Decrease of fetal radionuclide uptake by pharmaceuticals

Activity concentration of sup(131)I in rat fetuses grows gradually towards the end of pregnancy, but increases rapidly during the last 2 days. Thyroid blocking agents effectively decrease radioiodine accumulation in fetuses. The protective effect of thyroid blocking compounds depends on the quantity given, as well as on the time interval between the radioiodine uptake and the administration of the protective agent. Accordingly, the sup(131)I activities in the fetuses and their placentae decrease to 20-30% of those of the control when dams are provided with 1,0 mg of potassium iodine (KI) 2 h after the radioiodine intake. This amount of KI, however, seems to be embryotoxic in some cases. On the other hand, the quantity of KI can be reduced by 50-90%, if KI is combined with potassium perchlorate (KCLOsub(4)), without any loss of efficiency of protective effect. Radioactivity of fetuses can be decreased further by the decrease of time interval. (author)