6 Iodo-δ-lactone reproduces many but not all the effects of iodide

Iodide has direct effects on thyroid function. Several iodinated lipids are biosynthesized by the thyroid and they were postulated as intermediaries in the action of iodide. Among them 6 iodo-δ-lactone (IL-δ) has been identified and proposed to play a role in thyroid autoregulation. The aim of this study was to compare the effect of iodide and IL-δ on several thyroid parameters. Thyroid bovine follicles were incubated with the different compounds during three days. KI and IL-δ inhibited iodide uptake, total protein and Tg synthesis but only KI had an effect on NIS and Tg mRNAs levels. Both compounds inhibited Na +/K + ATPase and deoxy-glucose uptake. As PAX 8, FOXE 1 and TITF1 are involved in the regulation of thyroid specific genes their mRNA levels were measured. While iodide inhibited the expression of the first two, the expression of TITF1 was stimulated by iodide and IL-δ had no effect on these parameters. These findings indicate that IL-δ reproduces some but not all the effects of excess iodide. These observations apply for higher micromolar concentrations of iodide while no such effects could be demonstrated at nanomolar iodide concentrations.