Changes in thyroid function in puppies fed a high iodine commercial diet

Abnormally low I-131 uptakes were noticed in dogs fed with commercial diets at the University Animal Clinic in Buenos Aires, but the total iodine content of eight different commercial diets examined was found to provide an iodine intake above daily requirements. To investigate this anomaly, 18 dogs were distributed into three groups, fed either: (1) a home-prepared diet; (2) a commercial diet; (3) a home-prepared diet supplemented with potassium iodide equivalent to that found in the commercial diet. The I-131 uptake in dogs of groups B and C was significantly decreased, as was basal serum thyroxine (T-4) and free thyroxine (FT4), whereas urinary iodide excretion and serum thyroid stimulating hormone (TSH), were increased. The thyroid releasing hormone (TRH)-TSH test showed an increased response in dogs from group B, while the TRH-T, test was inhibited in both groups B and C. The results demonstrate that the excessive amount of iodine present in some commercial diets in Argentina causes a significant impairment of thyroid function and hypothyroidism. (C) 2001 Harcourt Publishers Ltd.