The change in the circulating insulin-like growth factor binding protein 1 isoform pattern during the course of oral glucose tolerance test

There is a tight connection between insulin-like growth factor binding protein 1 (IGFBP-1) and nutrient/energy supply, suggesting modulation of the short-term insulin-like activity and glucose homeostasis by IGFBP-1. Differential phosphorylation of IGFBP-1 alters its affinity for insulin-like growth factors (IGFs) and its capacity to modulate cellular response. The object of this study was to define the time course of changes in the IGFBP-1 isoform pattern during an oral glucose tolerance test. Besides changing in counterdirections, the alterations in glucose/insulin/C-peptide and IGF-I/IGFBP-1 concentrations were phase-shifted. Denaturing electrophoresis revealed that the IGFBP-1 proteolytic activity was not increased after glucose ingestion. In native electrophoresis, the isoform that moved most anodically, with the greatest phosphate content, was markedly reduced during the course of oral glucose tolerance test; and it disappeared after 3 hours. Our data show that both a change in the total amount of IGFBP-1 and an alteration in the relative amount (ratio) of the specific phosphoforms of IGFBP-1 are part of the mechanism involved in modulation of the insulin-like activity.