junctional receptor.
It is like a feedback receptor. It controls the release of NA by negative feedback and suppresses NA exocytosis
What will alpha 2 adrenoreceptor agonists do?
They will bind to the pre-synaptic alpha 3 adrenoreceptor and will suppress sympathetic function by suppressing NA release.
Name a non-selective SNS agonist?
*another term for SNS agonist is adrenoreceptor agonist
Adrenaline
Name an alpha-1 selective SNS agonist
Phenylephrine
Name an alpha-2 selective SNS agonist
Clonidine
name beta-1 selective SNS agonists
Dobutamine
Name a Beta-2 selective SNS agonist
Salbutamol
What is used for the treatment of anaphylaxis?
A shot of adrenaline is administered via EpiPen to someone in anaphylaxis. Remember that adrenalin is a non-selective SNS agonist.
What happens in an anaphylactic reaction?
- Airways- there is reduced breathing as anaphylaxis causes bronchoconstriction and difficulty swallowing
- Heart- anaphylaxis causes hypotension
- Vascular tone- anaphylaxis causes peripheral vasodilation
- GI- contraction of smooth muscle (cramps), vomiting diarrhoea
What causes anaphylaxis?
Antigen in bloodstream enters tissues and activates connective tissue mast cells throughout the body.
Mast cells degranulate and release inflammatory mediators.
How does adrenaline treat anaphylaxis?
- Airways- adrenaline will bind to beta-2 receptors causing bronchodilation
- Heart- adrenaline will bind to beta-1 receptors causing tachycardia (positive inotropic and chronotropic effect). This will help to restore BP
- Vascular tone- adrenaline will bind to alpha 1 receptors causing vasoconstriction. This will increase TPR and help to raise BP.
- Adrenaline will also supress mediatior release.
Is adrenaline more beta or alpha sensitive?
Adrenaline is more beta sensitive
NA is more alpha sensitive
Name 5 other clinical uses of adrenaline
- Bronchospasm (for airways, beta 2 receptors)
- Cardiogenic shock (beta 1 receptors to have an effect)
- Spinal anaesthetics (alpha 1 for anywhere else)- maintains BP
- Local anaesthesia- vasoconstricts (stops it entering the systemic circulation, prolonging the effect).
- Can also be used for glaucoma- used to managed increased intraocular pressure. Vasoconstricts ocular blood vessels, reducing blood flow and thus the production of aqueous humour- targets the alpha 1 receptors.
What are the unwanted effects of adrenaline?
- Secretions – reduced and thickened mucous (more of an immune effect)
- CNS – minimal
- CVS effects
- tachycardia, palpitations, arrhythmias
- cold extremities, hypertension
- overdose – cerebral haemorrhage, pulmonary oedema
- GIT – minimal
- Skeletal muscle - tremor
what is the use of the alpha 1 selective drug phenylephrine?
It is very similar (structurally) to adrenaline- except one hydroxyl group. This change makes it alpha 1 selective. It is most resistant to breakdown by COMT and MAO.
It is good for acting on peripheral tissues and is found in cold medicine. It vasoconstricts blood vessels
What are the main effects of phenylephrine?
- Mydriatic (dilate pupils)
- Nasal decongestant (less white cell infiltration and build-up of mucus/ fluids)
- Will bring BP up (vasoconstriction)
What does the alpha-2 selective drug do?
Clonidine is the agonist of the pre-junctional alpha 2 receptor- the negative feedback one. The result is sympathetic antagonism as NA is not being released.
