Many of the metabolic actions of
growth hormone (GH) are mediated through
insulin-like growth factors or
somatomedins. Recombinant human
insulin-like growth factor-I (rhIGF-I) has a dichotomous
insulin-like and GH-like action when used in different clinical situations in humans. Its effects on carbohydrate metabolism show a prominent increase in total
insulin sensitivity, causing
hypoglycemia in higher doses and maintaining normal
glucose homeostasis in lower doses. This
polypeptide selectively stimulates whole body
protein synthesis with no effect on proteolysis when given in doses of 100 micrograms/ kg subcutaneously twice daily for at least 5-7 days, effects which are indistinguishable from those of GH. This contrasts with the marked suppression of proteolysis observed when higher doses are given, similar to the effects observed with
insulin. When used in combination with rhGH, rhIGF-I has a synergistic effect, improving total
nitrogen retention in calorically deprived subjects, yet it does not cause any greater enhancement of whole body
protein anabolism in normally fed volunteers than giving rhGH and rhIGF-I individually. This suggests a common pathway for
IGF-I and GH enhancing
protein anabolism in the normally fed state. rhIGF-I also stimulates linear growth in children with defects in the GH receptor. Recent data show that this potent
growth factor has a potential advantage over GH in the treatment of severe
protein catabolic states, particularly the glucocorticosteroid-dependent model, as it ameliorates the marked increase in
protein catabolism caused by the
steroids, but without a diabetogenic effect. Here, a brief overview is provided of available human data on the actions of this
peptide on
carbohydrate,
lipid, and
protein metabolism, linear growth, and its
anabolic effects. rhIGF-I offers promise in the treatment of selective
growth disorders and in
protein catabolic and
insulin-resistant states.