Thyroid hormone receptor expression in rat placenta

The expression of c-erbA alpha and -beta encoded thyroid hormone receptors (TR) mas investigated in rat placenta between 16 and 21 days of gestation (dg), and in fetal liver and brain at 16 dg, using semi-quantitative RT-PCR and nuclear 3,5,3'-triiodothyronine. (T(3)) binding. TR alpha1, TR beta1, c-erbA alpha2 and c-erbA alpha3 mRNA abundance was unchanged in placenta between 16 and 21 dg, as was the dissociation constant (K(d)) of T(3) binding. The maximal T(3) binding capacity (B(max)) in placenta doubled over this period, suggesting placental TR binding activity is post-transcriptionally regulated. Transcript abundance in tissues at 16 dg can be summarized: TR alpha1, placenta=fetal liver<fetal brain; TR<beta>1, placenta=fetal: liver>fetal brain; c-erbA alpha2 and alpha3, placenta=fetal liver<fetal blain; TR<beta>2; none detected. T(3) binding in fetal liver and brain exhibited equivalent K(d) and B(max) the K(d) being less than 50 per cent of that in placenta, though B(max) was unchanged. The higher K(d) in placenta may reflect tissue-specific patterns of TR modification. In conclusion, rat placenta expresses significant levels of c-erbA alpha and -beta transcripts and protein, providing a possible mechanism of action for T(3) of maternal and fetal origin in this tissue. (C) 2001 Harcourt Publishers Ltd.