[Leptin and obesity]

Obesity appears as a result of the balance between the individual's calorie consumption and energy expenditure. There are numerous neuroendocrinological factors responsible for regulating the energy metabolism; however, it was the discovery of the leptin that opened the way for numerous investigations destined to lay bare the mechanisms involved in this homeostasis. The leptin is a peptide of 167 amino acids, with a signal sequence of 21 amino acids that split up before the leptin enters the circulatory torrent. The white adipose tissue is the main producer of leptin, acting as a "marker" of the body's energy reserves. Leptin intervenes in different physiological processes such as the regulation of the energy balance, the control of appetite and body weight, the metabolism of fats and glucides or reproduction, amongst others. There are numerous ob receptors on the central nervous system and in different regions of the hypothalamus that are involved in part of the observed effects of this hormone. Besides, there are ob receptors in numerous peripheral tissues such as the lung, kidney, liver, skeletal muscle, adipose tissue, testicles, pancreatic islets and haematopoietic cells. The study of its regulation, connections and effects on the central nervous system are proving to be essential for an understanding of the system of regulation of the energy balance and of the mechanisms involved in the development of obesity.