Effects of Selenium Deficiency on Tissue Selenium Content, Deiodinase Activity, and Thyroid Hormone Economy in the Rat during Development*

Abstract

The iodothyronine deiodinases, D1, D2, and D3, all contain selenium (Se) in the form of selenocysteine at their active sites, and they play crucial roles in determining the circulating and intracellular levels of the active thyroid hormone (TH), T3. However, not only are serum T3 levels normal in Se-deficient rats but phenotypic and reproductive abnormalities are minimal, and it has been suggested that regulatory mechanisms exist to conserve Se in critical tissues. The present study was designed to determine, in rats: 1) whether the effects of Se-deficiency are greater in the fetus and neonate than in the adult; 2) whether there are tissues other than brain and thyroid in which deiodinase activities are maintained; 3) whether the maintenance of deiodinase activity in a specific tissue is associated with a concomitant preservation of Se level in that tissue; and 4) whether TH economy and general health is maintained over several generations. The tissues studied included liver, cerebrum, thyroid, pituitary, skin, brown adipose tissue, uterus, ovary, testis, placenta, and the implantation site (uterus plus contents) at E9. The results have revealed that, with the exception of liver, skin, and nonpregnant uterus, all of the tissues studied maintained substantial deiodinase activity (>50%) during prolonged Se-deficiency. Second, although the ability of a tissue to maintain deiodinase activity in the face of dietary Se deprivation was associated in some tissues with a concomitant local preservation of Se concentration, this was not the case for all tissues. Only when Se levels were decreased by more than 80% was deiodinase activity markedly decreased. Third, the effects of Se-deficiency were no greater in the fetus than in the adult; and fourth, at the level of Se-deficiency employed in this study, TH economy and general health were successfully maintained over six generations of Se-deficient rats. How Se levels are maintained in specific tissues, whether Se is sequestered in specific cells of a tissue or organ during dietary Se deprivation, and the precise mechanisms by which plasma T3 levels are maintained in Se-deficient animals remain unanswered. Further insights may be gained by using diets that are even lower in Se than those that were used herein and/or by conducting studies using radioactive forms of Se and thyroid hormones.

The relationship between serum level of thyroid hormones, trace elements and antioxidant enzymes in dromedary camel (Camelus dromedarius)

“…Wichtel et al (1996) showed that the plasma concentration of total thyroxin was increased (P<0.001) by selenium treatment and Bik (2003) determined the effect of selenium and iodine oral supplements on the concentration of T 3 and T 4 in the serum of sheep. It is important to note that only when selenium levels decreased by more than 80%, deiodinase activity was markedly decreased (Bates et al 2000). Bates et al (2000) stated that with the exception of liver, skin and nonpregnant uterus, all of the tissues studied (including cerebrum, thyroid, pituitary, brown adipose tissue, ovary, testes and placenta) maintained substantial deiodinase activity (>50%) during prolonged selenium deficiency.…”

“…It is important to note that only when selenium levels decreased by more than 80%, deiodinase activity was markedly decreased (Bates et al 2000). Bates et al (2000) stated that with the exception of liver, skin and nonpregnant uterus, all of the tissues studied (including cerebrum, thyroid, pituitary, brown adipose tissue, ovary, testes and placenta) maintained substantial deiodinase activity (>50%) during prolonged selenium deficiency. Although the ability of a tissue to maintain deiodinase activity in the face of dietary selenium deprivation was associated in some tissues with a concomitant local preservation of selenium concentration, this was not the case for all tissues.…”

“…Although the ability of a tissue to maintain deiodinase activity in the face of dietary selenium deprivation was associated in some tissues with a concomitant local preservation of selenium concentration, this was not the case for all tissues. How selenium levels are maintained in specific tissues, whether selenium is sequestered in specific cells of a tissue or organ during dietary selenium deprivation and the precise mechanism by which plasma T 3 levels are maintained in selenium deficient animals remain unanswered (Bates et al 2000).…”

Hepatic iodothyronine deiodinase type 1 activity is decreased in two ΔF508 cystic fibrosis mouse models

“…Upon severe selenium deficiency, hepatic D1 activity in rat is decreased, although liver selenium levels and D1 activities do not tightly correlate [34]. In addition, in severely selenium deficient rats the drastically reduced hepatic D1 activities were not reflected in the moderate changes measured in thyroid hormone levels [35 -37].…”

Functional Effects of Short-Term Treatment with Amiodarone on Thyroid Tissues of the Rabbit

“…The enzymatic activity of 5MI has a strong inverse relationship to selenium deficiency [8]. Low selenium concentration effects in thyroid hormone levels can be completely reversed after selenium supplementation with sodium selenite [9].…”