Abstract
We studied the binding of triiodothyronine (T
3) to human placenta and decidua. Although the placenta effectively blocks transfer of thyroxine (T
4) and T
3 it may itself be a thyroid hormone-dependent tissue and may specifically bind T
3.
A single class of high-affinity binding sites was found (
K
a 3.8±0.31 s.e.m., and 3.3±10
9
m
−1) for both placenta and decidua. Limited capacity was also observed, viz., 0.117±0.01 and 0.102±0.018 fmoles/μg deoxyribonucleic acid (DNA), respectively. Endogenous T
3 nuclear saturation was 34 per cent. Our results are consistent with the proposal that placenta and decidua have similar T
3 specific nuclear binding sites and that T
3 may have a direct action in the placenta.
