SNS agonists. Flashcards
Understand the locations of key nervous system receptors -
a1, a2, b1, b2, nicotinic, muscarinic.
How do different adrenoceptors have their effects?
a1 - PLC, IP3, DAG.
a2 - reduced cAMP
b1 - increased cAMP
b2 - increased cAMP
Diagram outlining which SNS target organs have which receptors.
Why are adrenoceptors always only relatively selective.
All adrenoceptors can be activated by NA and A, but to varying degrees.
A > selectivity for NA than B.
B> selectivity for Adrenaline than A
Diagram outlining NA metabolism. Why are NA effects never particularly profound?
A2 is a feedback receptor - slowing down NA secretion. Autoinhibition.
Name an agonist for each adrenoceptor.
- Phenylephrine (a1)
- Clonidine (a2)
- Dobutamine (b1)
- Salbutamol (b2)
Why is adrenaline used in the reatment of anaphylaxis?
B2 receptors in airways bronchodilate
B1 receptors in heart increase heart rate (counteract hypotension with anaphylaxis).
a1 receptors vasoconstrict blood vessels to increase BP.
Increased SNS innervation has relaxing effect on gut, reducing stomach cramps.
Name some other clinical uses of adrenaline.
Acute bronchospasm associated with chronic bronchitis or emphysema - B2 –> increased airway mediator release.
Cardiogenic shock - sudden inability of heart to pump sufficient blood - B1 –> ionotropic effects.
During spinal anaesthesia to maintain BP
To prolong action of local anaethesia with local vasoconstriction so anaesthetic cannot leave area - A1
List some unwanted actions of adrenaline.
Secretions - reduced and thickened mucus.
CVS - tachycardia, palpitations, arrhythmia, cold extrmeties, hypertension. Overdose –> cerebral haemorrhage, pulmonary oedema.
Skeletal muscle - tremor.
What is phenylephrine selective for? what is it’s use and why?
Alpha selective. Used as nasal decongestant - vasoconstriction gives white cells less access to nose to generate mucus.
Pupil dilation.
Other uses related to vasoconstriction.
Why does phenylephrine last longer in peripheral tissues?
Resistant to COMT but not MAO. Chemically related to adrenaline.
Why does Clonidine appear to be an SNS antagonist?
Agonist for A2 receptor which promotes negative feedback, inhibiting SNS effects.
What is glaucoma characterised by? What causes it?
What are the potential complications if untreated?
Increase in intraocular pressure.
Poor drainage of aqueous humour.
Permanent damafe to optic nerve, blindess.
How can glaucoma be treated?
B1 receptor stimulation contributes to aqueous humour formation.
A2 agonist (-ve feedback, reducing B1 function) OR
A1 agonist (vasoconstriction - less blood available to create aqueous humour).
Give uses of clonidine.
Treatment of hypertension and migraine.
A2 receptor - inhibited NA, vasodilation.
What is isoprenaline selective for? What are its uses?
Beta selective.
Used for - cardiogenic shock, acute heart failure, myocardial infarction.
How is isoprenaline functionally different to adrenaline - more resistant to MAO and uptake 1.
Why might B2 receptor stimulation be a problem?
B2 receptors on VSMC stimulate NO release and significant vasodilation. Fall in TPR triggers a reflex tachycardia through baroreceptor stimulation.
Why might dobutamine be more useful than isoprenaline?
Lacks stimulation of reflex tachycardia.
However, plasma half life of only 2 minutes, rapidly metabolised by COMT.
Treat cardiogenic shock.
What is salbutamol derived from?
Catecholamine derivative with resistance to MAO and COMT.
Diagram outlining mechanism of action of salbutamol.
Give the clinical uses of salbutamol.
Asthma treatment - B2 relaxation of bronchial smooth muscle.
-inhibition of release of bronchoconstrictor substances from mast cells.
Treatment of threatened premature labour - B2 relaxation of uterine smooth muscle.
Side effects - reflex tachycardia, temor, blood sugar dysregulation.
