Measurement method for radioactive thyroxine, triiodothyronine, iodide, and iodoprotein in samples with low activity.
A method is described that incorporates resin extraction and thin layer chromatography to isolate and separate radioiodinated thyroxine (T4), triiodothyronine (T3), iodoprotein, and iodide in samples of human plasma up to 3 ml. Tracer studies using this method showed that reverse T3 and 3',5' diiodothyronine (T2), as well as T4, were detected in the "T4 fraction," and that 3-3' T2 and 3' monoiodothyronine, as well as T3, were detected in the "T3 fraction." Monoiodotyrosine and diiodotyrosine (DIT) migrated more slowly than did T4 on the chromatogram, and a large amount of DIT was in the unextracted "iodoprotein fraction." Kinetic studies in 14 normal subjects given intravenous commercial [125I]T3 (T3*) and [131I]T4 (T4*), confirmed the quantitative importance of an iodoprotein in later samples after T3* administration, and its presence after T4*. T4* contamination of commercial T3* also became quantitatively important. On the other hand, despite confirmation of in vivo conversion of T4* to T3*, T3* contributed little quantitatively to the total concentration of radioactivity present even late after T4* injection, due to the more rapid turnover and greater distribution volume of T3*.
D002855:Chromatography, Thin Layer / Q000379:methods; D006801:Humans; D007454:Iodides / Q000032:analysis*; D007467:Iodoproteins / Q000032:analysis*; D007700:Kinetics; D012116:Resins, Plant; D012711:Serum Albumin, Radio-Iodinated; D013974:Thyroxine / Q000032:analysis*; D014284:Triiodothyronine / Q000032:analysis*
D007454:Iodides; D007467:Iodoproteins; D012116:Resins, Plant; D012711:Serum Albumin, Radio-Iodinated; D014284:Triiodothyronine; D013974:Thyroxine