Nutritional regulation of the growth hormone and insulin-like growth factor-binding proteins

Both growth hormone (GH) and insulin-like growth factors (IGFs) associate with specific binding proteins. Besides control by hormones, these binding proteins are nutritionally regulated. The GH-binding protein (GHBP) is the extracellular portion of the GH receptor. Its concentrations in circulation are decreased in severe malnutrition, reflecting a decrease in tissue GH receptor abundance. IGFs are bound to 6 different binding proteins (IGFBPs). IGFBP-3 is relatively stable and is only depressed after prolonged periods of severe malnutrition. In contrast, IGFBP-1 is regulated acutely by nutrient intake, showing major elevations after overnight fasting and rapid postprandial decreases. IGFBP-2 is highly dependent on dietary protein intake. Nutritional factors may regulate the tissue availability and the biological actions of IGFs by their actions on IGFBPs.