TY - JOUR
T1 - Effect of short-term fasting on free/dissociable insulin-like growth factor I concentrations in normal human serum
AU - Bereket, Abdullah
AU - Wilson, Thomas A.
AU - Blethen, Sandra L.
AU - Fan, Jie
AU - Frost, Robert A.
AU - Gelato, Marie C.
AU - Lang, Charles H.
PY - 1996
Y1 - 1996
N2 - A small portion of circulating insulin-like growth factor I (IGF-I) is detected in the free or readily dissociable state, which is thought to be the metabolically active form. The amount of free/dissociable IGF-I in serum is dependent on a complex interplay between the production rate and the concentrations of IGF-I and IGF-binding proteins (IGFBPs). IGF availability is also influenced by posttranslational changes in IGFBPs that affect the affinity of IGFBPs for IGF-I. In the present study, we examined whether a short term fast (~12 h) alters the serum concentration of free/dissociable IGF-I, and whether these changes are associated with alterations in IGFBP-1 and the proteolysis status of IGFBP-3. Circulating free/dissociable IGF-I concentrations, as assessed by a two-site immunoradiometric assay, did not differ between fasting and 4 h after a morning meal (1.48 ± 0.07 vs. 1.50 ± 0.07 μg/L, respectively). Likewise, free/dissociable IGF-I levels measured by RIA after separation by centrifugal ultrafiltration were not different between the two groups (1.43 ± 0.14 vs. 1.38 ± 0.18 μg/L, respectively). IGF-I bioactivity, as measured by thymidine incorporation by fibroblasts, did not differ in fasting and 4-h postprandial sera. There was no difference in IGFBP-3 and total acid-ethanol-extractable IGF-I concentrations in serum from fasted and fed subjects. In contrast, the concentration of IGFBP-1 in the serum was increased ~5-fold in the fasted state compared to fed values. IGFBP-1 existed in a highly phosphorylated form under fasting conditions. There was no change in IGFBP-3 proteolysis assessed either in vivo or in vitro between the fasting and fed states. The results indicate that a physiologically relevant short term overnight fast does not alter the circulating levels of free/dissociable IGF-I despite a marked elevation in IGFBP-1.
AB - A small portion of circulating insulin-like growth factor I (IGF-I) is detected in the free or readily dissociable state, which is thought to be the metabolically active form. The amount of free/dissociable IGF-I in serum is dependent on a complex interplay between the production rate and the concentrations of IGF-I and IGF-binding proteins (IGFBPs). IGF availability is also influenced by posttranslational changes in IGFBPs that affect the affinity of IGFBPs for IGF-I. In the present study, we examined whether a short term fast (~12 h) alters the serum concentration of free/dissociable IGF-I, and whether these changes are associated with alterations in IGFBP-1 and the proteolysis status of IGFBP-3. Circulating free/dissociable IGF-I concentrations, as assessed by a two-site immunoradiometric assay, did not differ between fasting and 4 h after a morning meal (1.48 ± 0.07 vs. 1.50 ± 0.07 μg/L, respectively). Likewise, free/dissociable IGF-I levels measured by RIA after separation by centrifugal ultrafiltration were not different between the two groups (1.43 ± 0.14 vs. 1.38 ± 0.18 μg/L, respectively). IGF-I bioactivity, as measured by thymidine incorporation by fibroblasts, did not differ in fasting and 4-h postprandial sera. There was no difference in IGFBP-3 and total acid-ethanol-extractable IGF-I concentrations in serum from fasted and fed subjects. In contrast, the concentration of IGFBP-1 in the serum was increased ~5-fold in the fasted state compared to fed values. IGFBP-1 existed in a highly phosphorylated form under fasting conditions. There was no change in IGFBP-3 proteolysis assessed either in vivo or in vitro between the fasting and fed states. The results indicate that a physiologically relevant short term overnight fast does not alter the circulating levels of free/dissociable IGF-I despite a marked elevation in IGFBP-1.
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U2 - 10.1210/jc.81.12.4379
DO - 10.1210/jc.81.12.4379
M3 - Article
C2 - 8954045
AN - SCOPUS:0029797815
VL - 81
SP - 4379
EP - 4384
JO - Journal of Clinical Endocrinology and Metabolism
JF - Journal of Clinical Endocrinology and Metabolism
SN - 0021-972X
IS - 12
ER -