Incretin hormones primarily promote insulin secretion in response to meals. Which statement best describes their action?

• A. They increase insulin secretion and suppress glucagon in a glucose-dependent manner.
• B. They directly stimulate glucagon release.
• C. They have no effect on insulin.
• D. They inhibit glucose absorption from the gut.

Answer: (A)

Incretin hormones act as gut-derived signals that boost insulin release when nutrients enter the bloodstream. The main incretins, GLP-1 and GIP, enhance glucose-stimulated insulin secretion from pancreatic beta cells, but their effect depends on the current blood glucose level. This glucose-dependency means they raise insulin mainly when glucose is elevated, reducing the risk of hypoglycemia.

At the same time, incretins help tamp down glucagon secretion from alpha cells when glucose is high, which lowers hepatic glucose production after a meal. They do not directly stimulate glucagon; their glucagon-suppressing effect complements the insulin-raising action, all in a glucose-dependent manner. They don’t primarily inhibit glucose absorption from the gut—that's not their central role, though GLP-1 can slow gastric emptying.

So the statement that best captures their action is that they increase insulin secretion and suppress glucagon in a glucose-dependent manner.