Studies of Thyroid Function

Recent studies have revealed an abnormality in the peripheral metabolism of thyroxine in patients with active untreated Graves' disease (1). In such patients, an abnormally large fraction of the extrathyroidal pool of thyroxine is degraded daily. Other authors have also observed an accelerated fractional turnover of thyroxine in patients with untreated Graves' disease (2, 3) and have postulated that the rate of turnover of the hormone might be a function of its concentration in the blood (2). Alternatively, accelerated turnover of thyroxine might merely reflect the general speeding of metabolic processes which occurs during the hyperthyroid state. The present studies were designed to differentiate between these and other possibilities. Rates of turnover of thyroxine have been assessed in patients in whom the thyrotoxicity had been corrected by appropriate therapy, as well as in nonthyrotoxic subjects who were made hypermetabolic by the administration of thyroid hormone. A preliminary report of the data obtained has been published in abstract form (4). It has been shown that the induction of thyrotoxicosis medicamentosa does result in an augmentation of the fractional rate of turnover of thyroxine. However, it has also been demonstrated that accelerated fractional turnover of thyroxine frequently persists in patients with Graves' disease, despite