Effects of insulin‐like growth factor I treatment on the molecular distribution of insulin‐like growth factors among different binding proteins

The molecular distribution of insulin‐like growth factor I (IGF‐I) and IGF‐II among the IGF binding proteins (IGFBPs) was studied before and during IGF‐I therapy in Ecuadorean adults with growth hormone receptor deficiency (GHRD). Of the total circulating IGF‐I and IGF‐II, 70% was carried by the 150 kDa complex in normal subjects, while in patients with GHRD, 50% of serum IGF‐I, but only 30–35% of serum IGF‐II, was measured within the 150 kDa IGFBP‐3 region. Administration of IGF‐I altered the concentration of IGF‐I and IGF‐II, although the percentage of total IGF measured within each IGFBP region was not affected, as the increase in IGF‐I and the decrease in IGF‐II were proportional. Similarly, serum concentrations of IGFBP‐3 and the acid‐labile subunit, measured by radioimmunoassay, were unaltered. Thus, administration of IGF‐I to patients with GHRD was unable to correct the aberrant distribution of IGFs among the IGFBPs.