Why is the principle of receptor reserve important in interpreting dose-response relationships?

• A. Dose-response curves fall to the left of the receptor occupancy curve because of this principle
• B. Dose-response curves fall to the right of the receptor occupancy curve
• C. They are identical
• D. There is no relationship

Answer: (A)

Receptor reserve exists when spare receptors allow a maximal response to be produced without full receptor occupancy. Because of this amplification in signaling, you don’t need all receptors engaged to reach the top of the response. As a result, the dose needed to achieve a given effect is smaller than the dose needed to occupy the same fraction of receptors. Plotting effect versus dose therefore shows a leftward shift compared with a plot of effect versus receptor occupancy. If there were no spare receptors, the dose–response and occupancy curves would align more closely. This is why the correct statement describes the dose–response curve falling to the left of the occupancy curve.