Leptin regulation of the thyroids: negative regulation on thyroid hormone levels in euthyroid subjects and inhibitory effects on iodide uptake and Na+/I- symporter mRNA expression in rat FRTL-5 cells

Association between different metabolic phenotypes and the development of hypothyroidism: 9 years follow-up of Tehran thyroid study

PURPOSE

The association between metabolic phenotypes and thyroid function has not yet been established; therefore, this study examined whether different metabolic phenotypes are associated with the development of hypothyroidism.

METHODS

Study participants were selected from the Tehran Thyroid Study (TTS). A total of 3338 euthyroid adults were included and categorized into four obesity phenotype groups: metabolically healthy normal weight (MHNW), metabolically healthy obese (MHO), metabolically unhealthy normal weight (MUNW), and metabolically unhealthy obese (MUO). The participants were assessed at baseline and during three follow-up studies at three-year intervals. Multiple logistic regression analysis was used to examine the relationship between metabolic phenotypes and the development of hypothyroidism.

RESULTS

In the total population, the chi-square test was only significant (P=0.008) in 3^rd year with a higher prevalence of hypothyroidism in the MUNW phenotype, followed by MHO, MUO, and MHNW. Moreover, in the 3^rd and 9^th years of follow-up, hypothyroidism was more prevalent in MUO only in male subjects (P=0.002 and 0.035, respectively). In the unadjusted model, the MHO phenotype increased the odds of hypothyroidism compared with the MHNW phenotype (OR=1.51; 95% CI=1.04, 2.18; P-value=0.031). After adjusting for confounding factors, the odds of hypothyroidism were higher in the MUNW (OR=1.86; 95% CI=1.17, 2.96; P-value=0.008), MHO (OR=1.71; 95% CI=1.09, 2.67; P-value=0.018), and MUO (OR=1.64; 95% CI=1.03, 2.62; P-value=0.036) phenotypes than in the MHNW group. The MUNW phenotype increased the risk of hypothyroidism compared to MHNW, only in males. However, in females, the MHO phenotype increased the risk of hypothyroidism compared to MHNW.

CONCLUSION

Both obesity and metabolic abnormalities are associated with hyperthyroidism. Healthy metabolic and weight maintenance were associated with a lower risk of hypothyroidism in males and females.

The Role of Molecular and Hormonal Factors in Obesity and the Effects of Physical Activity in Children

Obesity and overweight are defined as abnormal fat accumulations. Adipose tissue consists of more than merely adipocytes; each adipocyte is closely coupled with the extracellular matrix. Adipose tissue stores excess energy through expansion. Obesity is caused by the abnormal expansion of adipose tissue as a result of adipocyte hypertrophy and hyperplasia. The process of obesity is controlled by several molecules, such as integrins, kindlins, or matrix metalloproteinases. In children with obesity, metabolomics studies have provided insight into the existence of unique metabolic profiles. As a result of low-grade inflammation in the system, abnormalities were observed in several metabolites associated with lipid, carbohydrate, and amino acid pathways. In addition, obesity and related hormones, such as leptin, play an instrumental role in regulating food intake and contributing to childhood obesity. The World Health Organization states that physical activity benefits the heart, the body, and the mind. Several noncommunicable diseases, such as cardiovascular disease, cancer, and diabetes, can be prevented and managed through physical activity. In this work, we reviewed pediatric studies that examined the molecular and hormonal control of obesity and the influence of physical activity on children with obesity or overweight. The purpose of this review was to examine some orchestrators involved in this disease and how they are related to pediatric populations. A larger number of randomized clinical trials with larger sample sizes and long-term studies could lead to the discovery of new key molecules as well as the detection of significant factors in the coming years. In order to improve the health of the pediatric population, omics analyses and machine learning techniques can be combined in order to improve treatment decisions.

Incidence of Thyroid Dysfunction Facing Metabolic Syndrome: A Prospective Comparative Study with 9 Years of Follow-Up

BACKGROUND

Studies assessing thyroid hormones in metabolic syndrome (MetS) patients are contradictory. Also, the effect of MetS on thyroid function over time is not yet evaluated. This study investigated the prevalence and incidence of thyroid dysfunction (TD) as well as time trends of thyroid hormones in subjects with and without MetS, during a 10-year follow-up in Tehranian adult population.

METHODS

This is a prospective cohort study conducted in the framework of Tehran Thyroid Study on 5,786 subjects aged ≥20 years: 4,905 eligible participants entered the study after excluding those with corticosteroid or radioactive iodine use, pregnancy, thyrotropin (TSH) <0.1 and >10 mU/L, and missing data. Physical examinations were performed and serum concentrations of TSH, free thyroxine (FT4), thyroid peroxidase antibody (TPOAb), fasting plasma glucose, insulin, and lipid profile were assessed at baseline and 3-year intervals during the follow-up. MetS was defined according to the Joint Interim Statement Definition.

RESULTS

At baseline, there were no difference in median serum concentrations of FT4 and TSH between MetS and non-MetS group after adjusting for age, sex, BMI, smoking, and TPOAb positivity. Although there was higher risk of overt (42%) and subclinical hypothyroidism (16%) in MetS compared with non-MetS subjects, no significant difference was observed in adjusted ORs for any TD between 2 groups. There were also no significant differences in time trends of TSH, FT4, TPOAb positivity, and incidence rates of TDs between MetS and non-MetS groups during 10 years, after adjustment for age, sex, BMI, smoking status, and TPOAb positivity.

CONCLUSION

MetS is not associated with thyroid hypofunction considering other important confounders such as age, sex, smoking, BMI, and TPOAb positivity. There is also no difference in the trend of thyroid hormones and incidence of TD between MetS and non-MetS subjects during a 10-year follow-up.

Association between different obesity phenotypes and hypothyroidism: a study based on a longitudinal health management cohort

PURPOSE

Obese individuals have an increased risk of hypothyroidism. This study investigated the sex-specific association between obesity phenotypes and the development of hypothyroidism.

METHODS

The study population was derived from a health management cohort in Shandong Provincial Hospital from 2012 to 2016. In total, 9011 baseline euthyroid adults were included and classified into four groups according to obesity phenotype: metabolically healthy nonobese (MHNO), metabolically healthy obese (MHO), metabolically unhealthy nonobese (MUNO), and metabolically unhealthy obese (MUO). The median follow-up time was 1.92 (1.00-2.17) years. Incidence density was evaluated and a generalized estimation equation method was used to investigate the associations between obesity phenotypes and the development of hypothyroidism.

RESULTS

The incidence densities of hypothyroidism in males with a consistent obesity phenotype were 12.19 (8.62-16.76), 15.87 (11.39-21.56), 14.52 (6.74-27.57), and 19.88 (14.06-27.34) per 1000 person-years in the MHNO, MHO, MUNO, and MUO groups, respectively. After adjusting for confounding factors, compared with the MHNO phenotype, the MHO, MUNO, and MUO phenotypes were independent risk factors for developing hypothyroidism in males. In the subgroup analysis, the MHO and MUO phenotypes were independent risk factors for developing hypothyroidism in males under 55 years, while the MUNO phenotype was an independent risk factor in males over 55 years. The MHO, MUNO, and MUO phenotypes were not independent risk factors for hypothyroidism in females.

CONCLUSION

Both obesity and metabolic abnormities are associated with a higher risk of hypothyroidism in males. The underlying mechanism of the sex and age differences in this association needs further investigation.

Association Between Body Mass Index and Thyroid Function in Euthyroid Chinese Adults

BACKGROUND Obesity can influence thyroid function through multiple routes, even in people who are euthyroid. The correlation between weight and thyroid function is a matter of debate. The present study investigated the relationship between body weight and thyroid function in euthyroid Chinese adults. MATERIAL AND METHODS A total of 1564 participants with serum thyrotropin (TSH) and thyroid hormone levels within the reference range were included. All of them were tested for thyroid function parameters and categorized, based on body mass index (BMI), into 3 groups: normal weight, overweight, and obese. The effects of BMI on thyroid function were examined using linear (continuous values) and logistic (dichotomous levels according to medians or means) regression and controlling for age and sex. RESULTS There were significant differences in free triiodothyronine (FT3) levels and FT3/free thyroxine (FT4) ratios among participants who were normal weight, overweight, and obese (both P<0.001). Multivariable regression analysis (P<0.001) showed that BMI was positively associated with FT3 levels and FT3/FT4 ratios. Compared with the normal weight group, the patients who were overweight or obese had significantly higher FT3 levels and FT3/FT4 ratios that were higher than average, according to logistic regression analyses. CONCLUSIONS We found that Chinese adults who are obese may have higher FT3 levels and FT3/FT4 ratios than those who are of normal weight, even if their thyroid function values are within the normal range.

Inflammation-Related Markers and Thyroid Function Measures in Pediatric Patients: Is the Grade of Obesity Relevant?

We aimed to investigate the effect of weight status on inflammation-related markers and thyroid function tests in overweight and obese pediatric patients. Children and adolescents diagnosed between January 2017 and January 2019 with overweight or obesity were included in the study. Neutrophil-to-lymphocyte ratio (NLR), platelet-to lymphocyte ratio (PLR) and systemic immune-inflammation index (SII) were calculated for the groups defined according to Body Mass Index (BMI)-for-age z-score: overweight (≥1 BMI-for-age z-score), obese (≥2 BMI-for-age z-score) and severely obese (≥3 BMI-for-age z-score). Severely obese patients had significantly higher value of white blood cells (WBC) counts (median = 7.92) compared with overweight patients (7.37, p = 0.014). Absolute lymphocyte count was significantly associated with obesity degree in children (Spearman’s Rho coefficient ρ = 0.228. p = 0.035), whereas absolute polymorphonuclear neutrophils (PMNCs) count was significantly higher in severely obese adolescents than overweight adolescents (overweight: 4.04 vs. severely obese: 5.3 (p = 0.029)). In 8.19% of patients an elevated thyroid-stimulating hormone (TSH) level was found, and 3.36% of patients had a low level of free thyroxine with an elevated level of TSH. Total absolute WBC count may be a reliable inflammation-related marker in obese pediatric patients without metabolic syndrome, but needs to be validated in the context of all possible covariates. Subclinical and overt hypothyroidism may develop from an early age in overweight or obese patients.

The role of thyroid hormone in metabolism and metabolic syndrome

Metabolic syndrome (MetS) and thyroid dysfunction are common in clinical practice. The objectives of this review are to discuss some proposed mechanisms by which thyroid dysfunctions may lead to MetS, to describe the bidirectional relationship between thyroid hormones (THs) and adiposity and finally, to resume a list of recent studies in humans that evaluated possible associations between thyroid hormone status and MetS or its clinical components. Not solely THs, but also its metabolites regulate metabolic rate, influencing adiposity. The mechanisms enrolled are related to its direct effect on adenosine triphosphate (ATP) utilization, uncoupling synthesis of ATP, mitochondrial biogenesis, and its inotropic and chronotropic effects. THs also act controlling core body temperature, appetite, and sympathetic activity. In a bidirectional way, thyroid function is affected by adiposity. Leptin is one of the hallmarks, but the pro-inflammatory cytokines and also insulin resistance impact thyroid function and perhaps its structure. MetS development and weight gain have been positively associated with thyroid-stimulating hormone (TSH) in several studies. Adverse glucose metabolism may be related to hyperthyroidism, but also to reduction of thyroid function or higher serum TSH, as do abnormal serum triglyceride levels. Hypo- and hyperthyroidism have been related to higher blood pressure (BP), that may be consequence of genomic or nongenomic action of THs on the vasculature and in the heart. In summary, the interaction between THs and components of MetS is complex and not fully understood. More longitudinal studies controlling each of all confounding variables that interact with endpoints or exposure factors are still necessary.

The Impact of Obesity on Thyroid Autoimmunity and Dysfunction: A Systematic Review and Meta-Analysis

Background: To help inform decision making in the clinical setting, we carried out a systematic review and meta-analysis to estimate the association of thyroid disease risks with obesity.

Methods: Pubmed, Embase, Web of Science, Cochrane database and Google Scholar electronic databases were searched from inception to October 31, 2018 without language restrictions to explore the relationship between thyroid disorders and obesity. The relative risk (RR) or odds risk (OR) for thyroid disorders were pooled using the SPSS and STATA software.

Results: A total of 22 studies were included in the study. (1) Meta-analysis showed that obesity was significantly associated with an increased risk of hypothyroidism (RR = 1.86, 95% CI 1.63–2.11, P < 0.001). Meta-analyses after stratification further showed that obese population had increased risks of overt hypothyroidism (RR = 3.21, 95% CI 2.12–4.86, P < 0.001) and subclinical hypothyroidism (RR = 1.70, 95% CI 1.42–2.03, P < 0.001). (2) Further meta-analysis also showed obesity was clearly associated with Hashimoto's thyroiditis (RR = 1.91, 95% CI 1.10–3.32, P = 0.022), but not with Graves' disease. (3) In the meta-analysis of antibodies, obesity was correlated with positive thyroid peroxidase antibody (TPOAb) (RR = 1.93, 95% CI 1.31–2.85, P = 0.001), but not with positive thyroglobulin antibody (TGAb).

Conclusions: Obesity was significantly related to hypothyroidism, HT, and TPOAb, implying that prevention of obesity is crucial for thyroid disorders.

Systematic Review Registration: PROSPERO: CRD42018096897.

Single photon emission computed tomography imaging for temporal dynamics of thyroidal and salivary radionuclide accumulation in 17-allyamino-17-demothoxygeldanamycin-treated thyroid cancer mouse model

Selective iodide uptake and prolonged iodine retention in the thyroid is the basis for targeted radioiodine therapy for thyroid cancer patients; however, salivary gland dysfunction is the most frequent nonthyroidal complications. In this study, we have used noninvasive single photon emission computed tomography functional imaging to quantify the temporal dynamics of thyroidal and salivary radioiodine accumulation in mice. At 60  min post radionuclide injection, radionuclide accumulation in the salivary gland was generally higher than that in thyroid due to much larger volume of the salivary gland. However, radionuclide accumulation per anatomic unit in the salivary gland was lower than that in thyroid and was comparable among mice of different age and gender. Differently, radionuclide accumulation per anatomic unit in thyroid varied greatly among mice. The extent of thyroidal radioiodine accumulation stimulated by a single dose of exogenous bovine TSH (bTSH) in triiodothyronine (T₃)-supplemented mice was much less than that in mice received neither bTSH nor T₃ (nontreated mice), suggesting that the duration of elevated serum TSH level is important to maximize thyroidal radioiodine accumulation. Furthermore, the extent and duration of radioiodine accumulation stimulated by bTSH was less in the thyroids of the thyroid-targeted RET/PTC1 (thyroglobulin (Tg)-PTC1) mice bearing thyroid tumors compared with the thyroids in wild-type (WT) mice. Finally, the effect of 17-allyamino-17-demothoxygeldanamycin on increasing thyroidal, but not salivary, radioiodine accumulation was validated in both WT mice and Tg-PTC1 preclinical thyroid cancer mouse model.

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.

Clinicopathologic significance of leptin and leptin receptor expressions in papillary thyroid carcinoma

BACKGROUND

Epidemiologic studies have shown that obesity is associated with an increased risk of thyroid cancer. Leptin, an adipocyte-derived cytokine, can act as a growth factor on certain normal and transformed cells. Aberrant expression of leptin or leptin receptor has been detected in some types of cancer. The aim of this study is to determine immunohistochemical expression of leptin and leptin receptor in papillary thyroid cancer to investigate the relationship between their expression and clinicopathologic features.

METHODS

The expression of leptin and leptin receptor was assessed in 49 primary neoplasms and 15 lymph node metastases using a semiquantitative immunohistochemical staining method.

RESULTS

Leptin and leptin receptor were expressed in 37% and 51% of papillary thyroid cancer, respectively. They were not expressed in normal follicles. In the primary neoplasms and the metastatic nodes, expression of leptin correlated closely with leptin receptor (P < .001 for the primary neoplasms and P = .017 for nodal metastases). Expression of either protein was associated with greater neoplasm size (leptin expression, 32.0 +/- 10.7 vs 20.5 +/- 8.4 mm; P = .001; leptin receptor expression, 27.9 +/- 11.5 vs 21.4 +/- 9.0 mm; P = .032). Coexpression of leptin and leptin receptor in primary neoplasms had greater incidence of lymph node metastasis (P = .038).

CONCLUSION

Expression of leptin and/or leptin receptor in papillary thyroid cancer is associated with neoplasm aggressiveness, including tumor size and lymph node metastasis.

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.

Acute and chronic leptin effect upon in vivo and in vitro rat thyroid iodide uptake

Leptin has stimulatory effects on the hypothalamic-pituitary-thyroid axis and on deiodinases activities. Here, we evaluated the effect of leptin injection upon in vivo and in vitro thyroid 125I uptake (RAIU). We designed two experiments: acute leptin (LepA) with a single dose of leptin (8 microg/100 g BW/sc), and chronic leptin (LepC), injected with the same dose of LepA, once a day, for 6 days. In parallel, control groups were saline-injected. For in vivo study, part of the animals were injected with 125I (3700 Bq) and killed after 15 or 120 min. In vivo thyroid RAIU was not changed in LepA animals. However, LepC animals showed higher in vivo thyroid RAIU (15 min:+130% and 120 min:+72%; p<0.05). For in vitro study, the other animals were killed and their thyroids were incubated with 125I. Thyroids explants from LepA and LepC groups presented lower thyroid 125I content (-32% and -29% p<0.05, respectively). The amount of our data suggest that, in vitro, leptin causes a direct inhibition of the rat thyroid RAIU, but in vivo, the effect of leptin was different according to the treatment period, which indicates that other indirect mechanisms are involved in the in vivo leptin chronic stimulation of the thyroid gland.

Thyroid and leptin

Leptin, which is produced by adipocytes, is known to be an important regulator of food intake and energy storage. Disturbance of thyroid function is associated with marked changes in both body weight and energy expenditure, and it has therefore been the subject of much research to study the mutual roles of leptin and thyroid hormones in this respect. Despite intensive research in this field, results are still not very clear. The aim of this review has been to update the current state of knowledge of leptin related to thyroid pathophysiology.

Expression of type 5 somatostatin receptor in TSH-secreting pituitary adenomas: a possible marker for predicting long-term response to octreotide therapy

In TSH-secreting pituitary adenomas (TSHoma), octreotide (OCT) therapy reduces tumor size and TSH secretion in some cases but not in others. As OCT acts through various types of somatostatin receptors (SSTRs), the different responses of TSHoma to OCT might be explained by the differences of SSTR expression. We therefore studied the expression of subtype-specific SSTR mRNA transcripts in tumor tissues by RT-PCR. Type 2 (SSTR2) mRNA transcripts were detected in all 8 tumors but those of SSTR3 and SSTR5 were demonstrated only in 5 of them. Serum TSH levels were decreased by OCT administration test in all patients but OCT therapy was effective in two patients out of three. SSTR5 mRNA was detected in two tumors from the responder, but not in one tumor that was resistant to OCT. These observations suggest that the temporal decrease of TSH by OCT may be mediated by SSTR2, and that the long term response to OCT therapy may be related with the expression of SSTR5. Therefore, the expression of SSTR5 in TSHoma may be a useful marker for predicting the outcome of the therapy, but further studies with larger numbers of patients are necessary.

Effects of central and systemic administration of leptin on neurotransmitter concentrations in specific areas of the hypothalamus

Leptin, a hormone produced by adipocytes, has been shown to affect a number of central functions, such as regulation of the hypothalamo-pituitary-adrenal axis, feeding, and body weight regulation. Because hypothalamic monoamines are intricately involved in the regulation of these functions, we hypothesized that leptin may produce its effects by altering the activity of these neurotransmitters. To test this hypothesis, male rats received peripheral (0, 100, or 500 μg ip), or central (0 or 5 μg icv) injections of leptin. The animals were killed 5 h later, and their brains were removed, frozen, and sectioned. Serum was collected to measure leptin and corticosterone by RIA. The paraventricular nucleus (PVN), arcuate nucleus (AN), ventromedial hypothalamus (VMH), dorsomedial dorsal nucleus (DMD), median eminence (ME), and medial preoptic area (MPA) were obtained using Palkovits' microdissection technique, and monoamine concentrations in these areas were determined using HPLC-EC. Intraperitoneal administration of leptin increased serum leptin concentrations in a dose-dependent manner ( P < 0.05). Both intraperitoneal and intracerebroventricular administration of leptin decreased serum corticosterone significantly ( P < 0.05). Norepinephrine (NE) concentration decreased significantly in the PVN, AN, and VMH after both intraperitoneal and intracerebroventricular administration of leptin ( P < 0.05). NE concentrations decreased significantly in the DMN after intracerebroventricular administration of leptin ( P < 0.05). Leptin treatment (both ip and icv) decreased dopamine concentrations significantly in the PVN. Serotonin (5-HT) concentration decreased significantly in the PVN after both intraperitoneal and intracerebroventricular injections of leptin and decreased in the VMH only with intracerebroventricular treatment of leptin. Leptin did not affect any of the monoamines in the ME and MPA. These results indicate that both central and systemic administration of leptin can affect hypothalamic monoamines in a region-specific manner, which, in turn, could mediate many of leptin's central and neuroendocrine effects.