Additionally, the relationship between GLP-1R and glucagon was shown, which was reflected in experimental studies: the level of glucagon positively correlated with GLP-1 in patients in the healthy donors (r = 0.527, p < 0.05) and negatively correlated with GLP-1 in patients with T2DM (r = −0.343, p < 0.05). Here, GCG is linked to type 2 diabetes mellitus.