Leptin

Leptin is an adipocyte hormone that signals nutritional status to the centr al nervous system (CNS) and peripheral organs. Leptin is also synthetized i n the placenta and in gastrointestinal tract, although its role in these ti ssues is not yet clear. Circulating concentrations of leptin exhibit pulsat ility and circadian rhythmicity. The levels of plasma leptin vary directly with body mass index and percentage body fat, and leptin contributes to the regulation of body weight. Leptin plasma concentrations are also influence d by metabolic hormones, sex, and body energy requirements. Defects in the leptin signaling pathway result in obesity in animal models. Only a few obe se humans have been identified with mutations in the leptin gene or in the leptin receptor; however, most cases of obesity in humans are associated wi th high leptin levels. Thus, in humans obesity may represent a state of lep tin resistance. Minute-to-minute fluctuations in peripheral leptin concentr ations influence the activity of the hypothalamic-pituitary-ovarian and hyp othalamic-pituitary-adrenal axes, indicating that leptin may be a modulator of reproduction, stress-related endocrine function, and behavior. This sug gests potential roles for leptin or its antagonists in the diagnosis, patho physiology and treatment of several human diseases. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.