RADIOACTIVE IODINE AS AN INDICATOR IN THYROID PHYSIOLOGY. IV. THE METABOLISM OF IODINE IN GRAVES' DISEASE 1

Abstract

The use of radioactive iodine as an indicator in thyroid physiology has been described by Hertz, Roberts and Evans (1) and by Hertz, Roberts, Means and Evans (2, 3). Hamilton and Soley (4) have published data obtained by the use of radioactive iodine on goiter patients of several types. We have administered radioactive iodine (mainly the 8-day isotope I's1), obtained by bombarding tellurium with deuterons in the Massa-chusetts Institute of Technology cyclotron, to 22 patients with Graves' disease and to 2 normal individuals. By this means we have investigated the absorption and excretion of labelled doses of iodine of various sizes, administered at various times during the course of pre-operative iodiniza-tion and at various intervals before operation. In addition, the amount of iodine taken up by the thyroid and the distribution of the labelled iodine between the iodine-containing fractions of the thyroid have been determined in 19 cases. PROCEDURE Patients with Graves' disease were selected who had had no iodine previous to hospital admission. Labelled iodine was administered as sodium iodide by mouth and all other iodinization was in the form of potassium iodide in saturated solution. Glands were obtained at operation in 19 cases, at which time an estimate of the residual tissue was made. The glands were then fractionated according to the method of Harington (5) following alkaline hydrolysis. The acid-soluble and acid-insoluble fractions were then determined for both total and labelled iodine. It was found that the thyroid uptake of labelled iodine could not be directly determined from tissue samples because of the markedly non-uniform distribution of the labelled iodine. In about half the cases, relative measurements of the ' amount of labelled iodine present in the thyroid were made by means of an external Geiger-Muller counter at various intervals after administration. The usual clinical observations were made, including the basal metabolic rate. Patients were at complete rest in the hospital and on an ordinary house diet. Fluid intake was not restricted. The procedure for each uniodinized patient was as follows: The basal metabolic rate was determined after a preliminary period of bed rest. Labelled iodine was then administered by mouth, and urines were collected in 12 cases. The uptake of labelled iodine by the thyroid was measured for 13 patients at various times after administration of the labelled iodine by means of an externally placed Geiger-Muller counter. No further iodine was given until these external measurements indicated that the thyroid iodine level had reached a relatively constant value. At this time routine iodinization (minims 5 saturated solution of KI, twice daily) was begun. When maximal metabolic and clinical response had been reached 6 to 10 days later, 19 patients were subtotally thyroidectomized and an estimate of the residual thyroid tissue was made. A small portion of the excised gland was reserved for histologic study, and the remainder was fractionated chemically. The two fractions obtained, which we call "T" and "D" according to the notation of Salter (6), represent the thyroxine-like and diiodo-tyrosine-like fractions of the thyroid iodine. These fractions were assayed for both ordinary (total) iodine content and for labelled iodine. The labelled iodine excreted in the urine was determined for most patients during the first few days following the administration of labelled iodine. Labelled blood iodine was determined in a few cases. Cases 1, 2, 3, 4, 5, 9, and 10 received ordinary iodine prior to the administration of the labelled dose. The interval of preiodinization given in Table I is the time between the first dose of ordinary iodine and the dose of labelled iodine. In only one of these cases, Case 10, was the patient totally iodinized by clinical standards before the administration of the labelled dose. Cases 16 and 28 were normal persons and were, of course, not operated upon. In addition, Cases 15, 17, and 22 were not operated upon for clinical reasons. The details of individual iodinization procedure are given in Table I. The first clinical experiments were designed to afford data on the thyroid uptake from a labelled dose of iodine at various degrees of iodinization 25