Activation and inactivation of thyroxine by cultured rat hepatoma cells |
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Authors: | Kenji Sorimachi Akira Niwa Yosihiro Yasumura |
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Affiliation: | Department of Microbiology, Dokkyo University School of Medicine, Mibu, Tochigi 321-02, Japan |
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Abstract: | The metabolism of thyroxine, 3,3′,5-triiodothyronine and 3,3′,5′-triiodothyronine was investigated in rat hepatoma cell cultures (R117-21B). These iodothyronines were labeled with 125I in the phenolic ring and the metabolites were analyzed by ion-exchange column chromatography.When thyroxine was incubated with the cells at 37°C, its glucuronide was the major product and a little increase in 125I? was detected. Although 3,3′,5-triiodothyronine was not observed in the incubation medium, this metabolite was clearly identified in the ethanol extract obtained from the cell homogenates after 24 h incubation.This cell line also metabolized labeled 3,3′,5-triiodothyronine added to culture medium. After 24 h incubation, 3,3′,5-triiodothyronine glucuronide was the major metabolite and iodothyronine sulfates were also formed. The sulfates contained, 3,3′,5-triiodothyronine and 3,3′-diiodothyronine sulfates and an unknown component.In the metabolism of 3,3′,5′-triiodothyronine, the cells were very active in carrying out glucuronidation and phenolic ring deiodination, and this metabolism yielded 3,3′,5′-triiodothyronine and 3,3′-diiodothyronine glucuronides. The iodide fraction contained a small amount of 3,3′-diiodothyronine sulfate.These results show that the R117-21B rat hepatoma cells metabolize the thyroid hormones and their analogs by phenolic and nonphenolic ring deiodinations, by glucuronidation and by sulfation. |
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Keywords: | Thyroid hormone metabolism Deiodination Glucuronidation Sulfation (Rat hepatoma cell) 3,3′,5-triiodothyronine 3,3′,5′-triiodothyronine |
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