A role of free insulin-like growth factor-I in dawn phenomenon in children and adolescents with type 1 diabetes mellitus.

It has been hypothesized that a decreased amount of the free form of insulin-like growth factor-I (fIGF-I) results in morning hyperglycemia in patients with type 1 diabetes mellitus. In this study, we attempted to clarify the role of fIGF-I in relation to total IGF-I (tIGF-I) and its related peptides or proteins in type 1 diabetes. Forty-seven patients with type 1 diabetes, mean age 13.7 years, were evaluated. Blood samples were obtained for the measurement of BG at 0200, 0400 and 0700, and of insulin, total IGF-I (tIGF-I), fIGF-I, IGFBP-1 and IGFBP-3 at 0700. The SD scores (SDS) were determined for the levels of tIGF-I, fIGF-I, IGFBP-1 and IGFBP-3 by using Japanese reference data. The morning increase in BG (OBG(4-7)) correlated significantly with fIGF-I SDS (r=-0.352, p=0.0152) and IGFBP-1 SDS (r=0.438, p=0.0021), but did not correlate significantly with the fIGF-I level itself or the ratio of fIGF-I to tIGF-I (f/t IGF-I ratio). Hereupon, the f/t IGF-I ratio correlated positively with fIGF-I SDS (r=0.541, p=0.0003). The mean ± SD in the f/t IGF-I ratio was 0.94±0.43%, and that in fIGF-I SDS was -0.50±1.32. The level of IGFBP-1 SDS correlated negatively with fIGF-I SDS (r=-0.472, p=0.0008) and insulin (r=-0.365, p=0.0116). We suggest that the morning level of fIGF-I SDS, rather than the fIGF-I level itself, may be a useful marker of decreased insulin-like bioactivity in the dawn phenomenon in type 1 diabetes mellitus.