SERUM GROWTH HORMONE BINDING PROTEIN ACTIVITY IN HEALTHY NEONATES, CHILDREN AND YOUNG ADULTS: CORRELATION WITH AGE, HEIGHT AND WEIGHT

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Abstract
Serum growth hormone binding protein (GHBP) activity was estimated in healthy neonates (n = 6), children and adolescents (n = 97) and young adults (n = 19). GHBP activity was measured by incubating 125I-hCG (human growth hormone) (.apprx. 25,000 c.p.m.) with serum (100 .mu.l) in the presence and in the absence of excess unlabelled hGH, followed by separation of specifically bound 125I-hGHBP complexes from free 125I-hGH by gel filtration on Ultrogel AcA44 minicolumns. The results are expressed as the percentage specific binding relative to an adult reference serum (%RSB), after correction for endogenous hGH of the unknown serum. The between-assay coefficients of variation for two sera of %RSB activity of 51.2 and 115.4% were 6.0 and 7.0% repectively. In neonates, low values of serum GHBP were found (%RSB = 27.1 .+-. 5.0 SEM) followed by a major rise during the first 6 years of life to a mean value (%RSB = 68.3 .+-. 4.1 SEM) which more than doubled that of neonates. Thereafter, values rose progressively throughout childhood and puberty to reach maximum values in young adults (%RSB = 95.0 .+-. 3.1 SEM). A novel observation was that serum GHBP activity correlated significantly with height standard deviation score (SDS) (males: r = 0.77, P < 0.001; females: r = 0.56, P = 0.01) and weight SDS (P < 0.001) for both sexes before puberty. During puberty GHBP correlated only with weight SDS in males (r = 0.60, P < 0.01). In all age groups studied, no correlation could be found between serum GHBP and height velocity.