[Response of thyrotropin (TSH) to the stimulation with hypothalamic releasing factor (TRF) in hypothyroid children].

The normal human serum thyrotropin (TSH) measured by radioimmunoassay in 36 children was 3.3 +/- 1.13 muUI/ml. No differences dependent on age or sex were found. Stimulation by intravenous injection of 100 mug of TRF has been carried out in 7 euthyroid children and in 14 with hypothyroidism. TSH was determined prior to, and during TRF stimulation. Among other thyroid tests included in this study were: serum T3 uptake, total thyroxine, serum protein-bound iodine, 131INa uptake and thyroid scanning. In the euthyroid children, TSH at zero time was 4.4 muUI/ml.; a significant increase was reached at 30-40 minutes. In 13 children with a light primary hypothyroidism, TSH was little increased in correlation with other parameters assessed. In two children with true primary hypothyroidism, TSH at zero time was X 465 muUI/ml., showing an increase at 30 minutes of X 550 muUL/ml. which was in agreement with the absence of thyroid tissue, showed by the scanning image and with the low concentration of thyroid hormones. The synthetic thyrotropin-releasing factor (TRF) should be a useful agent for clinical assessment of pituitary reserve. TSH, T3, T4 and T4I serum concentration measurement in pediatric age, makes possible to evaluate the physiopathology of the pituitary - thyroid axis.