Lecture 18 + 19: Pharmacodynamics 2

Question 1

When are spare receptors present?

Answer 1

When 100% response can be achieved with less than 100% occupancy

Question 2

What are 2 reasons why spare receptors exist?

Answer 2

1. Amplification in the signal transduction pathway so not all receptors have to be bound
2. Response limited by a post-receptor event

Question 3

Why have spare receptors?

Answer 3

Spare receptors increase sensitivity or potency, allowing responses at low concentrations of agonist

Question 4

What are the 3 things that receptor number can influence?

Answer 4

Agonist sensitivity
Agonist potency
Maximal response

Question 5

What is the difference between full and partial agonists?

Answer 5

Partial agonists are ligands that evoke responses that are lower than the maximal response of a full agonist - they have lower Emax values and so lower intrinsic activity

Question 6

What are the 3 forms of antagonism?

Answer 6

1. Reversible competitive antagonism
2. Irreversible competitive antagonism
3. Non-competitive antagonism

Question 7

What is reversible competitive antagonism?

Answer 7

Antagonists and agonists compete, antagonist Can bind and dissociate, so full response still achievable if agonists were increased

Question 8

What is IC50?

Answer 8

Concentration of antagonists giving 50% inhibition

Question 9

What is irreversible competitive antagonism?

Answer 9

Antagonists and agonists compete, but antagonists dissociates slowly or not at all, so maximum response cannot be achieved if there are no spare receptors

Question 10

What is non-competitive antagonism?

Answer 10

Binds to allosteric sites, doesn’t compete but it reduces orthosteric ligand affinity and/or efficacy

Question 11

What is functional antagonism?

Answer 11

Binding of an antagonist that causes a good therapeutic effect

Question 12

What is selectivity?

Answer 12

Drugs that preferentially activates a certain receptor

Question 13

What is specificity?

Answer 13

Drug only activates one receptor