SERUM PROTEIN-BOUND IODINE DURING INGESTION OF DESICCATED THYROID*

Abstract

IT HAS been demonstrated that hypothalamic-adenohypophyseal regulatory mechanisms maintain the production and release of thyroid hormone within euthyroid limits (1, 2). Previous observations from this laboratory have indicated that without exogenous thyroid or iodide intake the protein-bound iodine in healthy adults remains relatively constant (3). Granting adequate analytic precision, such constancy is compatible with, but does not necessarily support, the existence of a “feed-back” mechanism activated by changes in the plasma level of thyroid products. Introduction of exogenous thyroid products into such a system should provide evidence, however, concerning the presence and the efficiency of such adaptive responses. This report describes the effects of thyroid feeding on serum protein-bound iodine levels and other pertinent indices in euthyroid adult males. PROCEDURES Desiccated thyroid of the same lot number¹ was administered in amounts ranging between 1 and 6 grains per day to 9 presumably healthy adults during intervals up to eighteen weeks in length. In addition to serial determinations of circulating serum protein-bound or precipitable iodine (4, 5), frequently on two successive days, approximately one week apart, electrocardiographic tracing, basal metabolic rate, body weight, pulse rate, serum cholesterol (6), and creatine (7) measurements were obtained in a number of the studies. All of the subjects knew that they were receiving desiccated thyroid and were aware of the daily dosage.