How does increasing the concentration of a partial agonist affect the response produced by a full agonist?

How does increasing the concentration of a partial agonist affect the response produced by a full agonist?

• A. The full agonist response increases due to cooperative binding.
• B. The receptors become occupied by partial agonists, decreasing the response of the full agonist.
• C. The partial agonist increases the maximal response beyond the full agonist.
• D. There is no change in the full agonist response.

Answer: (B)

Increasing the concentration of a partial agonist reduces the full agonist response because they compete for the same receptor binding sites. A partial agonist has lower intrinsic efficacy, so when it binds, it produces only a submaximal effect. As more receptors become occupied by the partial agonist, fewer receptors are available for activation by the full agonist, pulling the overall response down and lowering the maximum achievable effect. In this setup, the partial agonist acts like a competitive antagonist in the presence of a full agonist. The other choices don’t fit: cooperative binding wouldn’t explain a decreased full agonist response, and a partial agonist cannot increase the full agonist response beyond its own lower efficacy.

Increasing the concentration of a partial agonist reduces the full agonist response because they compete for the same receptor binding sites. A partial agonist has lower intrinsic efficacy, so when it binds, it produces only a submaximal effect. As more receptors become occupied by the partial agonist, fewer receptors are available for activation by the full agonist, pulling the overall response down and lowering the maximum achievable effect. In this setup, the partial agonist acts like a competitive antagonist in the presence of a full agonist. The other choices don’t fit: cooperative binding wouldn’t explain a decreased full agonist response, and a partial agonist cannot increase the full agonist response beyond its own lower efficacy.