Abstract
In previous studies, we have shown that administration of hGH increases the half life of serum triodothyronine (T3). We have now examined the effect of hGH on a loading dose of T4 in 7 hypopituitary children (7 to 18 years of age). Before and after one month of hGH therapy (2 U t.i.w.) a single dose of T4 (1.2 mg/M2) was administered orally, serum levels of T3 and T4 were measured at 0,2,4,6,12,18,24 hrs. and daily thereafter for 6 days. Serum levels of T4 peaked between 4 to 6 hrs. post ingestion and declined slowly to baseline values by the 6th day. The values for serum levels of T4 were not affected by hGH therapy. There was a rise in serum levels of T3 as early as 2 hrs. post ingestion but no uniform peak was discernable. The baseline values for serum T3 were reached by the 6th day after several erratic fluctuations. Serum levels of T3 were significantly higher after hGH therapy. This increase was more pronounced when the values were expressed as the ratio of T3/T4. These data indicate that hGH causes an increase in serum levels of T3. Although this, in part, may be due to increase in half life of serum T3, the long lasting elevation of serum T3, as obtained in this study, can only be explained by an increase in extrathyroidal conversion of T4 to T3.
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Rezvani, I., Digeorge, A., Bourdony, C. et al. 332 ACTION OF HUMAN GROWTH HORMONE (hGH) ON THE PERIPHERAL METABOLISM OF THYROXINE (T4). Pediatr Res 12 (Suppl 4), 419 (1978). https://doi.org/10.1203/00006450-197804001-00337
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DOI: https://doi.org/10.1203/00006450-197804001-00337