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 recepto r deficiency (GHRD). Of the total circulating IGF-I and IGF-II, 70% wa s 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 m easured within the 150 kDa IGFBP-3 region. Administration of IGF-I alt ered 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. Simila rly, serum concentrations of IGFBP-3 and the acid-labile subunit, meas ured by radioimmunoassay, were unaltered. Thus, administration of IGF- I to patients with GHRD was unable to correct the aberrant distributio n of IGFs among the IGFBPs.