What are incretins and what is their effect on insulin secretion?

• A. GLP-1 and GIP; they amplify glucose-stimulated insulin secretion and GLP-1 also suppresses glucagon and slows gastric emptying.
• B. Insulin and C-peptide; they conditionally stimulate insulin release.
• C. Ghrelin and leptin; they inhibit insulin action.
• D. Cortisol and epinephrine increase insulin release.

Answer: (A)

Incretins are gut hormones released after a meal that boost insulin release in response to rising blood glucose. The main players are GLP-1 and GIP, and they work in a glucose-dependent way, meaning they amplify insulin secretion when glucose is high but don't push insulin out of proportion at normal levels. This is why oral glucose elicits a stronger insulin response than an equivalent amount given intravenously—the gut hormones enhance the pancreatic response. GLP-1 not only raises insulin secretion but also suppresses glucagon, slows gastric emptying, and can reduce appetite. GIP also stimulates insulin release, though its additional effects on glucagon suppression and gastric motility are less pronounced. Other hormones listed don’t function as incretins, so they don’t fit the described mechanism.