Endocrine Abstracts

Synthesis of thyroid hormones by the fetal thyroid requires the passage of iodide through the placenta. In the thyroid active iodide transport is facilitated by three transporters, the sodium iodide symporter (NIS), Pendrin (PDS) and the recently described the human apical iodide transporter (hAIT). Simultaneous expression of all three transporters appears to be thyroid restricted and although extrathyroidal expression of individual transporters has been reported, relatively little data exists on the human placenta. Similarly it is not known if the placenta acts as an iodide storage depot perhaps storing the products of iodide deiodination. The objective of this study was to investigate in human placenta expression of all three transporters using RT-PCR. RNA was extracted from total placenta tissue (a complete core of cotyledon), chorion and amnion membranes. RT-PCR analysis using GAPDH (the house-keeping gene) as a semi-quantitative control showed the presence of NIS and Pendrin (PDS) expression in total placental tissue and in both chorion and amnion membranes. Specific primers designed from the published sequence of hAIT were used for RT-PCR. The presence of hAIT, so far only identified in the thyroid, was also expressed in all placental tissues examined. As its name suggests, hAIT in thyroid is presumable involved in the efflux of iodide into the follicular lumen. Its presence in placenta may also play a role in moving iodide in the fetal direction. The presence of all three so far identified thyroid transporters in placental tissue suggests an active role for placenta in supplying iodide to the developing fetus.