Thyroid function and deiodinase activities in rats with marginal iodine deficiency

Area of Science:

• Endocrinology
• Nutritional Science
• Neuroscience

Background:

• Iodine is essential for thyroid hormone synthesis.
• Thyroid hormones regulate metabolism and development.
• Iodothyronine deiodinases (IDs) are key enzymes in thyroid hormone metabolism.

Purpose of the Study:

• To investigate the effect of marginal iodine deficiency on iodothyronine deiodinase activities in rat liver and brain.
• To differentiate the effects of iodine deficiency from food restriction on deiodinase activity.

Main Methods:

• Male rats were fed iodine-deficient or iodine-sufficient diets under restricted feeding conditions (60% of ad libitum intake) for 6 weeks.
• Thyroid weight, urinary iodine excretion, plasma thyroxine (T4), and triiodothyronine (T3) concentrations were measured.
• Activities of type I, II, and III deiodinases in liver and brain tissues were assessed.

Main Results:

• Iodine deficiency led to increased thyroid weight, reduced urinary iodine, and lower plasma T4.
• Liver type I and brain type III deiodinase activities remained unchanged.
• Brain type II deiodinase activity was significantly increased (28%) in iodine-deficient rats.
• Food restriction alone reduced plasma T3 and T4 and decreased brain type III deiodinase activity.

Conclusions:

• Marginal iodine deficiency selectively increases brain type II deiodinase activity in rats.
• Hepatic type I and brain type III deiodinase activities are resistant to marginal iodine deficiency under these conditions.
• Food restriction has independent effects on thyroid hormone levels and deiodinase activity, distinct from iodine deficiency.