NUTRITIONAL REGULATION OF INSULIN-LIKE GROWTH-FACTOR-I

Several lines of evidence indicate that in the human, insulin like gro wth factor-I (IGF-I) is nutritionally regulated. Both energy and prote in availability are required for maintenance of IGF-I. Measurements of serum IGF I constitute a sensitive means for monitoring the response of acutely ill patients to nutritional intervention. Serum IGF-I may a lso serve as a marker for evaluation of nutritional status. Our findin gs and those of others in animal models suggest that nutrients influen ce synthesis and action of IGF-I and its binding proteins (IGFBPs) at multiple levels. In fasting, liver growth hormone (GH) binding is decr eased, providing one explanation for decreased IGF-I. In protein restr iction, GH receptors are maintained, but there is evidence for a postr eceptor defects. The latter results from pretranslational and translat ional defects. Amino acid availability to the hepatocytes is essential for IGF-I gene expression. Protein malnutrition not only decreases IG F-I production rate, but also enhances its serum clearance and degrada tion. Finally, there is evidence for selective organ resistance to the growth-promoting effects of IGF-I in protein restricted rats. Copyrig ht (C) 1995 by W.B. Saunders Company.