Effect of Prednisone on Thyroxine-Binding Proteins

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Abstract
Administration of high doses of prednisone to 5 patients resulted in a progressive increase in the maximal binding capacity of thyroxine-binding prealbumin (TBPA) and a simultaneous decline in the binding capacity of thyroxine-binding globulin (TBG). In every instance the lowest TBG binding capacity reached fell below the established normal range. In 2 patients, the highest TBPA binding capacities induced by prednisone exceeded the upper normal limit. Densitometric analysis of starch gel patterns stained for protein indicated that the elevated binding capacities of TBPA were directly related to increased serum concentrations of TBPA. Since no changes in the net binding of thyroxine to plasma proteins were demonstrated by equilibrium dialysis, it appears that the rise in TBPA is effectively balanced by a reduction in the TBG binding capacity. Thus, the fall in serum PBI [protein-bound iodine] observed in 4 of these patients cannot be easily attributed to a primary disturbance in binding proteins. In vitro addition of glucocorticoids (prednisone, hydrocortisone) to serum and buffer had no effect on the maximal binding capacities of TBPA and TBG or the partition of tracer 131I-thyroxine among the serum binding proteins.