RADIOTHYROXINE TURNOVER STUDIES IN MYXEDEMA, THYROTOXICOSIS, AND HYPERMETABOLISM WITHOUT ENDOCRINE DISEASE

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Abstract
Estimation of the magnitude and turnover of the total body pool of thyroid hormone outside the thyroid gland was undertaken with I131 -labeled 1-thyroxine in normal subjects, patients with thyroid disease, and hypermetabolic patients without endocrine disease (leukemia, fever). Extrathyroidal organic iodine (EOI) pools were diminished in myxedema and increased in thyrotoxlcosis. Turnover rates of extrathyroidal hormone were slower than normal in myxedema, and accelerated in thyrotoxlcosis. The absolute organic I degradation rates, being the products of the pools and turnovers, showed even wider divergences between the different groups. The mean values + standard deviation in micrograms of I per day (adjusted to 1.73 m2 surface area) were as follows:.Normal 51[plus or minus] 9.Myxedema 18[plus or minus] 4.Thyrotoxlcosis 197[plus or minus] 35.Hypermetabolism 100[plus or minus]18.The hypermetabolic subjects without endocrine disease had increases in pools, turnovers, and degradation rates, although less pronounced than in thyrotoxicosis. The elevated values in non-specific hypermetabolism suggested that peripheral tissue metabolism, or some function thereof, has a major role in determining hormone degradation rate. Administration of large amounts of thyroxine or triiodothyronine or both to myxedematous subjects failed to alter the shape of the disappearance curve. This indicated turnover of a fixed proportion of the EOI pool daily, during short term studies, despite marked elevation of the plasma PBI concentration, enlargement of the EOI pool, and increase in the organic I degradation rate.