title: Hypothyroidism reduces ObRb-STAT3 leptin signalling in the hypothalamus and pituitary of rats associated with resistance to leptin acute anorectic action.
abstract: Leptin has been shown to regulate the hypothalamus-pituitary-thyroid axis, acting primarily through the STAT3 pathway triggered through the binding of leptin to the long-chain isoform of the leptin receptor, ObRb. We previously demonstrated that although hyperthyroid rats presented leptin effects on TSH secretion, those effects were abolished in hypothyroid rats. We addressed the hypothesis that changes in the STAT3 pathway might explain the lack of TSH response to leptin in hypothyroidism by evaluating the protein content of components of leptin signalling via the STAT3 pathway in the hypothalamus and pituitary of hypothyroid (0·03% methimazole in the drinking water/21 days) and hyperthyroid (thyroxine 5 μg/100 g body weight /5 days) rats. Hypothyroid rats exhibited decreased ObRb and phosphorylated STAT3 (pSTAT3) protein in the hypothalamus, and in the pituitary gland they exhibited decreased ObRb, total STAT3, pSTAT3 and SOCS3 (P<0·05). Except for a modest decrease in pituitary STAT3, no other alterations were observed in hyperthyroid rats. Moreover, unlike euthyroid rats, the hypothyroid rats did not exhibit a reduction in food ingestion after a single injection of leptin (0·5 mg/kg body weight). Therefore, hypothyroidism decreased ObRb-STAT3 signalling in the hypothalamus and pituitary gland, which likely contributes to the loss of leptin action on food intake and TSH secretion, as previously observed in hypothyroid rats.
authors.affiliation: Laboratório de Endocrinologia Molecular, Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Edificio do Centro de Ciencias da Saude, Bloco G CEP 21941-902, Rio de Janeiro, Brazil.
authors.forename: Camila
authors.initials: C
authors.lastname: Calvino
authors.forename: Luana L
authors.initials: LL
authors.lastname: Souza
authors.forename: Ricardo H
authors.initials: RH
authors.lastname: Costa-e-Sousa
authors.forename: Norma A S
authors.initials: NA
authors.lastname: Almeida
authors.forename: Isis H
authors.initials: IH
authors.lastname: Trevenzoli
authors.forename: Carmen C
authors.initials: CC
authors.lastname: Pazos-Moura
mesh_terms: D000208:Acute Disease; D000818:Animals; D000855:Anorexia / Q000139:chemically induced* / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D015536:Down-Regulation; D004351:Drug Resistance / Q000502:physiology; D004435:Eating / Q000187:drug effects / Q000502:physiology; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D007037:Hypothyroidism / Q000150:complications / Q000378:metabolism* / Q000473:pathology; D020738:Leptin / Q000378:metabolism* / Q000494:pharmacology*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D054411:Receptors, Leptin / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013972:Thyrotropin / Q000378:metabolism
chemical_list: D020738:Leptin; D054411:Receptors, Leptin; D050796:STAT3 Transcription Factor; C494088:Stat3 protein, rat; D013972:Thyrotropin