COMPARATIVE CONCENTRATIONS OF GROWTH HORMONE-BINDING PROTEIN IN MATERNAL CIRCULATION, FETAL CIRCULATION, AND AMNIOTIC-FLUID

Fetal growth is thought to be independent of the concentration of GH, although circulating levels of GH are high in the human fetus. To eluc idate the role of GH in fetal development, levels of GH-binding protei n (GHBP) were measured in the serum of nonpregnant and pregnant women and neonates as well as in amniotic fluid obtained at various stages o f gestation. Total GHBP (the sum of free GHBP and GHBP bound to GH) is measured by a ligand-mediated immunofunctional assay. GHBP concentrat ions in adult serum were not changed by pregnancy or the stage of gest ation. A significant correlation was observed between the concentratio n of GHBP in the umbilical artery and vein. No correlations were obser ved between the GHBP concentration and such measures of fetal growth a s fetal weight and fetal age. Although the neonatal concentrations of GHBP were significantly lower than those of pregnant women, no correla tion was observed between them. GHBP was also present in the amniotic fluid from early to late gestation at concentrations higher than in th e cord serum of the neonate. The amniotic GHBP concentration in late g estation was significantly higher than in early gestation. GHBP appear s to be derived from GH receptors of fetal organs (most probably fetal liver). The low level of GHBP in fetal serum may be the result of a d ecrease in GH receptors caused by high levels of circulating CH. GHBP levels in amniotic fluids may be related to the development or maturat ion of the fetus.