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 betw een 16 and 21 dg, as was the dissociation constant (K-d) of T-3 binding. Th e maximal T-3 binding capacity (B-max) in placenta doubled over this period , suggesting placental TR binding activity is post-transcriptionally regula ted. Transcript abundance in tissues at 16 dg can be summarized: TR alpha1, placenta=fetal liver<fetal brain; TR<beta>1, placenta=fetal: liver>fetal b rain; 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, thou gh B-max was unchanged. The higher K-d in placenta may reflect tissue-speci fic patterns of TR modification. In conclusion, rat placenta expresses sign ificant 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 thi s tissue. (C) 2001 Harcourt Publishers Ltd.