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The present study was undertaken to investigate the effects of selenite (SeIV) and selenate (SeVI) on the all-trans retinoic acid (RA)-nuclear retinoic acid receptor (RAR) complex formation in rat liver. We also present the data on the in vitro effects of SeIV on the RARalpha and the type I iodothyronine 5'-deiodinase gene expression in the GH4C1 rat pituitary tumor cells. SeIV at 1.0 micromol/L was found to reduce (p < 0.05) the RA specific binding to RAR in rat liver. Dithiothreitol (DTT), a protective agent for sulfhydryl groups, was found to be slightly effective in protecting the RAR binding properties when affected by SeIV. SeVI at 0.1 micromol/L reduced (p < 0.05) the RA specific binding to RAR in liver, as well. Seleno-L-methionine (Se-II) when compared to L-methionine did not exert any inhibitory effect on the formation of the RA-RAR complex. SeIV (up to 2.5 micromol/L) has no inhibitory effect on GH4C1 cell proliferation as well as the prolactin secretion. SeIV at 1.0 micromol/L significantly decreases the rate of mRNA synthesis and/or degradation of the alpha form of the RAR and causes the enhancement of the type I iodothyronine 5'-deiodinase gene expression in GH4C1 cells. The results based on in vitro experiments suggest that inorganic selenium may affect the RA specific binding to their cognate receptor molecules, and it may reduce expression of the gene encoding the RARalpha, with the cell vitality and the cell growth remaining unchanged.

The present study was undertaken in order to investigate the effects of sodium selenite on: Sodium selenite (up to 2.5 μM) has no inhibitory effect on GH4C1 cell proliferation as well as the prolactin secretion. On the other hand, 0.5 μM sodium selenite significantly decreases the rate of mRNA synthesis and/or degradation of both, the α1 form of the T3 receptor (TRα1) and the α2 isoform of the T3 receptor. At 1 μM of sodium selenine, significant changes in the electrophoretic profile of low molecular mass cytoplasmic proteins were found, moreover, sodium selenite (1 μM) also considerably affects phosphorylation of a higher molecular mass proteins. The results based on the in vitro experiments suggest that sodium selenite may affect specific processes at the pretranslational level as well as it may also take part in processes of posttranslational modification of protein(s), the cell vitality and the cell growth remaining unchanged.

The present study was undertaken to investigate the effects of selenite (SeIV) or selenate (SeVI) on nuclear T3 receptors of rat liver. Selenite at 0.1 microM (p0.01) inhibited the T3 specific binding to rat liver nuclear receptors. The specific binding of the T3 receptor was fully restored when even 1.0 microM selenite was separated from the T3 receptor by gel filtration. No inhibitory effect of selenite (up to 100 microM) on the T3 binding to nuclear receptor was found in the presence of 1.0 mM dithiothreitol. The rate of dissociation of the T3-nuclear receptor complex was effectively increased by 0.1 microM selenite. Selenate up to 1 mM as well as sulfite or sulfate up to 0.1 mM did not exert an inhibitory effect on T3 receptors. The results based on the in vitro experiments suggest that the selenium in the form of selenite may reversibly affect the T3 binding on the receptor molecule.