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      Nuclear Thyroxine Receptors and Cellular Metabolism of Thyroxine in Obese Subjects before and after Fasting

      Hormone Research in Paediatrics

      S. Karger AG

      Fasting, Mononuclear cells, Obesity, Thyroxine receptors, Deiodination

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          Nuclear binding of thyroxine (T<sub>4</sub>), cellular deiodination of T<sub>4</sub> and nuclear accumulation of endogenous triiodothyronine (T<sub>3</sub>) were investigated in mononuclear blood cells in 5 obese persons before and after 7 days of total fast. Serum-free T<sub>4</sub>, serum-free T<sub>3</sub> and serum thyrotropin (TSH) did not differ between lean persons and obese fed subjects, but fasting induced a significant decrease of serum-free T<sub>4</sub> and serum-free T<sub>3</sub> (T<sub>4</sub> from 16.6 to 14.4 pmol/l, T<sub>3</sub> from 5.7 to 3.2 pmol/l). The maximal specific binding capacity (MBC) for T<sub>4 </sub>was decreased in fed obese subjects (MBC = 0.6 fmol T<sub>4</sub>/100 µg DNA, p < 0.05) compared to normal weight persons (MBC =1.3 fmol T<sub>4</sub>/100 µg DNA), whereas the equilibrium association constant (k<sub>a</sub>) did not differ. During complete fast, the MBC increased (MBC =1.5 fmol T<sub>4</sub>/100 µg DNA, p < 0.05). Neither total deiodination of T<sub>4</sub> nor endogenous nuclear T<sub>3</sub> accumulation differed between the groups suggesting that cellular T<sub>4</sub> to T<sub>3</sub> conversion is independent of the nutritional state.We suggest that the observed increase in nuclear T<sub>4</sub> receptor capacity may compensate the decrease in serum thyroid hormone levels.

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          Author and article information

          Horm Res Paediatr
          Hormone Research in Paediatrics
          S. Karger AG
          26 November 2008
          : 21
          : 1
          : 60-65
          Department of Clinical Chemistry and Internal Medicine M, Odense University Hospital, Odense, Denmark
          180025 Horm Res 1985;21:60–65
          © 1985 S. Karger AG, Basel

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          Page count
          Pages: 6


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