Drugs of the ANS Flashcards
What are the nerve types in PNS and SNS?
PNS = cholinergic for both pre and post ganglionic. SNS = cholinergic for pre, and adrenergic for post ganglionic.
What type of receptors do cholinergic and adrenergic nerves act on in pre- and post-ganglionic?
Pre-ganglionic cholinergic nerves of ANS and SNS = nicotinic cholinoceptors.
Post-ganglionic cholinergic nerves of PNS = muscarinic cholinoceptors.
Post-ganglionic adrenergic nerves of ANS = adrenoceptors.
What NTs do adrenergic and cholinergic nerves synthesise and release?
Adrenergic = NA Cholinergic = Acetylcholine
Describe the actions of muscarinic M2 and M3 receptors.
M2 receptor = decrease HR
M3 receptors = contract smooth muscle and secrete glands.
Describe the actions of adrenergic receptors A1, B1 and B2.
A1 = contract vascular smooth muscle. B1 = increase HR and contractile force. B2 = dilate smooth muscle.
What are the adrenoceptor agonists?
Adrenaline, noradrenaline, phenylephrine, salbutamol.
Describe the action of adrenaline.
Works on ALL adrenoceptor subtypes.
Effects are dose dependent, with affinity for B2 adrenoceptors.
Local injection delivers HIGH dose initially (acts on A1 ARs, causing vasoconstriction), followed by vasodilation (acting on B2 ARs).
Describe clinical uses of adrenaline
Added to local anaesthetic to prolong action (vasoconstriction delay absorption) and to dilate airways.
Describe the action of noradrenaline.
Works on all adrenoceptors EXCEPT B2-ADRs. (no vasodilation)
Intravenous infusion of NA is used to treat hypotension. (A1 = vascular muscle constriction).
What is different about phenylephrine and salbutamol, compared to adrenaline/noradrenaline in delivery?
Phenylephrine and salbutamol are active orally.
Describe the action of phenylephrine.
Selective for A1-ADRs.
Treats nasal congestion through vascular contraction.
Describe the action of salbutamol.
Selective for B2-ADRs. Relieves bronchoconstriction through smooth muscle dilation.
For which adrenoceptors is antagonism clinically useful?
Antagonism of A1 and B1 adrenoceptors is clinically useful.
A1 - treat hypertension. B1 - treat CVD.
Describe the action of prazosin.
Selective for antagonising A1-ADRs.
Inhibits vasoconstriction, helping to treat hypertension.
Describe the action of propranolol.
Selectively antagonises B1 and B2-ADRs.
B1 - helpful for treating CVD and hypertension.
B2 - causes bronchoconstriction, which is not good.
Describe the action of metoprolol.
Selective antagonises B1 ADRs.
Inhibits contractile force and decreases HR. Helps to treat angina.
Describe the action of pilocarpine./
Activates M3 muscarinic cholinceptors. Causes contraction of smooth muscle to drain aqueous humour and reduce intraocular pressure.
Describe the action of atropine.
Antagonist for muscarinic cholinoceptors.
Used as therapy for anticholinesterase poisoning (pesticides)
Describe the action of tiotropium.
Antagonist for muscarinic cholinoceptors.
Used to treat COPD by dilating airwaysand reducing mucus secretion (M3 receptor, blocks contraction/secretion)
Describe the metabolism/removal of noradrenaline.
Adrenergic nerves release NA.
Undergoes reuptake via noradrenaline transporter (NAT), then transported into vesicles via VMAT or MAO.
Describe the action of amphetamine.
Amphetamine blocks NA reuptake by inhibiting VMAT and MAO.
Causes increase [NA] in synapses, causing vasoconstriction (A1) and increased HR and contraction (B1)
Describe the action of pseudoephedrine.
Increases NA release from nerves.
Can be easily converted to metamphetamine.
Describe the metabolism/removal of acetylcholine.
Cholinergic nerves release acetylcholine.
ACh is metabolised by acetylcholinesterase (AChE)
Anticholinesterases block AChE. (e.g. pesticides can be anticholinesterases)
What can anticholinesterases be used for, clinically?
Treat decreased sensitivity to ACh, e.g. in myasthenia gravis (muscle weakness).
E.g. Neostigmine.
