Zucker Obese (ZO) rats lack a functional leptin receptor, which results in hyperphagia, obesity and insulin resistance.11 Yet, these animals remain normoglycemic through a compensatory increase in insulin secretion maintained through increased β-cell mass and possibly function.12, 13, 14 Selective inbreeding of glucose-intolerant ZO rats led to the establishment of Zucker diabetic fatty (ZDF) rats.11 Male ZDF (mZDF) rats spontaneously develop diabetes between 6 and 12 weeks of age. This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.