A serum prolactin-binding protein: implications for growth hormone

Many membrane receptors have truncated soluble forms that circulate in the blood, and a protein in serum with characteristics of the extracellular dom ain of the human prolactin receptor has recently been identified. Because t he extracellular domain of the prolactin receptor binds human growth hormon e, does the prolactin-binding protein in serum affect the amount of bound c irculating growth hormone? A more general question is whether this serum pr otein has a minor or a major effect on the biological activities of growth hormone and prolactin.