Selenoenzyme Activities in Seleniumand Iodine-Deficient Sheep

Abstract

This study was conducted to evaluate the effects of single and combined deficiencies of selenium and iodine on selenoenzyme activities in sheep. Twenty-four male lambs were assigned to one of four semisynthetic diets: combined deficient A (Se-I), Se-deficient B (Se-I+), I-deficient C (Se+I-), and basal diet D (Se+I+). Thyroid hormones (T3, T4), thyroid stimulating hormone (TSH), and inorganic iodine (PII) were determined in plasma. Selenium and glutathione peroxidase activity (GSH-Px) were determined in erythrocytes, and tissue samples, including the thyroid, liver, kidney, and brain, were taken for selenoenzyme analysis. Plasma T3, T4, and TSH concentrations were similar in all groups. Type I deiodinase (ID-I) activity in liver and kidney remained unchanged in Se or I deficiency. In contrast, hepatic ID-I activity was increased by 70% in combined Se-I deficiency. Thyroidal cystolic GSHPx (c-GSH-Px) and phospholipid GSH-Px (ph-GSH-Px) activities remained constant in both Se-deficient groups, whereas thyroidal c-GSH-Px activity increased (57%) in I deficiency. Type II deiodinase (ID-II) activity was not detectable in the cerebrum and cerebellum, whereas cerebellum Type III deiodinase (ID-III) activity was decreased in I deficiency and combined Se-I deficiencies. The results of the present study support a sensitive interaction between Se and I deficiencies in sheep thyroid and brain. Furthermore, the lack of thyroidal ID-I activity, the preservation of the thyroidal antioxidant enzymes, and the increases in hepatic ID-I indicate that a compensatory mechanism(s) works toward retaining plasma T3 levels, mostly by de novo synthesis of T3 and peripheral deiodination of T4 in Se- and I-deficient sheep.

Regulation of Thyroid Oxidative State by Thioredoxin Reductase Has a Crucial Role in Thyroid Responses to Iodide Excess

“…Our study also showed that the mRNA levels of other selenoproteins (Gpx1, Gpx4, Sep15, Sepp1, Selk1, Selm, and Sbp2) were not modulated by I Ϫ treatment. Although it has been demonstrated that Se supply is directly associated with the control of selenoprotein expression (29,56,57), our results showed that Se supplementation (from 50 -500 nM) of cells treated with I Ϫ excess did not exert effects on selenoprotein modulation other than those reported here (data not shown).…”

Effects of high selenium and fat supplementation on growth performance and thyroid hormones concentration of broilers

“…Although the effects of Se deficiency on thyroid hormone metabolism have been studied extensively in a number of animals [5,6] including chicken [7], very little is known about the influence of excess Se on thyroid hormone metabolism and selenoenzyme activities. In humans, Se supplementation led to variable results, depending on the Se status of the examined population group, extending from non to substantial changes in thyroid function [8][9][10][11][12].…”

Parenteral Selenium and Vitamin E Supplementation to Lambs: Hematology, Serum Biochemistry, Performance, and Relationship with Other Trace Elements

“…More recently, Se was identified as a component of type I iodothyronine-5-deiodinase, the enzyme that converts T4 to T3 [1]. In addition, the effects of Se and/or iodine deficiency on the selenoenzymes activity in sheep were recently described [2]. An important interrelationship exists between Se, vit E, and the sulfur-containing amino acids in preventing some of the nutritional diseases caused by their deficiency [3].…”