Leptin is a protein hormone with important effects in regulating body weight, metabolism and reproductive function. The protein is approximately16 kDa in mass and encoded by the obese (ob)gene. leptin is expressed predominantly by adipocytes, which fits with the idea that body weight is sensed as the total mass of fat in the body. Smaller amounts of leptin are also secreted by cellsin the epithelium of the stomach and in the placenta. Leptin receptors are highly expressed in areas of the hypothalamus known to be important in regulating body weight, as well as in T lymphocytes and vascular endothelial cells Synonyms: OB Protein, Obesity Protein, OBS, Obesity factor.