GROWTH-HORMONE BIOACTIVITY IN GIRLS WITH TURNERS-SYNDROME - CORRELATION WITH INSULIN-LIKE GROWTH-FACTOR-I

We have recently developed a new bioassay for growth hormone (GH) in serum, which is based on the ability of GH to suppress glucose use in cultured murine adipocytes. We tested the hypothesis that bioactive GH (B-GH) concentrations would correlate better with the GH-dependent peptides, IGF-I, and IGF-binding protein-3 (IGFBP-3) than would GH determined by conventional RIA RIA-GH). Twenty-five girls with Turner's syndrome were studied. The subjects had ages ranging from 4.8 to 15.9 y and height SD from the mean (SD score) ranging from -0.77 to -5.67. Blood samples were obtained every 15 or 20 min for 12 h overnight. For each girl an equal aliquot of each overnight sample was pooled for determination of B-GH, RIA-GH, IGF-I, IGFBP-3, LH, FSH, and estradiol. Measurable estradiol concentrations were present in six girls and were sufficient to suppress gonadotropin concentrations in two girls, but they did not alter B-GH, RIA-GH, IGF-I, and IGFBP-3 concentrations compared with the age-matched girls without measurable estradiol concentrations. Hence, data for ah girls were combined for subsequent regression analyses. RIA-GH did not correlate significantly with B-GH, IGF-I, or IGFBP-3. B-GH exhibited a significant correlation with IGF-I (r = 0.407, p < 0.05), and the correlation with IGFBP-3 was better than that for RIA-GH (v = 0.355 versus 0.064, B-GH and RIA-GH, respectively). None of the B-GH, RIA-GH, IGF-I, or IGFBP-3 concentrations had a significant correlation with height SD score or height velocity SD score. These results indicate that B-GH correlates better with the GH-dependent peptides, IGF-I and IGFBP-3, than does RIA-GH, but neither measure of GH is useful in predicting height in girls with Turner's syndrome.