Party 4

Question 1

Constitutivley active receptor

Answer 1

A receptor that that spontaneously adopts an active conformation of and leads to basal receptor activation in abscence of agonist
Exist in 2 conformational states (active and inactive state) which are in equilibrium

Question 2

Effects of an agonist on conformational equilateral

Answer 2

Agonist has a higher affinity for the active state of the receptor R* than inactive state Ri
Agonist therefor shifts conformational equilibrium towards R*

Question 3

Effects of antagonist on conformational equilibrium

Answer 3

Antagonist has equal affinity for both R* and Ri
Therefor antagonist has no effect on the conformational equilibrium

Question 4

Effects of inverse agonist on conformational equilibrium

Answer 4

Inverse agonist has higher affinity for Ri
Inverse agonist shifts conformational equilibrium towards Ri

Question 5

Example of 2 state receptor

Answer 5

G protein coupled receptor

Question 6

Examples of drugs previously classified as neutral antagonist but now as inverse agonists

Answer 6

Propranolol -b2 adrenoceptor
Cetirizine- h1 histamine receptor
Ranitidine -h2 histamine receptor

Question 7

Antagonist

Answer 7

Binds to receptors but does not initiate any changes in the cell

Question 8

Explain the concept of spare receptors

Answer 8

The response of the cell to an agonist depends on the number of receptor-ligand complexes- the fewer the number of receptors in the cell surface the less sensitive the cell is to the ligand

Question 9

Example of spare receptor activity

Answer 9

For Acetylcholine in isolated tissues full agonists are capable to cause maximal response at low occupancies (when only few receptors are bound to receptor)

Question 10

Exa,pls of spare receptors

Answer 10

Erythroid progenitor cells can develop into erythrocytes in the presence of erythropoietin . On the erythroid progenitor cells there are 1000 receptors for EPO. only 100 receptors need to be bound to cause maximal response of cell

Question 11

Function of spare receptors

Answer 11

To increase sensitivity of receptor to agonist

Question 12

Receptor trafficking

Answer 12

When the cell surface receptors are moving from the surface to internal environment, so the number of receptors on cell surface are decreasing and leads to desensitisation of the tissue

Question 13

Desensitisation

Answer 13

A decrease in the response of a receptor to a drug due to the decrease in the effect of a drug, this occurs when the number of receptors have decreased
Also when a drug is repeatedly given , the effect of a drug gradually diminishes

Question 14

Tachyphylaxis

Answer 14

A rapid decrease in the response of a receptor to the drug after administration

Question 15

Tolerance

Answer 15

A more gradual decrease in the response of the receptor to the drug , can take days or weeks to develop
Develops slowly

Question 16

Example of a drug that carries out tachyphylaxis

Answer 16

Nicotine

Question 17

Example of drug that carries out tolerance

Answer 17

Opioids

Question 18

Refractoriness

Answer 18

Condition of patient is resistant to drug treatment

Question 19

Drug resistance

Answer 19

Loss of effectiveness of anti microbial., antiviral and anti tumour drugs when used over a certain time period

Question 20

Why does tachyphylaxis, tolerance, refractoriness and resistance occur

Answer 20

*change in receptors( desensitisation)
*exhaustion of mediators (drugs)
*translocation (trafficking) of receptors
* increased metabolic degradation of drug