Effect of oral thyrotrophin-releasing hormone on serum thyroxine in growth hormone deficient and normal children.

Oral administration of synthetic TRH in a dose of 80 mg/1-73 m-2 at 0 and 12 h to normal and constitutionally small children caused a significant increase of total serum thyroxine (T4) within 6-24 h. The mean maximal T4 increment was +3-7 plus or minus 1-1 and +3-8 plus or minus 1-2 mug/dl (mean plus or minus 1 SD) respectively in the two groups. Of seventeen euthyroid GH deficient children, fifteen showed a normal and two patients a slightly subnormal response. Of fifteen hypothyroid GH deficient children nine had a prompt and normal increase of serum T4 indicating primary TRH deficiency. Two had a delayed T4 response and four had no response, even after prolonged stimulation. The localization of the primary defect in these latter subjects with severe hypothyroidism can not be made by measuring T4 only, since the thyroid gland may become unresponsive to TSH after longstanding TSH deficiency. TSH measurements are necessary in these circumstances for a clear localization of the primary defect. One GH deficient patient with hypothalamic TRH deficiency was treated with high oral TRH doses for 7 months and showed no side effects.