NUTRITIONAL REGULATION OF THE GROWTH-HORMONE AND INSULIN-LIKE GROWTH FACTOR-BINDING PROTEINS

Both growth hormone (GH) and insulin-like growth factors (IGFs) associ ate 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 concentrat ions in circulation are decreased in severe malnutrition, reflecting a decrease in tissue GH receptor abundance. IGFs are bound to 6 differe nt 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 eleva tions after overnight fasting and rapid postprandial decreases. IGFBP- 2 is highly dependent on dietary protein intake. Nutritional factors m ay regulate the tissue availability and the biological actions of IGFs by their actions on IGFBPs.