Adrenergic and Cholinergic

Question 1

functions of adrenergic receptors (a1, a2, b1, b2 and b3)

Answer 1

alpha receptors mostly to shut down “fight or flight” - vasoconstrict and decrease secretions.
beta receptors mostly to activate “fight or flight” - vasodilator and increase secretions.
a1: vasocontrict vessels, shut down GIT, constrict bladder
a2: vasoconstrict vessels, decrease salivary secretion and GIT
b1: increase heart rate and contractility
b2: vasodilator, bronchodilator, activate GIT
b3: urinary continence and lipolysis

Question 2

direct adrenergic agonists

Answer 2

noradrenaline (b/a)
adrenaline (a/b)
dopamine (a1/b1)

phenylephrine (a1)
brimonidine (a2)
dobutamine (b1)
salbutamol (b2)
mirabegron (b3)

Question 3

indirect adrenergic agonists

Answer 3

blocks monoamine oxidase e.g. moclobemide (bioavailability increases actively)
blocks NA reuptake e.g. tricyclic (bioavailability increases actively)
displacing NA in vesicles e.g. ephedrine (bioavailability increases passively)

Question 4

direct adrenergic antagonist

Answer 4

prazosin (a1)
phenoxybenzamine (a2)
atenolol/betaxolol (b1)
propanolol/sotolol/timolol (b2)

no point inhibiting b3 (urinary continence and lipolysis)

Question 5

indirect adrenergic antagonist

Answer 5

a2 agonist binds to receptor to exert negative feedback

L-dopa analog to negative feedback on tyrosine hydroxylase

Question 6

general side effects of adrenergic agonists

Answer 6

• tachycardia/hypertension/arrhythmia AND reflex bradycardia
• diarrhoea
• specific to adrenaline: necrosis at the area of injection due to vasoconstriction

Question 7

general side effects of adrenergic antagonists

Answer 7

• bradycardia/postural hypotension AND reflex tachycardia
• constipation due to GI shutdown
• asthma due to bronchoconstriction
• diabetic patients due to b2 inhibitors masking the effects of hypoglycaemia which is a medical emergency

Question 8

phenylephrine

Answer 8

direct a1 agonist

used for hypotension and nasal decongestion

Question 9

brimonidine

Answer 9

direct a2 agonist

used for open angle glaucoma

Question 10

dobutamine

Answer 10

direct b1 agonist

used for congestive heart failure

Question 11

salbutamol

Answer 11

direct b2 agonist

used for asthma

Question 12

mirabegron

Answer 12

direct b3 agonist

used for BPH

Question 13

prazosin

Answer 13

direct a1 antagonist

used for chronic hypertension (by blocking the vasoconstriction and prevent aggravating of situation) and BPH

Question 14

phenoxybenzamine

Answer 14

direct a2 antagonist

used for pheochromocytoma

Question 15

atenolol

Answer 15

direct b1 antagonist

used for hypertension, angina, MI

Question 16

betaxolol

Answer 16

direct b1 antagonist

used for glaucoma

Question 17

propanolol

Answer 17

direct b2 antagonist

used for hypertension, angina

Question 18

sotolol

Answer 18

direct b2 antagonist

used for arrthymia

Question 19

timolol

Answer 19

direct b2 antagonist

used for glaucoma

Question 20

functions of muscarinic and nicotinic receptors

Answer 20

m1:
- found in the stomach
- to increase secretions and is involved in nausea vomiting pathways

m2:
- found in the heart
- increase rate and contractility

m3:
- found in other secretory cells (except in stomach) - salivary, lungs, GIT, bladder
- increases secretion and motility of all the above organs

Nm: neuromuscular found in the brain
Nn: neuronal found

Question 21

general adverse effects of cholinergic agonists

Answer 21

• diarrhoea and nausea
• excessive sweating
• frequency of urination
• contraindicated in asthma (same as b2 antagonists)

Question 22

direct cholinergic agonists

Answer 22

bethanechol
pilocarpine
nicotine (low doses)

Question 23

indirect cholinergic agonists

Answer 23

nicotine 
acetylcholinesterase inhibitors (e.g. donepezil, physostigmine, neostigmine, sarin)

Question 24

direct cholinergic antagonists

Answer 24

atropine (m1 to 3)
benzatropine (m3)
ipratropium (m3)
oxybutynin (m2 to 3)

non-depolarising neuromuscular agent e.g. pancuronium

Question 25

indirect cholinergic antagonists

Answer 25

nicotine at high doses
depolarising neuromuscular agent (succinylcholine)
botulinum toxin

Question 26

mechanism of action for non-depolarising neuromuscular agent

Answer 26

normally, influx of calcium causes release of Ach across NMJ to depolarise the muscle.

these agents will bind directly to Ach receptors to prevent depolarisation = paralysis of muscles

Question 27

mechanism of action for depolarising neuromuscular agent

Answer 27

these agents are essentially Ach receptor agonists and generate action potential for a longer period of time (they are resistant to acetylcholinesterase and hence is not metabolised).

this failure of repolarisation causes the receptor to be desensitised.

Question 28

bethanechol

Answer 28

direct agonist (m3)
used for gastric atony and urinary retention

Question 29

pilocarpine

Answer 29

direct agonist (m3)
used for narrow and wide angle glaucoma

Question 30

donepezil/physostigmine

Answer 30

indirect agonist

crosses BBB and hence used for Alzheimer’s

Question 31

neostigmine

Answer 31

indirect agonist

cannot cross BBB and used to reverse surgical anesthesia and also for myasthenia gravis (prevent neuropathy)

Question 32

sarin

Answer 32

indirect agonist

used as nerve agents - note that too much of it can cause SLUD (salivation, lacrimation, urination and diarrhoea)

Question 33

atropine

Answer 33

direct antagonist (m1-3)
used for bradycardia

Question 34

benzatropine

Answer 34

direct antagonist (m3)
used for second or third line Parkinson's disease

Question 35

ipratropium

Answer 35

direct antagonist (m3)
used for first line in COPD

Question 36

oxybutynin

Answer 36

direct antagonist (m2-3)
used for urinary incontinence

Question 37

pancuronium

Answer 37

indirect antagonist - non depolarising neuromuscular agent

used for induction of paralysis for surgery

Question 38

succinylcholine

Answer 38

indirect antagonist - depolarising neuromuscular agent

used for paralysis for brief surgery