Endocrine Abstracts

The production of iodine containing thyroid hormones necessary for brain development in the fetus depends not only on maternal dietary intake but also on placental iodine transport.

Previously, studies focused on finding the optimum level of iodine nutrition for expectant mothers. However, little knowledge exists on the ability of the placenta to either accumulate or even store iodine. This study aims to investigate iodine uptake and tissue iodine content in placental tissue obtained from mothers undergoing elective caesarean section. Samples (~1 cm³) of placental cotyledon (n=19), thyroid (n=4) and uterus (n=4) were incubated for 6 h with ¹²⁵I. To account for variation in tissue composition results were expressed in cpm/μg DNA. Median uptake for placental, thyroid and uterus tissue was 375, 1702 and 269 cpm/μg DNA respectively of which 30, 38 and 0% could be blocked by perchlorate (10 μM).The median iodine content of samples of tissue measured using an alkaline ashing technique was 27 ng/g (placenta; range 21–32 ng/g), 5.6 ng/g (uterus) and 456 μg/g (thyroid). The iodine content of different cotyledons from the same placenta could be remarkably homogeneous (32.0±1.47 ng/g; CV 4.5%) or highly variable (21.0±14.0 ng/g; CV 66.6%) and was only ~0.2% that of the adult thyroid. As neonatal iodine stores are very low and highly sensitive to fluctuations in maternal iodine supply, their bioavailability could nonetheless make a significant contribution to protection against neonatal hypothyroidism. These findings suggest the placenta has a role not only in uptake of iodine but also in iodine storage as a possible means of compensating the fetus for inadequacies in maternal dietary iodine intake.