[Leptin--a new way to diet?].

The relatively constant level of body fat in the adult mammal is explained by the lipostat theory as follows: A factor is released from adipose tissue in amounts that reflect total body fat content. This factor is then registered by the hypothalamic centres that regulate appetite. The theory has gained particular support from parabiotic experiments in genetically fat mice, amongst whom the so-called ob/ob mice appear to produce too little of the factor, whilst signal transduction to the satiety centre appears to be defective in the so-called db/db mice. The two genetic defects have recently been clarified, and it has been shown that the normal ob gene nodes for a protein called leptin. Leptin is released from adipose tissue, and its plasma concentration reflects total body fat. The normal db-gene codes for a hypothalamic receptor for leptin. These crucial discoveries have greatly supported the correctness of the lipostat theory. At present, extensive investigations of the roles of leptin and the leptin receptor in human adiposity are in progress.