Quantitative Aspects of the Secretion and Degradation of Thyroid Hormones During Adolescence

The thyroid iodine pool and the rate of hormone secretion were determined in 7 adolescents. The mean iodine content of the gland was 3.2±0.8 mg. The hormonal secretion rate constant was 1.4% of the pool per 24 hr. Accordingly, a mean daily hormone production of 34.3±4.6 μg thyroxine iodine, or of 0.94- ±0.1 μg/kg body weight, was found. The peripheral metabolism of radiothyroxine was studied in 17 adolescents. The figures were intermediary between those observed for children and those found for adults. The fractional turnover rate corresponded to 12.2±0.7% of the extrathyroid hormonal iodine pool, the latter being 340 ±27.5 μg thyroxine iodine. The quantity of thyroxine iodine metabolized per day was 38.9±2.06 μg or 1±0.04 μg/kg. From these data and those found in the literature, one may conclude that, expressed per unit of body weight or surface area, there is a progressive decrease of thyroid secretion and thyroxine utilization from adolescence to aulthood.