SNS agonists Flashcards
What do SNS agonists do?
- mimic the actions of adrenaline and noradrenaline by stimulating adrenoceptors
What is the molecular mechanism of alpha 1 adrenoceptors?
PLC is converted into IP3 and DAG
What is the molecular mechanism of alpha 2 adrenoceptors?
decrease cAMP
What is the molecular mechanism of beta 1 and 2?
increase cAMP
What effect will beta blockers have on the kidneys?
decrease renin release by blocking the B1 receptor - an increase in BP does not happen via the renin-angiotensin-aldosterone system
What effect will the beta blocker have on the heart?
the heart is controlled by beta 1 -to have positive inotropic and chronotropic effect
-this cannot happen with a beta blocker
What else will be effected besides the kidneys and heart with a beta blocker drug?
- liver - blocked ability to break down glycogen to generate glucose
- block the ability of the trachea and bronchioles to dilate
What adrenoceptors regulate blood vessels?
alpha 1
Which adrenoceptors can be activated by NA or adrenaline?
- all
- NA is more selective for alpha receptors
- adrenaline is more selective for beta receptors
How is noradrenaline synthesized?
- tyrosine from the diet is converted to DOPA by tyrosine hydroxylase
- DOPA is then converted to dopamine, which is converted to noradrenaline
What receptor helps regulate noradrenaline synthesis?
Presynaptic alpha 2 receptors
How do alpha 2 receptors do this?
if NA concentration is high in the synapse it will stimulate presynaptic alpha 2 receptors to reduce production of NA and release
What adrenoceptor does phenylephrine favour?
alpha 1
what adrenoceptor does clonidine favour?
alpha 2
what receptor does dobutamine favour?
beta 1
what receptor does salbutamol favour?
beta 2
what receptor does adrenaline favour ?
it is non-selective
bind to alpha and beta
What does selectivity depend on?
- CONCENTRATION
- at low conc. these drugs will be relatively selective but as you increase conc. the chance of binding to other receptors increases
How does hypersensitivity occur in the body?
- after first exposure to the antigen your body generates antibodies that circulate around the body and bind to mast cells
- in subsequent exposure the antigen cross-links with these antibodies and there is a massive release of mediators
What are the symptoms of hypersensitivity?
- lots of fluid moving into tissues as endothelial cells in blood vessel membranes move apart
- fall in circulating fluid volume = fall in BP
- anaphylactic shock that leads to a collapse in the circulatory system and hence unconsciousness
- this can also lead to contraction of bronchial smooth muscle and constriction of the muscles around the throat
Whys is adrenaline more effective than noradrenaline?
breathing- adrenaline acts more on beta receptors than NA which stimulates bronchodilation and relaxation of the throat muscles
- slows down release of histamine from mast cells
- tachycardia
- acts on alpha receptors to get vasoconstriction
List the other clinical uses of adrenaline?
- asthma
- acute bronchospasm associated with chronic bronchitis or emphysema
- glaucoma
- cardiogenic shock
- spinal anaesthesia
- local anaesthesia
List the unwanted actions of adrenaline?
- secretions become reduced and thickened mucus
- tachycardias, palpitations, arrhythmias
-cold extremities, hypertension - pulmonary oedema
GIT- minimal
-skeletal muscle tremor
Overdose can lead to cerebral haemorrhage
How is phenylephrine different to adrenaline?
- one hydroxyl group makes it more resistant to breakdown
- more resistant to COMT breakdown but NOT MAO degradation
