THE EFFECT OF VARYING QUANTITIES OF INORGANIC IODIDE (CARRIER) ON THE URINARY EXCRETION AND THYROIDAL ACCUMULATION OF RADIOIODINE IN EXOPHTHALMIC GOITER 1

Abstract

The renal clearance or excretion rate of iodide in patients with exophthalmic goiter was not significantly altered by variations in the quantity of stable (carrier) iodide in the range of 0-2g. The relative iodine-accumulating function of the thyroid was not significantly altered by increasing the amt. of stable carrier from 0 to 0.1 mg. More than 0.1 mg. significantly reduced the relative iodine-accumulating function as measured by extrarenal disposal rate. Quantities of carrier iodide of the order of 1 mg. reduced extrarenal disposal rate to euthyroid proportions; 10 mg. or more of carrier reduced it to negligible proportions. After doses containing carrier iodide in the range 0.001 to 0.1 mg. in vivo observations show that I131 progressively accumulates in the thyroid in a fairly smooth exponential manner. After doses of 10 mg. or more of carrier iodide the curve of thyroidal I131 rises rapidly to a peak in 2-3 hrs., and thereafter decreases rapidly in amt., paralleling the fall of radioactivity in serum. Doses containing carrier iodide between 0.1 and 10 mg. result in curves which appear to be intermediate between these extremes. The thyroidal function portrayed with the use of small quantities of carrier iodide (0.1 mg. or less) is predominantly for biosynthesis of thyroid hormone; and with large doses of carrier iodide is the concn. of inorganic iodide within the thyroid, called the iodide-trapping or iodide-concentrating function. The relative biosynthetic function may be suppressed by doses of iodide in excess of 0.1 mg. in subjects with exophthalmic goiter. In these subjects, the iodide-trapping function may not appear to be altered with doses in the range 0.1 to 100 mg. but may appear to be suppressed by doses of 500 mg. or more. The relative biosynthetic function appears to be suppressed or obscured at a serum concn. of inorganic iodide of the order of 5 [mu]g./100 cc. or less; the capacity of the trapping function appears to be exceeded at serum concentrations of inorganic iodide of the order of 2 [mu]g./100 cc. The iodide-trapping function of the thyroid can be evaluated in the human subject following high-carrier doses by comparison of the quantity of radioiodine in the thyroid with the concn. in the serum at the same time. The mean ratio of thyroidal content to serum concentration in seven cases of exophthalmic goiter tested disclosed a mean thyroidal iodide space of 9.5 liters. The method here employed was not found suitable for accurate evaluation of the thyroidal iodide-trapping mechanism in euthyroid patients, which appears to be of the order of 1 liter, or less.