Sodium salt of dextran sulfate ester (MDS-Kowa, Kowa Co., Japan) was administered intravenously to 4 euthyroid subjects, 7 patients with hyperthyroidism and 5 patients with hypothyroidism. Serum FFA rose to the level 4-6 times higher than the preinjection level 15min after the intravenous injection. At the same time, elutable fraction (EF) of T
4, free T
4, and binding capacity and concentration of TBPA increased, while binding capaty of TBG decreased. Addition of dextran sulfate to serum
in vitro caused no change in binding capacity of TBG and EF of T
4. Addition of palmitic acid to serum
in vitro with increasing concentration resulted in a gradual decrease in the distribution of
131I-T
4 to TBG and binding capacity of TBG, while EF of T
4 gradually increased. Intravenous injection of dextran sulfate ester following the prior injection of protamine sulfate in dog caused a mild rise in serum FFA, but failed to increase the EF of T
4. When reverse-flow paper electrophoresis was carried out after addition of
14C-palmitic acid to sera of normal and TBG-deficient subjects, it was confirmed that palmitic acid bound to albumin and TBG fraction. These results suggest that dextran sulfate ester raises serum FFA first, then the increased FFA combines with TBP at least with TBG, thus competing for binding sites with T
4, and released T
4 in turn increases free T
4 level in the serum.
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