Serum Growth Hormone-Binding Protein (GHBP) Activity is Decreased by Administration of Insulin-Like Growth Factor I in Three Laron Syndrome Siblings with Normal GHBP

Abstract

Three Laron Syndrome (LS) siblings with a post growth hormone (GH) receptor defect for insulin-like growth factor-l (IGF-I) synthesis were found to have serum GH-binding protein (GHBP) levels normal for age. Treatment with recombinant IGF-I (150 μg/kg/day) decreased serum GHBP activity to 62% of the basal value (P < 0.001) in two of the sibs in 1 week and in the third sib after 3 months of therapy. Scatchard analysis of the binding of [¹²⁵I]human GH (hGH) to GHBP in patients' sera before and during therapy revealed affinity constants K_a = 1.55-1.80 × 10⁹ M ^-1, similar to that of sera from healthy subjects. Variations in binding are due to changes in the binding capacity. IGF-I may be a regulatory factor for serum GHBP activity in man.