The effect of growth hormone on the insulin-like growth factor system during fasting.
The present study investigates the possible stimulatory effect of endogenous GH on IGF and IGF-binding protein (IGFBP) levels during fasting. Eight normal subjects were examined on four occasions: 1) in the basal postabsorptive state; 2) after 40 h of fasting; 3) after 40 h of fasting with somatostatin suppression of GH; and 4) after 40 h of fasting with suppression of GH and exogenous GH replacement. The two somatostatin experiments were identical in terms of hormone replacement (except for GH). Short-term fasting led to a 50% reduction in free IGF-I. The reduction in free IGF-I was paralleled by an increase in IGFBP-1, an increase in the complex formation of IGFBP-1 and IGF-I, and a modest reduction in IGFBP-3 proteolysis. GH deprivation during fasting led to a 35% reduction in total IGF-I and a 70% reduction in free IGF-I. GH replacement increased free and total IGF-I to levels similar to those observed during plain fasting and decreased IGFBP-1, however, without affecting IGFBP-1-bound IGF-I. Finally, IGFBP-3 proteolysis was slightly increased by GH replacement. In conclusion, the major new finding of the present study is that the GH hypersecretion seen during short-term fasting is not merely secondary to a reduction in IGF bioactivity.
Nørrelund
Helene
H
Medical Department M (Endocrinology and Diabetes), Aarhus Kommunehospital, Aarhus, Denmark.
Frystyk
Jan
J
Jørgensen
Jens Otto Lunde
JO
Møller
Niels
N
Christiansen
Jens Sandahl
JS
Ørskov
Hans
H
Flyvbjerg
Allan
A
D000328:Adult; D010450:Endopeptidases / Q000378:metabolism; D005215:Fasting / Q000502:physiology*; D006728:Hormones / Q000008:administration & dosage; D019382:Human Growth Hormone / Q000097:blood*; D006801:Humans; D015592:Immunoradiometric Assay; D007328:Insulin / Q000097:blood; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood*; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D013004:Somatostatin / Q000008:administration & dosage
D006728:Hormones; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D018972:Insulin-Like Growth Factor Binding Protein 3; D019382:Human Growth Hormone; D013004:Somatostatin; D007334:Insulin-Like Growth Factor I; D010450:Endopeptidases; C080473:insulin-like growth factor binding protein-3 protease