Orally administered glucose provokes a greater insulin response than an equivalent amount of intravenously administered glucose. The incremental response to ingested glucose is due to the effects of which of the following hormones?

a. Gastric inhibitory peptide

Orally administered glucose stimulates a greater insulin response than an equivalent amount of intravenous glucose through the release of enteric hormones that potentiate insulin secretion. This effect is known as the enteroinsular axis. Gastric inhibitory polypeptide (GIP) appears to be an important regulator of this effect, although other gut peptides, such as glucagon-like peptide I (GLP-1), may contribute to this effect as well. Nutrients that regulate insulin secretion include amino acids, such as arginine, lysine, and leucine, and free fatty acids. Hormones that stimulate insulin secretion include glucagon, GIP, and cholecystokinin, whereas somatostatin, amylin, and pancreastatin are inhibitory. Insulin is also stimulated by sulfonylurea compounds, which act independently of the glucose concentration and form the basis of treatment of type II, or insulin-independent, diabetes.