Synthesis of ¹²⁵I Monolabelled 3, 5, 3′-Triiodothyronine and Thyroxine of Maximum Specific Activity for Radioimmunoassay

Abstract

A chloramine T technique for the synthesis of monoiodinated 3,5,3′-¹²⁵I-T₃ and ¹²⁵I-T₄ is described using diiodothyronine and triiodothyronine as ¹²⁵I-acceptors. Specific activities in the order of 3000 mCi/mg T₃ are routinely obtained, i.e. approaching the theoretical maximum value. With these high specific activity products, which are at least 10 times higher than any previously described, it becomes possible to determine free T₃ (and T₄) directly in ultrafiltrates or dialysates of plasma samples.

Key Words:

• Free T₃
• free T₄
• iodination
• radioimmunoassay
• Sephadex-adsorption-chromatography
• specific activity
• thyroxine
• triiodothyronine