Thyroid hormone kinetics: improved method for quantitative separation and measurement of the various...

An accurate and reproducible method for measurement of radioactive species in blood after in vivo injection of labelled iodothyronines is described. By extraction with high-affinity antisera, radioactive reverse T3 and T3 are separated from serum quantitatively. Radioiodide is quantitatively separated from radio-thyronine species and serum proteins by Sephadex G50 filtration. The residual mixture of radio-T4 and iodoprotein is quantitatively resolved by ion-exchange adsorption. Minimal misclassification of radiospecies occurs, and can be corrected for. Mean recoveries of various radiospecies added to serum were: radioiodide 98.9%, radio-rT3 87.6%, radio-L-T3 94.5%, radio-T4 98.0% and radioiodoprotein 94.5%. The performance of the method is superior to that of chemical methods such as trichloracetic acid precipitation, ion-exchange or alkaline Sephadex extraction, and chromatographic separation.