In a scenario where exogenous angiotensin II is administered with a drug that blocks angiotensin II formation, what best describes the drug’s action?

• A. Full agonist at ATII receptor
• B. Partial agonist at ATII receptor
• C. Competitive antagonist at ATII receptor
• D. Irreversible inhibitor of ACE

Answer: (B)

Partial agonists activate receptors but produce a submaximal response compared with a full agonist. In this scenario, angiotensin II is the full agonist at AT1 receptors, so when a drug that blocks angiotensin II formation is present, any exogenous Ang II can still activate the receptors but to a lesser extent if the blocker acts as a partial agonist. The drug will occupy some receptors and provide only partial signaling, thereby dampening the overall Ang II–mediated effect. It’s not a pure antagonist because it still produces some receptor activity, and it’s not an irreversible ACE inhibitor since the action is at the receptor level, not the enzyme.