Exercise‐induced changes in insulin‐like growth factors and their low molecular weight binding protein in healthy subjects and patients with growth hormone deficiency

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Abstract
Serum concentrations of insulin‐like growth factors 1 and 2 (IGF‐1 and IGF‐2), the low molecular weight form of IGF binding protein (IGFBP‐1), insulin, C‐peptide and GH were determined in six healthy subjects and four patients with GH deficiency during 30 min of moderate physical exercise on the cycle ergometer. The load corresponded to 60% of individual maximal oxygen uptake. IGF‐1 and IGF‐2 were determined by radioimmunoassays developed with antibodies isolated from immunized hens egg‐yolk after separation by automated acid gel filtration of serum samples prior to assay. Significant increases in the serum concentrations (mean±SEM) of IGF‐1 (157±24 to 196 ± 29 μg l‐1, P‐1, P< 0.01) were seen in the healthy subjects after 10 min of exercise. The mean percentage increase was 26 ± 5% for IGF‐1 and 50± 11% for IGF‐2. No relation to the GH release was found. In GH‐deficient patients the mean IGF‐2 concentration rose 48 ± 17% from basal 216 ± 63 μg 1‐1 to a peak concentration of 324 ±115 μg 1‐1 (P‐1 to a peak concentration of 55 ±27 μg 1‐1 was not significant. The serum IGFBP‐1 concentration did not change during exercise, while insulin and C‐peptide concentrations, as well as blood glucose, decreased in both healthy subjects and GH‐deficient patients. In conclusion, exercise induced an increase in the serum concentrations of IGF‐1 and IGF‐2 independently of the GH response. It may be hypothesized that IGFs have a physiological role in the glucose transport into working muscles.