Thus, this model represents early uncomplicated phase of obesity and the results are not confounded by abnormalities of carbohydrate and lipid metabolism, insulin resistance, etc. We observed that the effects of intraperitoneally administered leptin on natriuresis and renal medullary Na+,K+-ATPase were impaired in obese animals. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.