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A Novel Specific Bioassay for Serum Human Growth Hormone

Department of Endocrinology and Metabolism, National Children’s Medical Research Center, (M.I., A.N., R.H., N.K., T.T.) Setagaya-ku, Tokyo 154-8509; The 1st Department of Internal Medicine, Toho University of School Medicine (M.I.), Ota-Ku, Tokyo 143-8541; Department of Pediatrics, Dokyo University School of Medicine (O.Y.), Shimotuka-gun, Ibaragi 321-0267; and Life Science Laboratories Mitsui Chemicals, Inc., (M.W., M.H.), Mobara, Chiba 297-0017, Japan

Address correspondence and requests for reprints to: Mayumi Ishikawa, Department of Endocrinology and Metabolism, National Children’s Medical Research Center, 3-35-31, Taishido, Setagaya-ku, Tokyo 154-8509, Japan.

Human GH receptor (hGHR) was recently expressed on a Ba/F3 cell line, which is a mouse pro-B cell lymphoma that has been induced to become a cloned cell line (Ba/F3-hGHR). Using a Ba/F3-hGHR cell line, we have established a bioassay for serum hGH.

hGH stimulated cell proliferation in a dose-dependent manner in concentrations ranging from 1 ng to 100 ng/mL. Cell proliferation was not influenced by other hormones or growth factors in the bioassay, with the exception of insulin-like growth factor I (IGF-I) and GH binding protein. Free IGF-I significantly stimulated the proliferation of Ba/F3-hGHR cells at concentrations over 25.85 ng/mL in this bioassay system, but serum IGF-I did not stimulate cell proliferation because the sensitivity of cell proliferation was insufficient for free IGF-I in serum. GH binding protein, however, did suppress cell proliferation at the highest concentration (100 ng/mL), but did not at the average concentration (20 ng/mL). Human serum stimulated cell proliferation, which was completely suppressed by anti-GH antibody. The GH bioactivity of serum samples from normal children and patients with non-GH deficient short stature correlated strongly with the serum hGH concentration determined by immunoradiometric assay (IRMA) (r = 0.967, r = 0.924, P < 0.0001, respectively). The ratio of bioactivity/IRMA was 1.01 ± 0.26 in sera from normal children and 1.18 ± 0.24 and 1.00 ± 0.29 at basal values and peak values in GH stimulation tests, respectively, in sera from patients with non-GH deficient short stature. The bioactivity/IRMA ratio for the serum GH bioactivity of a patient who had biologically inactive GH caused by an amino acid substitution was 0.333 ± 0.056 (mean ± SD).

In conclusion, we established a new sensitive bioassay for hGH that is specific for hGH somatogenic action and is useful for screening of patients with short stature caused by biologically inactive hGH.

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