Abstract
Although hGH has been shown to suppress the release of TSH, its action on the metabolism of thyroid hormones remains unknown. We examined the effect of hGH on a loading dose of T3 in 11 hypopituitary children (3 to 18 years). Six patients were on oral L-thyroxine because of TSH deficiency. Before and after one month of hGH therapy (2U three times weekly), a single dose of T3 (50 to 100 ug) was administered orally; serum levels of T3 and T4 were measured at 0, 4, 6, 12, 18 and 24 hours. Both before and after hGH therapy, serum levels of T3 peaked at 4 hours and returned to normal by 24 hours. After hGH therapy, significantly higher levels of T3 were achieved at 0, 4, 6, 18 and 24 hours (p values from 0.003 to 0.03). In contrast, following T3 ingestion, serum levels of T4 decreased and reached a nadir at 18 hours. The decrease in serum levels of T4 were of similar magnitude whether the patients were or were not receiving replacement therapy with L-thyroxine. Therefore, these changes could not be explained by T3 induced suppression of thyroid gland. The decrease in serum levels of T4 was not influenced by hGH therapy. In conclusion, hGH causes an increase in the basal level of serum T3 and an augmentation of T3 levels following a loading dose of T3; mechanisms for these changes are not known. The decrease in serum levels of T4 following a T3 load, although not altered by hGH, is of special interest. This effect seems to be due to changes in extrathyroidal metabolism of T4.
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Rezvani, I., Digeorge, A., Dowshen, S. et al. ACTION OF HUMAN GROWTH HORMONE (hGH) ON T3 METABOLISM. Pediatr Res 11, 431 (1977). https://doi.org/10.1203/00006450-197704000-00370
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DOI: https://doi.org/10.1203/00006450-197704000-00370
