Reduced thyroxine production in young household contacts of tuberculosis patients increases active tuberculosis disease risk.

In the current study, we followed 839 household contacts (HHCs) of tuberculosis (TB) patients for 2 years and identified the factors that enhanced the development of TB. Fourteen of the 17 HHCs who progressed to TB were in the 15- to 30-year-old age group. At baseline (the "0" time point, when all the individuals were healthy), the concentration of the thyroid hormone thyroxine (T4) was lower, and there were increased numbers of Tregs in PBMCs of TB progressors. At baseline, PBMCs from TB progressors stimulated with early secretory antigenic target 6 (ESAT-6) and 10 kDa culture filtrate antigen (CFP-10) produced less IL-1α. Thyroid hormones inhibited Mycobacterium tuberculosis (Mtb) growth in macrophages in an IL-1α-dependent manner. Mtb-infected Thra1PV/+ (mutant thyroid hormone receptor) mice had increased mortality and reduced IL-1α production. Our findings suggest that young HHCs who exhibit decreased production of thyroid hormones are at high risk of developing active TB disease.

Thyroid hormone synthesis continues despite biallelic thyroglobulin mutation with cell death.

Complete absence of thyroid hormone is incompatible with life in vertebrates. Thyroxine is synthesized within thyroid follicles upon iodination of thyroglobulin conveyed from the endoplasmic reticulum (ER), via the Golgi complex, to the extracellular follicular lumen. In congenital hypothyroidism from biallelic thyroglobulin mutation, thyroglobulin is misfolded and cannot advance from the ER, eliminating its secretion and triggering ER stress. Nevertheless, untreated patients somehow continue to synthesize sufficient thyroxine to yield measurable serum levels that sustain life. Here, we demonstrate that TGW2346R/W2346R humans, TGcog/cog mice, and TGrdw/rdw rats exhibited no detectable ER export of thyroglobulin, accompanied by severe thyroidal ER stress and thyroid cell death. Nevertheless, thyroxine was synthesized, and brief treatment of TGrdw/rdw rats with antithyroid drug was lethal to the animals. When untreated, remarkably, thyroxine was synthesized on the mutant thyroglobulin protein, delivered via dead thyrocytes that decompose within the follicle lumen, where they were iodinated and cannibalized by surrounding live thyrocytes. As the animals continued to grow goiters, circulating thyroxine increased. However, when TGrdw/rdw rats age, they cannot sustain goiter growth that provided the dying cells needed for ongoing thyroxine synthesis, resulting in profound hypothyroidism. These results establish a disease mechanism wherein dead thyrocytes support organismal survival.

Metribuzin-induced non-adverse liver changes result in rodent-specific non-adverse thyroid effects via uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT) modulation.

Metribuzin is a herbicide that inhibits photosynthesis and has been used for over 40 years. Its main target organ is the liver and to some extent the kidney in rats, dogs, and rabbits. Metribuzin shows a specific thyroxine (T4) profile in rat studies with T4 increases at low doses and T4 decreases at higher doses. Only the T4 decreases occur together with histopathological changes in the thyroid and weight changes of liver and thyroid. A set of experiments was conducted to investigate metribuzin's endocrine disruptor potential according to European guidance and regulations. The results indicate that a liver enzyme modulation, i.e. of the uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT), is most likely responsible for both increased and decreased plasma thyroxine level and for thyroid histopathological observations. Animals with high T4 levels show low UGT activity, while animals with low T4 levels show high UGT activity. A causal relationship was inferred, since other potentially human-relevant mode of action (MOA) pathways were excluded in dedicated studies, i.e. inhibition of deiodinases (DIO), inhibition of thyroid peroxidase (TPO) or of the sodium importer system (NIS). This liver metabolism-associated MOA is considered not relevant for human hazard assessment, due to species differences in thyroid homeostasis between humans and rats and, more importantly, based on experimental data showing that metribuzin affects UGT activity in rat but not in human hepatocytes. Further, we discuss whether or not increased T4 levels in the rat, in the absence of histopathological changes, should be considered as adverse and therefore used as an appropriate hazard model for humans. Based on a weight of evidence approach, metribuzin should not be classified as an endocrine disruptor with regard to the thyroid modality.

Influence of in utero di-n-hexyl phthalate and di-cyclohexyl phthalate exposure on the endocrine glands and T3, T4, and TSH hormone levels of male and female rats: Postnatal outcomes.

The present study was designed to evaluate the effects of di-n-hexyl phthalate (DHP) and di-cyclohexyl phthalate (DCHP) on endocrine organs in rats. Oil control, 20-, 100-, and 500 mg/kg dose groups were selected and administered to pregnant rats on gestational days 6-19 by oral gavage. The neonatal stages of rats continued until postnatal day 20 and the- juvenile stages of rats continued until postnatal day of 32. The rats were allowed to mature until the neonatal and juvenile stages and there after, they were divided into four groups corresponding to the treatment levels. Body and organ weights were recorded, serum was collected, and thyroid, pancreas, pituitary gland, and adrenal gland were removed. There was a decrease in body weights in the 20- and 500mg/kg DHP and in the 20-mg/kg DCHP dose groups in neonatal male rats. In contrast, for female rats, there was an increase in body weights in the 100-mg/kg DCHP dose group and there was a decrease in body weights in the 500-mg/kg DHP dose group. Body weights were increased at 20 and 500 mg/kg in the DHP-exposed juvenile male rats. Serum thyroid-stimulating hormone (TSH) levels were increased in neonatal male rats, while they were increased in the 100-mg/kg DHP group of neonatal and juvenile female rats. Serum triiodothyronine (T3) levels were increased at the high dose of DHP for neonatal male rats and at the low and high dose levels of DCHP for female rats. Serum thyroxine (T4) levels were increased in neonatal rats for DHP. Also, some histopathological changes were observed in the thyroid, pancreas, adrenal, and pituitary gland. In conclusion, it was shown that DHP and DCHP caused negative effects on T3, T4, and TSH hormone levels.

The effect of thyroid dysfunction and treatment on adropin, asprosin and preptin levels in rats.

OBJECTIVES: Thyroid hormones have important roles in normal development and energy regulating mechanisms as well as signaling mechanisms that affect energy consumption through central and peripheral pathways. The aim of this study was to determine the effects of thyroid dysfunction on adropin, asprosin and preptin levels in rat. METHODS: The study was performed on the 38 male Wistar-albino rats. Experiment groups were designed as follows. 1-Control, 2-Hypothyroidism; To induce hypothyroidism PTU was applied by intraperitoneal as 10 mg/kg/day for 2 weeks. 3-Hypothyroidism + Thyroxine; Previously animals were made with hypothyroidism by 1 week PTU application and then 1 week l-thyroxine was given by intraperitoneal as 1.5 mg/kg/day. 4-Hyperthyroidism; Rats were made with hyperthyroidism by 3 weeks l-thyroxine (0.3 mg/kg/day). 5-Hyperthyroidism + PTU; Animals were made hyperthyroisim by l-thyroxine as groups 4, then 1 week PTU was applied to treatment of hiperthyrodism. At the end of supplementation animals were sacrificed and blood samples were collected for FT3, FT4, adropin, asprosin, preptin analysis. RESULTS: FT3 ve FT4 levels were reduced significantly in hypothyroidism while increased in hyperthyroidism (p<0.001). Hipothyrodism led to reduces adropin, asprosin and preptin levels. And also hyperthyroidism reduced adropin and preptin levels (p<0.001). CONCLUSIONS: The results of study show that experimental hypothyroidism and hyperthyroidism lead to significantly change to adropin, asprosin and preptin levels. However, correction of thyroid function caused to normals levels in asprosin and preptin.

Non-Specific Porins of Yersinia pseudotuberculosis as Inductors of Experimental Hyperthyroidism in Mice.

In vivo experiments showed that antibodies to OmpC and OmpF porins of Yersinia pseudotuberculosis increased thyroxine (T4) level in the blood of experimental animals. The mice were immunized with different antigens: recombinant OmpF porin in a soluble monomeric form, trimers of OmpC and OmpF porins isolated from the outer membrane, or antibodies to them. The level of thyroxine in the blood of mice immunized with OmpF and OmpC porins increased by 5.47 and 22.3 times, respectively; after immunization with antibodies to these proteins, blood thyroxine increased by 9.28 and 14.29 times. Immunization with recombinant OmpF porin induced no reliable increase in thyroxine level. Hence, the serum to recombinant OmpF porin contains no antibodies specific to conformational antigenic determinants that are present in the protein trimer and, according to our previous findings from molecular docking studies, determine cross-reactions between OmpF porin of Y. pseudotuberculosis and thyroidstimulating hormone receptor.

The role of thyroglobulin in thyroid hormonogenesis.

In humans, the thyroid hormones T3 and T4 are synthesized in the thyroid gland in a process that crucially involves the iodoglycoprotein thyroglobulin. The overall structure of thyroglobulin is conserved in all vertebrates. Upon thyroglobulin delivery from thyrocytes to the follicular lumen of the thyroid gland via the secretory pathway, multiple tyrosine residues can become iodinated to form mono-iodotyrosine (MIT) and/or di-iodotyrosine (DIT); however, selective tyrosine residues lead to preferential formation of T4 and T3 at distinct sites. T4 formation involves oxidative coupling between two DIT side chains, and de novo T3 formation involves coupling between an MIT donor and a DIT acceptor. Thyroid hormone synthesis is stimulated by TSH activating its receptor (TSHR), which upregulates the activity of many thyroid gene products involved in hormonogenesis. Additionally, TSH regulates post-translational changes in thyroglobulin that selectively enhance its capacity for T3 formation - this process is important in iodide deficiency and in Graves disease. 167 different mutations, many of which are newly discovered, are now known to exist in TG (encoding human thyroglobulin) that can lead to defective thyroid hormone synthesis, resulting in congenital hypothyroidism.

Neurodevelopment and Thyroid Hormone Synthesis Inhibition in the Rat: Quantitative Understanding Within the Adverse Outcome Pathway Framework.

Adequate levels of thyroid hormone (TH) are needed for proper brain development, deficiencies may lead to adverse neurologic outcomes in humans and animal models. Environmental chemicals have been linked to TH disruption, yet the relationship between developmental exposures and decline in serum TH resulting in neurodevelopmental impairment is poorly understood. The present study developed a quantitative adverse outcome pathway where serum thyroxin (T4) reduction following inhibition of thyroperoxidase in the thyroid gland are described and related to deficits in fetal brain TH and the development of a brain malformation, cortical heterotopia. Pregnant rats were exposed to 6-propylthiouracil (PTU 0, 0.1, 0.5, 1, 2, or 3 parts per million [ppm]) from gestational days 6-20, sequentially increasing PTU concentrations in maternal thyroid gland and serum as well as in fetal serum. Dams exposed to 0.5 ppm PTU and higher exhibited dose-dependent decreases in thyroidal T4. Serum T4 levels in the dam were significantly decreased with exposure to 2 and 3 ppm PTU. In the fetus, T4 decrements were first observed at a lower dose of 0.5 ppm PTU. Based on these data, fetal brain T4 levels were estimated from published literature sources, and quantitatively linked to increases in the size of the heterotopia present in the brains of offspring. These data show the potential of in vivo assessments and computational descriptions of biologic responses to predict the development of this structural brain malformation and use of quantitative adverse outcome pathway approach to evaluate brain deficits that may result from exposure to other TH disruptors.

Hypothyroidism induced by loss of the manganese efflux transporter SLC30A10 may be explained by reduced thyroxine production.

SLC30A10 and SLC39A14 are manganese efflux and influx transporters, respectively. Loss-of-function mutations in genes encoding either transporter induce hereditary manganese toxicity. Patients have elevated manganese in the blood and brain and develop neurotoxicity. Liver manganese is increased in patients lacking SLC30A10 but not SLC39A14. These organ-specific changes in manganese were recently recapitulated in knockout mice. Surprisingly, Slc30a10 knockouts also had elevated thyroid manganese and developed hypothyroidism. To determine the mechanisms of manganese-induced hypothyroidism and understand how SLC30A10 and SLC39A14 cooperatively mediate manganese detoxification, here we produced Slc39a14 single and Slc30a10/Slc39a14 double knockout mice and compared their phenotypes with that of Slc30a10 single knockouts. Compared with wild-type controls, Slc39a14 single and Slc30a10/Slc39a14 double knockouts had higher manganese levels in the blood and brain but not in the liver. In contrast, Slc30a10 single knockouts had elevated manganese levels in the liver as well as in the blood and brain. Furthermore, SLC30A10 and SLC39A14 localized to the canalicular and basolateral domains of polarized hepatic cells, respectively. Thus, transport activities of both SLC39A14 and SLC30A10 are required for hepatic manganese excretion. Compared with Slc30a10 single knockouts, Slc39a14 single and Slc30a10/Slc39a14 double knockouts had lower thyroid manganese levels and normal thyroid function. Moreover, intrathyroid thyroxine levels of Slc30a10 single knockouts were lower than those of controls. Thus, the hypothyroidism phenotype of Slc30a10 single knockouts is induced by elevated thyroid manganese, which blocks thyroxine production. These findings provide new insights into the mechanisms of manganese detoxification and manganese-induced thyroid dysfunction.

Thyroid hormone biosynthesis and release.

Thyroid hormones (TH) 3,5,3',5'- tetraiodothyronine or thyroxine (T4) and 3,5,3'- triiodothyronine (T3) contain iodine atoms as part of their structure, and their synthesis occur in the unique structures called thyroid follicles. Iodide reaches thyroid cells through the bloodstream that supplies the basolateral plasma membrane of thyrocytes, where it is avidly taken up through the sodium/iodide symporter (NIS). Thyrocytes are also specialized in the secretion of the high molecular weight protein thyroglobulin (TG) in the follicular lumen. The iodination of the tyrosyl residues of TG preceeds TH biosynthesis, which depends on the interaction of iodide, TG, hydrogen peroxide (H2O2) and thyroid peroxidase (TPO) at the apical plasma membrane of thyrocytes. Thyroid hormone biosynthesis is under the tonic control of thyrotropin (TSH), while the iodide recycling ability is very important for normal thyroid function. We discuss herein the biochemical aspects of TH biosynthesis and release, highlighting the novel molecules involved in the process.

Sepsis leads to thyroid impairment and dysfunction in rat model.

Sepsis was a systemic response to a local infection. Apoptosis was observed in the experimental sepsis. In this study, cecal ligation and puncture (CLP)-induced sepsis was established in rats. We found that sepsis decreased thyroid hormone levels, including triiodothyronine (T3), thyroxine (T4), free T3 (fT3), and free T4 (fT4). Besides, we detected the increasing expression level of Caspase-3 and increasing ratio of TUNEL positive cells in the thyroid after sepsis. Furthermore, a series of pathological ultrastructural changes were observed in thyroid follicular epithelial cells by CLP-induced sepsis. This study established a sepsis animal model and provided the cellular and molecular basis for decoding the pathological mechanism in thyroid with the occurrence of sepsis.

Neuro-Modulation of Immuno-Endocrine Response Induced by Kaliotoxin of Androctonus Scorpion Venom.

Kaliotoxin (KTX), a specific blocker of potassium channels, exerts various toxic effects due to its action on the central nervous system. Its use in experimental model could help the understanding of the cellular and molecular mechanisms involved in the neuropathological processes related to potassium channel dysfunctions. In this study, the ability of KTX to stimulate neuro-immuno-endocrine axis was investigated. As results, the intracerebroventricular injection of KTX leads to severe structural-functional alterations of both hypothalamus and thyroid. These alterations were characterized by a massive release of hormones' markers of thyroid function associated with damaged tissue which was infiltrated by inflammatory cell and an imbalanced redox status. Taken together, these data highlight that KTX is able to modulate the neuro-endocrine response after binding to its targets leading to the hypothalamus and the thyroid stimulation, probably by inflammatory response activation and the installation of oxidative stress in these organs.

Chemistry and Biology in the Biosynthesis and Action of Thyroid Hormones.

Thyroid hormones (THs) are secreted by the thyroid gland. They control lipid, carbohydrate, and protein metabolism, heart rate, neural development, as well as cardiovascular, renal, and brain functions. The thyroid gland mainly produces l-thyroxine (T4) as a prohormone, and 5'-deiodination of T4 by iodothyronine deiodinases generates the nuclear receptor binding hormone T3. In this Review, we discuss the basic aspects of the chemistry and biology as well as recent advances in the biosynthesis of THs in the thyroid gland, plasma transport, and internalization of THs in their target organs, in addition to the deiodination and various other enzyme-mediated metabolic pathways of THs. We also discuss thyroid hormone receptors and their mechanism of action to regulate gene expression, as well as various thyroid-related disorders and the available treatments.

Rapid preoperative blockage of thyroid hormone production / secretion in patients with Graves' disease.

PRINCIPLES: Preoperative management of hyperthyroid patients with Graves' disease who are unable to tolerate thionamides or have poor adherence to therapy is a challenging clinical problem. The goal of our study was to demonstrate the clinical efficacy of a rapid preoperative thyroid hormone blocking protocol and to assess specific surgical and treatment-related complications. METHODS: Ten patients with thyrotoxicosis due to Graves' disease were treated with a rapid thyroid hormone blocking protocol of Lugol's solution, dexamethasone and a beta-blocker. Two patients continued to receive antithyroid therapy with carbimazole. Adrenal function was assessed 4-6 weeks postoperatively with a low dose (1 µg) adrenocorticotrophic hormone-stimulation test. RESULTS: Before treatment, all patients had severe hyperthyroidism. Baseline median and interquartile range (IQR) of fT4 was 68.9 (45.7-92.1) pmol/l, and baseline median fT3 and IQR, 30 (19.1-40.9) pmol/l. After 10 days of treatment, the levels of free hormones were significantly reduced with fT4 concentrations slightly elevated (fT4, 26.7 [17-36.4] pmol/l, p <0.001 compared with corresponding pretreatment values), and the fT3 concentration was normal in 8/10 patients (fT3, 6.1 [4.6-7.6] pmol/l, p <0.001 compared with corresponding pretreatment values). All patients were clinically euthyroid with a heart rate of <80/min. Drug tolerability was excellent, and there were no side effects or exacerbation of hyperthyroidism. The peri- and postoperative course was uneventful in all cases. Adrenal function was normal in 7 out of 10 patients 4-6 weeks postoperatively. Three patients showed prolonged secondary adrenal insufficiency with normalisation of adrenal function after 3 to 6 months. CONCLUSION: Rapid and effective preoperative preparation of patients with Graves' disease is achievable with Lugol's solution, dexamethasone and a beta-blocker. The risk of temporary hypothalamic-pituitary-adrenal axis suppression has to be taken into account.

The effects of subclinical hypothyroidism on serum lipid level and TLR4 expression of monocyte in peripheral blood of rats.

OBJECTIVE: To observe effect of subclinical hypothyroidism (SCH) on serum lipid level and expression of toll-like receptor 4 (TLR4) in rats' peripheral blood mononuclear cells (PBMC). METHODS: Fifty Wistar female rats were divided into three groups: normal control (NC group; n=10), sham group (n=10), and L-T-4 (L-thyroxine) group (n=30, with thyroidectomy, fed with rich-calcium water after operation. 5 weeks later, abdominal subcutaneous injection of L-T-4: 0.95 µg/100g/d). 8 weeks later, the rats were killed then the peripheral blood was collected to determine the levels of serum thyroid-stimulating hormone (TSH), total thyroid hormone (TT4), total cholesterol (TC) and low density lipoprotein cholesterin (LDL-C). Rats in L-T-4 group were divided into normal lipid (NL) group) and high lipid (HL) group) according to lipid value of NC group. Monocytes were separated from blood to determine TLR4 expression by flow cytometry. RESULTS: In NL and HL groups TSH were higher than in NC and Sham groups (p<0.05). TT4 have no significant differences (p>0.05). TLR4, TLR4 mRNA, NF-κB (p65) were increased (p<0.05). TNF-α, IL-6 and IL-1ß were higher than in NC and sham groups (p<0.01). There were no significant differences of TLR4, TLR4 mRNA, NF-κB (p65), TNF-α, IL-6 and IL-1ß expression between NL and HL groups (p>0.05). CONCLUSION: TLR4, TLR4 mRNA, NF-κB (p65) of PBMC and TNF-α, IL-6, IL-1ß expression in serum were all increased in SCH rats, which was not related to serum dyslipidemia.

Supraphysiologic doses of levothyroxine as adjunctive therapy in bipolar depression: a randomized, double-blind, placebo-controlled study.

OBJECTIVE: Suboptimal availability of circulating thyroid hormones may contribute to the high rate of treatment failures in bipolar disorder. This study tested the efficacy of adjunctive treatment with supraphysiologic doses of levothyroxine in patients with bipolar depression and the hypothesis that women would display a better outcome compared to men. METHOD: The aims of this multicenter, 6-week, double-blind, randomized, placebo-controlled fixed-dose (300 µg/d) trial conducted from 2004 to 2009 were to assess efficacy and tolerability of levothyroxine adjunctive to continuing treatment with mood stabilizer and/or antidepressant medication for patients with bipolar I or II disorder, currently depressed (DSM-IV), and to investigate gender differences in treatment response. The primary efficacy variable was mean change in Hamilton Depression Rating Scale (HDRS) score. RESULTS: Of 74 patients enrolled in the study, 62 (35 with bipolar I; mean age = 44.9 years) were randomized. Mean change in HDRS score from randomization to week 6 was larger in the levothyroxine group compared to the placebo group, with a 2.7-point difference (decline of -7.8 [38.3%] vs -5.1 [25.5%]; last-observation-carried-forward analysis). The course of HDRS scores over time from randomization to week 6 was significantly different between groups at week 4 (P = .046) but not at the end of the placebo-controlled phase (P = .198). The secondary analysis of women (n = 32) revealed a significant difference between groups in mean change in HDRS score (-16.6% placebo vs -42.4% levothyroxine, P = .018). A mixed-effects model for repeated-measures analysis showed a significant between-group difference in HDRS score (6.8, P = .012) for women. High thyroid-stimulating hormone levels, indicating suboptimal levels of circulating thyroid hormones, were predictive for positive treatment outcome in women treated with levothyroxine in a linear regression model (F3 = 3.47; P = .05). DISCUSSION: This trial demonstrated that patients treated with levothyroxine did numerically better than those treated with placebo; however, the study failed to detect a statistically significant difference between the 2 groups in the primary outcome measure due to a high placebo response rate. Previous findings that women show better improvement in depression scores with levothyroxine compared to men were confirmed. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01528839.

Effects of perchlorate on BDE-47-induced alteration thyroid hormone and gene expression of in the hypothalamus-pituitary-thyroid axis in zebrafish larvae.

To investigate the effects of perchlorate on thyroid hormone disturbances induced by 2,2',4',4-tetrabromodiphenyl ether (BDE-47) via thyroid hormone (TH)-mediated pathways, zebrafish embryos were exposed to a combination of BDE-47 and PER from the time of fertilisation to 14 d (dpf). The whole-body content of TH and the expression of genes and proteins related to the hypothalamic-pituitary-thyroid (HPT) axis were analysed. Co-exposure to BDE-47 and PER decreased the body weight and increased malformation rates relative to the effects of exposure to only BDE-47. Compared with the exposure to BDE-47 alone, the exposure to a combination of BDE-47 (10 µg/L) and PER (3.5 mg/L) significantly up-regulated the expression of genes involved in TH synthesis (NIS and Nkx2.1a) and significantly down-regulated the expression of genes related to the regulation of the HPT axis (CRH and TSHß). The expression of TG at the gene and protein levels was significantly up-regulated, but the expression of TTR was significantly down-regulated in the co-exposures relative to BDE-47 treated alone. In addition, the larger reduction in the T4 level resulting from exposure to the mixture of BDE-47 and PER demonstrated that PER enhanced the thyroid-disruptive effects of BDE-47. These results help to elucidate the complicated chemical interactions and the molecular mechanism of action of these two TH disruptors.

[Characteristics of primary cell culture from neonatal thyroid grand of pigs: folliculogenesis, hormone and growth].

In the study, comprehensive assessment of proliferative and hormonal activity of primary cell cultures derived from neonatal pig thyroid has been carried out for the first time. We have evaluated the basal and TSH-stimulated secretion of thyroxine and morphological features of culture, depending on the initial state of the material placed in culture: in the form of single cells or follicular conglomerates. Folliculogenesis and formation of dome structures were observed in culture spontaneous and under chronic TSH stimulation. The ability of the cells to expression of ß-III-tubulin during prolonged cultivation in the presence of NGF has been demonstrated in the study.

Experimental hyperthyroidism decreases gene expression and serum levels of adipokines in obesity.

AIMS: To analyze the influence of hyperthyroidism on the gene expression and serum concentration of leptin, resistin, and adiponectin in obese animals. MAIN METHODS: Male Wistar rats were randomly divided into two groups: control (C)-fed with commercial chow ad libitum-and obese (OB)-fed with a hypercaloric diet. After group characterization, the OB rats continued receiving a hypercaloric diet and were randomized into two groups: obese animals (OB) and obese with 25 µg triiodothyronine (T(3))/100 BW (OT). The T(3) dose was administered every day for the last 2 weeks of the study. After 30 weeks the animals were euthanized. Samples of blood and adipose tissue were collected for biochemical and hormonal analyses as well as gene expression of leptin, resistin, and adiponectin. RESULTS: T(3) treatment was effective, increasing fT(3) levels and decreasing fT(4) and TSH serum concentration. Administration of T(3) promotes weight loss, decreases all fat deposits, and diminishes serum levels of leptin, resistin, and adiponectin by reducing their gene expression. CONCLUSIONS: Our results suggest that T(3) modulate serum and gene expression levels of leptin, resistin, and adiponectin in experimental model of obesity, providing new insights regarding the relationship between T(3) and adipokines in obesity.