Leptin and the pituitary-thyroid axis: a comparative study in lean, obese, hypothyroid and hyperthyroid subjects

Body Composition and Serum Concentration of Thyroid Hormones in Euthyroid Men and Women from General Population

Body composition, especially an increased amount of fat mass and decreased lean body mass, is connected with metabolic complications. Thyroid hormones can influence body composition pattern. To date, scarce data defining the relationships between thyroid hormones and parameters of body composition using dual-energy X-ray absorptiometry (DXA), especially in cohort studies, are available. Therefore, the aim of the present study was to investigate the relationships among serum concentrations of (thyroid-stimulating hormone (TSH), thyroid hormones, and distribution of fat tissue assessed using the DXA method in a euthyroid cohort from the Białystok PLUS study. We examined 582 euthyroid subjects who were divided into lean (body mass index (BMI) < 25 kg/m2) and overweight/obese (BMI ≥ 25 kg/m2) (84 lean men, 182 overweight/obese men, 160 lean women, and 156 overweight/obese women). Serum concentrations of TSH, free T3 (fT3), and free T4 (fT4) were assessed, and DXA was performed. We observed lower serum levels of fT4 (p = 0.03) and higher serum levels of fT3 (p = 0.04) in overweight/obese vs. lean men, whereas serum levels of TSH did not differ between these groups (p = 0.38). In lean men, we only observed a relationship between serum levels of TSH and visceral adipose tissue (VAT) (r = −0.24, p = 0.02). In overweight/obese men, we found that serum levels of fT3 were positively connected with total fat mass (r = 0.16, p = 0.02), android fat mass (r = 0.15, p = 0.03), and gynoid fat mass (r = 0.17, p = 0.01), but not with VAT (r = 0.03, p = 0.63). We did not observe differences in serum levels of TSH, fT3, and fT4 between lean and overweight/obese women. Additionally, we did not notice relationships between serum levels of thyroid hormones and fat in different regions estimated by DXA in lean and overweight/obese women (all p > 0.05). We concluded that the serum concentration of TSH is connected with VAT in lean men, whereas, in overweight/obese men, higher fT3 is connected with an increased fat amount. These associations are absent in women.

Role of Leptin with hypothyroidism in Iraqi diabetic type 2 patients

In thyroid subjects, leptin hormone and thyroid-stimulating hormone levels connect; both are emphatically corresponding with adiposity. “Leptin hormone was essentially raised in the hypothyroid topic,” to levels like those seen in corpulent thyroid topic. This study aimed to determine leptin hormone levels, T3, T4, TSH, HbA1c %, FBG, lipid profile in diabetic and diabetic with hypothyroidism patients and compare the outcome with the healthy group. 90 samples were registered in this study with their ages ranging between (40 - 65) years that dole out into 3 groups as follows: thirty healthy groups (G1), thirty patients with diabetes (G2), and category three (G3) include diabetic patients and hypothyroidism as an associated disease. This study revealed a slightly significant elevated leptin in G3, contrasting to G2 and G1. Meantime no significant elevated spotted between G2 and G1. The conclusion could be from this investigation that leptin levels were changed in patients’ gatherings that might be utilized in checking and early analysis of thyroid dysfunction in these patients relying upon the significant connection for leptin chemical with T3, T4, and TSH.

Leptin counteracts hypothermia in hypothyroidism through its pyrexic effects and by stabilizing serum thyroid hormone levels

Objective

Thyroid hormones (TH) are essential for the homeostatic control of energy metabolism and the regulation of body temperature. The hypothalamic–pituitary–thyroid (HPT) axis is regulated by negative feedback mechanisms, ensuring that TH levels are maintained at a constant level. However, the feedback mechanisms underlying the resetting of the HPT axis regulation in the control of body temperature are still not fully understood. Here, we aimed to determine the thermoregulatory response in hypothyroid mice to different environmental temperatures and the underlying mechanisms.

Methods

Distinct thermogenic challenges were induced in hypothyroid female C57BL/6N and leptin-deficient ob/ob mice through housing at either room temperature or thermoneutrality. The thermogenic and metabolic effects were analyzed through metabolic chambers, 18F-FDG-PET/MRI, infrared thermography, metabolic profiling, histology, gene expression and Western blot analysis.

Results

In hypothyroid mice maintained at room temperature, high leptin serum levels induce a pyrexic effect leading to the stabilization of body temperature through brown adipose tissue thermogenesis and white adipose tissue browning. Housing at thermoneutrality leads to the normalization of leptin levels and a reduction of the central temperature set point, resulting in decreased thermogenesis in brown and white adipose tissue and skeletal muscle and a significant decline in body temperature. Furthermore, anapyrexia in hypothyroid leptin-deficient ob/ob mice indicates that besides its pyrexic actions, leptin exerts a stimulatory effect on the HPT axis to stabilize the remaining TH serum levels in hypothyroid mice.

Conclusion

This study led to the identification of a previously unknown endocrine loop in which leptin acts in concert with the HPT axis to stabilize body temperature in hypothyroid mice.

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Thyroid hormones are essential for the regulation of body temperature.

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Thyroid hormone-deficient (hypothyroid) mice show distinct leptin serum concentrations in response to changes in ambient housing temperature.

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High leptin serum levels confer a stimulatory effect on the hypothalamic-pituitary-thyroid axis.

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High leptin serum level prevents fall in body temperature in hypothyroid mice at room temperature through its pyrexic effects.

The Effects of 8 Weeks of Levothyroxine Replacement Treatment on Metabolic and Anthropometric Indices of Insulin Resistance in Hypothyroid Patients

BACKGROUND

Insulin resistance (IR) is an independent cardiovascular risk factor. IR predisposes to metabolic syndrome and diabetes. Meanwhile, little evidence exists about the effect of levothyroxine replacement treatment (LRT) on IR in hypothyroid patients.

OBJECTIVE

To investigate metabolic and anthropometric indices of IR in hypothyroid patients before and after 8 weeks of LRT.

METHODS

This pre-post study evaluated the 8 weeks outcomes of LRT on 66 patients with recently diagnosed hypothyroidism. Outcome measures included body mass index (BMI), waist circumferences (WC), waist to hip ratio (WHR), waist to height ratio (WHtR), body fat percent (BF%), free thyroxin (FT4), triglyceride (TG), low density lipoprotein (LDL), fasting plasma levels of glucose (FPG) and insulin. Sex- specific cut offs of two metabolic indices i.e. the triglyceride-glucose (TyG) and the homeostasis model assessment (HOMA) were used for IR diagnosis. The changes in TyG and HOMA were also compared after LRT.

RESULTS

Participants were overt and subclinical hypothyroidism 71% and 29%, respectively. After LRT the mean values of the following anthropometric indices significantly decreased: weight (79.61 vs. 78.64), BMI (29.53 vs. 29.2), WC (98.25 vs. 97.39) and BF% (35.34 vs. 34.95). After LRT the HOMA and TyG had no significant changes relative to their initial values. Also, IR that was determined on the basis of these metabolic indices more commonly observed in participants.

CONCLUSION

Despite decreasing some anthropometric indices, the diagnosis of IR based on metabolic indices increased following 8 weeks LRT in hypothyroid cases.

Cardiovascular and metabolic consequences of the association between chronic stress and high-fat diet in rats

Obesity and chronic stress are considered independent risk factors for the development of cardiovascular diseases and changes in autonomic system activity. However, the cardiovascular consequences induced by the association between high-fat diet (HFD) and chronic stress are not fully understood. We hypothesized that the association between HFD and exposure to a chronic variable stress (CVS) protocol for four weeks might exacerbate the cardiovascular and metabolic disturbances in rats when compared to these factors singly. To test this hypothesis, male Wistar rats were divided into four groups: control-standard chow diet (SD; n = 8); control-HFD (n = 8); CVS-SD (n = 8); and CVS-HFD (n = 8). The CVS consisted of repeated exposure of the rats to different inescapable and unpredictable stressors (restraint tress; damp sawdust, cold, swim stress and light cycle inversion). We evaluated cardiovascular function, autonomic activity, dietary intake, adiposity and metabolism. The HFD increased body weight, adiposity and blood glucose concentration (∼15%) in both control and CVS rats. The CVS-HFD rats showed decreased insulin sensitivity (25%) compared to CVS-SD rats. The control-HFD and CVS-HFD rats presented increased intrinsic heart rate (HR) values (∼8%). CVS increased cardiac sympathetic activity (∼65%) in both SD- and HFD-fed rats. The HFD increased basal HR (∼10%). Blood pressure and baroreflex analyzes showed no differences among the experimental groups. In conclusion, the present data indicate absence of interaction on autonomic imbalance evoked by either CVS or HFD. Additionally, HFD increased HR and evoked metabolic disruptions which are independent of stress exposure.

Association of prothrombotic adipokine (plasminogen activator inhibitor-1) with TSH in metabolic syndrome: a case control study

Background

Metabolic syndrome (MetS) involves a cluster of cardiovascular risk factors, including abnormal lipids, insulin resistance and hypertension. The aim of the present study is to investigate associations between thyroid profile and the pro-thrombotic mediator, plasminogen activator inhibitor-1 (PAI-1), in MetS and identify associated biochemical markers.

Materials and methods

The present study was a case control study and consisted of 50 diagnosed cases of MetS and 50 healthy volunteers as controls. MetS cases were further divided into two groups based on the presence and absence of subclinical hypothyroidism (SCH). Data collected included demographic profile, clinical history and routine lab investigation. Special investigations included the thyroid function test and serum PAI-1 levels.

Results

The mean serum thyroid-stimulating hormone (TSH) levels were significantly higher in MetS cases as compared to controls (5.7 ± 1.2 mIU/L vs. 2.3 ± 1.6 mIU/L, p < 0.0001), although the mean triiodothyronine (T3) and thyroxine (T4) levels were comparable in two groups. The mean levels of serum PAI-1 were significantly higher in MetS cases as compared to controls(231 ± 87 ng/mL vs. 185 ± 96 ng/mL, p = 0.013). TSH and PAI-1 levels were positively correlated with various markers of MetS and negatively correlated with high-density lipoprotein (HDL).

Conclusion

The present study points towards the presence of thyroid dysfunction, in the form of subclinical hypothyroidism (SCH), in cases of MetS. In the presence of thyroid dysfunction, abnormal adipocytes may release adipokines, such as PAI-1, which lead to increased risk of thrombotic episodes in these patients. Hence, SCH should be appropriately managed.

Serum Thyroid-Stimulating Hormone Levels and Body Mass Index Percentiles in Children with Primary Hypothyroidism on Levothyroxine Replacement

OBJECTIVE

To determine the association, if any, between thyroid-stimulating hormone (TSH) levels and body mass index (BMI) percentiles in children with primary hypothyroidism who are chemically euthyroid and on treatment with levothyroxine.

METHODS

This retrospective cross-sectional study consisted of a review of medical records from RUSH Medical Center and Stroger Hospital, Chicago, USA of children with primary hypothyroidism who were seen in the clinic from 2008 to 2014 and who were chemically euthyroid and on treatment with levothyroxine for at least 6 months. The patients were divided into two groups based on their TSH levels (0.34-<2.5 mIU/L and ≥2.5-5.6 mIU/L). The data were analyzed by Spearman rank correlation, linear regression, cross tabulation and chi-square, Mann-Whitney U test, and Kruskal-Wallis test.

RESULTS

One hundred and forty-six children were included, of which 26% were obese (BMI ≥95%), 21.9% overweight (BMI ≥85-<95%), and 52.1% of a healthy weight (BMI ≥5-<85%). There was a significant positive correlation between TSH and BMI percentiles (r=0.274, p=0.001) and a significant negative correlation between TSH and serum free T4 (r=-0.259, p=0.002). In the lower TSH group, 68.4% of the children had a healthy weight, while the percentage of obese children was 60.5% in the upper TSH group (p=0.012).

CONCLUSION

In children diagnosed with primary hypothyroidism who are chemically euthyroid on treatment with levothyroxine, there is a positive association between higher TSH levels and higher BMI percentiles. However, it is difficult to establish if the higher TSH levels are a direct cause or a consequence of the obesity. Further studies are needed to establish causation beyond significant association.

Levothyroxine Dosing Following Bariatric Surgery

BACKGROUND

Based on the mechanisms of drug absorption, increased levothyroxine requirements are expected after bariatric surgery. However, there are conflicting data on this topic. This review evaluates the effects of bariatric surgery on levothyroxine dosing.

METHODS

Data were obtained from PubMed, Scopus, and review of published bibliographies.

RESULTS

Six of 10 studies demonstrated decreased postoperative requirements. Most demonstrated correlations between weight loss and dose. Only 3 case reports and 1 case series demonstrated increased levothyroxine requirements, attributed to malabsorption.

CONCLUSIONS

The loss of both fat and lean body mass may counteract malabsorptive effects from surgery, resulting in decreased postoperative levothyroxine requirements. In addition, the reversal of impaired levothyroxine pharmacokinetics and an altered set point of thyroid hormone homeostasis may also contribute to postoperative levothyroxine reductions.

High Thyroid-stimulating Hormone Levels Increase Proinflammatory and Cardiovascular Markers in Patients with Extreme Obesity

BACKGROUND AND AIMS

Obesity is an important health problem worldwide and many studies have suggested a relationship between obesity and thyroid function, with controversial results. Interestingly, high TSH levels have been involved with the presence of inflammatory state and risk for developing cardiovascular diseases in hypothyroid and obese patients. The aim in this work was to determine the prevalence of hypothyroidism in patients with extreme obesity and to determine whether their TSH levels were related to increased serum levels of inflammatory and cardiovascular markers.

METHODS

A cross-sectional study in 101 patients with extreme obesity (BMI ≥40) was performed. Anthropometric (weight, height and waist circumference) and biochemical (fasting glucose, glycosylated hemoglobin, triglycerides, total cholesterol, LDL-C, HDL-C and insulin) parameters were measured. TSH and FT4 levels as well as clinical exploration for diagnosis of hypothyroidism were carried out. Serum concentration of IL-10, IL-6, adiponectin, resistin, leptin, ICAM-1, VCAM-1 and E-selectin were determined.

RESULTS

A high prevalence for diabetes (37.6%), prediabetes (50.5%), dyslipidemia (74.3%), hypertension (61.4%) and hypothyroidism (48.5%) was observed in patients with extreme obesity. The presence of hypothyroidism increased serum concentration of proinflammatory cytokines IL-6 and leptin and decreased the antiinflammatory cytokine adiponectin. In addition, serum TSH levels showed a correlation for waist circumference, weight, BMI, A1c, insulin, IL-6, leptin, ICAM-1 and E-selectin.

CONCLUSION

There is a high prevalence for hypothyroidism in patients with extreme obesity. High levels of TSH contribute to elevate proinflammatory and cardiovascular risk markers, increasing the risk for development of cardiovascular diseases.

Iodine deficiency is higher in morbid obesity in comparison with late after bariatric surgery and non-obese women

BACKGROUND

Iodine deficiency and obesity are worldwide-occurring health problems. Our purpose was to investigate the relationship between morbid obesity and iodine status, including subjects who lost weight after bariatric surgery.

METHODS

Ninety morbidly obese women, 90 women with at least 18 months follow-up after bariatric surgery, and 45 healthy non-obese women were recruited. Urinary iodine concentration (UIC) was measured in a spot urinary sample and expressed as the iodine-to-creatinine ratio.

RESULTS

Obese women showed a significantly lower UIC in comparison with non-obese women (96.6 (25.8-267.3) vs. 173.3 (47.0-493.6) μg/g; p < 0.001), with a lesser proportion of subjects with adequate iodine status (46.6 vs. 83.3 %, p < 0.001). The mean UIC significantly increased among women who underwent bariatric surgery before the collection of the urinary sample (96.6 (25.8-267.3) vs. 131.9 (62.9-496.4) μg/g; p < 0.001). No difference in UIC was detected between laparoscopic Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy. Univariate analysis showed that UIC negatively correlated with body mass index (BMI) (r = -0.278, p < 0.001) and positively with age (r = 0.206, p = 0.002). Finally, multiple linear regression analyses showed that BMI was independently associated with UIC (beta = -0.312, p < 0.001; R (2) = 0.166).

CONCLUSION

Obesity is an independent risk factor to iodine deficiency, almost in women. Whether more obese population needs to be considered as a vulnerable group and whether bariatric surgery can reverse iodine deficiency still remain to be elucidated.

Triiodothyronine modulates the expression of leptin and adiponectin in 3T3-L1 adipocytes

Objective

To study the effect of different doses of triiodothyronine on gene expression of the adipokines leptin and adiponectin, at different times, and to evaluate the difference in expression between the two adipokines in each group.

Methods

3T3-L1 adipocytes were incubated with triiodothyronine at physiological dose (10nM) and supraphysiological doses (100nM or 1,000nM), or without triiodothyronine (control, C) for 0.5, 6, or 24 hours. Leptin and adiponectin mRNA was detected using real-time polymerase chain reaction (RT-PCR). One-way analyses of variance, Tukey’s test or Student’s t test, were used to analyze data, and significance level was set at 5%.

Results

Leptin levels decreased in the 1,000nM-dose group after 0.5 hour. Adiponectin levels dropped in the 10nM-dose group, but increased at the 100nM dose. After 6 hours, both genes were suppressed in all hormone concentrations. After 24 hours, leptin levels increased at 10, 100 and 1,000nM groups as compared to the control group; and adiponectin levels increased only in the 100nM group as compared to the control group.

Conclusion

These results demonstrated fast actions of triiodothyronine on the leptin and adiponectin expression, starting at 0.5 hour, at a dose of 1,000nM for leptin and 100nM for adiponectin. Triiodothyronine stimulated or inhibited the expression of adipokines in adipocytes at different times and doses which may be useful to assist in the treatment of obesity, assuming that leptin is increased and adiponectin is decreased, in obesity cases.

Changes in the before and after thyroxine treatment levels of adipose tissue, leptin, and resistin in subclinical hypothyroid patients

BACKGROUND

Subclinical hypothyroidism (SH) occurs when serum thyroid stimulating hormone (TSH) concentrations are raised and serum thyroid hormone concentrations are normal. The effect of SH on the proinflammatory adipose cytokine releasing visceral adipose tissue (VAT) is not clear. The aim of this study is to identify the difference between the pre and posttreatment levels of VAT, leptin, and resistin in SH patients.

METHODS

There were 51 SH patients and 43 age- and gender-matched healthy subjects included in the study. Thyroid functions, biochemical tests, leptin, resistin, and visceral and subcutaneous fat measurements were made. The measurements were repeated in the SH group in the third month following L-thyroxin treatment.

RESULTS

Initially, high sensitivity C-reactive protein, carotid artery intima-media thickness (mm), leptin, and resistin levels were significantly higher in the SH group compared to the controls, while the other parameters were similar. While no correlation was observed between TSH levels and adipokines, a positive correlation was detected between waist circumference and leptin levels (r = 0.549, p < 0.01). Visceral adipose tissue was positively correlated to age, waist circumference, and leptin levels, but negatively correlated to free thyroxin (T4) levels (r = 0.419, p = 0.009; r = 0.794, p < 0.01; r = 0.515, p < 0.01 and r = - 0.416, p = 0.009, respectively). A significant decrease was observed in VAT volume, leptin, and resistin levels of SH patients following levothyroxine treatment. Conclusion The reduced VAT volume, leptin, and resistin levels in SH patients following treatment may support the idea that TSH affects adipose tissue functions.

Laparoscopic sleeve gastrectomy leads to reduction in thyroxine requirement in morbidly obese patients with hypothyroidism

BACKGROUND

The impact of laparoscopic sleeve gastrectomy (LSG) on various co-morbidities including type II diabetes mellitus, hypertension, and sleep apnea is well established. However, its effect on hypothyroidism has not been given due attention evidenced by the scant literature on the subject. The purpose of this report is to assess the change in thyroxine (T4) requirement in morbidly obese patients with clinical hypothyroidism after LSG.

METHODS

We conducted a retrospective review of morbidly obese patients on T4 replacement therapy for clinical hypothyroidism who underwent LSG from August 2009 to July 2012 at our institution.

RESULTS

Of the 200 patients who underwent LSG during this period, 21 (10.5 %) were on T4 replacement therapy preoperatively for clinical hypothyroidism. Two patients were lost to follow-up. The remaining 19 patients were categorized into two groups. Group 1 comprised 13 patients with decreased T4 requirements after LSG. Group 2 comprised six patients in whom the T4 dose remained unaltered. The mean change in T4 requirement in group 1 was 42.07 % (12-100 %). Group 1 patients had a significantly higher mean preoperative body mass index (48.7 vs. 43.0 kg/m(2); p = 0.03) than the group 2 patients. There was a significant correlation between the percentage excess weight loss and the percentage change in T4 requirement in group 1 (r = 0.607, p = 0.028).

CONCLUSIONS

Sleeve gastrectomy has a favorable impact on hypothyroid status as seen by a reduction in T4 requirement in the majority of morbidly obese patients with overt hypothyroidism.

Laparoscopic sleeve gastrectomy leads to reduction in thyroxine requirement in morbidly obese patients with hypothyroidism

BACKGROUND

The impact of laparoscopic sleeve gastrectomy (LSG) on various co-morbidities including type II diabetes mellitus, hypertension, and sleep apnea is well established. However, its effect on hypothyroidism has not been given due attention evidenced by the scant literature on the subject. The purpose of this report is to assess the change in thyroxine (T4) requirement in morbidly obese patients with clinical hypothyroidism after LSG.

METHODS

We conducted a retrospective review of morbidly obese patients on T4 replacement therapy for clinical hypothyroidism who underwent LSG from August 2009 to July 2012 at our institution.

RESULTS

Of the 200 patients who underwent LSG during this period, 21 (10.5 %) were on T4 replacement therapy preoperatively for clinical hypothyroidism. Two patients were lost to follow-up. The remaining 19 patients were categorized into two groups. Group 1 comprised 13 patients with decreased T4 requirements after LSG. Group 2 comprised six patients in whom the T4 dose remained unaltered. The mean change in T4 requirement in group 1 was 42.07 % (12-100 %). Group 1 patients had a significantly higher mean preoperative body mass index (48.7 vs. 43.0 kg/m(2); p = 0.03) than the group 2 patients. There was a significant correlation between the percentage excess weight loss and the percentage change in T4 requirement in group 1 (r = 0.607, p = 0.028).

CONCLUSIONS

Sleeve gastrectomy has a favorable impact on hypothyroid status as seen by a reduction in T4 requirement in the majority of morbidly obese patients with overt hypothyroidism.

Subclinical hypothyroidism, weight change, and body composition in the elderly: the Cardiovascular Health Study

BACKGROUND

Subclinical hypothyroidism is common in the elderly, yet its relationship with weight and body composition is unclear.

OBJECTIVE

We examined the relationship between subclinical hypothyroidism and weight change and body composition in older adults.

METHODS

A total of 427 subclinically hypothyroid and 2864 euthyroid U.S. individuals ≥65 years old enrolled in the Cardiovascular Health Study and not taking thyroid preparations were included. Analyses of 6-year weight change were performed, compared by thyroid status. A cross-sectional analysis of thyroid status and body composition was performed in a subset of 1276 participants who had dual-energy x-ray absorptiometry scans. Models were risk factor-adjusted and stratified by sex.

RESULTS

Overall, participants lost weight during follow-up (-0.38 kg/y in men, -0.37 kg/y in women). Subclinical hypothyroidism, when assessed at a single time point or persisting over 2 years, was not associated with a difference in weight change compared with euthyroidism. Subclinical hypothyroidism was also not associated with differences in lean mass, fat mass, or percent fat compared with euthyroidism. A TSH level 1 mU/L higher within the euthyroid or subclinical hypothyroid range was associated with a 0.51-kg higher baseline weight in women only (P < .001) but not with weight change in either sex. A 1 ng/dL higher free T4 level was associated with lower baseline weight and 0.32 kg/y greater weight loss in women only (P = .003). Baseline weight and weight change did not differ by T3 levels.

CONCLUSIONS

Our data do not support a clinically significant impact of subclinical hypothyroidism on weight status in the elderly.

Thyroid hormones are associated with exposure to persistent organic pollutants in aging residents of upper Hudson River communities

The aim of this study was to evaluate the association between persistent organic pollutants (POPs) and thyroid hormones in an aging population. Forty-eight women and 66 men, aged 55-74 years and living in upper Hudson River communities completed a questionnaire and provided blood specimens. Serum was analyzed for thyrotropin (thyroid stimulating hormone, TSH), free (fT4) and total thyroxine (T4), total triiodothyronine (T3), and for POPs. POPs included 39 polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE) determined by gas chromatography with electron capture detection (GC-ECD), and nine polybrominated diphenyl ethers (PBDEs) determined by high-resolution gas chromatography with high-resolution mass spectrometry detection (HRGC-HRMS). Multivariable linear regression analysis was used to evaluate associations between thyroid hormones and sums of POPs, adjusted for covariates and stratified by sex. Effects were expressed as differences in thyroid hormone levels associated with a doubling in the level of exposure. Among women, DDT+DDE increased T4 by 0.34μg/dL (P=0.04) and T3 by 2.78ng/dL (P=0.05). Also in women, sums of PCBs in conjunction with PBDEs elicited increases of 24.39-80.85ng/dL T3 (P<0.05), and sums of PCBs in conjunction with DDT+DDE elicited increases of 0.18-0.31μg/dL T4 (P<0.05). For men estrogenic PCBs were associated with a 19.82ng/dL T3 decrease (P=0.003), and the sum of estrogenic PCBs in conjunction with DDT+DDE elicited an 18.02ng/dL T3 decrease (P=0.04). Given age-related declines in physiologic reserve, the influence of POPs on thyroid hormones in aging populations may have clinical implications and merits further investigation.

Triiodothyronine increases mRNA and protein leptin levels in short time in 3T3-L1 adipocytes by PI3K pathway activation

The present study aimed to examine the effects of thyroid hormone (TH), more precisely triiodothyronine (T3), on the modulation of leptin mRNA expression and the involvement of the phosphatidyl inositol 3 kinase (PI3K) signaling pathway in adipocytes, 3T3-L1, cell culture. We examined the involvement of this pathway in mediating TH effects by treating 3T3-L1 adipocytes with physiological (P=10nM) or supraphysiological (SI=100 nM) T3 dose during one hour (short time), in the absence or the presence of PI3K inhibitor (LY294002). The absence of any treatment was considered the control group (C). RT-qPCR was used for mRNA expression analyzes. For data analyzes ANOVA complemented with Tukey’s test was used at 5% significance. T3 increased leptin mRNA expression in P (2.26 ± 0.36, p< 0.001), SI (1.99 ±0.22, p< 0.01) compared to C group (1± 0.18). This increase was completely abrogated by LY294002 in P (1.31±0.05, p< 0.001) and SI (1.33±0.31, p< 0.05). Western blotting confirmed these results at protein level, indicating the PI3K pathway dependency. To examine whether leptin is directly induced by T3, we used the translation inhibitor cycloheximide (CHX). In P, the presence of CHX maintained the levels mRNA leptin, but was completely abrogated in SI (1.14±0.09, p> 0.001). These results demonstrate that the activation of the PI3K signaling pathway has a role in TH-mediated direct and indirect leptin gene expression in 3T3-L1 adipocytes.

Impact of body mass index on thyroid functions in Indian children

OBJECTIVE

There is controversy about the relation of thyroid functions and body mass index. The present study was aimed to assess the relationship between thyroid function and body mass index in Indian school children.

DESIGN

Population survey.

PATIENTS

Data were collected from 25 schools in 19 cities across five different geographical zones of India. Children, who consented, were evaluated for anthropometry and blood tests. Children were categorized as overweight and obese based on standard BMI criteria.

MEASUREMENTS

Serum samples were analysed for free T3, free T4, TSH and anti-TPO antibodies.

RESULTS

A total of 13,691 children in the age group of 5-18 years formed the study population. The mean age and mean BMI were 11·9 ± 3·0 years and 18·48 ± 3·89 kg/m² respectively. Among these, 2119 (15·5%) children were overweight and 536 (3·9%) were obese. Subclinical hypothyroidism was present in 943 (6·9%) children.FT3 and TSH levels increased and FT4 levels decreased with increasing BMI in euthyroid boys and girls. Prevalence of SCH was significantly higher in obese/overweight children (9·0%, vs 6·5%; P = 0·034) as compared with normal BMI children.

CONCLUSIONS

Serum FT3 and TSH were positively while FT4 was negatively associated with BMI in apparently healthy euthyroid children.

The role of leptin in obesity and the potential for leptin replacement therapy

Leptin (from the Greek word "lepto'' meaning "thin") is a 167-amino acid peptide hormone encoded by the obesity (ob) gene and secreted by white adipocytes. Blood leptin concentrations are increased in obese individuals. Leptin is a satiety hormone that provides negative feedback to the hypothalamus, controlling appetite and energy expenditure. Leptin binds to presynaptic GABAergic neurons to produce its effect, raising the distinct possibility that GABAergic axon terminals are the ultimate subcellular site of action for its effects. Released into the circulation, leptin crosses the blood-brain barrier and binds to leptin receptors, influencing the activity of various hypothalamic neurons, as well as encoding orexigenic and anorexigenic neuropeptides. Moreover, leptin affects a wide range of metabolic functions in the peripheral tissue. In this review, we discuss some physiologic functions of leptin, including effects on obesity and some effects of leptin replacement therapy.

The effect of vitamin A supplementation on thyroid function in premenopausal women

OBJECTIVE

Vitamin A and its retinoid derivates play an important role in regulation of normal growth and development. Vitamin A has been shown to regulate thyroid hormone metabolism and inhibit thyroid-stimulating hormone (TSH) secretion via down regulation of TSH-β gene expression; however, the effect of vitamin A on thyroid function in obese individuals who are at higher risk of subclinical hypothyroidism is still unclear. In the present study we investigate the impact of vitamin A supplementation on thyroid function in obese women.

METHOD

A 4-month randomized, double blind controlled trial was conducted among 84 healthy women aged 17-50 years old: 56 were obese (body mass index [BMI] 30-35 kg/m(2)) and 28 were nonobese (BMI 18.5-24.9 kg/m(2)). Obese women were randomly allocated to receive either vitamin A (25,000 IU/d retinyl palmitate) or placebo. Nonobese women received vitamin A. At baseline and 4 months after intervention, serum concentrations of TSH, total thyroxine (T4), total triiodothyronine (T3), retinol-binding protein (RBP), and transthyretin (TTR) were measured.

RESULTS

Baseline concentrations of thyroid hormones, RBP and TTR were not significantly different between groups. Vitamin A caused a significant reduction in serum TSH concentrations in obese (p = 0.004) and nonobese (p = 0.001) groups. Serum T3 concentrations also increased in both obese and nonobese vitamin A-treated groups (p < 0.001). Serum T4 decreased in all 3 groups after treatment. The results showed a significant reduction in serum RBP in the obese group after vitamin A supplementation (p = 0.007), but no significant change was seen in serum TTR.

CONCLUSIONS

Serum TSH concentrations in vitamin A-treated subjects were significantly reduced; therefore, vitamin A supplementation might reduce the risk of subclinical hypothyroidism in premenopausal women.

A Review of the Pharmacokinetics of Levothyroxine for the Treatment of Hypothyroidism

Thyroxine hormone has been recognised since the early part of the nineteenth century and levothyroxine has been available since the mid-nineteenth century as a replacement for deficient thyroid hormones. While levothyroxine remains the staple treatment for hypothyroidism even to this day, its optimal use can be challenging. As is often the case with older drugs, the pharmacokinetics of levothyroxine is often under-appreciated or misunderstood and many factors influence the optimal dosing of levothyroxine. This article will review the pharmacokinetics of levothyroxine in the treatment of hypothyroidism and highlight major concepts that should aid both clinicians and researchers.

A comparative genotoxicity study of a supraphysiological dose of triiodothyronine (T₃) in obese rats subjected to either calorie-restricted diet or hyperthyroidism

This study was designed to determine the genotoxicity of a supraphysiological dose of triiodothyronine (T₃) in both obese and calorie-restricted obese animals. Fifty male Wistar rats were randomly assigned to one of the two following groups: control (C; n = 10) and obese (OB; n = 40). The C group received standard food, whereas the OB group was fed a hypercaloric diet for 20 weeks. After this period, half of the OB animals (n = 20) were subjected to a 25%-calorie restriction of standard diet for 8 weeks forming thus a new group (OR), whereas the remaining OB animals were kept on the initial hypercaloric diet. During the following two weeks, 10 OR animals continued on the calorie restriction diet, whereas the remaining 10 rats of this group formed a new group (ORS) given a supraphysiological dose of T₃ (25 µg/100 g body weight) along with the calorie restriction diet. Similarly, the remaining OB animals were divided into two groups, one that continued on the hypercaloric diet (OB, n = 10), and one that received the supraphysiological dose of T₃ (25 µg/100 g body weight) along with the hypercaloric diet (OS, n = 10) for two weeks. The OB group showed weight gain, increased adiposity, insulin resistance, increased leptin levels and genotoxicity; T₃ administration in OS animals led to an increase in genotoxicity and oxidative stress when compared with the OB group. The OR group showed weight loss and normalized levels of adiposity, insulin resistance, serum leptin and genotoxicity, thus having features similar to those of the C group. On the other hand, the ORS group, compared to OR animals, showed higher genotoxicity. Our results indicate that regardless of diet, a supraphysiological dose of T₃ causes genotoxicity and potentiates oxidative stress.

Effects of thyroxin therapy on different analytes related to obesity and inflammation in dogs with hypothyroidism

Hypothyroidism in dogs is accompanied by changes in intermediary metabolism including alterations in bodyweight (BW), insulin resistance, and lipid profile. In this study, changes in selected adipokines (adiponectin, leptin), butyrylcholinesterase (BChE), and acute phase proteins, including C-reactive protein, haptoglobin (Hp) and serum amyloid A (SAA), were studied in dogs with hypothyroidism under thyroxin therapy. Blood samples were collected when hypothyroidism was diagnosed (before treatment) and after treatment with thyroxin. Twenty-eight of 39 dogs exhibited a good therapeutic response (group A), whereas the remainder were considered to have been insufficiently treated (group B). Following treatment, group A dogs demonstrated a statistically significant decrease in canine thyroid stimulating hormone (c-TSH) (P<0.001) and an increase in free thyroxine (fT4) (P<0.001) concentrations, associated with a significant decrease in BW (P<0.05), leptin (P<0.01), and adiponectin, (P<0.001) and an increase in BChE (P<0.01) and Hp (P<0.05). Group B dogs showed no statistically significant changes in c-TSH, but had a significant increase in fT4 (P<0.001) accompanied by a significant decrease in adiponectin (P<0.05) of lower magnitude than group A. No significant changes in the mean circulating levels of APPs were observed in both groups, with the exception of an increase in Hp (P<0.05) in group A. In summary, the successful treatment of hypothyroidism reduces circulating levels of adiponectin and leptin, while increasing BChE activity in dogs. The mean increase in Hp values and decrease in SAA for some of the dogs after treatment warrants further investigation.

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 (T₃)/100 BW (OT). The T₃ 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. T₃ treatment was effective, increasing fT₃ levels and decreasing fT₄ and TSH serum concentration. Administration of T₃ 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 T₃ modulate serum and gene expression levels of leptin, resistin, and adiponectin in experimental model of obesity, providing new insights regarding the relationship between T₃ and adipokines in obesity.

Thyroid function in childhood obesity and metabolic comorbidity

Childhood obesity is a worldwide health problem and its prevalence is increasing steadily and dramatically all over the world. Obese subjects have a much greater likelihood than normal-weight children of acquiring dyslipidemia, elevated blood pressure, and impaired glucose metabolism, which significantly increase their risk of cardiovascular and metabolic diseases. Elevated TSH concentrations in association with normal or slightly elevated free T4 and/or free T3 levels have been consistently found in obese subjects, but the mechanisms underlying these thyroid hormonal changes are still unclear. Whether higher TSH in childhood obesity is adaptive, increasing metabolic rate in an attempt to reduce further weight gain, or indicates subclinical hypothyroidism or resistance and thereby contributes to lipid and/or glucose dysmetabolism, remains controversial. This review highlights current evidence on thyroid involvement in obese children and discusses the current controversy regarding the relationship between thyroid hormonal derangements and obesity-related metabolic changes (hypertension, dyslipidemia, hyperglycemia and insulin resistance, nonalcoholic fatty liver disease) in such population. Moreover, the possible mechanisms linking thyroid dysfunction and pediatric obesity are reviewed. Finally, the potential role of lifestyle intervention as well as of therapy with thyroid hormone in the treatment of thyroid abnormalities in childhood obesity is discussed.

Thyroid hormone levels predict the change in body weight: a prospective study

BACKGROUND

Different studies, mostly cross-sectional, have found an association between low levels of thyroid hormones, even within the normal range, and a greater body mass index. The aim of this study was to determine the association between thyroid function and the risk for obesity.

MATERIALS AND METHODS

In this population-based prospective study, measurements were made of anthropometric parameters, thyroid hormone function and urinary iodine in a cohort of the Pizarra Study (n = 937), and repeated 6 years later (n = 784). At the second point, measurements were also made of leptin and adiponectin.

RESULTS

Among the persons who were not obese at the start of the study, the odds ratio (OR) of becoming obese for those in the fourth quartile (Q(4)) for free triiodothyronine (FT3) (versus those in Q(1)) was 2·94 (1·46-5·90) (P = 0·005). The OR of becoming obese in persons in Q(4) of FT4 (versus those in Q(1)) was 3·06 (1·23-7·43) (P = 0·01). Those persons in Q(4) of weight gain had a higher FT3 at the 6-year follow-up than those whose weight gain was in Q(1) (P < 0·001). Leptin correlated with thyrotropin (β = 0·58, P = 0·001) and the FT4 (β = -1·12, P = 0·005). Adiponectin correlated with FT3 (r = -0·24, P < 0·001). The urinary iodine correlated negatively with both the BMI (β = -0·08, P = 0·01) and the increase in weight (β = -0·08, P = 0·04).

CONCLUSIONS

The changes in the thyroid hormones could be the consequence, rather than the cause, of the increase in weight. The same pathophysiological mechanisms that induce obesity might also be modifying the thyroid hormone pattern.

Leptin: a correlated Peptide to papillary thyroid carcinoma?

Introduction. Leptin as an adipose-tissue-related peptide hormone contributes to the control of food intake, energy expenditure, and other activities such as cell proliferation. Therefore, association of leptin level with thyroid cancer has been suggested recently. Considering that thyroid cancer is the most common endocrine cancer, the aim of this study was evaluation of leptin levels in thyroid cancer. Materials and Methods. 83 patients with papillary thyroid cancer (35 males and 48 females) with 90 healthy persons as control group (40 male and 50 females) were selected. serum thyroxine, thyrotropin, and leptin levels were determined in both groups. As a body fat tissue affects leptin level, so height and weight were measured and body mass index was calculated too. Results. There was no statistically significant difference in age, serum Thyroxine, and Thyrotropin levels. BMI in women was more than in men in both groups. Serum leptin levels in thyroid cancer group were significantly higher than control group (P < 0.05). Conclusion. The results of this study showed an acceptable association between the hormone Leptin levels with papillary thyroid cancer, so it may be considerad as a correlated peptide which may help in the diagnosis or confirmation of thyroid cancer beside in other specific tumor markers.

Thyroid disorders and diabetes mellitus

Studies have found that diabetes and thyroid disorders tend to coexist in patients. Both conditions involve a dysfunction of the endocrine system. Thyroid disorders can have a major impact on glucose control, and untreated thyroid disorders affect the management of diabetes in patients. Consequently, a systematic approach to thyroid testing in patients with diabetes is recommended.

Male sex, African American race or ethnicity, and triiodothyronine levels at diagnosis predict weight gain after antithyroid medication and radioiodine therapy for hyperthyroidism

OBJECTIVE

To determine whether racial or ethnic differences affect weight gain after treatment of hyperthyroidism and to reassess established risk factors such as sex, age, and cause of hyperthyroidism.

METHODS

We conducted a retrospective review of medical records of 111 patients treated with radioiodine (RAI) for hyperthyroidism, with or without preceding antithyroid medication, during 2002 to 2005. We ascertained age, sex, race or ethnicity, insurance status, compliance with visits, serum triiodothyronine (T3) level at diagnosis, and cause of hyperthyroidism. Weights and serum thyroidstimulating hormone levels were obtained at diagnosis, at time of RAI therapy, and at 0 to 4 months, 4 to 8 months, 8 to 12 months, and 24 months after RAI treatment.

RESULTS

There was a significant weight increase after treatment of hyperthyroidism. Levels of T3 at initial diagnosis of hyperthyroidism, male sex, and black or Hispanic ethnicity were found to be independent predictors of weight gain after RAI treatment. We found a significant interaction between race or ethnicity and sex in multivariate models. There was no difference in thyroid function across racial or ethnic groups or the sexes. Age, cause of hyperthyroidism, posttreatment thyroid-stimulating hormone level, compliance, and insurance status were not found to be significant predictors of weight gain.

CONCLUSION

The T3 level at the time of diagnosis of hyperthyroidism is a strong predictor of weight gain after treatment of hyperthyroidism. Black race or ethnicity and male sex are also risk factors for weight gain.

Insulin action in hyperthyroidism: a focus on muscle and adipose tissue

Hyperthyroidism leads to an enhanced demand for glucose, which is primarily provided by increased rates of hepatic glucose production due to increased gluconeogenesis (in the fasting state) and increased Cori cycle activity (in the late postprandial and fasting state). Adipose tissue lipolysis is increased in the fasting state, resulting in increased production of glycerol and nonesterified fatty acids. Under these conditions, increased glycerol generated by lipolysis and increased amino acids generated by proteolysis are used as substrates for gluconeogenesis. Increased nonesterified fatty acid levels are necessary to stimulate gluconeogenesis and provide substrate for oxidation in other tissues (such as muscle). In the postprandial period, insulin-stimulated glucose uptake by the skeletal muscle has been found to be normal or increased, mainly due to increased blood flow. Under hyperthyroid conditions, insulin-stimulated rates of glycogen synthesis in skeletal muscle are decreased, whereas there is a preferential increase in the rates of lactate formation vs. glucose oxidation leading to increased Cori cycle activity. In hyperthyroidism, the Cori cycle could be considered as a large substrate cycle; by maintaining a high flux through it, a dynamic buffer of glucose and lactate is provided, which can be used by other tissues as required. Moreover, lipolysis is rapidly suppressed to normal after the meal to facilitate the disposal of glucose by the insulin-resistant muscle. This ensures the preferential use of glucose when available and helps to preserve fat stores.

Investigations of thyroid hormones and antibodies in obesity: leptin levels are associated with thyroid autoimmunity independent of bioanthropometric, hormonal, and weight-related determinants

OBJECTIVES

Obesity can alter the thyroid hormone status as a result of a dysregulated endocrine loop between the hypothalamo-pituitary unit and adipose tissue. The adipocytokine leptin has been shown to promote autoimmunity; hence, we aimed to clarify whether leptin excess of obesity could increase the susceptibility to develop autoimmune thyroid disease (AITD).

STUDY DESIGN

This cross-sectional study was performed in a tertiary care center.

METHODS

Free thyroid hormones, TSH, thyroglobulin, and antithyroid antibodies levels were tested in 165 obese and 118 lean subjects. Results were plotted against variables related to body composition, leptin levels, glucose homeostasis, energy expenditure, and pattern of weight accrual.

RESULTS

Compared with controls, obese patients had lower free T3 levels and free T4 levels (P<0.01), greater prevalence of hypothyroidism (P<0.05), and higher commonness of antithyroid antibodies (P<0.05). As a marker of AITD, thyroid peroxidase antibodies were more frequent in the obese group (P<0.01). Correlation analysis showed that leptin levels were associated with AITD (P<0.01) independent of bioanthropometric variables. Multiple logistic regression analysis in pooled groups identified female sex and leptin as significant predictors of AITD.

CONCLUSIONS

Obesity increases the susceptibility to harbor AITD with an emerging role for leptin as a peripheral determinant, which needs to be confirmed in future investigations.

Acute exogenous TSH administration stimulates leptin secretion in vivo

TSH-receptor (TSHR) has been found in a variety of cell types, including preadipocytes and adipocytes. In vitro, TSH-mediated preadipocyte and adipocyte responses include proliferation, differentiation, survival, and lipolysis. Objective To measure the response of serum leptin to exogenous administration of recombinant human TSH (rhTSH) in vivo. Patients One hundred patients with differentiated thyroid cancer already treated by total thyroidectomy and (131)I remnant ablation were enrolled. Mean (+/-s.e.m.) body mass index (BMI) was 26.9+/-0.6 kg/m(2). Methods Patients received a standard dose of rhTSH for measurement of thyroglobulin in the follow-up of their disease. Blood samples were taken for the assay of TSH and leptin before the first administration of rhTSH (time 0), and 24 h (time 1), 48 h (time 2), 72 h (time 3), and 96 h (time 4) after the first administration of rhTSH. Results Significant mean serum leptin increments, with respect to basal value, were 16, 13, 18, and 11% at times 1, 2, 3, and 4 respectively. Significant positive correlations of leptin-area under the curve with respect to basal leptin levels (r=0.43; P<0.0001) and BMI (r=0.32; P<0.005) were observed. Conclusions Acute rhTSH administration in hypothyroid subjects under l-thyroxine therapy produces a rise in serum leptin. This increase is proportional to the adipose mass suggesting that a functioning TSHR is expressed on the surface of adipocytes. The role that TSHR activation in adipocytes might play in physiological and pathological conditions remains a matter of investigation.

Neonatal nicotine exposure alters leptin signaling in the hypothalamus-pituitary-thyroid axis in the late postnatal period and adulthood in rats

AIMS

Postnatal nicotine exposure causes precocious primary hypothyroidism and programs for overweight, hyperleptinemia and secondary hypothyroidism in adulthood. As leptin and thyroid hormones share the ability to increase energy expenditure, we studied the effects of maternal nicotine exposure during lactation on the leptin signaling in the hypothalamus-pituitary-thyroid axis of suckling and adult offspring.

MAIN METHODS

Two days after delivery, osmotic minipumps were implanted in lactating rats, and nicotine (NIC, 6 mg/kg/day s.c.) or saline (C) was administered for 14days. Offspring were killed at 15 and 180 days-old. Proteins belonging to leptin signaling were analyzed by Western blot. Significant differences had p<0.05.

KEY FINDINGS

In the hypothalamus, NIC offspring showed higher OB-R and pSTAT-3 content (+58%,+1.34x) at 15 days, and lower OB-R, JAK-2 and pSTAT-3 (-61%, -42%, -56%) at 180 days. In the pituitary gland, NIC offspring showed lower JAK-2 content (-52%) at 15 days, but no differences in adulthood. In the thyroid gland, the NIC group presented lower OB-R, JAK-2 and STAT-3 (-44%, -50%, -47%) and higher pSTAT-3 expression (+80%) at 15 days. At 180 days-old, NIC offspring presented higher thyroid OB-R (+1.54x) and lower pSTAT-3 content (-34%).

SIGNIFICANCE

Neonatal primary hypothyroidism induced by maternal nicotine exposure during lactation may be partially explained by decreased leptin signaling in the thyroid, though the early stimulation of the central leptin pathway did not prevent the thyroid dysfunction. Long-term effects of postnatal nicotine exposure on leptin signaling in the hypothalamus and thyroid appear to involve central and peripheral leptin resistance in adulthood.

Endocrinology of obesity

Obesity is a growing health concern in humans and companion animals. Obesity is highly associated with various endocrine abnormalities that are characterized by hormonal imbalance and/or resistance. Weight reduction generally normalizes these endocrine alterations, implicating obesity as a direct cause. Most data in this area have been derived from obese humans, with little data pertaining to hormonal changes in obese dogs and cats. Because the literature contains inconsistent results and because considerable hormone-hormone interactions occur, we have a limited understanding of the obesity-induced changes on the endocrine system in dogs and cats.

Thermogenic response and leptin levels rise after recovery of the euthyroid state

OBJECTIVE

The aims of the study were to compare: a) the thermogenic responses in subclinical hypothyroidism (SH) and euthyroid state; b) the relationship between thermogenic response and leptin level.

METHODS

Thirty women diagnosed with SH (mean age 39.9+/-4.1 yr; body mass index 23.2+/-2.5 kg/m(2)) were enrolled in the study. Thyroid function tests, leptin, and lipid profiles were measured during SH and after stable euthyroidism was recovered. Thermogenic response was measured by Water Immersion Calorimetry during SH and after the euthyroid state was attained.

RESULTS

The mean level of thermogenic response was found to be 1.45+/-0.43 kcal/kg*h in women with SH. It changed to 1.54+/-0.77 kcal/kg*h (p=0.01) in the euthyroid state; the change was statistically significant. Mean level of leptin was found to be 7.22+/-2.6 ng/ml in SH; and 15.8+/-8.0 ng/ml in the euthyroid state. There was a positive correlation between leptin and free T(3) (r=0.460, p=0.009) levels in SH. There were positive correlations between leptin level and fat mass in SH (r=0.820, p=0.01) and in the euthyroid state (r=0.700, p=0.03).

CONCLUSIONS

No correlations were found between thermogenic response and leptin levels in SH and in the euthyroid state. Thermogenic response and leptin levels rose after the euthyroid state was recovered.

Obesity and thyroid function

A moderate elevation of thyrotropin (TSH) concentrations, which is associated with triiodothyronine (T3) values in or slightly above the upper normal range, is frequently found in obese humans. These alterations seem rather a consequence than a cause of obesity since weight loss leads to a normalization of elevated thyroid hormone levels. Elevated thyroid hormone concentrations increase the resting energy expenditure (REE). The underlying pathways are not fully understood. As a consequence of the increased REE, the availability of accumulated energy for conversion into fat is diminished. In conclusion, the alterations of thyroid hormones in obesity suggest an adaptation process. Since rapid weight loss is associated with a decrease of TSH and T3, the resulting decrease in REE may contribute towards the difficulties maintaining weight loss. Leptin seems to be a promising link between obesity and alterations of thyroid hormones since leptin concentrations influence TSH release.

Leptin levels in thyroid cancer

BACKGROUND

Leptin has physiological roles in multiple systems, and has possible effects on several carcinogenesis steps. The aim of this study was to investigate the leptin levels in thyroid papillary carcinoma (TPC) patients.

METHODS

Forty-three female TPC patients and 30 healthy female control subjects were recruited for the study. TPC was diagnosed by fine needle aspiration biopsy. TPC patients had a bilateral total thyroidectomy operation and their leptin levels were measured before and 20 days after the operation.

RESULTS

Serum leptin levels of TPC patients were higher than in control group subjects (21.15 +/- 14.12 ng/mL vs. 9.89 +/- 0.21 ng/mL, p < 0.05). The leptin levels decreased after total thyroidectomy (13.92 +/- 10.55 ng/mL) compared to prethyroidectomy levels (22.94 +/- 14.67 ng/mL) in 34 patients who came to the follow-up visit (p < 0.05). However, the decreased post-thyroidectomy levels of leptin were still statistically significantly higher than the control group levels. Multivariate regression analysis showed that the leptin levels in TPC patients were not related to age, menopausal status or pathologic occult status but were directly related to the cancer group.

CONCLUSION

Leptin levels were elevated in thyroid cancer, decreased after total thyroidectomy, and might be associated with thyroid papillary carcinogenesis.

Administration of physiologic levels of triiodothyronine increases leptin expression in calorie-restricted obese rats, but does not influence weight loss

Obesity has become a major public health problem, most commonly treated via dietary restriction to promote weight loss. Although leptin and thyroid hormones are involved in the regulation of energy balance, the role of these hormones after the stabilization of weight loss remains unclear. This study was designed to analyze the effect of thyroid hormone on sustained weight loss and leptin gene expression in obese animals after a loss of 5% to 10% of body weight. Thirty-day-old male Wistar rats were separated into 4 groups: control, obese, calorie restriction (CR), and calorie restriction with triiodothyronine administration (CRT). The obese group had increased weight and adiposity, leptin and insulin levels, and leptin gene expression. Dietary restriction in the CR group resulted in decreased body weight and adiposity, diminished leptin, and increased thyroid hormone receptor beta expression. The CRT group, submitted to dietary restriction with concomitant administration of a physiologic triiodothyronine dose, had thyroid hormone receptor beta expression at levels comparable with those observed in the control group and simultaneously increased leptin expression as compared with that in the CR group, suggesting that thyroid hormone modulates leptin expression under conditions of calorie restriction. Increased leptin expression in the CRT group did not result in increased circulating leptin or a statistically significant reduction in body weight during the treatment period. These data provide impetus for further study, as a longer treatment period may result in increased circulating leptin and, thus, further reduction in body weight during calorie restriction in an obesity model.

Obesity and thyrotropinemia

OBJECTIVE

To study the relation between body mass index (BMI) and TSH in euthyroid and subclinical hypothyroid obese children and compared serum TSH level among obese and overweight children.

METHODS

Fifty consecutive children (aged 2-18 yr) presenting for obesity were studied. All cases with TSH > 10, low T3/T4, organic and syndromic obesity were excluded. Patients were divided into Group 1: Overweight (n=20) (BMI between 85(th) to 95(th) centile) and Group 2: Obesity (n=30) (BMI > 95(th) centile). Fisher's exact test, Mann-Whitney U test and Pearson's correlation were used for statistical analysis. P value < 0.05 was considered significant.

RESULTS

Elevated TSH level (between 4.5-10 mIU/L) with normal T3, T4 was seen in 4/20 overweight and 9/30 of obese children (P=0.5219). The mean TSH was comparable in both the groups (3.22 +/- 3.1 mIU/L vs. 3.63 +/- 2.2 mIU/L, P=0.3491). Overall TSH showed no correlation with BMI (r= 0.0014, P=0.9924).

CONCLUSION

The preliminary data did not show any relation between severity of obesity and TSH level. Further large scale data from population are required to confirm these findings.

Serum leptin in overt and subclinical hypothyroidism: effect of levothyroxine treatment and relationship to menopausal status and body composition

BACKGROUND

The relationship between thyroid status, including subclinical hypothyroidism (SH) and serum leptin is controversial or uncertain. Therefore we evaluated serum leptin in SH and overt hypothyroidism (OH) and determined the effects of levothyroxine (LT(4)) replacement on serum leptin in these disorders.

METHODS

Serum leptin, thyrotropin (TSH), free thyroxine, insulin, glucose, and body composition parameters were compared in 55 SH, 20 OH, and 28 euthyroid (EU) pre- and postmenopausal women. In addition, the effect of LT(4) treatment on serum leptin in SH and OH was assessed.

RESULTS

The mean +/- SD (median) serum leptin concentrations in the OH and SH groups were higher than in the EU group (35.1 +/- 27.2 [33.0] and 36.6 +/- 21.9 [30.6] ng/mL, respectively, vs. 23.2 +/- 19.3 [17.9] ng/mL, p = 0.011), but the difference was only significant in postmenopausal women. The body mass index (BMI), fat mass index (FMI), and the homeostasis model assessment-insulin resistance (HOMA-IR) index values were not different among these groups. In premenopausal women there was no correlation between leptin, BMI, or FMI and serum TSH levels (r(s) = 0.009, p = 0.474; r(s) = 0.043, p = 0.367; r(s) = 0.092, p = 0.232). In the postmenopausal women, the partial correlation coefficient between TSH and leptin was present, even when controlling for BMI (r(s) = 0.297, p = 0.042) and FMI (r(s) = 0.275, p = 0.050). LT(4) treatment was associated with a reduction of serum leptin concentrations in the OH group (p = 0.008). In SH group there were no differences between LT(4) replacement or no treatment, since a fall in serum leptin levels was detected in both SH subgroups, despite a more pronounced fall with LT(4) use. Treatment of the SH and OH groups with LT(4) did not influence HOMA-IR index or body composition.

CONCLUSIONS

Serum leptin concentrations are elevated in postmenopausal women with SH or OH. A relationship between thyroid status and serum leptin is further supported by the fact that LT(4) treatment, to restore the EU status, reduced serum leptin levels in OH in the absence of significant effects on BMI. In women, hypothyroidism influences either leptin secretion or degradation and this effect is more pronounced in postmenopausal than in premenopausal women.

Postnatal early overnutrition changes the leptin signalling pathway in the hypothalamic-pituitary-thyroid axis of young and adult rats

Postnatal early overnutrition (EO) is a risk factor for obesity in adult life. Rats raised in a small litter can develop hyperinsulinaemia, hyperphagia, hyperleptinaemia and hypertension as adults. Since leptin regulates the hypothalamic-pituitary-thyroid axis and the metabolism of thyroid hormones, we studied the leptin signalling pathway in pituitary and thyroid glands of the postnatal EO model. To induce EO, at the third day of lactation the litter size was reduced to three pups per litter (SL group). In control litters (NL group), the litter size was adjusted to 10 pups per litter. Body weight and food intake were monitored. Rat offspring were killed at 21 (weaning) and 180 days old (adulthood). Plasma thyroid hormones, thyroid-stimulating hormone (TSH) and leptin were measured by radioimmunoassay. Proteins of the leptin signalling pathway were analysed by Western blotting. Body weight of offspring in the SL group was higher from the seventh day of lactation (+33%, P < 0.05) until 180 days old (+18%, P < 0.05). Offspring in the SL group showed higher visceral fat mass at 21 and 180 days old (+176 and +52%, respectively, P < 0.05), but plasma leptin was higher only at 21 days (+88%, P < 0.05). The SL offspring showed higher plasma TSH, 3,5,3'-triiodothronine (T(3)) and thyroxine (T(4)) at 21 days (+60, +91 and +68%, respectively, P < 0.05), while the opposite was observed at 180 days regarding thyroid hormones (T(3), -10%; and T(4), -30%, P < 0.05), with no difference in TSH levels. In hypothalamus, no change was observed in the leptin signalling pathway at 21 days. However, lower janus thyrosine kinase 2 (JAK2) and phosphorilated-signal transducer and activator of transcription-3 (p-STAT3) content were detected in adulthood. In pituitary, the SL group presented higher leptin receptors (Ob-R), JAK2 and p-STAT3 content at 21 days and lower JAK2 and STAT3 content at 180 days old. In contrast, in thyroid, the Ob-R expression was lower in young SL rats, while the adult SL group presented higher Ob-R and JAK2 content. We showed that postnatal EO induces short- and long-term effects upon the hypothalamic-pituitary-thyroid axis. These changes may help to explain future development of metabolic and endocrine dysfunctions, such as metabolic syndrome and hypothyroidism.

Daylong pituitary hormones in morbid obesity: effects of bariatric surgery

Moderate obesity is known to be associated with multiple endocrine abnormalities. Less information is available on the hormonal status of patients with morbid obesity and on the effects of major weight loss. We studied 16 severely obese (BMI 40.6-69.9 kg/m(2)) nondiabetic patients and 7 nonobese (BMI range 24.6-27.7 kg/m(2)), sex- and age-matched healthy volunteers. During 24 h in a metabolic ward, four meals were administered and hourly blood samples were drawn from a central venous catheter for the measurement of glucose, insulin, leptin, thyrotropic hormone (TSH), growth hormone (GH) and prolactin. Insulin sensitivity was measured by a euglycaemic hyperinsulinaemic clamp. Studies were repeated 6 months after biliopancreatic diversion, a mainly malabsorptive surgical approach, which caused an average weight loss of 35+/-4 kg (or 26+/-2% of initial weight). Compared with controls, patients were hyperinsulinaemic (290+/-31 vs 88+/-4 pmol l(-1), P=0.0002), insulin resistant (23.5+/-2.8 vs 52.9+/-4.9 micromol min(-1) kg(FFM)(-1), P=0.0006) and hyperleptinaemic (52.5+/-5.8 vs 10.9+/-3 ng ml(-1), P=0.0002). Plasma TSH levels were increased throughout the day-night cycle (averaging 2.02+/-0.18 vs 1.09+/-0.19 muU ml(-1) of controls, P=0.01), whereas serum GH levels were suppressed (0.46+/-0.10 vs 3.01+/-1.15, P=0.002). Following surgery, the hyperinsulinaemia and insulin resistance were fully normalized; in concomitance with a major drop in leptin levels (to 14.4+/-2.7 ng ml(-1), P=0.02), TSH decreased and GH increased to near-normal levels. In the whole dataset, mean 24-h leptin levels were directly related to mean 24-h TSH levels after controlling for confounders this relationship was lost only after adjusting for fat mass. We conclude that in morbid obesity leptin is a determinant of changes in pituitary function.

Localization of leptin and leptin receptor in the bovine adenohypophysis

The present study was carried out to detail the cellular localization of leptin (Lep) and the leptin receptor (LepR) in the bovine adenohypophysis. Lep immunoreactivity (Lep-ir) was found in about 30% of adenohypophysial cells in the gland. Immunochemistry of Lep and specific hormones using serial sections revealed that Lep-ir was present in 60.4% of somatotrophs, 15.9% of gonadotrophs, 6.5% of mammotrophs, 6.5% of thyrotrophs and 2.4% of corticotrophs. Both the common short isoform (OBRa) and the long isoform (OBRb) of LepR mRNA were expressed in the bovine adenohypophysis. LepR immunoreactivity (LepR-ir) was found in only 2.8% of the adenohypophysial cells and over 50% of LepR-ir cells were gonadotrophs, in which most of the cells were distributed in the zona tuberalis. The findings on Lep and LepR in the adenohypophysial cells indicate that Lep may regulate gonadotroph function through autocrine/paracrine pathway in the bovine adenohypophysis.