SALIVARY AND THYROIDAL RADIOIODIDE CLEARANCES OF PLASMA IN VARIOUS STATES OF THYROID FUNCTION

Abstract

Serous saliva was obtained by catheterization of a parotid duct and its radioiodide concentration following administration of a tracer dose to patients with various states of thyroid function was determined at various intervals. Iodide clearance of plasma by the parotid was com-pared with that by the thyroid gland and was observed to be independent of thyroid function. The ratio of salivary to plasma 1131 concentration which is sometimes used as a thyroid function test, is mainly determined by the plasma concentration of the isotope. In addition to all the factors which determine the plasma concentrations this ratio is influenced by the rate of salivary flow and by the extent of dilution of serous by mucous saliva, the latter probably not containing any I. By frequent determina-tions of both the salivary and the thyroidal plasma clearance of iodide during the first 2 hours following administration it was found that the thyroidal clearance decreased significantly during this period. It was concluded that the thyroidal uptake of iodide is a two-rate function with the rate of iodine binding being slower than the rate of iodide trapping. Double estimations of the thyroidal clearance using the newly available, short-lived I132 have shown that iodine metabolism in its early phase may be subject to considerable daily variations.