SNS agonists Flashcards
What receptors are found in the sympathetic nervous system?
adrenergic receptors/adrenoceptors - stimulated by NA
What are the signalling mechanisms of all the adrenoceptors once stimulated?
a1 - PLC, IP3, DAG
a2 - downregulates cAMP
b1 - upregulates cAMP
b2 - upregulates cAMP
SNS agonist mimic the action of NA/A by binding to and stimulating adrenoceptors
Draw diagram indicating all the parts of the body that are affected by which adrenoceptor
See diagram
Describe the selectivity of NA and A
a adrenoceptors are more NA selective
b adrenoceptors are more A selective
Describe Noradrenaline metabolism
See notes and lecture 1
What is a non-specific SNS agent?
Adrenaline
What is used to treat anaphylactic shock?
See lecture for what is anaphylactic shock.
Adrenaline reverses the effects of histamine: b2 - bronchodilation, b1 - tachycardia + increases contraction which increases CO, a1 - vasoconstriction
There are also beta receptors on the mast cells so adrenaline binds there to suppress the mediator (histamine/bronchoconstrictor substances) release
Where is adrenaline used?
Asthma (emergencies) b2
Acute bronchospasm associated with chronic bronchitis or emphysema b2
Cardiogenic shock - sudden inability of heart to pump sufficient oxygen rich blood b1
Spinal anaesthesia a1 to maintain BP. Anaesthetics tends to decrease BP
Local anaesthesia a1 vasoconstricts resulting in prolonged action. The anaesthetic stays in that area for longer
What are the general effects of all the adrenoceptors?
b2 - (airways mediator release + smooth muscle relaxation/dilation) Upregulate cAMP
b1 - (inotropic effect: effect on the heart) Upregulate cAMP
a1 - maintains BP and vasoconstricts
a2 - have an inhibitory effect/negative feedback effect on the sympathetic NS
What are the unwanted effects of adrenaline?
Secretions - reduced and thickened mucous CNS - minimal CVS effects - see lecture GIT - minimal Skeletal muscle - tremor
Name two alpha selective agents?
Phenylephrine - in order of most selective a1»a2»>b1/b2 (not very beta selective)
a1 selective
chemically related to A - more resistant to COMT but not MAO
Clonidine - inorder of most selective
a2»a1»>b1/b2
a2 selective
Why is phenylephrine used as a decongestant?
When you’re congested you have inflammation in the nasal sinus so capillary plasma leakage occurs. So phenylephrine causes vasoconstriction at the nasal sinus - a1 agonist.
Also can be used as a mydriatic
Describe clonidine
It is a a2 agonist binding to a2 which is a prejunctional receptor. The a2 receptor decreases NA release meaning you have a reduced sympathetic effect.
Used to treat hypertension, migraine and glaucoma
Reduces sympathetic tone:
1) a2 adrenoceptor mediated presynaptic inhibition of NA release
2) Central action within the brainstem to reduce sympathetic outflow
What is a glaucoma and how can you treat it?
See lectures and notes
a1 - vasoconstriction of capillaries
a2 - decrease aqueous humour formation
Name beta selective agents
Isoprenaline - in order of most selective
b1=b2»_space;» a1/a2
Chemically related to adrenaline - more resistant to MAO and uptake 1
Dobutamine - in order of most selective
b1»_space; b2»_space;> a1/a2
Rapidly metabolised by COMT
Salbutamol (ventolin) - in order of most selective
b2»b1»>a1/a2
