Down regulation of receptors is defined as

Down regulation of receptors is defined as

• A. Increased receptor numbers
• B. Decreased number of drug receptors
• C. No change in receptor numbers
• D. Increased receptor affinity

Answer: (B)

Down regulation describes a decrease in the number of receptors available for drug binding on the cell surface after sustained exposure to an agonist. This happens as receptors are removed from the membrane or degraded, or as their synthesis is reduced. With fewer receptors present, the same drug produces a smaller response, and the maximal effect can be diminished—an idea you see with tolerance or tachyphylaxis. This concept is different from upregulation (which would increase receptor numbers) and from changes in receptor affinity (which would alter how tightly a drug binds rather than how many receptors are present).

Down regulation describes a decrease in the number of receptors available for drug binding on the cell surface after sustained exposure to an agonist. This happens as receptors are removed from the membrane or degraded, or as their synthesis is reduced. With fewer receptors present, the same drug produces a smaller response, and the maximal effect can be diminished—an idea you see with tolerance or tachyphylaxis. This concept is different from upregulation (which would increase receptor numbers) and from changes in receptor affinity (which would alter how tightly a drug binds rather than how many receptors are present).