Focus on leptin, a pleiotropic hormone

Leptin, the product of the obese gene located on human chromosome 7 (7q31.3), is a cytokine-type hormone mainly secreted by the white adipose tissue and in a lesser extent by placenta, skeletal muscle, gastric mucosa, mammary and salivary glands. Leptin, released by the adipocytes into the bloodstream in positive correlation to the fat mass, plays a key role in the body weight control. Indeed, it suppresses the appetite and increases the metabolic rate, primarily acting through central pathways. Conversely, during starvation leptinemia rapidly falls, leading to a reduction of the energy expenditure and allowing a longer survival. Recently, pleiotropic effects of leptin have been identified, consisting in modulation of several processes, such as thermogenesis, reproduction, hemostasis, angiogenesis, hematopoiesis, osteogenesis, chondrogenesis, neuroendocrine and immune functions, as well as arterial pressure control. Leptin has been also suggested as neuroendocrinologic marker of hypervigilant state. Ultimately, it may be the signal that integrates metabolic, vascular, neuroendocrine, immune and behavioural responses. In this paper, the more recent information on leptin is reviewed and summarized.