3. Receptors III

Question 1

Describe Competitive antagonists.

Answer 1

• The agonist and antagonist bind to the same site.
• the block can be overcome by increasing the concentration of an agonist.
• Introduction shifts the Dose response curve to the right decreasing pD2 so more is needed for the same effect, but has no effect on Emax, all graphs are parallel.

Question 2

Describe Non-competitive antagonists.

Answer 2

• The antagonist binds to a different site on the receptor or acts irreversibly.
• The block cannot be overcome by increasing the concentration of the agonist.
• Introduction decrease Emax but pD2 is not changed the dose-response curves at different concentrations are not parallel.

Question 3

Describe what factors affect the antagonist ability to block receptors.

Answer 3

-The relative affinity of the agonist (KD) and antagonist (KA) for the receptor.

-The relative concentrations of the agonist [D] and antagonist [A].

Question 4

Describe Dose Ratio.

Answer 4

The ratio of the agonist concentration that elicits the same response either in the absence[D0] or the presence[DA] of the antagonist. If the response in the presence and absence of the antagonist is the same, then assume that receptor occupancy by the agonist is the same.