Effects of insulin-like growth factor-I and growth hormone in models of parenteral nutrition

Background: Administration of growth factors such as growth hormone (GH) an d insulin-like growth factor-I (IGF-I) is being investigated as a strategy to promote nitrogen accretion in catabolic patients who may require total p arenteral nutrition (TPN). IGF-I has advantages compared with GH because IG F-I enhances insulin sensitivity, is effective in conditions of GH resistan ce, and selectively stimulates the gastrointestinal and immune systems. Met hods: Experiments were conducted to evaluate the anabolic and metabolic eff ects associated with administration of recombinant human GH or IGF I in rat s subjected to clinically relevant stress and maintained with TPN. Results: Administration of IGF-I, but not GH, attenuates dexamethasone-induced prot ein catabolism and increases insulin sensitivity. Simultaneous treatment wi th GH and IGF-I additively increases the serum concentration of IGF-I, whol e-body anabolism, and lipid oxidation. GH or IGF-I when given alone produce s similar increases in the serum concentration of IGF-I. However, GH select ively increases skeletal muscle mass whereas IGF-I selectively attenuates t he intestinal atrophy and abnormal intestinal ion transport induced by TPN. These tissue-selective anabolic effects of GH and IGF-I are associated wit h differential increases in protein synthesis in skeletal muscle and jejunu m, respectively. Conclusions: Simultaneous treatment with GH and IGF-I may offer the greatest clinical efficacy because of improved nitrogen retention in association with enhanced lipid oxidation and stimulation of protein sy nthesis in multiple tissue types.