Conversion of Thyroxine to Triiodothyronine and Reverse Triiodothyronine in Human Placenta and Fetal Membranes

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Abstract
Conversion of thyroxine (T4) to 3,5,3''-triiodothyronine (T3) and reverse 3,3'',5''-triiodothyronine (rT3) was measured in vitro in human placenta and fetal membranes. T4 (5 .mu.g/ml) was incubated in 0.15 mol/l phosphate buffer with tissue homogenates for 2 h at 37.degree. C, and the T3 and rT3 generated were determined in ethanol extract using radioimmunoassay methods. The placenta and chorion homogenates converted more T4 to T3 than to rT3; the placenta was more active than the chorion. In both tissues the highest converting activity was found in microsomal fractions.