Table 1410

Production by many cells, especially the liver

Production dependent on HGH

Production requires the presence of androgens

Actions much like insulin

Can produce hypoglycemia

Increases protein synthesis and anabolic activity

Levels decrease with severe trauma, infection

Attenuates stress-induced hypermetabolism receptor is expressed in many different tissues, and the active peptide is bound in plasma by IGF binding proteins. IGF increases systemic nitrogen retention and protein synthesis. However, its anabolic activity is difficult to distinguish from that of HGH, as HGH needs to be present in order for IGF-1 to be produced and to have anabolic actions (Table 14.10). The combination of HGH and IGF-1 delivery results in a synergistic anabolic effect.66

The wound effects of HGH are also considered to be due in part to IGF-1.66 IGF-1 production is also dependent on sufficient levels of circulating androgens.62 Therefore, a close interrelationship exists between all of the anabolic hormones. IGF-1 levels are decreased with aging and also with a major bodily insult, such as trauma or sepsis, as are the other anabolic hormones. The decrease in IGF-1 levels increases the net nitrogen losses caused by wounding.

Results of Exogenous igf-1 Use

Properties of IGF-1 are summarized in Table 14.11. Metabolic properties include increased protein synthesis, a decrease in blood glucose, and an attenuation of stress-induced hypermetabolism, the latter two properties being quite different from HGH.67-69 The attenuation of stress-induced hypermetabolism is a favorable property of IGF-1. The major complication is hypoglycemia. Clinical trials using an IGF-1 infusion have focused on demonstrating increased anabolic activity.74-76 Increased protein synthesis and nitrogen retention has been reported in burns, head injury, and HIV-induced catabolic states.7475

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