[Effect on metabolism of thyroid hormones in deficient to subtoxic selenium supply levels]

In an experiment with 72 male weanling Sprague Dawley rats the effect of varying selenium intake on parameters of thyroid hormone metabolism was investigated. The animals were divided into 6 groups. One of the groups was fed a semi-synthetic diet based on casein which was poor in selenium (38 micrograms/kg). The other groups were fed the same diet supplemented with Na2SO3.5H2O to achieve a selenium concentration of 50, 100, 300, 600 and 3,000 micrograms/kg. The experiment lasted 40 days. Different selenium intake had no effect on food intake, weight gain, hematological and selected clinical-chemical parameters. Determination of glutathione peroxidase activity and selenium concentration of serum showed a selenium deficiency in animals fed the diet not supplemented with selenium. Serum T3 concentration and hepatic type-I-deiodinase activity were decreased in the group without selenium supplementation in contrast to the groups fed diets adequate in selenium (100, 300 micrograms/kg). A diet supplementation of 50 micrograms/kg already increased hepatic type-I-deiodinase activity to levels of the groups fed diets adequate in selenium. In groups supplemented with 600 and 3,000 micrograms/kg diet, serum T3 concentration was reduced by half of groups fed diets adequate in selenium. Supplementation with 3,000 micrograms Se/kg lowered the type-I-deiodinase activity in contrast to groups fed diets adequate in selenium, but not significantly. Serum concentrations of T4 and fT4 were not changed by various selenium intake. The results of this investigation show an alteration in thyroid hormone metabolism at low selenium intake as well as at high selenium intake.