Agonists and Antagonists

Question 1

What is an agonist?

Answer 1

A drug or natural ligand which binds to a receptor and activates it, inducing a response in that receptor.

Question 2

What two properties do agonists exert?

Answer 2

Agonists have affinity and efficacy on a receptor.

Question 3

What is an antagonist?

Answer 3

A drug which blocks or reduces the action of an endogenous ligand or other drugs which act on that target.

Question 4

State which properties antagonists do and do not exert?

Answer 4

Antagonists have affinity but no efficacy on the receptor.

Question 5

Constitutively Active

Answer 5

When a receptor is capable of producing a response in the absence of a bound ligand.

Question 6

Full Agonist

Answer 6

A drug or ligand which is capable of inducing the maximal possible response of a given system or tissue.

Question 7

Partial Agonist

Answer 7

A drug or ligand which cannot induce a maximal response even when at high concentrations or maximal receptor occupancy.

Question 8

Inverse Agonist

Answer 8

A drug or ligand which, when bound, induces an effect on the receptor which opposes the effect of an agonist and can reduce the base response of a constitutively active receptor.

Question 9

Reversible Competitive Antagonists

Answer 9

At binding site.
Agonist can still induce maximal response.
Potency of agonist is lowered.

Question 10

Irreversible Competitive Antagonist

Answer 10

At binding site.
Reduces maximal response possible.

Question 11

Non-competitive Antagonist

Answer 11

At other part of the receptor.
Reduces maximal response possible.