Metabolic homeostasis is ensured by complex interactions between the Central Nervous System (CNS) and peripheral tissues. The CNS controls the periphery by regulating the fraction of energy which enters the organism (food intake) and that which leaves the organism (thermogenesis). To be able to exert this role, the CNS receives signals from peripheral organs which convey information on the extent of body energy stores. When this information is integrated, the CNS responds via efferent regulatory signals channeled mostly via the endocrine and the autonomic nervous system. Amongst the several feedback signals arising from peripheral tissues, leptin and ghrelin are important ones. Leptin is a hormone that is synthesized in adipose tissue. Once secreted into the blood and reaching the CNS, leptin acts as a satiety factor upon binding to its long hypothalamic receptor isoform. Ghrelin is a hormone synthesized in the stomach. It is the endogenous ligand for the growth-hormone secretagogue receptor, but it also stimulates food intake. At the level of the hypothalamus, leptin and ghrelin regulate several neuropeptides having effects on both food intake and energy dissipation. Anorectic neuropeptides, such as corticotropin-releasing hormone (CRH), "Cocaine-and- Amphetamine-Regulated Transcript" (CART), the melanocortin system comprising "Proopiomelanocortin" (POMC), the "a-Melanocyte- Stimulating Hormone" (α-MSH), and the MC3-MC4 types of receptors, are stimulated by leptin, thereby decreasing food intake. In contrast, orexigenic neuropeptides, such as neuropeptide Y (NPY), "Melanin-Concentrating Hormone" (MCH), the "Agouti-Related Peptide" (AgRP) and orexins, are inhibited by leptin, but stimulated by ghrelin, resulting in a decrease, or an increase in food intake, respectively.

Nephrology