The Behavior of Radioiodine in the Blood 1

Abstract

Radioiodine has been used to study the function of the human thyroid gland in various ways. The quantity of radioiodine collected by the thyroid has been determined directly by in vivo measurements (Hamilton, Sole-and co-workers [1][2][3][4]; Hertz and co-workers [5] ), and indirectly by estimations from the total quantity excreted in the urine over a fixed period (Hertz and coworkers [5]; Rawson and co-workers [6,7]). The distribution of iodine in the thyroid has been studied by autoradiograms (3) or by chemical analysis of excised tissue (5). Most recently the capacity of the thyroid to concentrate radioiodide has been studied by Stanley and Astwood (8) after previous administration of an antithyroid drug such as mercaptoimidazol.Keating, Power, Berkson, and Haines (9) have employed radioiodine to investigate the kinetics of iodine metabolism. They studied the urinary excretion of radioiodine by collecting all the urine in short periods for three days or longer. By plotting cumulative urinary excretion against time, they obtained an exponential curve from which were estimated four quantities: (1) a renal fraction (that part of the dose of radioiodine primarily excreted. in the urine); (2) a disappearance rate (which they inferred to represent the proportional rate of disappearance of radioiodine from the blood); (3) a r'enal excretiop rate (the proportional rate of excretion into the urine) ; and (4) a so-called collection rate (the proportional rate of disappearance into other sites than the kidneys, of which the most important is the thyroid). The most significant measure of thyroid activity was the collection rate, which was much less than normal in hypothyroid

An Estimation of the Renal and Extrarenal Clearance of Radioiodine in Man

“…The methods employed for collections and analyses have been described elsewhere (1,5). Clearances were calculated by the method described by Berkson and associates (6).…”

“…the renal excretion of iodide as estimated by the renal clearance of iodide (1)(2)(3). In addition, it has been suggested that the most explicit and precise measure of the iodine-accumulating function of the thyroid gland may be the clearance of iodide by the thyroid (3,4), defined by analogy as the volume of plasma or serum cleared by the thyroid gland of its iodide content per minute, and determined from multiple observations in vivo of the thyroid itself compared with observations of serum.…”

The Measurement of the Iodine-Accumulating Function of the Human Thyroid Gland

“…In so far as the thyroid is the most important site for the extrarenal disposal of iodide, the latter value should provide an index of the rate of iodine accumulation by the thyroid. In support of the interpretation of Keating and co-workers, McConahey and associates (15) determined the rate of disappearance of radioiodine from blood directly from measurements of samples of plasma and found good agreement with estimates of this value obtained from curves of urinary excretion by the method employed by Keating, Power, Berkson and Haines. Luellen and co-workers (5) observed that the rate constants estimated from curves simultaneously obtained from: 1) in vivo observation of radioiodine in the thyroid in counts per second; 2) measurement of radioactivity in peripheral tissues (the thigh); and 3) urinary excretion of radioiodine, all appeared to be the same as the rate of disappearance of radioiodine from blood as determined directly.…”

Relative Measurement in Vivo of Accumulation of Radioiodine by the Human Thyroid Gland: Comparison With Radioactivity in Peripheral Tissues 1

“…The former they felt to be a relative quantity depending on the capacity of the thyroid and of other tissues to dispose of iodine as well as of the kidney to excrete it, and the latter they inferred to be the rate of disappearance of radioiodine from blood. McConahey and co-workers (8) The counter tube was kept in an assembly attached to a standard so that it could be raised, lowered or turned in any direction (Figure 1). The assembly consisted of a lead cylinder with a wall 16 mm.…”

“…Six studies were made on six myxedematous patients. Studies of the blood and urine were carried out as described in previous papers (7,8). In order to place all subjects on a comparable basis as far as dosage was concerned, observations of radioactivity were expressed as counts per second per millicurie of dosage.…”