An autoradiographic study on the localization of 131I-labeled thyroid hormones in the tissues of the pig.

Autoradiographic studies on the localization of 131I-labeled thyroxine and triiodothyronine in the various organs and tissues of the pig have been conducted. The isotopes were compared as to the intensity of radioactivity on the basis of the concentration of developed silver grains in the tissues following the respective radioactive hormone injections. In general, for an identical dose of the isotope and with analogous processing procedures, the autoradiographs of most of the tissues after triiodothyronine were relatively more radioactive than after thyroxine. In both the hormone treatments, the tissues from younger pigs were relatively more radioactive than the tissues of older pigs. The various tissormones. Based on differential localization of radioactivity, the pigs excreted more radioiodine through bile, pancreatic and salivary secretions and in urine.