Different tissue responses for iodine and iodide in rat thyroid and mammary glands

This research describes the effects of short-term elemental iodine (I₂) and iodide (I⁻) replacement on thyroid glands and mammary glands of iodine-deficient (ID) Sprague-Dawley female rats. Iodine deficiency causes atypical tissue and physiologic changes in both glands. Tissue histopathology and the endocrine metabolic parameters, such as serum TT₄, tissue and body weights, and vaginal smears, are compared. A moderate reduction in thyroid size from the ID control (IDC) was noted with both I⁻ and I₂, whereas serum total thyroxine approached the normal control with both I⁻ and I₂, but was lower in IDC. Thyroid gland IDC hyperplasia was reduced modestly with I₂, but eliminated with I⁻. Lobular hyperplasia of the mammary glands decreased with I₂ and increased with I⁻ when compared with the IDC; extraductal secretions remained the same as IDC with I₂, but increased with I⁻; and periductal fibrosis was markedly reduced with I₂, but remained severe with I⁻. Thus, orally administered I₂ or I⁻ in trace doses with similar iodine availability caused different histopathological and endocrine patterns in thyroid and mammary glands of ID rats. The significance of this is that replacement therapy with various forms of iodine are tissue-specific.