Localization of radioiodine in the tissues of swine: an autoradiographic study.

An attempt was made to visualize the sites of accumulation and distribution of 131I and 125I in the organs and tissues of swine by a modified autoradiographic dipping technique. Radioactivity was substantially higher with the injection of 125I than that of 131I. There was a tendency in all tissues for concentration of radioiodine to vary with the age of the animals. Concentration was evident in the lung, muscle, liver, pancreas, intestinal mucosa, thymus and spleen, in addition to the known accumulation sites, such as the adrenal, pituitary and gonads. The isotopes were concentrated at the striated border of the epithelial cells of the duodenum. The submandibular gland had a marked concentration in the collecting ducts and a lesser one in the secretory parenchyma of the gland. The most radioactive organ examined was the thyroid gland. The readioactivity was consistently higher in the follicular epithelial cells than in the connective tissue between the follicles. The bound radioiodine formed rings over the colloid-cell interface.