Abstract
The effects of overfeeding and triiodothyronine (T 3) administration on basal serum thyrotropin (TRH) concentrations and the TSH response to thyrotropin-releasing hormone (TRH) was studied in normal subjects. Eight normal volunteers were fed their usual diet plus 2000 kcal carbohydrate daily for 7 days. Their mean serum T 3 concentrations increased from 102 ± 6 (SEM) ng/dl to 126 ± 10 ng/dl; there were no changes in serum thyroxine (T 4) and basal serum TSH concentrations or the serum TSH response to TRH. Five of these subjects were fed their usual diet plus 10 μg T 3 for 3 days and 20 μg T 3 for 4 days in divided doses. Their mean serum T 3 concentrations increased from 104 ± 6 ng/dl to 140 ± 8 ng/dl. Mean serum T 4 and basal serum TSH concentrations declined and serum TSH responses to TRH were significantly reduced. In both instances serum T 3 concentrations remained within the normal range. These results indicate that increases in serum T 3 concentrations of similar magnitude induced by augmented extrathyroidal T 3 production and T 3 administration have different effects on thyrotroph function.
Published Version
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