Regulation of the growth hormone binding proteins in human plasma

The plasma high affinity growth hormone binding protein corresponds to the extracellular binding domain of the liver membrane receptor. A distinct higher molecular weight protein, which binds GH with low affinity and high capacity, is present in the human plasma. In man, the biosynthesis and the exact functions of the GH binding proteins have to be clarified. The GH binding proteins are differently regulated; they are under a multihormonal control. The high affinity binding protein is low in neonates, increases after the first year of life, and reaches its highest value in young adult, without sex differences. GH is able to induce the high affinity binding protein, whereas sex steroids can decrease it. States of GH resistance, such as chronic renal failure, and certain idiopathic short statures, are associated with low levels of GH binding protein; in Laron-type dwarfism a defect of the GH receptor gene probably results in the absence of plasma GH binding activity. Recent findings on the regulation of the GH binding protein in man support a parallel regulation of liver membrane GH receptors and plasma binding protein.