ON THE MECHANISM OF IODIDE ACCUMULATION BY THE THYROID GLAND*†

Abstract

AUNIQUE property of the thyroid gland is its ability to extract the iodide ion from the blood and concentrate it; this property is retained by the thiouracilized gland in vivo (1, 2) and thyroid slice in vitro (3). In the chronically thiouracilized hypertrophied thyroid an augmentation of this accumulating ability occurs. Under these conditions this iodide exists in the gland almost entirely in the form of the iodide ion. It is not precipitated with proteins, it is dialyzable and ultrafiltrable (1, 2), and it can be oxidized to iodine by periodate (2, 3). Its potentiometric titration curve is that of the iodide ion (1). Furthermore, animals given thiouracil and a high iodine diet may maintain a nearly normal thyroid iodine concentration, but this iodine on fractionation proves to be inorganic (4). In contrast, animals similarly treated with thiocyanate and iodine fail to accumulate inorganic iodine (4, 5). Also, thiocyanate is able to cause the quantitative discharge of iodide accumulated within the thiouracilized gland (1).