Obesity is associated with multiple alterations in the endocrine system, including abnormal circulating blood hormone concentrations, which can be due to changes in the pattern of their secretion and/or metabolism, altered hormone transport and/or action at the level of target tissues. In recent years a great stimulus in both basic and clinical research has, on one hand, produced a great deal of knowledge on the pathophysiology of obesity, and, on the other, led to the discovery of new hormones, such as leptin (1) and orexins (2).
This chapter reviews the main alterations in the classic endocrine systems, specifically those related to the hypothalamic-pituitary-gonadal (HPG) axis, the growth hormone/insulin-like growth factor 1 (GH/IGF-1) axis, and the hypothalamic-pituitary-adrenal (HPA) axis. The discussion will focus on human endocrinology, and animal studies will be referred to only when relevant to the organization of current knowledge. Several other endocrine systems will not be discussed, and readers are referred to extensive recent reviews in the field (3,4).
The recent discovery of the product of the ob gene, leptin, has pointed to the role of adipose tissue as an endocrine organ, capable of interacting with the central nervous system and other peripheral tissues by an integrated network, mainly devoted to the regulation of the energy balance and fuel stores.
The impressive growth of knowledge that has followed the discovery of leptin in 1996 is under continuous investigation. Other chapters of this book review this exciting topic, which will probably radically modify our clinical and therapeutic approach to obesity and related metabolic disorders in the next few years.
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