On the Permeability of Guinea Pig Placenta for Thyroxine

Abstract

Summary. The permeability of the guinea pig placenta to I 131 ‐labeled thyroxine and inorganic I 131 has been studied. The pertinent foetal and maternal samples were taken 3 to 4 ½ hr. after the administration of the radioactive compounds in question. The result goes to prove that thyroxine does not permeate the placenta in the first hours after its administration. Under similar test conditions more radioactivity was observed in the foetuses than in the mother animal after injection of inorganic I 131 .