Certainly, human patients with T2DM display a blunted incretin effect of GLP-1, and defects in meal-induced intestinal GLP-1 secretion (91), suggesting that the paracrine action of alpha-cell-derived GLP-1 may be necessary to combat this diminished peripheral incretin action of gut-derived GLP-1. Here, GLP1R is linked to type 2 diabetes mellitus.