Receptor Theory III and IV

Question 1

What is the equation to measure response from a concentration response curve?

Answer 1

Response = max.[Xa]^n/
                     ([Xa]^n + [EC50]^n)
Max = max response
Xa = concentration of agonist
n = slope factor
EC50 = concentration of agonist evoking 50% of the response

Question 2

What is EC50 a measure of?

Answer 2

Agonist potency

Question 3

What will the potency of an agonist depend on?

Answer 3

Affinity, efficacy and spare receptors

Question 4

What is efficacy?

Answer 4

A measure of a single agonist-receptor’s ability to produce a response

Question 5

What properties determine the effect of a drug in a living system?

Answer 5

Specificity, affinity (agonists and antagonists), efficacy (agonists only)

Question 6

What value for efficacy will a full agonist have?

Answer 6

1

Question 7

The affinity of a competitive antagonist for a receptor is constant, T or F?

Answer 7

T

Question 8

What are the 5 different classes of antagonists?

Answer 8

Chemical, pharmacokinetic, physiological, non-competitive, competitive by receptor block

Question 9

What are chemical antagonists?

Answer 9

Substances combine in solution and the effect of the active drug is lost

Question 10

What is an example of chemical antagonism?

Answer 10

Inactivation of heavy metals (mercury, lead) whose toxicity is reduced with the addition of a chelating agent (dimercaprol)

Question 11

What are the types of pharmacokinetic antagonism?

Answer 11

Reduction in the amount of drug absorbed (opiates reduced absorption as they reduce gut motility)
Change in drug metabolism (antibiotics stimulate the metabolism of warfarin and reduce their effectiveness)

Question 12

What are physiological antagonists?

Answer 12

The interaction of two drugs with opposing actions in the body

Question 13

What is an example of physiological antagonism?

Answer 13

Noradrenaline raises arterial blood pressure, histamine lowers arterial arterial blood pressure through vasodilation

Question 14

What is non-competitive antagonism?

Answer 14

Blocks some steps in the process between receptor activation and response but does not compete with the agonist for the receptor site and therefore non-competitive

Question 15

What effect does increasing the concentration of a reversible competitive antagonist have on the concentration response curve?

Answer 15

Shifts it parallel to the right but has no effect on the max

Question 16

What is the dose ratio?

Answer 16

How many more times agonist is needed in the presence of an antagonist

Question 17

What is the equation for the dose ratio?

Answer 17

DR = [agonist] in presence of antagonist

[agonist] in absence of antagonist

Question 18

What does Schild analysis measure?

Answer 18

The antagonist affinity

Question 19

What is the effect of increasing the time a irreversible competitive antagonist is present on the concentration response curve?

Answer 19

The max response of the agonist decreases

Question 20

What is irreversible competitive antagonism?

Answer 20

Antagonism that cannot be reversed by washing the tissue, it is also time-dependent

Question 21

Why might desensitisation occur?

Answer 21

When given continuously or repeatedly it can lead to internalisation by endocytosis of the receptors, change in the receptor (phosphorylation), exhaustion of mediators, increased metabolic degradation, physiological adaptation