Radioiodine concentration by the fetal mouse thyroid.

Abstract

Twenty-four hours following subcutaneous injection of radioiodine into pregnant mice various fetal and maternal tissues were removed, weighed and their radioactivity measured. Measurements at various days of gestation show the fetal mouse thyroid first concentrates iodine between the 14th and 15th days of gestation in mice with an average gestational period of 19 days. Development of the ability to concentrate iodine precedes bymore than a day the formation of follicles and colloid in the gland. As the iodine uptake of the litter increases greatly toward term, there is indication of a corresponding decrease in the iodine uptake by the maternal thyroid. Near term, the concentration of iodine in fetal thyroids and the total uptake by thyroids of whole litters equals or exceeds the concentration, in and uptake by, the maternal thyroid. It is suggested that changes in the placenta in mass and in capacity to concentrate and transmit iodine, particularly between the 17th and 18th days, may affect the iodine con...