8 Drugs & Receptors / pharmacokinetics

Question 1

What is efficacy?

Answer 1

likelihood of ligand causing activation

Question 2

What is potency?

Answer 2

combination of both affinity & efficacy

governed by a number of receptors

Question 3

What is an agonist?

Answer 3

binds to receptor and activates it

Question 4

What is a partial agonist?

Answer 4

only causes slight activation

Question 5

What is an antagonist?

Answer 5

binds to receptor, (prevents ligand binding) and prevents receptors from being activated

Question 6

What is competitive antagonism?

Answer 6

complete with agonists for binding - the inhibition is surmountable (can overcome)

Question 7

What is non-competitive antagonism?

Answer 7

endogenous (from body) ligand binds to orthosteric site, antagonist binds to allosteric sites (not the agonist site where it can potentially alter conformation of receptor), reducing effects of agonist, doesn’t compete for ligand binding site, but affects orthosteric ligand affinity and or efficacy

Question 8

Ligand

Answer 8

has affinity for receptors

Question 9

What is intrinsic activity?

Answer 9

the response that receptor causes - the higher up the curve, the more the intrinsic activity (up to 100%)

Question 10

What is intrinsic efficacy?

Answer 10

the affinity to activate receptor

Question 11

What is functional antagonism?

Answer 11

2 agonists interact with different receptors to produce opposing effects e.g. adrenaline –> ß2-adrenoceptors (GPCR) –> relaxation of bronchioles
opposing contraction of smooth muscles of airways in asthma

Question 12

What is reversible competitive antagonism?

Answer 12

bind to receptor, preventing agonist from binding, however, will dissociate in which agonist can then bind to the receptor
out competed through increased agonist concentration
greater [agonist] = greater inhibition
cause parallel shift to the right of the [agonist]-response (%) curve

Question 13

What is irreversible competitive antagonism?

Answer 13

once antagonist bound, doesn’t dissociates / dissociates slowly, inhibition is not surmountable (increased [antagonist] or time, more receptors blocked by antagonist
cause parallel shift to the right and decrease in size of [agonist]-response curve
right: spare receptors filled by antagonists, down as insufficient receptors for full response

Question 14

What is desensitisation?

Answer 14

when receptor decreases its response to a signalling molecule

Question 15

What is tolerance?

Answer 15

diminished response to a drug due to repeated use and body adapts to the continued presence of the drug by turning down the number of receptors present as fewer ligands binding to the receptors are required for the same effect

Question 16

What is supersensitivity?

Answer 16

receptor has enhanced response towards a ligand

Question 17

What is homologous desensitisation?

Answer 17

the process by which ONLY the signal from the stimulated receptor is induced

Question 18

What is heterologous desensitisation?

Answer 18

the process when receptors for several agonists become less effective even though only 1 receptor has been continuously stimulated

Question 19

What are adaptive changes which can occur in receptor populations when exposed to agonists?

Answer 19

overuse of agonist (morphine) can cause the sensitivity of the receptor to be turned down because there is too much of the ligand present and not a lot of receptors is required to generate the response

Question 20

What are adaptive changes which can occur in receptor populations when exposed to antagonists?

Answer 20

when an antagonist (buprenorphine) bind, the (reduced number) of receptors quickly becomes occupied with the antagonists, so when the agonist is introduced, the receptors are blocked by the antagonists (high affinity)
(high affinity but low response - partial agonist / mixed agonist & antagonist)

Question 21

What is Kd?

Answer 21

concentration of antagonist needed to give 50% occupancy

Question 22

What is IC50?

Answer 22

concentration of antagonists giving 50% inhibition

Question 23

What is affinity?

Answer 23

likelihood of ligand binding to receptor