Serum Levels of Free Insulin-Like Growth Factor (IGF)-I in Normal Children.
Serum levels of free insulin-like growth factor (IGF)-I were measured by immunoradiometric assay (IRMA) in fasting sera of 137 normal boys and 120 normal girls aged from 8 to 15 yr to study relationships between free IGF-I levels and ages, total IGF-I, IGF binding protein (IGFBP)-1, IGFBP-3, and acid-labile subunit (ALS) levels. In both sexes, serum free IGF-I levels and the ratios of free IGF-I to total IGF-I were significantly higher in the pubertal age groups than in the prepubertal age groups. Serum levels of free IGF-I showed a significant positive correlation with those of total IGF-I, IGFBP-3 and ALS, while they showed a significant negative correlation with those of IGFBP-1. These observations suggest that increase in serum free IGF-I levels during puberty is caused by a dramatic increase in total IGF-I, rather than IGFBP-3, and a decrease in IGFBP-1. Also, high free IGF-I levels may play an important role in pubertal growth spurt.
Department of Growth and Puberty, National Research Institute for Child Health and Development, Tokyo, Japan ; Department of Growth and Puberty, National Research Institute for Child Health and Development, Tokyo, Japan.
Atsuko
A
Nimura
Department of Growth and Puberty, National Research Institute for Child Health and Development, Tokyo, Japan.
Noriyuki
N
Katsumata
Department of Growth and Puberty, National Research Institute for Child Health and Development, Tokyo, Japan.
Toshiaki
T
Tanaka
IGF binding protein (IGFBP)-1; IGFBP-3; acid-labile subunit (ALS); free insulin-like growth factor (IGF)-I; total IGF-I