title: Underlying Mechanisms of Pituitary-Thyroid Axis Function Disruption by Chronic Iodine Excess in Rats.
abstract: Iodine is essential for thyroid hormone synthesis and is an important regulator of thyroid function. Chronic iodine deficiency leads to hypothyroidism, but iodine excess also impairs thyroid function causing hyperthyroidism, hypothyroidism, and/or thyroiditis. This study aimed to investigate the underlying mechanisms by which exposure to chronic iodine excess impairs pituitary-thyroid axis function.
  
  
  
  Male Wistar rats were treated for two months with NaI (0.05% and 0.005%) or NaI+NaClO4(0.05%) dissolved in drinking water. Hormone levels, gene expression, and thyroid morphology were analyzed later.
  
  
  
  NaI-treated rats presented high levels of iodine in urine, increased serum thyrotropin levels, slightly decreased serum thyroxine/triiodothyronine levels, and a decreased expression of the sodium-iodide symporter, thyrotropin receptor, and thyroperoxidase mRNA and protein, suggesting a primary thyroid dysfunction. In contrast, thyroglobulin and pendrin mRNA and protein content were increased. Kidney and liver deiodinase type 1 mRNA expression was decreased in iodine-treated rats. Morphological studies showed larger thyroid follicles with higher amounts of colloid and increased amounts of connective tissue in the thyroid of iodine-treated animals. All these effects were prevented when perchlorate treatment was combined with iodine excess.
  
  
  
  The present data reinforce and add novel findings about the disruption of thyroid gland function and the compensatory action of increased thyrotropin levels in iodine-exposed animals. Moreover, they draw attention to the fact that iodine intake should be carefully monitored, since both deficient and excessive ingestion of this trace element may induce pituitary-thyroid axis dysfunction.
authors.affiliation: 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo , São Paulo, Brazil .
authors.forename: Jamile
authors.initials: J
authors.lastname: Calil-Silveira
authors.affiliation: 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo , São Paulo, Brazil .
authors.forename: Caroline
authors.initials: C
authors.lastname: Serrano-Nascimento
authors.affiliation: 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo , São Paulo, Brazil .
authors.forename: Raquel Cardoso
authors.initials: RC
authors.lastname: Laconca
authors.affiliation: 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo , São Paulo, Brazil .
authors.forename: Letícia
authors.initials: L
authors.lastname: Schmiedecke
authors.affiliation: 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo , São Paulo, Brazil .
authors.forename: Rafael Barrera
authors.initials: RB
authors.lastname: Salgueiro
authors.affiliation: 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo , São Paulo, Brazil .
authors.forename: Ayrton Kimidi
authors.initials: AK
authors.lastname: Kondo
authors.affiliation: 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo , São Paulo, Brazil .
authors.forename: Maria Tereza
authors.initials: MT
authors.lastname: Nunes
mesh_terms: D000818:Animals; D000931:Antidotes / Q000627:therapeutic use; D005786:Gene Expression Regulation / Q000187:drug effects*; D007453:Iodide Peroxidase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D007455:Iodine / Q000737:chemistry / Q000506:poisoning* / Q000652:urine; D008297:Male; D010472:Perchlorates / Q000627:therapeutic use; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D011041:Poisoning / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology* / Q000517:prevention & control; D012333:RNA, Messenger / Q000378:metabolism; D017208:Rats, Wistar; D011989:Receptors, Thyrotropin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D065667:Renal Elimination; D017670:Sodium Compounds / Q000627:therapeutic use; D012974:Sodium Iodide / Q000008:administration & dosage; D027981:Symporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D013966:Thyroiditis / Q000209:etiology*; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism; D013974:Thyroxine / Q000097:blood / Q000378:metabolism; D036401:Toxicity Tests, Chronic; D066007:Toxicokinetics; D014284:Triiodothyronine / Q000097:blood / Q000378:metabolism; D000099209:Sodium-Iodide Symporters
chemical_list: D000931:Antidotes; D007453:Iodide Peroxidase; D007455:Iodine; D010472:Perchlorates; D012333:RNA, Messenger; D011989:Receptors, Thyrotropin; D017670:Sodium Compounds; D012974:Sodium Iodide; D027981:Symporters; D013972:Thyrotropin; D013974:Thyroxine; D014284:Triiodothyronine; D000099209:Sodium-Iodide Symporters; C031068:sodium perchlorate