Evaluation of growth hormone bioactivity using the Nb-2 cell bioassay in children with growth disorders

The Nb-2 cell bioassay could be a useful tool for evaluating human growth h ormone (hGH) bioactivity, but is not specific for hGH since it relies on th e ability of the hormone to produce effects by cross-reacting with the lact ogenic receptor on Nb-2 cells. We studied the biological activity of both e ndogenous and exogenous hGH in short patients using the Nb-2 bioassay after inhibiting the mitogenic effect of the other lactogenic hormone, that is h uman prolactin (hPRL), by adding a specific antibody against hPRL to each a ssay. The in vitro study showed a significant (p<0.0001) increase in Nb-2 c ell proliferation when increasing concentrations of highly purified hGH wer e added to the cell culture. A complete inhibition of Nb-2 cell replication was observed after adding a specific antibody against hGH. The in vivo stu dy showed a significantly (p<0.0001) lower hGH bioactivity (4.90+/-0.28 ng/ ml) evaluated during stimulation tests in 9 children with total idiopathic GH deficiency, mean age 9.25+/-1.99 years, in comparison with that found in 11 short children with normal growth velocity, mean! age 8.22+/-1.41 years (12.25+/-1.19 ng/ml). Likewise, serum GH levels measured by immunofluorome tric assay IFMA in the same serum samples were significantly (p<0.001) lowe r in the 9 GH-deficient (1.97+/-0.37 ng/ml) than in the 11 short children ( 21.85+/-2.71 ng/ml). Moreover, we evaluated GH concentrations using both IF MA and the Nb-2 cell bioassay in serum samples collected from another 11 id iopathic GH-deficient children, mean age 10.71+/-1.18 years, before and the n, 6 and 24 hours following the 1st injection of r-hGH (0.1 IU/kg sc), Seru m GH values measured by both IFMA and Nb-2 bioassay significantly (p<0.0001 ) increased 6 hours after r-hGH administration and decreased to reach basal levels after 24 hours. In conclusion, the Nb-2 cell bioassay with minor mo difications seems to provide a specific and sensitive assessment of hGH bio activity. (C),1998, Editrice Kurtis.