Preparation of 125I-labelled thyroid hormones for use in radioimmunoassay. Part of a coordinated programme on quality control of techniques in-vitro assay of thyroid-related hormones (Latin America)

The primary objective was to prepare 125I labelled thyroid hormones for use in radioimmunoassays. T4 and T3 of very high specific activity was obtained by just labelling T2. With a molar relation of T2:125I as 1:2 and Chloramine T:125I as 60:1 it was possible to produce T4125I of approximately 3,300 to 3,800 uc/ug and T3125I of 1,800 and 2,500 uc/ug with reaction times of 60'' to 90''. Simultaneous production from T2 of both labelled T4 and T3 of high specific activity appears to be the best choice for routine radioimmunoassays. Various permutations of the molar relations between T2 and 125I and between chloramine T and 125I it was possible to produce labelled T3 and T4 of varying degrees of specificities. The labelled products can be separated by sephadex G25 chromatography with good resolution. The separation is still improved if sephadex LH-20 is used. T4 and T3 of very high specific activity is preserved best for about a month in Cyst-PG-Alb. Low specific activity material can be preserved in the same medium for about 3 months