Cholinoreceptor antagonist

Question 1

affinity

Answer 1

ability to bind to a receptor
stronger affinity= longer lasting complex
agonist and antagonist

Question 2

efficacy

Answer 2

ability to induce biological response

agonists only

Question 3

where are nicotinic receptors present?

Answer 3

all autonomic ganglia

Question 4

what are nicotinic receptor antagonists called

Answer 4

ganglion blocking drugs (GBD)

Question 5

two main action of GBDs

Answer 5

1) anatagonise the receptor
2) physically block off the ion-channel it is linked to
- use dependent
- incomplete

Question 6

concept of use-dependent blocks (ion channel)

Answer 6

drug is more effective when the channel is open so the more the receptor is used , the more it is blocked

[for receptors, more drug does not mean more effectiveness as they compete for the same receptor]

Question 7

incomplete blocking (ion channel)

Answer 7

partial ion channel blockage (some ions can still pass_

Question 8

why can some GBDs be said to have no affinity?

Answer 8

they don’t bind to the receptor but block the ion-channel only

Question 9

CVS effects of GBD

Answer 9

hypotension- blood vessel vasoconstriction is inhibited and renin secretion is inhibited (no ANG II)

Question 10

smooth muscle effects of GBD

Answer 10

• pupil dilation
• decreased GI tone
• bladder dysfunction
• bronchodilation

Question 11

exocrine secretion effects of GBD

Answer 11

decreased secretion

Question 12

examples of GBDs

Answer 12

hexamethonium- 1st antihypertensive but lots of side effects

trimetaphan- uses for hypertension during surgery, short acting and IV

Question 13

hexamethonium

Answer 13

ion channel blocker

not alot of affinity

Question 14

trimetaphan

Answer 14

receptor antagonist therefore has affinity

Question 15

irreversible GBD

Answer 15

alpha- bungarotoxin of the common krait snake

Question 16

how is alpha bungarotoxin different to the other GBDs

Answer 16

binds to mainly somatic nicotinic receptors
(to immobilise the prey’s skeletal muscles)

the other GBDs bind to autonomic nicotinic receptors

Question 17

what are muscarinic receptor antagonists (MRA)?

Answer 17

PNS antagonists (except sweat glands musc receptors)

therefore mainly inhibits PNS stimulation

Question 18

examples of MRA

Answer 18

• atropine

- hyoscine

Question 19

CNS effect of atropine

Answer 19

normal dose- little effect

toxic dose- mild restlessness–> agitation

Question 20

CNS effect of hyoscine

Answer 20

normal dose- sedation, amnesia

toxic dose- CNS depression (or paradoxical CNS excitation, associated with pain- possibly due to greater permeability through BBB)

Question 21

how do hyoscine and atropine have varying effects despite their similar structures

Answer 21

hyoscine is more M1 selective than atropine

Question 22

what is used to examine the retina

Answer 22

tropicamide

dilation/mydriasis of the eye (constriction in inhibited) so the pupil expands so the retina can be examined

Question 23

use of MRAs in anaesthetic pre medication

Answer 23

block PNS
block bronchoconstriction 
block watery secretions
decreased heart rate and contractility 
sedation

Question 24

treating motion sickness (neurological)

Answer 24

hyoscine patch

• inhibits the muscarine receptors of the vomiting centre
• sickness due to sensory mismatch between eyes and labyrinth)

Question 25

treatment of Parkinson’s (lack of dopamine)

Answer 25

PD involves the substantial Niagra neurones (Which are lost) producing dopamine for the striatum

MRA decreases the negative inhibition of dopamine release into striatum from another source so dopamine can be released continually

D1 receptors are upregulated by blocking M4 receptors

Question 26

what MRA is used to treat asthma and COPD

Answer 26

ipratropium bromide
-causes bronchodilation
similar in shape to atropine
-has extra nitrogen-containing polar group attached that allows it to linger more in the lungs without crossing the mucosa in to the blood, like atropine would

Question 27

GI effects of MRA

Answer 27

treatment of IBS

- MRA decreases GI tone and secretions

Question 28

unwanted effects of MRA

Answer 28

1) hot- due to decreased sweating and thermoregulation defects
2) dry- decreased secretions
3) blind- cyclopegia (paralysis of eye muscles, no accommodation)
4) mad- CNS disturbance

Question 29

which drugs would be used to treat atropine poisoning?

Answer 29

1) physostigmine (anti cholinesterase)
2) ecothiopate (irreversible anti cholinesterase)
3) bethanechol (muscarinic receptor agonist)

atoprine competes with ACh, having anti cholinesterase means more ACh remains to outcompete the atropine

Question 30

what does the botulinum toxin do?

Answer 30

blocks the SNARE complex (ACh vesicles) stopping them from docking and being exocytosed.