GIP (1-39) is a highly potent insulinotropic peptide, it is the endogenous truncated form of the incretin hormone GIP (Glucose-dependent Insulinotropic Polypeptide, or Gastric Inhibitory Polypeptide), a 42-amino acid peptide released by the K cells of the duodenum and jejunum in response to food intake. GIP (1-39) is more potent at stimulating glucose-dependent insulin secretion from rat pancreatic β-cells than GIP and loss of the incretin effect is an early characteristic of type 2 diabetes