Cholinergic (Parasympathetic) Nervous System Antagonists

Question 1

Muscarinic receptors bind to?

Answer 1

Acetylcholine (ACh)

Question 2

Where are M2 muscarinic receptors located?

Answer 2

heart

Question 3

What are the effects of activation of M2 muscarinic receptors?

Answer 3

Decreased HR and contractility

Question 4

What happens to SA node spontaneous depolarization when M2’s are activated?

Answer 4

it is slowed; this leads to a decreased HR

Question 5

What happens in the AV node when M2s are activated?

Answer 5

conduction velocity is slowed

Question 6

What happens in the atrium when M2s are activated?

Answer 6

decreased refractory period leads to decreased contractility

Question 7

Where are M3/M5 muscarinic receptors found?

Answer 7

Vasculature

Question 8

Does the vasculature have parasympathetic innervation?

Answer 8

Hell no!

Question 9

So then why are there muscarinic receptors in the vasculature?

Answer 9

The have an indirect action of stimulating nitrous oxide (NO)

Question 10

Are the M3/M5 receptors Gq or Gi coupled?

Answer 10

Gq; this leads to increased IP3, increased DAG, and increased intracellular Ca2+

Question 11

Are the M2 receptors Gq or Gi coupled?

Answer 11

Gi; this leads to inhibition of adenylyl cyclase and decreased cAMP; this leads to activation of K channels and inhibition of Ca2+ channels

Question 12

What are ACh’s effects on CV system?

Answer 12

vasodilate, decrease HR, decrease AV node conduction velocity (dromotropic), decrease atrial contractility (inotropic)

Question 13

ACh’s direct cardiac effects are mediated by M2 receptors which does?

Answer 13

Inhibits adenylyl cyclase thus decreasing cAMP thus activating K channels and inactivating Ca2+ channels

Question 14

ACh’s indirect cardiac effects.. How do they happen?

Answer 14

ACh opposes Beta 1 mediated increases in cAMP, and it inhibits NE release

Question 15

In the AV node, ACh acts to slow conduction. If this process is overdone, what can happen?

Answer 15

AV block

Question 16

What does IV ACh do to BP?

Answer 16

Lowers it by acting on M3/M5 receptors which activate NO which vasodilates

Question 17

When IV ACh lowers BP what is the heart’s response?

Answer 17

Reflex tachycardia

Question 18

What is atropine’s effect on the heart at low dose?

Answer 18

decreases HR

Question 19

What is atropine’s effect on the heart at high dose?

Answer 19

increases HR

Question 20

When given alone, what is atropine’s effect on the vasculature?

Answer 20

Nothing

Question 21

When given in high doses, what peculiar side effect can atropine cause?

Answer 21

atropine flush (in the cheeks)

Question 22

What is atropine’s utility clinically?

Answer 22

Atropine raises the HR when it has been lowered by some drug that has activated vagal stimulation

Question 23

Ok so.. what is atropine?

Answer 23

It is an ACh antagonist

Question 24

You have a patient who’s HR and BP are scary low because they took too much of a parasympathomimetic drug. What do you give them?

Answer 24

IV Atropine