Abstract

This paper is the first description of a radioimmunoassay (RIA) for triiodothyronine sulfate (T₃S). Rabbits were immunized against T₃S coupled to bovine serum albumin using carbodiimide. All animals produced antibodies to T₃S but also even higher titers of T₃ antibodies. Ka values for binding of T₃ and T₃S to these antisera varied between 2×10¹⁰ and 8×10¹⁰ M⁻¹. One of the antisera (#8193) was selected for use in the T₃S RIA because of a high titer of T₃S antibodies (final dilution 1: 50,000), a high sensitivity to T₃S (<2.5 fmol/tube), and a low crossreactivity by T₃ (0.4%). This RIA provides a tool for the study of the importance of sulphation as a metabolic pathway for T₃.