Observations on the Production of Goiter in Rats With Propylthiouracil Andon Goiter Prevention1

Rats fed propylthiouracil and injected with sodium-l-thyroxine (1.0 to 2.5 µg. per rat per day) developed goiter in the presence of normal concentrations of plasma protein-bound iodine. At all dose levels of thyroxine, rats fed low residue diets had greater serum bound iodine concentrations than animals fed commercial laboratory chow. Since goiter was found in presence of normal or high bound iodine concentrations, this may mean (a) goiter can develop despitelow plasma levels of thyrotropin under these conditions or (b) plasmaproteinbound iodine may have an abnormal composition or influence in these types of experiments. A method is presented for determination of plasma protein-bound iodine by isotope dilution.