8 Drugs and Receptors

Question 0

What is the equation for Molarity?

Answer 0

Molarity (M) = g/L
——————–
Molecular weight

Question 1

What type of receptor is a popular target for drugs?

Answer 1

GPCR

Question 2

What is a drug ‘agonist’?

Answer 2

A ligand that causes a response so has both affinity and intrinsic efficacy.

Question 3

What is a drug ‘antagonist’?

Answer 3

A ligand that binds to a receptor without producing a response. They only has affinity with NO intrinsic efficacy.

Question 4

Define ‘affinity’

Answer 4

Affinity is the ability of a ligand to bind to a receptor

Question 5

Define ‘intrinsic efficacy’

Answer 5

Intrinsic efficacy is the ability of a ligand to cause a response when bound to a receptor.

Question 6

What is Kd?

Answer 6

Kd is the dissociation constant of a drug. It is a measure of affinity.
The lower the Kd, the higher the affinity.

Question 7

What is the E50?

Answer 7

The effective concentration giving 50% of the maximal response. It is a measure of potency depending on both affinity and intrinsic efficacy.

Question 8

What are the problems in treating asthma with B-adrenoreceptor agonists?

Answer 8

The therapeutic target is B2-adrenoceptors which causes bronchodilation. However the drugs also bind to other B-adrenoceptors which have side effects such as increasing the heart rate.

Question 9

List the factors that determine the potency of a drug

Answer 9

Affinity
Intrinsic Efficacy
Cell/Tissue dependent factors

Question 10

Define the term ‘spare receptors’

Answer 10

A spare receptor is when a 100% response of a drug is reached without filling all the available receptors therefore leaving some spare.

Question 11

What is the purpose of spare receptors?

Answer 11

Spare receptors increase the sensitivity to a drug as responses can be generated at low concentrations of agonist.

Question 12

What is ‘up-regulation’ of receptors and when does it occur?

Answer 12

Receptor numbers are increased with low activity.

Question 13

What is ‘down-regulation’ and when does it occur?

Answer 13

Decreasing the number of receptors occurs when there is high activity.

Question 14

What is a ‘partial agonist’?

Answer 14

A agonist that cannot produce a full response even with all receptors occupied.

Question 15

Name a clinically used partial agonist

Answer 15

Opioids

Question 16

What is ‘withdrawal’?

Answer 16

Withdrawal results in the opposite to acute drug effects. It occurs when a patient stops taking a drug they have been on for a long time.

Question 17

Explain how drugs can reduce the effects of withdrawal

Answer 17

A partial agonist can act as an ANTAGONIST for a full agonist.
Eg. Buprenorphine has a higher affinity than heroin for the same receptors. The receptors become saturated with Buprenorphine so the effects of heroin are not felt.

Question 18

When can partial agonists act as full agonists?

Answer 18

If the number of receptors increases enough to produce a full response

Question 19

Reversible competitive antagonism

i. ) What happens when the antagonist is present?
ii. ) Is the inhibition surmountable?
iii. ) Give an example

Answer 19

i. ) The antagonist compete with the agonists for binding
ii. ) Yes
iii. ) Naloxone is a competitive antagonist at u-opioid receptors

Question 20

Irreversible competitive antagonism

i. ) What happens when the antagonist is present?
ii. ) Is the inhibition surmountable?
iii. ) Give an example

Answer 20

i. )The antagonist competes for the binding sites but does not dissociate from the receptor
ii. ) No
iii. ) Phenoxybenzamine-non-selective is an irreversible a1-adrenoceptor blocker

Question 21

Non-competitive antagonism

i. ) What happens when the antagonist is present?
ii. ) Is the inhibition surmountable?
iii. ) Give an example

Answer 21

i. ) Antagonist binds to an allosteric site on the receptor
ii. ) Varies
iii. ) NMDA receptor is a ligand-gated ion channel. Ketamine can bind intrinsically.