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

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Abstract
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 [plus or minus] 0.8 mg. The hormonal secretion rate constant was 1.4% of the dool/24 hr. Accordingly, a mean daily hormone production of 34.3 [plus or minus] 4.6 [mu]g thyroxine iodine, or cf 0.94 [plus or minus] 0.1 [mu]g/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 [plus or minus] 0.7% of the extrathyroid hormonal iodine pool, the latter being 340 [plus or minus] 27.5 [mu]g thyroxine iodine. The quantity of thyroxine iodine metabolized per day was 38.9 [plus or minus] 2.06 [mu]g or 1 [plus or minus] 0.04 [mu]g/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 adulthood.