Comparison of serum growth hormone activity by radioreceptor assay and radioimmunoassay following administration of exogenous growth hormone in deficient children

To test the hypothesis that persistence of biologically active growth hormone (hGH) in serum might explain the growth response in children who receive hGH as infrequently as once a week, we compared serum hGH activity by RRA and RIA following exogenous hGH administration in 17 hGH deficient children. Serum hGH concentrations as measured by RRA and RIA were parallel, peaking at 2 hours at 50.2 ± 8.8 and 53.8 ± 7.1 ng/ml, respectively, and returning to basal concentrations by 24 hours. Serum hGH concentrations by RRA were less at each time period than RIA concentrations, though only the six-hour difference was statistically significant. Prolonged serum hGH bioactivity, as assessed by the RRA, does not explain the growth response to weekly hGH injections. Most likely, protein synthetic mechanisms beyond the binding of hGH to its receptor explain its prolonged biologic activity after disappearance from the blood.