GCG and obesity due to melanocortin 4 receptor deficiency: Specifically, the administration of 1 mg/kg of Tacrolimus during 15 days in rats with established obesity and metabolic syndrome, induced hyperglycaemia and changes in specific beta cell nuclear factors like MafA, FoxO1A, PDX-1, NeuroD1, insulin and glucagon and reduced beta cell proliferation with no signs of apoptosis.