Uptake of Iodothyronines by Erythrocytes in vitro in Various Species

Abstract

IT has been shown that the electrophoretic mobility of thyroxine labelled with iodine-131 in human serum corresponds with the inter-α zone globulins, thyroxine-binding protein (TBG). The capacity of the serum TBG for thyroxine is limited but the physiological ‘saturation’ of its binding sites varies with the state of thyroid activity. It is relatively saturated with endogenous thyroxine in the hyperthyroid and relatively unsaturated in the hypothyroid state¹. Thus the binding of thyroxine added to serum varies inversely with the thyroid function. If the competition between red cells and the binding sites of TBG is expressed in terms of in vitro ‘uptake’ of radioactive tri-iodothyronine (‘Trix’) by red cells, the uptake is higher in thyrotoxic and lower in myxœdematous persons², and the binding coefficient of red blood cell uptake of ‘Trix’ is negatively correlated with the TBG capacity.