A clinical approach to brown adipose tissue in the para-aortic area of the human thorax.

BACKGROUND: Human thoracic brown adipose tissue (BAT), composed of several subdivisions, is a well-known target organ of many clinical studies; however, the functional contribution of each part of human thoracic BAT remains unknown. The present study analyzed the significance of each part of human thoracic BAT in the association between regional distribution, cellularity, and factors involved in the functional regulation of thoracic BAT. METHODS: We analyzed 1550 healthy adults who underwent medical check-ups by positron-emission tomography and computed tomography (PET-CT) imaging, 8 cadavers, and 78 autopsy cases in an observational study. We first characterized the difference between the mediastinum and the supraclavicular areas using counts of BAT detection and conditions based on PET-CT outcomes. The measurable important area was then subjected to systematic anatomical and immunohistochemical analyses using anti-uncoupling protein 1 (UCP1) antibody to characterize the cellularity in association with age and sex. RESULTS: In PET-CT scanning, the main site of thoracic BAT was the mediastinum rather than the supraclavicular area (P < 0.05). Systemic macroanatomy revealed that the thumb-sized BAT in the posterior mediastinal descending para-aortic area (paBAT) had feeding vessels from the posterior intercostal arteries and veins and sympathetic/parasympathetic innervation from trunks of the sympathetic and vagus nerves, respectively. Immunohistochemical analysis indicated that the paBAT exhibited immunoreactivity for tyrosine hydroxylase and vesicular acetylcholine transporter located in the pericellular nervous fibers and intracellular UCP1. The brown adipose cells of paBAT showed age-dependent decreases in UCP1 expression (P < 0.05), accompanied by a significant increase in vacuole formation, indicating fat accumulation (P < 0.05), from 10 to 37 years of age (P < 0.01). CONCLUSIONS: paBAT may be one of the essential sites for clinical application in BAT study because of its visible anatomy with feeding vessels and sympathetic/parasympathetic innervation functionally affected by outer condition and senescence.

Brain-derived neurotrophic factor, corticotropin-releasing factor, and hypothalamic neuronal histamine interact to regulate feeding behavior.

Brain-derived neurotrophic factor (BDNF), corticotropin-releasing factor (CRF), and hypothalamic neuronal histamine are anorexigenic substances within the hypothalamus. This study examined the interactions among BDNF, CRF, and histamine during the regulation of feeding behavior in rodents. Food intake was measured after treatment with BDNF, α-fluoromethyl histidine (FMH; a specific suicide inhibitor of histidine decarboxylase that depletes hypothalamic neuronal histamine), or CRF antagonist. We measured food intake in wild-type mice and mice with targeted disruption of the histamine H1 receptor (H1KO mice) after central BDNF infusion. Furthermore, we investigated CRF content and histamine turnover in the hypothalamus after BDNF treatment, and conversely, BDNF content in the hypothalamus after histamine treatment. We used immunohistochemical staining for histamine H1 receptors (H1-R) in BDNF neurons. BDNF-induced feeding suppression was partially attenuated in rats pre-treated with FMH or a CRF antagonist, and in H1KO mice. BDNF treatment increased CRF content and histamine turnover in the hypothalamus. Histamine increased BDNF content in the hypothalamus. Immunohistochemical analysis revealed that H1-Rs were expressed on BDNF neurons in the ventromedial nucleus of the hypothalamus. These results indicate that CRF and hypothalamic neuronal histamine mediate the suppressive effects of BDNF on feeding behavior and body weight.

Nesfatin-1, corticotropin-releasing hormone, thyrotropin-releasing hormone, and neuronal histamine interact in the hypothalamus to regulate feeding behavior.

Nesfatin-1, corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH), and hypothalamic neuronal histamine act as anorexigenics in the hypothalamus. We examined interactions among nesfatin-1, CRH, TRH, and histamine in the regulation of feeding behavior in rodents. We investigated whether the anorectic effect of nesfatin-1, α-fluoromethyl histidine (FMH; a specific suicide inhibitor of histidine decarboxylase that depletes hypothalamic neuronal histamine), a CRH antagonist, or anti-TRH antibody affects the anorectic effect of nesfatin-1, whether nesfatin-1 increases CRH and TRH contents and histamine turnover in the hypothalamus, and whether histamine increases nesfatin-1 content in the hypothalamus. We also investigated whether nesfatin-1 decreases food intake in mice with targeted disruption of the histamine H1 receptor (H1KO mice) and if the H1 receptor (H1-R) co-localizes in nesfatin-1 neurons. Nesfatin-1-suppressed feeding was partially attenuated in rats administered with FMH, a CRH antagonist, or anti-TRH antibody, and in H1KO mice. Nesfatin-1 increased CRH and TRH levels and histamine turnover, whereas histamine increased nesfatin-1 in the hypothalamus. Immunohistochemical analysis revealed H1-R expression on nesfatin-1 neurons in the paraventricular nucleus of the hypothalamus. These results indicate that CRH, TRH, and hypothalamic neuronal histamine mediate the suppressive effects of nesfatin-1 on feeding behavior.

Obesity-related chronic kidney disease is associated with spleen-derived IL-10.

BACKGROUND: Obesity is associated with systemic low-grade inflammation and is a risk factor for chronic kidney disease (CKD), but the molecular mechanism remains uncertain. We noticed spleen-derived interleukin (IL)-10 because it is observed that obesity reduces several cytokines in the spleen. METHODS: We examined whether spleen-derived IL-10 regulates CKD caused by a high-fat diet (HF)-induced obesity as follows: (i) male mice were fed with HF (60% fat) during 8 weeks and IL-10 induction from the spleen was examined, (ii) glomerular hypertrophy, fibrosis, inflammatory responses in the kidney and systolic blood pressure (SBP) were evaluated in splenectomy (SPX)-treated mice fed HF, (iii) exogenous IL-10 was systemically administered to HF-induced obese mice and the alteration of obesity-induced pathogenesis caused by IL-10 treatment was assessed. (iv) IL-10 knockout (IL-10KO) mice were treated with SPX and glomerular hypertrophy, fibrosis and the inflammatory condition in the kidney and SBP were also investigated. RESULTS: Obesity decreased serum levels of only IL-10, an anti-inflammatory cytokine even though pro- and anti-inflammatory cytokine expression in the spleen was significantly lower in the obese group. SPX aggravated HF-induced inflammatory responses in the kidney and hypertension. These HF-induced alterations were inhibited by systemically administered IL-10. Moreover, SPX had little effect on inflammatory responses and SBP in the kidney of IL-10KO mice. CONCLUSIONS: We suggest that obesity reduces IL-10 induction from the spleen, and spleen-derived IL-10 may protect against the development of CKD induced by obesity.

A novel anti-inflammatory role for spleen-derived interleukin-10 in obesity-induced inflammation in white adipose tissue and liver.

Obesity is associated with systemic low-grade inflammation and obesity-related metabolic disorders. Considering that obesity decreases the expression of proinflammatory cytokines in the spleen, we assessed the role of interleukin (IL)-10, an anti-inflammatory cytokine produced by the spleen, in the pathogenesis of obesity. Changes in obesity-related pathogenesis, including inflammatory responses in multiple organs, were assessed after systemic administration of exogenous IL-10 to splenectomy (SPX)-treated obese wild-type and IL-10 knockout (IL-10KO) mice. Obesity resulted in the inability of the spleen to synthesize cytokines, including IL-10, and proinflammatory cytokines in obesity are then likely to emerge from tissues other than the spleen because serum levels of IL-10, but not proinflammatory cytokines, decreased despite the expression of these cytokines in the spleen being reduced in high fat-induced obese mice. SPX aggravated the inflammatory response in white adipose tissue (WAT) and the liver and suppressed adiposity in WAT. However, it accentuated adiposity in the liver. These SPX-induced changes were inhibited by systemic administration of IL-10. Moreover, SPX had little effect on the inflammatory responses in WAT and the liver of IL-10KO mice. These data show the role of spleen-derived IL-10 in diet-induced changes as a result of inflammatory responses in WAT and the liver.

Spleen-derived interleukin-10 downregulates the severity of high-fat diet-induced non-alcoholic fatty pancreas disease.

Obesity is associated with systemic low-grade inflammation and is a risk factor for non-alcoholic fatty pancreas disease (NAFPD), but the molecular mechanisms of these associations are not clear. Interleukin (IL)-10, a potent anti-inflammatory cytokine, is released during acute pancreatitis and is known to limit inflammatory responses by downregulating the release of proinflammatory mediators. The origin of IL-10 that suppresses pancreatitis has not been investigated. Since obesity is known to reduce expression of proinflammatory cytokines in the spleen, we examined whether spleen-derived IL-10 regulates NAFPD caused by high-fat (HF) diet-induced obesity. The following investigations were performed: 1) IL-10 induction from spleen was examined in male mice fed a HF diet; 2) triglyceride content, expression of pro- and anti-inflammatory cytokines and infiltration of M1 and M2 macrophages were determined to evaluate ectopic fat accumulation and inflammatory responses in the pancreas of splenectomy (SPX)-treated mice fed HF diet; 3) exogenous IL-10 was systemically administered to SPX-treated obese mice and the resulting pathogenesis caused by SPX was assessed; and 4) IL-10 knockout (IL-10KO) mice were treated with SPX and ectopic fat deposition and inflammatory conditions in the pancreas were investigated. Obesity impaired the ability of the spleen to synthesize cytokines, including IL-10. SPX aggravated fat accumulation and inflammatory responses in the pancreas of HF diet-induced obese mice and these effects were inhibited by systemic administration of IL-10. Moreover, SPX had little effect on fat deposition and inflammatory responses in the pancreas of IL-10KO mice. Our findings indicate that obesity reduces IL-10 production by the spleen and that spleen-derived IL-10 may protect against the development of NAFPD.

Intraportal administration of DPP-IV inhibitor regulates insulin secretion and food intake mediated by the hepatic vagal afferent nerve in rats.

Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion and suppresses food intake. Recent studies indicate that the hepatic vagal afferent nerve is involved in this response. Dipeptidyl peptidase-IV (DPP-IV) inhibitor extends the half-life of endogenous GLP-1 by preventing its degradation. This study aimed to determine whether DPP-IV inhibitor-induced elevation of portal GLP-1 levels affect insulin secretion and feeding behavior via the vagal afferent nerve and hypothalamus. The effect of DPP-IV inhibitor infusion into the portal vein or peritoneum on portal and peripheral GLP-1 levels, food intake, and plasma insulin and glucose was examined in sham-operated and vagotomized male Sprague-Dawley rats. Analyses of neuronal histamine turnover and immunohistochemistry were used to identify the CNS pathway that mediated the response. Intraportal administration of the DPP-IV inhibitor significantly increased portal (but not peripheral) GLP-1 levels, increased insulin levels, and decreased glucose levels. The DPP-IV inhibitor suppressed 1- and 12- but not 24-h cumulative food intake. Intraportal infusion of the DPP-IV inhibitor increased hypothalamic neuronal histamine turnover and increased c-fos expression in several areas of the brain. These responses were blocked by vagotomy. Our results indicate that DPP-IV inhibitor-induced changes in portal but not systemic GLP-1 levels affect insulin secretion and food intake. Furthermore, our findings suggest that a neuronal pathway that includes the hepatic vagal afferent nerve and hypothalamic neuronal histamine plays an important role in the pharmacological actions of DPP-IV inhibitor.

A novel anti-inflammatory role for spleen-derived interleukin-10 in obesity-induced hypothalamic inflammation.

Obesity can be associated with systemic low-grade inflammation that contributes to obesity-related metabolic disorders. Recent studies raise the possibility that hypothalamic inflammation contributes to the pathogenesis of diet-induced obesity (DIO), while another study reported that obesity decreases the expression of pro-inflammatory cytokines in spleen. The following study examines the hypothesis that obesity suppresses the splenic synthesis of the anti-inflammatory cytokine, interleukin (IL)-10, thereby resulting in chronic hypothalamic inflammation. The results showed that due to oxidative stress or apoptosis, the synthesis of splenic IL-10 was decreased in DIO when compared with non-obesity rats. Splenectomy (SPX) accelerated DIO-induced inflammatory responses in the hypothalamus. Interestingly, SPX suppressed the DIO-induced increases in food intake and body weight and led to a hypothalamic pro-inflammatory state that was similar to that produced by DIO, indicating that hypothalamic inflammation exerts a dual effect on energy metabolism. These SPX-induced changes were inhibited by the systemic administration of IL-10. Moreover, SPX had no effect on hypothalamic inflammatory responses in IL-10-deficient mice. These data suggest that spleen-derived IL-10 plays an important role in the prevention of hypothalamic inflammation and may be a therapeutic target for the treatment of obesity and hypothalamic inflammation.

Retinol binding protein 4 concentrations are influenced by renal function in patients with type 2 diabetes mellitus.

Retinol binding protein 4 (RBP-4), a newly discovered adipocytokine, has been involved in glucose and lipid metabolism. We assess the impacts of renal function on plasma RBP-4 levels in patients with type 2 diabetes mellitus with a wide range of nephropathy. Plasma RBP-4 levels were measured using the enzyme immunoassay method in 38 type 2 diabetes mellitus patients with nephropathy and were compared with those in 20 patients with normoalbuminuria. The levels of plasma RBP-4 were increased by 1.4- and 3.3-fold in patients with renal disease with macroalbuminuria (P = .04) and end-stage renal disease (plasma creatinine level >2.0 mg/dL) (P < .0001) compared with those in patients with normal renal function. In addition, RBP-4 levels were correlated with the creatinine level and 24-hour creatinine clearance (Ccr) on simple and multiple regression analyses in all patients. Furthermore, in patients having Ccr of more than 60 mL/min, RBP-4 levels were correlated with the homeostasis model assessment (HOMA)-r index and triglyceride (TGL) both on simple and multiple regression analyses. Interestingly, in patients having Ccr of less than 60 mL/min, RBP-4 levels were not correlated with the HOMA-r index and TGL on simple regression analysis. The RBP-4 concentrations are influenced by renal function in type 2 diabetes mellitus patients. In addition, RBP-4 levels were correlated with HOMA-r and TGL in diabetic subjects without end-stage renal disease.

Effects of pravastatin on obesity, diabetes, and adiponectin in diet-induced obese mice.

OBJECTIVE: The aim of this study was to investigate the in vivo effects of pravastatin on the development of obesity and diabetes in diet-induced obese (DIO) mice. METHODS AND PROCEDURES: We examined food intake, body-weight changes, visceral white adipose tissue (WAT) adiponectin and resistin levels, and energy metabolism. RESULTS: Treatment with 100 mg/kg/day pravastatin for 28 days decreased diet-induced weight gain and visceral adiposity. In addition, the weight of the WAT, the triglyceride (TG) contents of the liver and muscles, and the levels of serum insulin improved in the pravastatin-treated DIO mice. Furthermore, pravastatin treatment changed the WAT adiponectin and resistin mRNA expression and serum levels compared with the controls. Finally, pravastatin treatment increased oxygen consumption and decreased the respiratory quotient (RQ). DISCUSSION: Pravastatin treatment prevents the development of obesity and diabetes in DIO mice. The prevention of obesity may be mediated by increased oxygen consumption and a decrease in the RQ. These results provide novel insights into the use of pravastatin as a therapeutic tool for metabolic syndromes.

Hypoadiponectinemia in type 2 diabetes mellitus in men is associated with sympathetic overactivity as evaluated by cardiac 123I-metaiodobenzylguanidine scintigraphy.

Hypoadiponectinemia is associated with insulin resistance. However, there is very limited information about the relationship between plasma adiponectin and cardiac autonomic nervous function. We tested the hypothesis that hypoadiponectinemia is associated with cardiac sympathetic overactivity in patients with type 2 diabetes mellitus. Thirty-three male type 2 diabetic patients not on insulin treatment were classified into a hypoadiponectinemia group (plasma adiponectin concentration, <4.0 microg/mL; age, 58.6 +/- 8.6 years [mean +/- SD]; n = 14) and an age-matched normoadiponectinemia group (serum adiponectin concentration, >/=4.0 microg/mL; age, 58.2 +/- 8.1 years; n = 19). In each patient, baroreflex sensitivity, heart rate variability, plasma norepinephrine concentration, and cardiac (123)I-metaiodobenzylguanidine (MIBG) scintigraphic findings were assessed. Compared with the normoadiponectinemia group, the hypoadiponectinemia group had a higher body mass index (P < .01), higher plasma concentrations of glucose and insulin (P < .05 and P < .01, respectively), higher homeostasis model assessment of insulin resistance (HOMA-IR) values (P < .005), higher plasma triglyceride levels (P < .05), and lower plasma high-density lipoprotein cholesterol levels (P < .05). In the hypoadiponectinemia group, the autonomic function measurements included a lower baroreflex sensitivity (P< .05) and a lower delayed myocardial uptake of (123)I-MIBG (P < .01) with a higher washout rate (P < .05). Multiple regression analysis revealed that the plasma adiponectin level was independently associated with HOMA-IR (F = 9.916) and the percent washout rate of (123)I-MIBG (F = 5.985). Our results suggest that in middle-aged men with type 2 diabetes mellitus, hypoadiponectinemia is associated with cardiac sympathetic overactivity as determined by (123)I-MIBG scintigraphy.

Apelin, an APJ receptor ligand, regulates body adiposity and favors the messenger ribonucleic acid expression of uncoupling proteins in mice.

Apelin, the endogenous ligand of the APJ receptor, has been identified in a variety of tissues, including stomach, heart, skeletal muscle, and white adipose tissue. We sought to clarify the effects of apelin on body adiposity and the expression of uncoupling proteins (UCPs) in C57BL/6 mice. Treatment with ip apelin at a dose of 0.1 mumol/kg.d for 14 d decreased the weight of white adipose tissue and serum levels of insulin and triglycerides, compared with controls, without influencing food intake. Apelin treatment also decreased body adiposity and serum levels of insulin and triglycerides in obese mice fed a high-fat diet. Apelin increased the serum adiponectin level and decreased that of leptin. Additionally, apelin treatment increased mRNA expression of UCP1, a marker of peripheral energy expenditure, in brown adipose tissue (BAT) and of UCP3, a regulator of fatty acid export, in skeletal muscle. In addition, immunoblot bands and relative densities of UCP1 content in BAT were also higher in the apelin group than controls. Furthermore, apelin treatment increased body temperature and O(2) consumption and decreased the respiratory quotient. In conclusion, apelin appears to regulate adiposity and lipid metabolism in both lean and obese mice. In addition, apelin regulates insulin resistance by influencing the circulating adiponectin level, the expression of BAT UCP1, and energy expenditure in mice.

Hyperhomocysteinemia is associated with visceral adiposity in Japanese patients with type 2 diabetes mellitus.

This study aims to investigate the relationship between the circulating level of homocysteine and body adiposity in Japanese patients with type 2 diabetes mellitus. We measured the body mass index (BMI), waist and hip circumferences, visceral and subcutaneous adiposities, visceral/subcutaneous (V/S) adiposity ratio, and insulin resistance as assessed by the Homeostasis Model Assessment (HOMA) index in patients with hyperhomocysteinemia. The study group consisted of 17 Japanese patients with type 2 diabetes and hyperhomocysteinemia (age: 62+/-10 years, mean+/-S.D.), and the control group consisted of 24 age-matched type 2 diabetes patients with normohomocysteinemia (60+/-11 years). The visceral adiposity, HOMA index, and V/S ratio were significantly higher in the hyperhomocysteinemia group than in the normohomocysteinemia group (P<0.05). In contrast, the BMI, hip circumference, and subcutaneous adiposity were similar between the two groups (P>0.1). Furthermore, multiple regression analysis showed that hyperhomocysteinemia was closely related to insulin resistance and visceral adiposity. Our results indicate that the presence of hyperhomocysteinemia in our population of Japanese patients with type 2 diabetes-associated insulin resistance was associated with increased visceral but not subcutaneous adiposity.

Telmisartan prevents obesity and increases the expression of uncoupling protein 1 in diet-induced obese mice.

The aim of the present study was to clarify the effect of telmisartan, an angiotensin II receptor blocker, on the development of obesity and related metabolic disorders in diet-induced obese mice. Treatment with telmisartan dissolved in drinking water at a dosage of 5 mg/kg per day for 14 days attenuated the diet-induced weight gain without affecting food intake in diet-induced obese mice compared with controls using nontreated water. Telmisartan treatment decreased the weight of visceral adipose tissue and the triglyceride content in the liver and skeletal muscle. In addition, hyperglycemia, hyperinsulinemia, and hypertriglyceridemia in diet-induced obese mice all improved with telmisartan treatment. Furthermore, telmisartan treatment increased adiponectin mRNA in visceral white adipose tissue and was associated with a concomitant change in the serum adiponectin level. In contrast, the treatment reduced the serum level of resistin. Finally, telmisartan treatment increased the mRNA expression of uncoupling protein 1 in brown adipose tissue and was accompanied by an increase in oxygen consumption. In conclusion, telmisartan treatment might prevent the development of obesity and related metabolic disorders by altering the levels of adiponectin, resistin, and uncoupling protein 1 in diet-induced obese mice. Our results indicate that telmisartan can be used as a therapeutic tool for metabolic syndrome, including visceral obesity.

Leptin downregulates ghrelin levels in streptozotocin-induced diabetic mice.

Ghrelin, an orexigenic peptide produced in the stomach, is increased in streptozotocin (STZ)-induced diabetic (DM) mice. This study clarifies the regulation of ghrelin levels by leptin in STZ-DM mice. STZ-DM mice had higher plasma ghrelin concentrations and greater ghrelin mRNA expression than control mice. Changes in ghrelin levels were dose dependently attenuated by the subcutaneous injection of leptin (0-27 nmol x kg(-1) x day(-1) over 7 days). Leptin treatment also partially reversed the hyperphagia and hyperglycemia observed in STZ-DM mice, but not the hypoinsulinemia, and there was a decrease in plasma ghrelin concentrations and ghrelin mRNA levels compared with STZ-LEP pair-fed mice. These results indicate that leptin treatment partially reverses elevated plasma ghrelin levels in STZ-DM mice independent of food intake and insulin, and suggest that hypoleptinemia in STZ-DM mice upregulates ghrelin.

Ghrelin regulates adiposity in white adipose tissue and UCP1 mRNA expression in brown adipose tissue in mice.

To examine the involvement of ghrelin in obesity, we investigated the effects of treatment with peripherally administered ghrelin on food intake, adiposity, and expression of uncoupling protein (UCP) mRNA in brown (BAT) and white (WAT) adipose tissue in mice. Acute bolus administration of ghrelin at a dose of 120 nmol/kg increased cumulative food intake over 4 and 24 h as compared to controls (p<0.05 for each), whereas 12 nmol/kg/day ghrelin showed no remarkable effect (p>0.1). Chronic repeated treatment with 12 nmol/kg/day ghrelin for 7 days increased body weight and adiposity assessed by the weight of adipose tissue, triglyceride content in WAT (p<0.05 for each versus control). In addition, the same treatment decreased and increased mRNA expression of BAT UCP1 and WAT UCP2, respectively (p<0.05 for each). In conclusion, ghrelin can regulate body weight, adiposity and UCPs mRNA expression in mice. The present results provide evidence for a new regulatory loop involving ghrelin and UCP, and add novel insights into the regulatory mechanisms of obesity.

Dual regulatory effects of orexins on sympathetic nerve activity innervating brown adipose tissue in rats.

This study examined how orexin regulates the activity of the sympathetic nerves that innervate brown adipose tissue (BAT) in rats. Infusion of orexin A at a dose of 0.3 nmol into the third cerebral ventricle decreased BAT sympathetic nerve activity, compared with the effect of PBS (P < 0.05), whereas infusion of orexin B at the same dose caused a significant increase (P < 0.05). Pretreatment with a third cerebral ventricle injection of 2.24 micromol/kg alpha-fluoromethylhistidine, an irreversible inhibitor of the histamine-synthesizing enzyme histidine decarboxylase, attenuated the orexin B-induced response of BAT sympathetic nerve activity, but not that induced by orexin A. These results indicate that orexins may regulate both BAT energy expenditure and thermogenesis through their dual effects on sympathetic nerve activity. In particular, orexin B regulates BAT sympathetic nerve activity via neuronal histamine in the hypothalamus.

Regulation of QT indices mediated by autonomic nervous function in patients with type 2 diabetes.

Both the QT interval and QT dispersion in diabetic patients have been reported to increase with the progression of cardiac autonomic neuropathy and to have a prognostic value. We assessed the cardiac autonomic influences on QT indices using the measurements of baroreflex sensitivity, heart rate variability, and cardiac (123)I-metaiodobenzylguanidine scintigraphic findings in patients with type 2 diabetes mellitus. Forty-two consecutive patients with type 2 diabetes (mean+/-SD: 54+/-10 years, 22 women and 20 men) were studied. Baroreflex sensitivity negatively correlated with the maximum and minimum QTc intervals as well as QT/QTc dispersion. However, the high-frequency power and the ratio of low-frequency power to high-frequency power of heart rate variability did not correlate with any QT indices. The percent washout rate of (123)I-metaiodobenzylguanidine positively correlated with QT/QTc dispersion, but not with maximum and minimum QTc intervals. Our findings suggest that cardiac vagal dysfunction is related to QT interval prolongation while both sympathetic and vagal dysfunctions are related to increased QT dispersion in type 2 diabetic patients. Baroreflex sensitivity and percent washout rate of (123)I-metaiodobenzylguanidine may be useful parameters indicating the abnormalities of the cardiac ventricular repolarization in this population.