A full agonist and a partial agonist act at the same receptor. Which statement correctly describes a partial agonist?
- A It produces submaximal response even at complete receptor occupancy and can antagonize a full agonist ✓
- B It binds the receptor but produces no intrinsic activity
- C It shifts the full agonist curve to the left, increasing its potency
- D It irreversibly binds the receptor, permanently reducing available receptors
Correct answer: A. It produces submaximal response even at complete receptor occupancy and can antagonize a full agonist
Explanation
B partial agonist has intrinsic activity between zero and that of a full agonist, so even at full receptor occupancy it produces a submaximal response. In the presence of a full agonist, it competes for the receptor and reduces the overall response, thus acting as a functional antagonist. Buprenorphine at the mu-opioid receptor is the classic example used in pharmacology teaching.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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