STUDIES OF THE RATE OF DISAPPEARANCE OF LABELED THYROXINE FROM THE INTRAVASCULAR COMPARTMENT*

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Abstract
A method is described for the determination of the rate at which equilibrium between intravascular and extravascular thyroxine pools is approached. This measurement, termed the "acute thyroxine disappearance rate" was found to be shorter in Graves'' disease than in other subjects with comparable thyroidal activity. Even when functionally athyrotic, patients with Graves'' disease handled thyroxine differently from athyrotic subjects without Graves'' disease. No significant shortening of thyroxine disappearance rate was noted in patients with toxic nodular goiter or in normals fed exogenous thyroid. These observations suggest that plasma or extravascular protein binding of thyroxine in Graves'' disease may be altered, and indicate a qualitative difference between toxic nodular goiter and Graves'' disease. Greatly prolonged thyroxine disappearance rates were seen in subjects with liver disease, indicating the importance of the liver in handling thyroxine.