Radioactive Iodine as an Indicator of the Metabolism of Iodine

According to Harington, two fractions, one “thyroxine-like” and the other “diiodotyrosine-like,” can account for all of the organic iodine found in the thyroid gland (1). The metabolism of these compounds has been reviewed recently by Salter (2). The labeling of iodine by radioactivity provides for the first time a desirable tool for the study of the endogenous or normal rates of formation of these fractions. In the present investigation tracer doses of radioiodine (3) were administered to normal sheep and rats, and at various intervals thereafter the amounts of labeled thyroxine and diiodotyrosine deposited in the thyroid gland were measured.