Drugs acting on the sympathetic nervous system (L11)

Question 1

where does NA act as a neurotransmitter?

Answer 1

sympathetic nervous system only

Question 2

what is the sympathetic nervous system?

Answer 2

fight or flight response

• short preganglionic fibre
• long postganglionic fibre
• prepanglionic ACh
• postganglioic NA

Question 3

NA pharmacology

Answer 3

• precursor is AA tyrosine
• its transported into neurone by an AA transporter
• synthesis of NA
• NA kept in vesicles for protection against cytosolic enzymes
• NA taken back up by NA transporter and is then broken down by monoamine oxidase or recycled

Question 4

3 enzymes involved in the synthesis of NA

Answer 4

tyrosine hydroxylase
DOPA decarboxylase
DA beta-hydroxylase

Question 5

the 2 classes of NA receptors

Answer 5

alpha

beta

Question 6

alpha noradrenergic receptors

Answer 6

alpha1,2
located in effector tissues/targets of the sympathetic system
GPCP
slow response - seconds

Question 7

beta noradrenergic receptors

Answer 7

beta1,2,3
located in effector tissues/targets of the sympathetic system
GPCP
slow response - seconds

Question 8

what are sympathetic effects on the body

Answer 8

• pupils dilate
• lens of eye adjusts for far vision
• airways in lungs dilate
• HR increases
• blood vessels to limb muscles dilate
• blood vessels to visceral organs and skin constrict
• brain activity general alertness

Question 9

what sympathetic effects do alpha1 receptors mediate?

Answer 9

• pupils dilate
• blood vessels to visceral organs and skin constrict
• brain activity and general alterness

Question 10

what sympathetic effects do alpha2 receptors mediate?

Answer 10

• they are presynaptic receptors
• they turn off further release - negative feedback
• inhibits neurotransmitter release - both NA and ACh

autoreceptor = own type of neurone 
heteroreceptor = different neurone

Question 11

what sympathetic effects do beta1 receptors mediate?

Answer 11

HR increases

force of contraction increases

Question 12

what sympathetic effects do beta2 receptors mediate?

Answer 12

• lens of eye adjusts for far vision
• airways in lung dilate
• blood vessels to limb muscle dilate

Question 13

what sympathetic effects do beta3 receptors mediate?

Answer 13

increases lipolysis - breakdown of triglycerides to fatty acids

Question 14

noradrenergic agonists

Answer 14

adrenaline 
clonidine 
dobutamine 
salbutamol 
clenbuterol

Question 15

adrenaline

Answer 15

noradrenergic agonist

agonist against all NA receptors - not selective

Question 16

clonidine

Answer 16

noradrenergic agonist

finish

Question 17

dobutamine

Answer 17

noradrenergic agonist

finish

Question 18

salbutamol

Answer 18

noradrenergic agonist

finish

Question 19

clenbuterol

Answer 19

noradrenergic agonist

finish

Question 20

noradrenergic antagonists

Answer 20

prazosin 
tamsulson 
propranolol
atenolol 
timolol

Question 21

prazosin

Answer 21

noradrenergic antagonist

Question 22

tamsulson

Answer 22

noradrenergic antagonist

Question 23

propranolol

Answer 23

noradrenergic antagonist

Question 24

atenolol

Answer 24

noradrenergic antagonist

Question 25

timolol

Answer 25

noradrenergic antagonist

Question 26

drugs affecting NA synthesis

Answer 26

drugs can give a false substrate methylDOPA (meDOPA) acts as a false substrate for DOPA decarboxylase

Question 27

drugs affecting NA storage

Answer 27

reserpine disrupts storage of NA in synaptic vesicles overall decrease in NA neurotransmission

Question 28

drugs affecting NA release

Answer 28

NA release is subject to auto inhibitory control via presynaptic alpha2 auto receptors clonidine (alpha2 agonist) causes inhibition of NA release • overall decrease in NA neurotransmission • used to treat hypertension

Question 29

drugs affecting NA reuptake

Answer 29

NA reuptake can be blocked by NA reuptake inhibitors this will prolong the action of NA in the synapse

Question 30

drugs affecting NA metabolism

Answer 30

NA is metabolised by monoamine oxidase (MAO) and catecholamine transferase (COMT) by blocking these enzymes the amount of NA available for release is increased tranylcypromine blocks MAO and allows more NA to be recycled so increases NA neurotransmission

Question 31

cheese reaction

Answer 31

tranylcypramine and other MAOIs not only block the metabolism of NA but also block the metabolism of dietary amines (e.g. commonly found in cheese, marmite) and amines found in popular cold remedies accumulation of dietary amines can have a sympathomimetic effect and result in hypertension