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 (Kd). We have determined that 11 normal subjects had a MBC for T3 of 324 ± 34 fm/mg (±SE) protein and a Kd 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 <0.05 compared to normal) and was 1620 ± 160 fm/mg protein for T4 (P <0.01 compared to normal). During fasting, the average T3 MBC increased to 410 ± 52 fmol/mg protein and the average T4 MBC increased to 2150 ± 18 fmol/mg protein, values that are both significantly higher than those in the fed period (P<.05); the dissociation constants were unaltered in obese subjects (compared to normals) in fed and fasting states. In separate experiments, 12 normal subjects had a T3 MBC of 520 ± 60 fm/mg protein (mean ±SE) and a T3 Kd of 4.5 ± 0.4 × 10−10M, while 7 diabetic subjects had a T3 MBC of 290 ± 50 fm/mg protein (P <.05) and a T3 Kd of 3.0 ± 0.4 × 10−10M. The T4 MBC in these normal subjects was 1540 ± 130 fm/mg protein and the T4 Kd was 2.0 ± 0.5×10−10M, while in the diabetics T4 MBC was not altered being 1470 ± 230 fm/mg protein with a T4 Kd of 3.5 ± 0.7×10−10M.