USE OF NEUTRON ACTIVATION ANALYSIS FOR STUDYING STABLE IODIDE UPTAKE BY THE THYROID*

Abstract

A technique of neutron activation analysis was used to measure trace quantities of inorganic iodide in urine. Anion exchange resins and selective elution permitted removal of interfering sodium and chloride from urine prior to activation. Uptake of stable iodide by the thyroid was determined by measuring the radioiodine uptake and specific activity (I131/I127) of simultaneously excreted urine. In 34 fasting euthyroid subjects mean iodide uptake by the thyroid was 3 i 2 [mu]g per hour. Plasma concentration of inorganic iodide averaged 0.005 ug per ml. Variation in iodide intake produced corresponding variation in amounts of stable iodide accumulated by the thyroid, since iodide accumulation approximated a first-order reaction. Prolonged administration of exogenous iodide gradually decreased radioiodine accumulation. This decreased accumulation of stable iodide only after several weeks of greatly increased iodide uptake by the thyroid. A mechanism to explain dynamics of iodide accumulation by the thyroid was presented.