Alterations in T3 and T4 receptor binding in fasting and diabetes mellitus

In order to assess interactions between thyroid hormone receptor kinetics and various metabolic states, we have developed a receptor assay for T3 and T4 in solubilized nuclear extracts from circulating human mononuclear cells and have compared observations in normal individuals to those during fasting and in diabetes mellitus. This assay utilizes the technique of salt solubilization to isolate nuclear receptors and employs standard saturation analysis for T3 and T4 to determine maximal binding capacity (MBC) and equibilibrium dissociation constants (K d). We have determined that 11 normal subjects had a MBC for T3 of 324 ± 34 fm/mg (±SE) protein and a K d of 2.4 ± 0.2 × 10 −10 M; the T4 MBC was 2283 ± 239 fm/mg protein and the Kd was 2.7 ± 0.3 × 10 −10 M. Obese subjects (n=12) had a basal fed MBC that was 253 ± 31 fm/mg protein for T3 (P