Adaptation of Male and Female Rats to Iodine Deficiency

Summary

The response of the hypothalamic pituitary axis to chronic iodine deficiency was compared in male and female Sprague-Dawley rats. The animals were kept on a low iodine diet for 12 weeks. Blood samples as well as thyroid and pituitary weights were obtained every two weeks. Baseline values of thyroid weight and serum thyroxine (T₄) were similar in both sexes. However, females had lower serum TSH and higher serum triiodothyronine (T₃), pituitary weight and pituitary TSH content. After initiation of the low iodine diet, both sexes showed similar decreases in serum T₄ and similar increases of serum TSH and thyroid weight. Serum T₃, pituitary weight and TSH content remained higher in females throughout the study. Pituitary TSH was directly correlated with serum TSH in both sexes. When adjusted for pituitary TSH and analyzed by a stepwise regression analysis, serum TSH was lower in females suggesting a difference in TSH secretion between males and females.

Our studies demonstrate significant sex differences in the regulation of TSH secretion and maintenance of serum T₃ level in response to a chronic stimulus.

Key-Words

Iodine Deficiency - Pituitary Function - Thyroid Function - Serum Thyroxine - Serum Triiodothyronine - Serum TSH