Selenoenzyme activities in selenium- and iodine-deficient sheep

Area of Science:

• Animal Nutrition
• Biochemistry
• Endocrinology

Background:

• Selenium and iodine are essential micronutrients crucial for thyroid hormone metabolism and antioxidant defense.
• Deficiencies in these elements can disrupt physiological processes, particularly in the thyroid gland.
• Understanding the interplay between selenium and iodine is vital for animal health and productivity.

Purpose of the Study:

• To investigate the effects of single and combined selenium (Se) and iodine (I) deficiencies on selenoenzyme activities in sheep.
• To analyze the impact on thyroid hormone levels and deiodinase activities in various tissues.
• To elucidate potential compensatory mechanisms in response to nutrient deficiencies.

Main Methods:

• Twenty-four lambs were fed semisynthetic diets with controlled deficiencies: combined Se-I, Se-only, I-only, or a control diet.
• Plasma levels of thyroid hormones (T3, T4), TSH, and inorganic iodine were measured.
• Erythrocyte glutathione peroxidase (GSH-Px) activity and tissue selenoenzyme activities (ID-I, ID-II, ID-III) were analyzed.

Main Results:

• Plasma thyroid hormone and TSH levels remained similar across all groups.
• Hepatic Type I deiodinase (ID-I) activity significantly increased (70%) in combined Se-I deficiency.
• Thyroidal cystolic GSH-Px activity increased (57%) in I deficiency, while Type III deiodinase (ID-III) activity decreased in I and combined Se-I deficiencies.

Conclusions:

• Selenium and iodine deficiencies interact sensitively in sheep thyroid and brain tissues.
• Compensatory mechanisms, including increased hepatic ID-I and preserved thyroid antioxidant enzymes, likely maintain plasma T3 levels.
• These adaptations involve de novo T3 synthesis and peripheral T4 deiodination in deficient sheep.