Thyroid Status in the Obese Syndrome of Rats

Summary

The thyroid function was explored by comparing serum total and free iodothyronine levels in young male genetically obese Zucker rats and in their lean littermates, aged from 6 to 8 weeks old. Total and free thyroxine (T₄) and 3,5,3′triiodothyronine (T₃) levels were significantly decreased in obese rat serum while total 3,3',5'-triiodothyronine (rT₃) remained constant. Radioactive T₄ half life is slower in the plasma of obese rats. Peripheral synthesis of T₃ from deiodination of T₄ is also decreased in obese rat liver homogenate. These modifications produce changes in liver mitochondria oxidative phosphorylation and in marker enzyme activity, which are usually associated with hypothyroidism and hypothalamic disturbances.

Genetic obesity probably involves activation of peripheral deiodination of T₄ to rT₃ which induces biochemical and metabolic changes.

Key-Words:

Obese Rats - Thyroid Hormones - Deiodination - Mitochondria