A DPP-4 inhibitor (sitagliptin) exerts its antidiabetic effect primarily by:

• A Mimicking GLP-1 action at incretin receptors on beta cells
• B Preventing degradation of endogenous GLP-1 and GIP, prolonging their action ✓
• C Blocking glucagon secretion directly from alpha cells
• D Stimulating insulin secretion independent of glucose concentration

Explanation

DPP-4 (dipeptidyl peptidase-4) is the enzyme responsible for rapid inactivation of incretin hormones GLP-1 and GIP in the circulation (half-life of active GLP-1 is ~2 minutes). Sitagliptin inhibits DPP-4, increasing the plasma concentration and duration of action of endogenous GLP-1 and GIP, which then stimulate glucose-dependent insulin secretion and suppress glucagon. Because the effect is glucose-dependent, DPP-4 inhibitors carry minimal hypoglycaemia risk as monotherapy.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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