Effects of human growth hormone administration on growth rate and growth-stimulating activity of serum, measured by lymphocyte bioassay in hypopituitary children

The acute effect of human growth hormone (hGH) upon the serum bioassayable growth-stimulating activity was compared to the long-term effects of hGH on growth rate in two groups of hypopituitary patients aged 2-18 years. 12 patients had complete GH deficiency with GH peak below 3.5 ng/ml at two stimulation tests. 15 others, having both GH peaks below 8 ng/ml and at least one above 3.5 ng/ml, were considered as having partial GH deficiency. The growth-stimulating activity of serum was measured by its effect at concentrations 0.03 to 1.25% upon thymidine incorporation into lectin-activated normal human lymphocytes, named thymidine activity (TA). In patients with complete GH deficiency, the pre-treatment TA was positively correlated with the peak response of GH to stimulation tests. The increase of TA after 3-4 days of hGH treatment was positively correlated with the pretreatment TA level, and negatively correlated with the peak GH level. The effect of a 6-12 months therapeutic course of hGH upon the growth rate was positively correlated with the acute increase of TA. No such correlations were found in patients with partial GH deficiency. Many works have discussed the relationship of acute somatomedin responses and long-term clinical results of treatment with hGH in GH-deficient children. The present data, using a highly sensitive bioassay of serum stimulating activity, suggest that the degree of GH deficiency is an important factor to be considered. The response of GH-dependent serum growth factors to acute treatment with hGH could have more predictive value in cases with total lack of growth hormone than in cases of partial deficiency.