LHD - Pharmacodynamics II

Question 1

What are 2 formulae for fractional occupancy (r)?

Answer 1

r = DR/R(total)

r = [D]/([D] +Kd)

Question 2

What shape is the graph of fractional occupancy (r) against [Drug]?

Answer 2

Rectangular hyperbola

Question 3

What is [Drug] at r = 1/2

Answer 3

[D] = Kd

Question 4

What shape is the graph of fractional occupancy (r) against log[Drug]?

Answer 4

Sigmoidal

Question 5

What are 2 examples of complex drug-receptor interactions?

Answer 5

• Receptors which bind 2 drug molecules at once (NICOTINIC)
• Receptors which convert between high and low-affinity forms

Question 6

What is an example of 2 drug molecules binding at once?

Answer 6

• When first Ach binds, it induces a conformational change, increasing the receptor’s affinity for Ach
• Upon second Ach binding, the channel opens

Question 7

What is an example of receptors converting between affinities?

Answer 7

• The binding of an agonist stabilises the G-protein and receptor complex due to the high affinity
• After, the G-protein complex dissociates as the affinity becomes low

Question 8

What is response [E] proportional to? (2)

Answer 8

Number of receptors occupied (Occupancy Theory)

Rate of receptor occupation (Rate theory)

Question 9

What is pD2

Answer 9

A measure of the affinity of agonists to the receptors in the tissue

• The negative log of the agonist concentration that gives half maximal response

Question 10

At what concentration do drugs with high pD2 values act at?

Answer 10

Low concentrations

Question 11

Is pD2 always positive?

Answer 11

Yes