Response to Fukui et al.

In response to the letter by Fukui et al. (1) in this issue of Diabetes Care, we first must comment on the possible interaction between leptin and insulin, independent of body fatness. Leptin is mainly an adipocyte-secreted protein. Leptin, the obese (ob) gene product, is an adipose tissue hormone that has been closely linked to the amount of body-fat stores. Most of the research following the discovery of leptin was focused on the role it plays in body weight regulation, aiming to illuminate the pathophysiology of human obesity. However, more data are emerging that show that leptin is not only important in the regulation of food intake and energy balance, but that it also has a function in metabolism, as well as in normal sexual maturation and reproduction. Leptin may thus be considered a new endocrine mediator, besides its obvious role in body weight regulation. A possible interaction between leptin and insulin was first suggested by the …