Gastrointestinal inhibitory peptide GIP

Glucose, the principal stimulus to insulin secretion, is permissive for the action of many other secretogogues. Glucose provokes insulin secretion more effectively when taken orally than when administered intravenously because the oral route induces the release of GI hormones and stimulates vagal activity. Several GI hormones promote insulin secretion, the most potent of which are glucose-dependent insulinotropic peptide (GIP, also known as gastrointestinal inhibitory peptide) and glucagon-like peptide-1 (GLP-1). 

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