IODINE FIXATION IN THE THYROID AS INFLUENCED BY THE HYPOPHYSIS AND OTHER FACTORS

Abstract

The specific ability of the thyroid to fix I has been confirmed. Expts. with radio-active iodate and diiodotyrosine suggest that only ionized I can be withdrawn from the blood stream by the thyroid gland. The smaller the dose of I administered, the more efficiently it is fixed by the thyroid. When doses of half a mg. or more of I per 100 g. of body wt. are injected intravasc., the thyroid becomes saturated with I and is no longer able to fix I selectively, i.e., the capacity of the thyroid for I is limited. Exchange phenomena or chem. transformations play little or no role in the penetration of ionized I into the thyroid. After being saturated with I, the thyroid recovers its normal ability to fix I in a little more than 3 days. The extent of the decrease in I fixation after hypophysectomy and of its increase after inj. of thyrotrophic extract indicate that the hypophysis does influence the specificity of the thyroid activity, but regulates the fixation of I by controlling to some extent the amt. and efficiency of the thyroid tissue.