Chronic mild stress induces variations in locomotive behavior and metabolic rates in high fat fed rats

Chronic mild stress (CMS) has been often associated to the pathogenesis of many diseases including obesity. Indeed, visceral obesity has been linked to the development of metabolic syndrome features and constitutes a serious risk factor for cardiovascular diseases and diabetes. In order to study possible mechanistic relationships between stress and the onset of obesity, we developed during 11 weeks a model of high-fat dietary intake (cafeteria diet) together with a CMS regimen in male Wistar rats. During the experimental period, basal metabolism by indirect calorimetry, rectal temperature, food intake, and locomotive markers were specifically analyzed. After 77 days, animals were sacrificed and body, adiposity and plasma biochemical profiles were also examined. As expected, cafeteria diet in unstressed animals induced a significative increase in body weight, adiposity, and insulin resistance markers. Locomotive variables, specifically distance, rearing and meander, were significantly increased by CMS on the first weeks of stress. Moreover, this model of CMS in Wistar rats increased significantly energy expenditure, and apparently interplayed with the dietary treatment on the muscle weight/fat weight ratio. In summary, this chronic stress model did not affected weight gain in control and high fat fed animals, but induced an interaction concerning the metabolic muscle/fat repartitioning.     

Dehydroepiandrosterone prevents age-associated alterations, increasing insulin sensitivity

The age decline in DHEA levels has been associated with the appearance of age-related disorders such as obesity and insulin resistance. The aim of this study was to analyse the effect of chronic administration (13 weeks) of DHEA (5 g/kg diet) to old female rats fed on a high-fat diet on body weight and adiposity, and concretely on the expression of the adipokines related to obesity and insulin resistance, such as leptin, adiponectin and resistin. DHEA treatment induced a decrease in body weight, adipose tissue mass and serum insulin, adiponectin and leptin levels. Adiponectin mRNA expression in visceral fat depots decreased with aging, but this reduction was attenuated by DHEA treatment. DHEA treatment also stimulated resistin gene expression in the ovaric and renal adipose depots, which is associated with an increase in its circulating levels. In conclusion, DHEA treatment decreases body weight and adiposity in old female rats fed a high-fat diet, leading to an improvement of the HOMA index for insulin sensitivity, with decreasing circulating insulin levels, and preventing the age-associated decline of visceral-adipose adiponectin expression.     

Serum and gene expression levels of leptin and adiponectin in rats susceptible or resistant to diet-induced obesity

The aim of the present study was to identify the role of leptin and adiponectin in the development of resistance or susceptibility to diet-induced obesity in rats. For this purpose, male Wistar rats were fed with standard laboratory diet (control group) or cafeteria diet. After 15 days, two groups of rats with different response respect to the cafeteria diet were identified, and were assigned as diet-induced obesity (DIO) and diet resistant (DR) rats. The high-fat diet induced a very significant increase in both body and fat mass weight in DIO group. However, DR rats, gained even less weight than control-fed animals. Food intake was increased in cafeteria-fed rats (both DIO and DR) in comparison to control group; but hyperphagia was higher in DIO rats. In addition, feed efficiency (the ratio of weight gained to calories consumed) was significantly decreased in DR as compared to DIO rats. Regarding leptin, a significant increase in both adipose tissue gene expression and serum levels was observed in DIO rats in comparison with other groups (control and DR). A significant increase in both adiponectin circulating levels and adipose tissue mRNA expression was also observed in DIO animals as compared with the other groups. These data suggest that the susceptibility to obesity of DIO rats might be secondary, at least in part, to an earlier development of leptin resistance, which could lead to alterations in food intake (hyperphagia) and energetic metabolism. However, neither changes in leptin or adiponectin seem to be involved in the adaptive mechanisms that confer resistance to high fat intake.     

Influence of dietary macronutrient composition on adiposity and cellularity of different fat depots in Wistar rats

The aim of this study was to investigate the role of dietary macronutrient content on adiposity parameters and adipocyte hypertrophy/hyperplasia in subcutaneous and visceral fat depots from Wistar rats using combined histological and computational approaches. For this purpose, male Wistar rats were distributed into 4 groups and were assigned to different nutritional interventions: Control group (chow diet); high-fat group, HF (60% E from fat); high-fat-sucrose group, HFS (45% E from fat and 17% from sucrose); and high-sucrose group, HS (42% E from sucrose). At day 35, rats were sacrificed, blood was collected, tissues were weighed and fragments of different fat depots were kept for histological analyses with the new softwareAdiposoft. Rats fed with HF, HFS and HS diets increased significantly body weight and total body fat against Control rats, being metabolic impairments more pronounced on HS rats than in the other groups. Cellularity analyses usingAdiposoft revealed that retroperitoneal adipose tissue is histologically different than mesenteric and subcutaneous ones, in relation to bigger adipocytes. The subcutaneous fat pad was the most sensitive to the diet, presenting adipocyte hypertrophy induced by HF diet and adipocyte hyperplasia induced by HS diet. The mesenteric fat pad had a similar but attenuated response in comparison to the subcutaneous adipose tissue, while retroperitoneal fat pad only presented adipocyte hyperplasia induced by the HS diet intake after 35 days of intervention. These findings provide new insights into the role of macronutrients in the development of hyperplastic obesity, which is characterized by the severity of the clinical features. Finally, a new tool for analyzing histological adipose samples is presented.     

Modulatory role of food, feeding regime and physical exercise on body weight and insulin resistance

Energy intake and expenditure is a highly conserved and well-controlled system with a bias toward energy intake. In times of abundant food supply, individuals tend to overeat and in consequence to increase body weight, sometimes to the point of clinical obesity. Obesity is a disease that is not only characterized by enormous body weight but also by rising morbidity for diabetes type II and cardiovascular complications. To better understand the critical factors contributing to obesity we performed the present study in which the effects of energy expenditure and energy intake were examined with respect to body weight, localization of fat and insulin resistance in normal Wistar rats. It was found that a diet rich in fat and carbohydrates similar to "fast food" (cafeteria diet) has pronounced implication in the development of obesity, leading to significant body weight gain, fat deposition and also insulin resistance. Furthermore, an irregularly presented cafeteria diet (yoyo diet) has similar effects on body weight and fat deposition. However, these rats were not resistant to insulin, but showed an increased insulin secretion in response to glucose. When rats were fed with a specified high fat/carbohydrate diet (10% fat, 56.7% carbohydrate) ad lib or at the beginning of their activity phase they were able to detect the energy content of the food and compensate this by a lower intake. They, however, failed to compensate when food was given in the resting phase and gained more body weight as controls. Exercise, even of short duration, was able to keep rats on lower body weight and reduced fat deposition. Thus, inappropriate food intake with different levels of energy content is able to induce obesity in normal rats with additional metabolic changes that can be also observed in humans.     

Effect of vitamin A content in cafeteria diet on the expression of nuclear receptors in rat subcutaneous adipose tissue

The aim of this study was to determine the effects of cafeteria diet containing control or elevated level of vitamin A on the expression of nuclear receptors in adipose tissue. Male Wistar rats were submitted to 3 experimental diets during 8 weeks, a standard diet and two hyper-energetic, hyperlipidic "cafeteria" diets containing normal (Caf) or higher (Caf+) vitamin A level. During the experiment, body weights and energy intakes were measured. At the end of the experimental period, subcutaneous adipose tissue (Swat) and all the fat mass were removed and weighted. Nuclear receptors mRNA levels of RARalpha, RARgamma, RXRalpha, PPARgamma were measured in the Swat by a real-time semi-quantitative RT-PCR method. We observed that energy intake of Caf+ and Caf groups was significantly higher than that of the control group. Despite a higher increase of the energy intake in the Caf group compared to the Caf+ group, no significant difference was observed in the body weight gain of the Caf+ compared to the Caf group. The Caf+ and Caf diets led to a significant increase of adipose tissue in cafeteria groups as observed in the Swat depot. The mRNA levels of PPARgamma and RXRalpha were significantly increased in the Caf+ group as compared to control group, with a significant positive correlation between these two parameters. Expressions of RARalpha and RARgamma were not modified in experimental groups compared to controls. In conclusion, 8-week exposure to cafeteria diets with normal and higher levels of vitamin A led to an increase of adiposity in rats, associated, only in the group fed with the higher vitamin A level cafeteria diet, with an increase of PPARgamma and RXRalpha expressions in subcutaneous adipose tissue.     

Beneficial Effects of Calcitriol on Hypertension,Glucose Intolerance,Impairment of Endothelium-Dependent Vascular Relaxation,and Visceral Adiposity in Fructose-Fed Hypertensive Rats

Besides regulating calcium homeostasis, the effects of vitamin D on vascular tone and metabolic disturbances remain scarce in the literature despite an increase intake with high-fructose corn syrup worldwide. We investigated the effects of calcitriol, an active form of vitamin D, on vascular relaxation, glucose tolerance, and visceral fat pads in fructose-fed rats. Male Wistar-Kyoto rats were divided into 4 groups (n = 6 per group). Group Con: standard chow diet for 8 weeks; Group Fru: high-fructose diet (60% fructose) for 8 weeks; Group Fru-HVD: high-fructose diet as Group Fru, high-dose calcitriol treatment (20 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding; and Group Fru-LVD: high-fructose diet as Group Fru, low-dose calcitriol treatment (10 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding. Systolic blood pressure was measured twice a week by the tail-cuff method. Blood was examined for serum ionized calcium, phosphate, creatinine, glucose, triglycerides, and total cholesterol. Intra-peritoneal glucose intolerance test, aortic vascular reactivity, the weight of visceral fat pads, adipose size, and adipose angiotensin II levels were analyzed at the end of the study. The results showed that the fructose-fed rats significantly developed hypertension, impaired glucose tolerance, heavier weight and larger adipose size of visceral fat pads, and raised adipose angiotensin II expressions compared with the control rats. High- and low-dose calcitriol reduced modestly systolic blood pressure, increased endothelium-dependent aortic relaxation, ameliorated glucose intolerance, reduced the weight and adipose size of visceral fat pads, and lowered adipose angiotensin II expressions in the fructose-fed rats. However, high-dose calcitriol treatment mildly increased serum ionized calcium levels (1.44 ± 0.05 mmol/L). These results suggest a protective role of calcitriol treatment on endothelial function, glucose tolerance, and visceral adiposity in fructose-fed rats.     

The effect of high-fat diet on plasma ghrelin and leptin levels in rats

Ghrelin and leptin regulate appetite and energy homeostasis in humans and rodents. The effects of different nutritional factors on ghrelin and leptin secretion are not well documented in rats. Therefore, the aim of our study was to investigate the effect of a high-fat diet on plasma ghrelin and leptin levels and on adiposity. Twenty male Wistar rats, body weight220–260 g, were used in the study. Rats were randomized either on a standard chow diet (n=10) or on a high-fat diet (a mixture of nuts) forad libitum 11-week period. Body weight was measured once per week. At the end of the nutritional period, rats were sacrificed. Blood was collected for determination of lipids and glucose, as well as plasma ghrelin and leptin levels by ELISA method. The weight of different organs was determined. Rats fed on a high-fat diet showed significant increase in total body weight compared to control group. The long-term intake of high-fat diet caused hyperleptinemia and hypoghrelinemia. There was a significant positive correlation between plasma leptin levels and epididymal fat mass, liver and heart. In contrast, ghrelin levels showed inverse correlation with epididymal fat mass and liver weight. In conclusion, long-term intake of high-fat diet induced changes in plasma ghrelin and leptin in male rats, as well as in epididymal fat mass, liver and heart weights.     

Early and Long-term Undernutrition in Female Rats Exacerbates the Metabolic Risk Associated with Nutritional Rehabilitation

Human studies have suggested that early undernutrition increases the risk of obesity, thereby explaining the increase in overweight among individuals from developing countries who have been undernourished as children. However, this conclusion is controversial, given that other studies do not concur. This study sought to determine whether rehabilitation after undernutrition increases the risk of obesity and metabolic disorders. We employed a published experimental food-restriction model. Wistar female rats subjected to severe food restriction since fetal stage and controls were transferred to a moderately high-fat diet (cafeteria) provided at 70 days of life to 6.5 months. Another group of undernourished rats were rehabilitated with chow. The energy intake of undernourished animals transferred to cafeteria formula exceeded that of the controls under this regime and was probably driven by hypothalamic disorders in insulin and leptin signal transduction. The cafeteria diet resulted in greater relative increases in both fat and lean body mass in the undernourished rats when compared with controls, enabling the former group to completely catch up in length and body mass index. White adipose tissues of undernourished rats transferred to the high-lipid regime developed a browning which, probably, contributed to avoid the obesigenic effect observed in controls. Nevertheless, the restricted group rehabilitated with cafeteria formula had greater accretion of visceral than subcutaneous fat, showed increased signs of macrophage infiltration and inflammation in visceral pad, dyslipidemia, and ectopic fat accumulation. The data indicate that early long-term undernutrition is associated with increased susceptibility to the harmful effects of nutritional rehabilitation, without causing obesity.     

Effects of adrenalectomy on energy balance, diet-induced thermogenesis and brown adipose tissue in adult cafeteria-fed rats

Feeding adult male rats a palatable cafeteria diet stimulated energy intake and expenditure but also raised body weight and energy gains. Bilateral adrenalectomy (ADX) had little effect on stock-fed animals, but prevented the development of obesity in cafeteria-fed rats by depressing food intake and energetic efficiency. Adrenalectomy also markedly increased the thermogenic activity of brown adipose tissue, and depressed insulin levels, particularly in the cafeteria group.     

Effects of a beta3-adrenergic agonist on glucose uptake and leptin expression and secretion in cultured adipocytes from lean and overweight (cafeteria) rats

The increase in body and white adipose tissue weights induced by a high-fat diet were prevented by treatment with the beta3-adrenergic agonist Trecadrine. Plasma insulin levels were slightly elevated in overweight rats, while a decrease was observed in Trecadrine-treated groups. Insulin-dependent glucose uptake was impaired in adipocytes of the overweight rats in relation to lean animals. The beta3-adrenergic agonist induced an increase in insulin-stimulated glucose uptake by adipocytes as compared to the nontreated animals. In fact, Trecadrine treatment was able to restore to control values the impairment in insulin-mediated glucose uptake induced by the cafeteria diet, suggesting that Trecadrine prevents the development of insulin resistance in overweight animals. Basal leptin secretion was increased in adipocytes of the overweight rats in relation to lean animals. Trecadrine treatment induced a decrease in basal leptin secretion compared to the untreated animals. Insulin-stimulated leptin secretion reached similar levels in adipocytes of the overweight rats as in lean animals. There was a trend for insulin-induced leptin secretion to be lower at 24 h in Trecadrine-treated rats, but it did not reach statistical significance. In conclusion, adipocytes of diet-induced overweight animals have a higher basal leptin secretion, which is reduced by treatment with Trecadrine. However, neither the cafeteria diet nor the Trecadrine treatment significantly alters the ability of adipocytes to increase leptin secretion in response to insulin.     

Physical exercise mitigates high-fat diet-induced adiposopathy and related endocrine alterations in an animal model of obesity

The dysregulation of adipokine secretion owing to adiposopathy can contribute to the pathogenesis of obesity-related disorders. Being that exercise is an advised strategy against obesity-induced adiposopathy, we aimed to analyze the role of physical exercise as a preventive and therapeutic strategy against high-fat diet (HFD)-induced adipokine and ghrelin alterations. Rats were pair-fed the Lieber De Carli standard diet (S, 35 Kcal% fat) or HFD (71 Kcal% fat) over 17 weeks. Animals were assigned into four groups as follows: standard diet sedentary (SS), standard diet voluntary physical activity (SVPA), high-fat diet sedentary (HS), and high-fat diet voluntary physical activity (HVPA). After 9 weeks of dietary treatment, half of the SS and HS animals were submitted to an 8-week endurance training program, standard diet endurance training (SET), and high-fat-diet endurance training (HET) groups, maintaining the respective diets. Although there were no changes in body weight, HFD increased visceral adiposity, percentage of large adipocytes, hypoxia inducible factor (HIF)-1α, and leptin contents in epididymal adipose tissue (eWAT) and decreased plasma content of adiponectin (AdipQ). Both VPA and ET decreased visceral adiposity and percentage of large adipocytes in HFD-fed animals, but ET also increased the percentage of small- to medium-sized adipocytes. VPA increased plasma growth hormone secretagogue receptor (GHS-R) and decreased leptin protein in HVPA group. ET decreased plasma insulin and leptin levels and eWAT HIF-1α and leptin expression in HET group. Moreover, ET improved insulin sensitivity, plasma high molecular weight, and AdipQ and ghrelin levels and increased eWAT and GHS-R expression. Our data suggest that exercise, particularly ET, reverted adiposopathy and related endocrine alterations induced by an isocaloric HFD pair-fed diet.     

Green tea reduces body fat accretion caused by high-fat diet in rats through beta-adrenoceptor activation of thermogenesis in brown adipose tissue

The aim of the present study was to investigate body fat-suppressive effects of green tea in rats fed on a high-fat diet and to determine whether the effect is associated with beta-adrenoceptor activation of thermogenesis in brown adipose tissue. Feeding a high-fat diet containing water extract of green tea at the concentration of 20g/kg diet prevented the increase in body fat gain caused by high-fat diet without affecting energy intake. Energy expenditure was increased by green tea extract which was associated with an increase in protein content of interscapular brown adipose tissue. The simultaneous administration of the beta-adrenoceptor antagonist propranolol(500 mg/kg diet) inhibited the body fat-suppressive effect of green tea extract. Propranolol also prevented the increase in protein content of interscapular brown adipose tissue caused by green tea extract. Digestibility was slightly reduced by green tea extract and this effect was not affected by propranolol. Therefore it appeared that green tea exerts potent body fat-suppressive effects in rats fed on a high-fat diet and the effect was resulted in part from reduction in digestibility and to much greater extent from increase in brown adipose tissue thermogenesis through beta-adrenoceptor activation.     

Responses to cafeteria feeding in mice after the removal of interscapular brown adipose tissue

Feeding acafeteria diet to mice resulted in an increased energy intake of approximately 30% and this led to increases in the wet weight, total protein content , and total cytochrome oxidase activity of interscapular and dorso-cervical brown adipose tissue. Surgical removal of interscapular brown adipose tissue, followed by cafeteria feeding, gave rise to an elevation in dorso-cervical brown adipose tissue wet weight, total protein content, and total cytochrome oxidase activity, compared to intact cafeteria-fed mice. Cafeteria feeding with or without the removal of interscapular brown adipose tissue did not lead to significant increases in body weight compared to stock-fed control mice, but both cafeteria-fed groups of mice showed significant elevations in body fat content indicating that the induced hyperphagia led to a relative obesity in the cafeteria-fed groups. The results presented are consistent with an increased thermogenic activity in the brown adipose tissue of cafeteria-fed mice, and the effect of the removal of interscapular brown adipose tissue further indicates the quantitative importance of the tissue in the control of body weight.     

Effects of different intermittent peptide YY (3-36) dosing strategies on food intake, body weight, and adiposity in diet-induced obese rats

Chronic administration of anorexigenic substances to experimental animals by injections or continuous infusion typically produces either no effect or a transient reduction in food intake and body weight. Our aim here was to identify an intermittent dosing strategy for intraperitoneal infusion of peptide YY(3-36) [PYY(3-36)] that produces a sustained reduction in daily food intake and adiposity in diet-induced obese rats. Rats (665+/-10 g body wt, 166+/-7 g body fat) with intraperitoneal catheters tethered to infusion swivels had free access to a high-fat diet. Vehicle-treated rats (n=23) had relatively stable food intake, body weight, and adiposity during the 9-wk test period. None of 15 PYY(3-36) dosing regimens administered in succession to a second group of rats (n=22) produced a sustained 15-25% reduction in daily food intake for >5 days, although body weight and adiposity were reduced across the 9-wk period by 12% (594+/-15 vs. 672+/-15 g) and 43% (96+/-7 vs. 169+/-9 g), respectively. The declining inhibitory effect of PYY(3-36) on daily food intake when the interinfusion interval was >or=3 h appeared to be due in part to an increase in food intake between infusions. The declining inhibitory effect of PYY(3-36) on daily food intake when the interinfusion interval was <3 h suggested possible receptor downregulation and tolerance to frequent PYY(3-36) administration; however, food intake significantly increased when PYY(3-36) treatments were discontinued for 1 day following apparent loss in treatment efficacies. Together, these results demonstrate the development of a potent homeostatic response to increase food intake when PYY(3-36) reduces food intake and energy reserves in diet-induced obese rats.     

Changes in gene expression foreshadow diet-induced obesity in genetically identical mice

High phenotypic variation in diet-induced obesity in male C57BL/6J inbred mice suggests a molecular model to investigate non-genetic mechanisms of obesity. Feeding mice a high-fat diet beginning at 8 wk of age resulted in a 4-fold difference in adiposity. The phenotypes of mice characteristic of high or low gainers were evident by 6 wk of age, when mice were still on a low-fat diet; they were amplified after being switched to the high-fat diet and persisted even after the obesogenic protocol was interrupted with a calorically restricted, low-fat chow diet. Accordingly, susceptibility to diet-induced obesity in genetically identical mice is a stable phenotype that can be detected in mice shortly after weaning. Chronologically, differences in adiposity preceded those of feeding efficiency and food intake, suggesting that observed difference in leptin secretion is a factor in determining phenotypes related to food intake. Gene expression analyses of adipose tissue and hypothalamus from mice with low and high weight gain, by microarray and qRT-PCR, showed major changes in the expression of genes of Wnt signaling and tissue re-modeling in adipose tissue. In particular, elevated expression of SFRP5, an inhibitor of Wnt signaling, the imprinted gene MEST and BMP3 may be causally linked to fat mass expansion, since differences in gene expression observed in biopsies of epididymal fat at 7 wk of age (before the high-fat diet) correlated with adiposity after 8 wk on a high-fat diet. We propose that C57BL/6J mice have the phenotypic characteristics suitable for a model to investigate epigenetic mechanisms within adipose tissue that underlie diet-induced obesity.     

下丘脑Orexin 对肥胖大鼠能量代谢的影响

目的:探讨下丘脑注射OXR-1选择性受体拮抗剂ACT-335827对肥胖大鼠代谢的效果。方法:通过高脂饮食建立肥胖大鼠模型,采用CODA 8通道高通量非侵入性血压系统(EMKA)测量血压;所有脂类都使用商品酶试剂盒和TOSHIBA-40FR全自动分析仪测量;空腹血糖采用葡萄糖氧化酶法;空腹胰岛素采用放射免疫法测定。肥胖大鼠出现代谢紊乱后,给予ACT-335827处理,检测大鼠体重、血压、脂肪、甘油三酯、总胆固醇、高密度脂蛋白、低密度脂蛋白、游离脂肪酸(NEFA)、瘦素、空腹血糖及空腹胰岛素等的变化。结果:与普通饮食组相比,经过10周高脂饮食,高脂饮食组大鼠体重显著升高(P0.05),给予ACT-335827处理后,普通大鼠的体重、血压、脂肪含量、脂代谢等均无明显变化;与高脂饮食和高脂饮食加生理盐水处理组大鼠比较,高脂饮食加ACT-335827处理组肥胖大鼠的体重显著下降(P0.05),腹部和附睾脂肪含量下降(P0.05),低密度脂蛋白、甘油三酯、总胆固醇、瘦素水平下降(P0.05),空腹血糖及空腹胰岛素也显著降低(P0.05),但血压、肠系膜脂肪和肩胛棕色脂肪、高密度脂蛋白和NEFA无明显变化(P0.05)。结论:ACT-335827对肥胖大鼠的代谢紊乱具有改善作用,对肥胖大鼠有一定的减肥作用。