COPA and diabetes mellitus: In thisregard, xenin has been shown to potentiate the insulinotropic actions of GIP inrodent models of diabetes.18, , , -22,24, -26 Whilst the precisemechanism of xenin-induced GIP potentiation remains to be fullyelucidated,25,27,37 it may be linked to acetylcholine M3 receptorsignalling on pancreatic beta cells.25 However, there is also good evidence for a direct effect of xenin on beta cells,6 that is reinforced by knowledge that xenin is produced and secretedlocally within islets.10