DPP4 and type 2 diabetes mellitus: Both the mRNA of proGIP and a biologically active, truncated form of GIP (1-30) have been localized to alpha cells of both mouse and human islets, which is stimulated and secreted in response to arginine.109 The DPP4-mediated degradation product GIP 3-42 has also been demonstrated to act as a GIPR antagonist.43 However, the importance of DPP4-mediated regulation of GIP within the islet is complicated by observations that in states of T2D, the GIPR undergoes desensitization and degradation.110, , -113