Abstract
Most of serum IGF-I circulates as a complex bound to a specific binding protein (BP 3) and to an acid-labile subunit. It has been described that in adults 5% of total serum IGF-I can circulate as a free (F) fraction and it has been proposed that the free fraction would be a better marker of biological actions than the bound fraction. The aim of the present work was to evaluate serum F IGF-I by absorbing the F fraction with a cartridge of octadecyl silyl silica (SEP-PAK C18) and eluting it with 75% ethanol acid 0.01 M HCI, following the technique of Hizuka et al. Twenty one normal children (chronological age 0.32-7 years) and 5 normal adults were studied. A significant decrease of serum F IGF-I (y = 7.26 ng/ml -0.48 x, r= -0.445, p < 0.043) and of % F IGF-I (r=â0.55, p < 0.01) as a function of age was observed in children, to reach adult values (X ± DS F IGF-I: 5.04 ± 1.97 ng/ml, percentage of total 4.15 ± 1.7) by the age of 7 years. It is concluded that, different to serum total IGF-I, serum F IGF-I shows parallelism with growth velocity during the first years of life.
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