Measurement of Thyroid Hormone Concentrations in Human Placenta

Summary

Concentrations of thyroxine (T₄), 3,5,3′-triiodothyronine (T₃) and 3,3′,5′-triiodothyronine (rT₃) in the placenta were measured in 7 patients with abortion, in 9 patients with premature delivery, in 16 normal pregnancies and in 4 pregnant women with Graves' disease.

The placentas, obtained at delivery, were homogenized and centrifuged at 800 × g. T₄, T₃ and rT₃ concentrations in the supernatants were extracted with 3 vol. of 99% ethanol and measured by RIAs.

In normal pregnancy, placental T₄, T₃ and rT₃ concentrations were 18.8 ± 5.9 (mean ± SD), 0.026 ± 0.012, and 1.70 ± 0.49 ng/g tissue, respectively. Ratios of rT₃/T₃ and rT₃/T₄ in the placenta were about 12 and 2.3 times as high as those in the fetal sera, respectively. There was a significant positive correlation between the placental T₄ and the maternal or cord serum T₄ concentrations. However, no correlation was found between the placental T₃ or rT₃ concentrations and the maternal or cord T₃ or rT₃ concentrations. In 4 patients with Graves' disease, the placental T₄ concentration was elevated.

These results indicate that the placental T₄ concentration is influenced by both the maternal and fetal serum T₄, and elevated ratios of rT₃/T₃ and rT₃/T₄ in the placenta might be due to the active placental 5-monodeiodination.

Key-Words

Thyroxine-3,5,3′-Triiodothyronine - 3,3′,5′-Triiodothyronine - Placenta