What is an agonist and what is an antagonist in receptor pharmacology?

• A. Agonist activates receptor to produce a response; antagonist blocks receptor without intrinsic activity
• B. Agonist blocks receptor; antagonist activates receptor
• C. Agonist inhibits enzyme; antagonist stimulates enzyme
• D. Agonist decreases receptor number; antagonist increases receptor number

Answer: (A)