Assessment of thyrotropin concentrations in children with somatotropin deficiency treated with growth hormone

BACKGROUND: There are contradictory literature opinions on the influence of GH therapy on the hypothalamus-hypophysis-thyroid gland axis concerning TSH secretion. Some researchers describe the possibility of complete inhibition of TSH secretion followed by overt hypothyroidism, the others do not confirm it. OBJECTIVE: The aim of the study was to assess influence of the rGH therapy on TSH concentrations in GH-deficient children, who were euthyroid prior to the treatment. MATERIAL AND METHODS: The study was carried out in a group of 32 children with isolated GH-deficiency in the 1st stage of sexual development according to the Tanner scale, in whom disorders of thyroid gland were excluded (T4, T3, fT4, fT3, TRH test). Recombinant GH (Genotropin a 16U-Pharmacia) was used for the treatment in the dose of 0.7 U/kg/week. Before the treatment, as well as in the 6th and 12th month of GH administration, the TRH test was performed and TSH levels were assessed in 0', 20', 30', 60' and 120 minute. The results were statistically analysed [p(alpha)<0.05]. RESULTS: Basal TSH levels prior to rGH administration were within normal range and the TSH response on TRH was normal with the maximal increase in the 20th minute. A statistically significant decrease of TSH concentrations was noted after 6 and 12 months of treatment in respective minutes of the test in all children. However, decreased TSH concentrations during the therapy were within normal range. CONCLUSIONS: During rGH therapy there is a decrease of basal and simulated TSH concentrations, however within the normal range. This phenomenon is probably connected with a direct effect of administered rGH on the release of somatostatin, a natural TSH inhibitor.