The effect of GH administration (5 mg twice daily for 5 days) on the serum concentration of insulin-like growth factors I and II (IGF I and IGF II) was compared in GH-deficient subjects during a period of fasting and a period of normal food intake. Before treatment with GH, the mean concentration of IGF I was 35.2 ± 7.5 ng⁄ml. After 5 days of GH treatment in the fed state, IGF I increased nearly 10-fold to 317.4 ± 55.9 ng⁄ml (P < 0.001 vs. pretreatment value). During fasting, identical treatment of this group resulted in only a modest increase of IGF I to 81 ± 23 ng⁄ml (P < 0.001 vs. fed state response). The mean serum concentration of IGF II before therapy was reduced to only 174 ± 37 ng⁄ml. With GH given in the fed state, IGF II increased to 793 ± 171 ng⁄ml. These data suggest that IGF II, like IGF I, is GH dependent and, hence, a somatomedin. GH therapy in the fasted state increased IGF II o t 437 ± 70 ng⁄ml (P = 0.05 vs. fed state response).

I n a second study, six normal subjects were fasted for 72 h. The integrated serum IGF I concentration (24 samples⁄subject) decreased 42% by the third day of fasting; IGF II decreased 27% during the same period.

The data from both studies are consistent with the conclusion that the metabolic milieu of fasting inhibits IGF secretion in man. IGF I appears to be affected more than IGF II. (J Clin Endocrinol Metab55: 999, 1982)