[Insulin-like growth factors. Future treatment in catabolism?]

Growth is the result of complex interactions between nutrition, stimulating and inhibiting signal substances, and target cell response to these substances. The insulin-like growth factors, IGF-I and IGF-II, are important growth factors throughout life, and function both as endocrine and paracrine hormones. Their anabolic and growth promoting actions are mediated via the IGF-I receptor, present in all cells apart from liver and adipose cells, which contains the homologous insulin receptor. IGF-I expression is regulated both by nutrition and by other hormones such as insulin and growth hormone (GH), though GH regulation of IGF-I first starts after birth when growth becomes GH- dependent. Treatment with recombinant IGF-I has been shown to normalise growth in children with GH receptor deficiency. IGF peptides in serum and other fluids are always associated with binding proteins (IGFBPs). A family of six polypeptides have been characterised. The various IGFBPs have been suggested to function as storage or transport proteins, or modulators of IGF action on target cells. Proteases which cleave IGFBPs are assumed to increase the bioavailability of IGFs. Most of the IGFs in serum are bound to the GH-dependent IGFBP-3 in ternary complexes which cannot leave the circulation. The serum IGF-I concentration manifests an age-dependent pattern, mainly owing to the age-dependent level of GH production. After increasing during puberty, IGF-I levels then decrease with increasing age.(ABSTRACT TRUNCATED AT 250 WORDS)