Cyclic AMP is degraded to 5'-AMP by the enzyme phosphodiesterase. A drug that inhibits phosphodiesterase would have which of the following immediate effects on a cell responding to epinephrine?

• A Decreased activity of protein kinase A
• B Accelerated inactivation of Gsα by enhanced GTPase activity
• C Reduced binding of epinephrine to its receptor
• D Prolonged elevation of intracellular cAMP and sustained PKA activation ✓

Explanation

Phosphodiesterase (PDE) hydrolyzes cAMP to 5'-AMP, terminating PKA activation. Inhibiting PDE (e.g., with theophylline or methylxanthines) slows cAMP degradation, leading to higher and more prolonged cAMP levels, sustained PKA activation, and enhanced downstream effects such as glycogenolysis and lipolysis. Epinephrine receptor binding and Gsα GTPase activity are not directly affected by PDE inhibition.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.