Abstract
Summary
In vitro deiodination of 131I-T4 as an index of T4 to T3 conversion, was assessed in homogenates of fetal and adult rat liver and kidney, to explore whether differences existed which might account for the low fetal concentrations of serum T3 observed by others. The deiodination rate per milligram of protein was greater for both kidney and liver homogenates in the fetus than in adult rats. These results suggest that fetal T4 deiodination is not decreased in comparison to the neonatal or adult rat. Thus, the mechanism for the low serum T3 concentration in the fetus does not appear to be a decreased production of T3 from T4, insofar as in vitro T4 deiodination may reflect in vivo T4 to T3 conversion.
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