The insulin-like growth factor binding protein-1 in low and high insulin responders before and during dexamethasone treatment

Abstract

To investigate the influence of normal insulin levels on levels of the insulin-like growth factor binding protein-1 (IGFBP-1), we measured this peptide postabsorptively and during hyperglycemic clamp in 17 healthy subjects, nine with low insulin response (LIR) and eight with high insulin response (HIR). The study was performed before and after 60 hours of treatment with dexamethasone 6 mg/d. The fasting levels of IGFBP-1 were significantly higher in LIR, 36 ± 2.5 μg/L, than in HIR, 22 ± 2.6 μg/L ( P < .01), while no differences in glucose, insulin, and C-peptide concentrations were found. Dexamethasone induced an increase in basal concentrations of insulin, while IGFBP-1 levels decreased to 18.8 ± 2 μg/L in LIR ( P < .01) and to 14.0 ± 0.9 μg/L in HIR ( P < .05). There was no correlation between the individual basal IGFBP-1 concentrations and basal insulin levels. In contrast, basal levels of IGFBP-1 were inversely correlated to the integrated insulin or C-peptide concentrations during the hyperglycemic clamp both before ( r = −.67, P < .01) and during dexamethasone ( r = −.79, P < .001). Dexamethasone, which increased the insulin resistance, did not change the relationship between basal IGFBP-1 and the glucose-induced insulin release. In conclusion, the morning levels of IGFBP-1 in healthy subjects reflect the acute β-cell responsiveness to glucose, which may correspond to integrated diurnal insulin levels. The inhibitory effects of dexamethasone on the morning levels of IGFBP-1 can be explained by attendant hyperinsulinemia.