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) and insulin-like growth factor-I (IGF-I) is being investigated as a strategy to promote nitrogen accretion in catabolic patients who may require total parenteral nutrition (TPN). IGF-I has advantages compared with GH because IGF-I enhances insulin sensitivity, is effective in conditions of GH resistance, and selectively stimulates the gastrointestinal and immune systems.
METHODS: Experiments were conducted to evaluate the anabolic and metabolic effects associated with administration of recombinant human GH or IGF-I in rats subjected to clinically relevant stress and maintained with TPN.
RESULTS: Administration of IGF-I, but not GH, attenuates dexamethasone-induced protein catabolism and increases insulin sensitivity. Simultaneous treatment with GH and IGF-I additively increases the serum concentration of IGF-I, whole-body anabolism, and lipid oxidation. GH or IGF-I when given alone produces similar increases in the serum concentration of IGF-I. However, GH selectively increases skeletal muscle mass whereas IGF-I selectively attenuates the intestinal atrophy and abnormal intestinal ion transport induced by TPN. These tissue-selective anabolic effects of GH and IGF-I are associated with differential increases in protein synthesis in skeletal muscle and jejunum, 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 synthesis in multiple tissue types.