Lec 5- Drug targets 3, Page 36-45

Question 1

EC50 or pD2

Answer 1

the measure of agonist potency

• the lower the EC50, the greater the potency
• the higher the pD2, the greater the potency

Question 2

EC50

Answer 2

Effective Concentration that produces 50% of the maximum effect

Question 3

ED50

Answer 3

Effective Dose that produces 50% of the maximum effect

Question 4

Competitive Reversible Antagonism

Answer 4

Antagonist competes directly w the agonist for binding to the receptor

Question 5

pA2

Answer 5

• ve log concentration of antagonist which causes a two-fold shift in the concentration-response curve
• may vary at different receptors and against different

Question 6

Non-Competitive Antagonism

Answer 6

• Do not bind to the same receptor as the agonist nor alter agonist-receptor binding
• Act by interfering with the cascade of events initiated by agonist-receptor binding
  Eg. Ca2+ channel blockade
• Non parallel rightwards shift of the conc-response curve with depression in max response

Question 7

Physiological Antagonism

Answer 7

• Occurs when the actions of two agonists working at two different receptor types have opposing (antagonising) actions
  Eg. Histamine acting at H1 receptors to cause bronchoconstriction and adrenaline acting at B2 receptors to cause bronchodilation

Question 8

Partial Agonists

Answer 8

Show full receptor occupancy but do not elicit a maximal response
- Efficacy less than 1
Eg. Methysergide at 5HT receptors
- Can act as antagonists to full agonists

Question 9

Inverse Agonists

Answer 9

• Some receptors show “constitutive” activity
  Eg. Benzodiazepine receptor: preference of the activated state (this can also occur in disease states
  -Ligands showing a preference for blinding to the resting state can shift the equilibrium towards this state and reduce the level of constitutive activation
• Most receptors prefer the inactive state when no ligand is present resulting in no practical difference between an AntagCR and inverse agonist