Drugs of the ANS

Question 1

What are the nerve types in PNS and SNS?

Answer 1

PNS = cholinergic for both pre and post ganglionic.
SNS = cholinergic for pre, and adrenergic for post ganglionic.

Question 2

What type of receptors do cholinergic and adrenergic nerves act on in pre- and post-ganglionic?

Answer 2

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.

Question 3

What NTs do adrenergic and cholinergic nerves synthesise and release?

Answer 3

Adrenergic = NA
Cholinergic = Acetylcholine

Question 4

Describe the actions of muscarinic M2 and M3 receptors.

Answer 4

M2 receptor = decrease HR

M3 receptors = contract smooth muscle and secrete glands.

Question 5

Describe the actions of adrenergic receptors A1, B1 and B2.

Answer 5

A1 = contract vascular smooth muscle.
B1 = increase HR and contractile force.
B2 = dilate smooth muscle.

Question 6

What are the adrenoceptor agonists?

Answer 6

Adrenaline, noradrenaline, phenylephrine, salbutamol.

Question 7

Describe the action of adrenaline.

Answer 7

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).

Question 8

Describe clinical uses of adrenaline

Answer 8

Added to local anaesthetic to prolong action (vasoconstriction delay absorption) and to dilate airways.

Question 9

Describe the action of noradrenaline.

Answer 9

Works on all adrenoceptors EXCEPT B2-ADRs. (no vasodilation)

Intravenous infusion of NA is used to treat hypotension. (A1 = vascular muscle constriction).

Question 10

What is different about phenylephrine and salbutamol, compared to adrenaline/noradrenaline in delivery?

Answer 10

Phenylephrine and salbutamol are active orally.

Question 11

Describe the action of phenylephrine.

Answer 11

Selective for A1-ADRs.

Treats nasal congestion through vascular contraction.

Question 12

Describe the action of salbutamol.

Answer 12

Selective for B2-ADRs. Relieves bronchoconstriction through smooth muscle dilation.

Question 13

For which adrenoceptors is antagonism clinically useful?

Answer 13

Antagonism of A1 and B1 adrenoceptors is clinically useful.

A1 - treat hypertension. B1 - treat CVD.

Question 14

Describe the action of prazosin.

Answer 14

Selective for antagonising A1-ADRs.

Inhibits vasoconstriction, helping to treat hypertension.

Question 15

Describe the action of propranolol.

Answer 15

Selectively antagonises B1 and B2-ADRs.
B1 - helpful for treating CVD and hypertension.
B2 - causes bronchoconstriction, which is not good.

Question 16

Describe the action of metoprolol.

Answer 16

Selective antagonises B1 ADRs.

Inhibits contractile force and decreases HR. Helps to treat angina.

Question 17

Describe the action of pilocarpine./

Answer 17

Activates M3 muscarinic cholinceptors. Causes contraction of smooth muscle to drain aqueous humour and reduce intraocular pressure.

Question 18

Describe the action of atropine.

Answer 18

Antagonist for muscarinic cholinoceptors.

Used as therapy for anticholinesterase poisoning (pesticides)

Question 19

Describe the action of tiotropium.

Answer 19

Antagonist for muscarinic cholinoceptors.

Used to treat COPD by dilating airwaysand reducing mucus secretion (M3 receptor, blocks contraction/secretion)

Question 20

Describe the metabolism/removal of noradrenaline.

Answer 20

Adrenergic nerves release NA.

Undergoes reuptake via noradrenaline transporter (NAT), then transported into vesicles via VMAT or MAO.

Question 21

Describe the action of amphetamine.

Answer 21

Amphetamine blocks NA reuptake by inhibiting VMAT and MAO.

Causes increase [NA] in synapses, causing vasoconstriction (A1) and increased HR and contraction (B1)

Question 22

Describe the action of pseudoephedrine.

Answer 22

Increases NA release from nerves.

Can be easily converted to metamphetamine.

Question 23

Describe the metabolism/removal of acetylcholine.

Answer 23

Cholinergic nerves release acetylcholine.
ACh is metabolised by acetylcholinesterase (AChE)

Anticholinesterases block AChE. (e.g. pesticides can be anticholinesterases)

Question 24

What can anticholinesterases be used for, clinically?

Answer 24

Treat decreased sensitivity to ACh, e.g. in myasthenia gravis (muscle weakness).
E.g. Neostigmine.