TY - CHAP M1 - Book, Section TI - Chapter 520. Mechanisms of Hormone Action A1 - Grimberg, Adda A1 - Dimeglio, Linda A. A2 - Rudolph, Colin D. A2 - Rudolph, Abraham M. A2 - Lister, George E. A2 - First, Lewis R. A2 - Gershon, Anne A. PY - 2011 T2 - Rudolph's Pediatrics, 22e AB - A hormone is a molecule that is secreted into the circulation to influence the function of target cells in another tissue or organ. In addition to distant targets via the circulation (endocrine action), many hormones also influence the function of the cells that secreted them (autocrine action) or that of adjacent cells (paracrine action). For example, when insulin, produced by pancreatic beta cells, stimulates glucose storage and oxidation, protein synthesis, and lipid storage in the liver, muscle and fat, it is acting in an endocrine fashion; when it inhibits glucagon secretion by the nearby pancreatic alpha cells, it is acting in a paracrine fashion. Frequently, the endocrine and autocrine/paracrine actions of a hormone lead to the same effect. For example, growth hormone (GH) stimulates hepatic production of insulin-like growth factor I (IGF-I), the main mediator of somatic growth in childhood. It has been shown that mice with targeted deletion of IGF-I expression in only the liver grow to normal size, despite a 75% reduction in their circulating IGF-I concentration.1 This seminal experiment demonstrated the importance of autocrine and paracrine IGF-I production to body growth. SN - PB - The McGraw-Hill Companies CY - New York, NY Y2 - 2024/03/28 UR - accesspediatrics.mhmedical.com/content.aspx?aid=7052294 ER -