Concentration of Iodine-131 across the Placenta of the Guinea Pig and the Rabbit

Abstract

DURING the course of an investigation on the structure and function of the guinea pig fœtal thyroid, it was noted that a concentration gradient of iodine-131 is established across the placenta after a single injection of iodine-131 is given to the mother. 3 mgm. of propylthiouracil per 100 gin. body-weight was injected subcutaneously in the pregnant animals, thus preventing organic binding of iodine. Forty to forty-five minutes later the dose was repeated and 100 µc. of carrier-free sodium iodide-131 in 2 ml. of distilled water was injected subcutaneously in the right axilla. One hour later the animal was anæsthetized with ‘Nembutal’ and ether, a midline abdominal incision was made, the uterus opened and the fœtuses exposed and individually bled from the umbilical cord or from the heart. Maternal blood was collected by heart puncture before and after the removal of the fœtuses. Both maternal and fœtal blood was collected in heparinized centrifuge tubes. Either 0.5- or 1-ml. samples of plasma were diluted with distilled water to a volume of 10 ml. in 12-ml. glass containers and the radioactivity counted in a Geiger–Müller multiple counter¹.