Growth hormone-binding proteins in plasma.
Two growth hormone-binding proteins (GHBPs), one with high and the other with low affinity, have recently been described in the blood of humans and several other species. The high-affinity GHBP represents a circulating fragment of the GH receptor, encompassing its extracellular domain. The molecular nature of the low-affinity GHBP is not known in detail. GHBPs form complexes with circulating GH, prolong its biological half-life, restrict its distribution in the body, and modulate the binding of GH to receptors in tissues. Their net effect in vivo is to enhance GH action. The level of high-affinity GHBP in plasma probably reflects receptor concentrations in tissues. The level/activity of GHBP is linked to GH action, and several congenital or acquired conditions with altered GHBP levels are characterized by parallel changes in GH action (Laron-type dwarfism, pygmy dwarfism, malnutrition, obesity, insulin-dependent diabetes mellitus, liver cirrhosis, renal insufficiency). The GHBP/receptor level is nutritionally regulated, with levels low in undernutrition and high in overnutrition. Regulation of lean body mass anabolism/catabolism at the level of the GHBP/receptor provides a rational explanation for the derangements in the GH axis and their biological consequences (retarded or accelerated somatic growth) observed in nutrition disorders.
Baumann
G
G
Department of Medicine, Northwestern University Medical School, Chicago, Illinois 60611.
Mercado
M
M
D000818:Animals; D002352:Carrier Proteins / Q000097:blood* / Q000378:metabolism / Q000502:physiology; D005786:Gene Expression Regulation; D013006:Growth Hormone / Q000378:metabolism / Q000502:physiology; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D051379:Mice; D009748:Nutrition Disorders / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D011986:Receptors, Somatotropin / Q000235:genetics / Q000378:metabolism; D013002:Somatomedins / Q000378:metabolism
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D011986:Receptors, Somatotropin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; C051815:somatotropin-binding protein