DICKHOFF, W.W.; Northwest Fisheries Science Center, Seattle; Univ. Washington, Seattle: ENDOCRINE CONTROL OF GROWTH IN VERTEBRATES: AN ALTERNATE VIEW

The conventional view of endocrine control of vertebrate growth is the growth hormone-insulin-like growth factor axis (GH-IGF axis). Operation of the axis is usually described in the sequence of pituitary GH stimulating production of IGF, and both influence growth of tissues. Although this depiction of the GH-IGF axis has heuristic value, it does not give an accurate impression of the operation of the axis in response to the main determinants of growth: dietary ration, dietary composition, and temperature (for poikilotherms). Fasting of vertebrates results almost universally in elevation of plasma GH, and increasing dietary ration typically results in elevation of IGF and reduction in GH. The GH-IGF axis gives the impression that there is a top-down hierarchy of events for endocrine control of growth with the pituitary gland as the main regulator acting through GH production. The role of IGF binding proteins (IGFBP) is de-emphasized in the GH-IGF axis, and the role of GH is over-emphasized. Recent studies of endocrine control of growth argue for a greater importance of IGF, IGFBPs, and insulin than GH. The proposed alternate is the pancreas-liver growth axis in which nutritional input from the gut influences the hepatic production of IGF and IGFBPs and pancreatic production of insulin, which also regulates IGF and IGFBPs. The roles of GH in the alternate axis include seasonal regulation of growth and production of dwarf forms. At the top of the hierarchy in this alternate growth axis are the pancreas and liver, rather that the pituitary gland. It is hoped that this alternate view of the endocrine control of growth will be a useful concept for understanding how vertebrate growth is controlled.