INS and obesity due to melanocortin 4 receptor deficiency: Abdel-Halim et al. previously demonstrated that AC3 mRNA expression in pancreatic islets of GK rat was overexpressed compared with Wistar rat.11 GK rat is the spontaneously diabetic animal model and useful to study the defective β-cell function with resulting impairment of glucose-stimulated insulin release.12 In men, there is a co-dependent relationship between T2D and obesity,27 whereas the GK rat is diabetic but not obese.