Cafeteria-fed Rats Research Articles

Brown Adipose Tissue: A Short Historical Perspective.

Brown adipose tissue (BAT) was first identified by Conrad Gessner in 1551, but it was only in 1961 that it was firmly identified as a thermogenic organ. Key developments in the subsequent two decades demonstrated that: (1) BAT is quantitatively important to non-shivering thermogenesis in rodents, (2) uncoupling of oxidative phosphorylation through a mitochondrial proton conductance pathway is the central mechanism by which heat is generated, (3) uncoupling protein-1 is the critical factor regulating proton leakage in BAT mitochondria. Following pivotal studies on cafeteria-fed rats and obese ob/ob mice, BAT was then shown to have a central role in the regulation of energy balance and the etiology of obesity. The application of fluorodeoxyglucose positron emission tomography in the late 2000s confirmed that BAT is present and active in adults, resulting in renewed interest in the tissue in human energetics and obesity. Subsequent studies have demonstrated a broad metabolic role for BAT, the tissue being an important site of glucose disposal and triglyceride clearance, as well as of insulin action. BAT continues to be a potential target for the treatment of obesity and related metabolic disorders.

Glucagon Shows Higher Sensitivity than Insulin to Grapeseed Proanthocyanidin Extract (GSPE) Treatment in Cafeteria-Fed Rats.

The endocrine pancreas plays a key role in metabolism. Procyanidins (GSPE) targets β-cells and glucagon-like peptide-1 (GLP-1)-producing cells; however, there is no information on the effects of GSPE on glucagon. We performed GSPE preventive treatments administered to Wistar rats before or at the same time as they were fed a cafeteria diet during 12 or 17 weeks. We then measured the pancreatic function and GLP-1 production. We found that glucagonemia remains modified by GSPE pre-treatment several weeks after the treatment has finished. The animals showed a higher GLP-1 response to glucose stimulation, together with a trend towards a higher GLP-1 receptor expression in the pancreas. When the GSPE treatment was administered every second week, the endocrine pancreas behaved differently. We show here that glucagon is a more sensitive parameter than insulin to GSPE treatments, with a secretion that is highly linked to GLP-1 ileal functionality and dependent on the type of treatment.

Minocycline-induced microbiome alterations predict cafeteria diet-induced spatial recognition memory impairments in rats

Diets rich in sugar and saturated fat are associated with cognitive impairments in both humans and rodents with several potential mechanisms proposed. To test the involvement of diet-induced pro-inflammatory signaling, we exposed rats to a high-fat, high-sugar cafeteria diet, and administered the anti-inflammatory antibiotic minocycline. In the first experiment minocycline was coadministered across the diet, then in a second, independent cohort it was introduced following 4 weeks of cafeteria diet. Cafeteria diet impaired novel place recognition memory throughout the study. Minocycline not only prevented impairment in spatial recognition memory but also reversed impairment established in rats following 4 weeks cafeteria diet. Further, minocycline normalized diet-induced increases in hippocampal pro-inflammatory gene expression. No effects of minocycline were seen on adiposity or dietary intake across the experiments. Cafeteria diet and minocycline treatment significantly altered microbiome composition. The relative abundance of Desulfovibrio_OTU31, uniquely enriched in vehicle-treated cafeteria-fed rats, negatively and significantly correlated with spatial recognition memory. We developed a statistical model that accurately predicts spatial recognition memory based on Desulfovibrio_OTU31 relative abundance and fat mass. Thus, our results show that minocycline prevents and reverses a dietary-induced diet impairment in spatial recognition memory, and that spatial recognition performance is best predicted by changes in body composition and Desulfovibrio_OTU31, rather than changes in pro-inflammatory gene expression.

The anomeric nature of glucose and its implications on its analyses and the influence of diet: are routine glycaemia measurements reliable enough?

Background: Glucose is the main inter-organ energy supplying metabolite in humans and other vertebrates. In clinical analyses, its measurement is probably the most performed and used for diagnostic, monitoring and control of the physiological status. However, glucose chemical structure, specially its anomeric forms (alpha/beta), may deeply interfere in their own analyses, often resulting in misleading results. Methods: These effects on glucose estimation were studied by using a common glucose oxidase/peroxidase based method, in the presence or absence of added mutarotase, which speeds up the alpha/beta conversion rate. Glucose concentrations were measured in pure standards and plasma samples from control and cafeteria diet-fed rats. Results: The addition of mutarotase resulted in higher glucose readings, independently of glucose concentration and its initial anomeric proportions in the sample. In the absence of mutarotase, cafeteria-fed rats had higher glucose levels than controls, but the differences disappeared in its presence, because under experimental conditions, a proportion of the alpha-anomer was not isomerized and thus was not measured. Conclusions: Diet altered the proportion of anomers, suggesting that glucose usage by physiological processes affects the anomers’ ratio and may have an important metabolic meaning, which deserves a detailed study in addition to the need to correct the methods in use to obtain real “total glucose” readings. J Endocrinol Metab. 2019;9(3):63-70 doi: https://doi.org/10.14740/jem555

The Anomeric Nature of Glucose and Its Implications on Its Analyses and the Influence of Diet: Are Routine Glycaemia Measurements Reliable Enough?

Background: Glucose is the main inter-organ energy supplying metabolite in humans and other vertebrates. In clinical analyses, its measurement is probably the most performed and used for diagnostic, monitoring and control of the physiological status. However, glucose chemical structure, specially its anomeric forms (alpha/beta), may deeply interfere in their own analyses, often resulting in misleading results. Methods: These effects on glucose estimation were studied by using a common glucose oxidase/peroxidase based method, in the presence or absence of added mutarotase, which speeds up the alpha/beta conversion rate. Glucose concentrations were measured in pure standards and plasma samples from control and cafeteria diet-fed rats. Results: The addition of mutarotase resulted in higher glucose readings, independently of glucose concentration and its initial anomeric proportions in the sample. In the absence of mutarotase, cafeteria-fed rats had higher glucose levels than controls, but the differences disappeared in its presence, because under experimental conditions, a proportion of the alpha-anomer was not isomerized and thus was not measured. Conclusions: Diet altered the proportion of anomers, suggesting that glucose usage by physiological processes affects the anomers’ ratio and may have an important metabolic meaning, which deserves a detailed study in addition to the need to correct the methods in use to obtain real “total glucose” readings. J Endocrinol Metab. 2019;9(3):63-70 doi: https://doi.org/10.14740/jem555

Commentary: Cafeteria diet impairs expression of sensory-specific satiety and stimulus-outcome learning.

Commentary: Cafeteria diet impairs expression of sensory-specific satiety and stimulus-outcome learning.

Effects of long-term cycling between palatable cafeteria diet and regular chow on intake, eating patterns, and response to saccharin and sucrose

When exposed to a diet containing foods that are rich in fat and sugar, rats eat to excess and gain weight. We examined the effects of alternating this diet with laboratory chow on intake of each type of diet, the eating elicited by a palatable food (biscuits), and the drinking elicited by sweet solutions that did (sucrose) or did not (saccharin) contain calories. Each week for 13weeks, cycled rats were provided with the cafeteria diet for three successive days/nights and the chow diet for the remaining four days/nights, whereas other rats received continuous access to either the cafeteria or the chow diets. On each of the 13weeks, cycled rats ate more across the first 24hour exposure to the cafeteria diet than rats continuously fed this diet. In contrast, cycled rats ate less across the first 24hour exposure to the chow diet than rats continuously fed this diet and ate less when presented a novel palatable biscuit than chow-fed rats. The three groups exhibited similar licks per cluster to saccharin, but cafeteria-fed and cycled rats showed fewer clusters than chow-fed rats. In contrast, chow-fed rats and cycled rats exhibited more licks per cluster to sucrose than cafeteria-fed rats, but all three groups had a similar number of clusters. The results were discussed in relation to the effects of diet cycling on eating patterns, body weight, and ‘wanting’ and ‘liking’. These findings with rats may have important implications for yo-yo dieting in people.

Extended exposure to a palatable cafeteria diet alters gene expression in brain regions implicated in reward, and withdrawal from this diet alters gene expression in brain regions associated with stress

Like people, rodents exposed to energy-rich foods over-eat and become overweight. Removal of this diet activates stress systems, which may explain why people have difficulty dieting. We exposed rats to energy-rich foods in order to identify changes in the brain induced by that diet and by its removal. Sprague Dawley rats were fed lab-chow or an energy-rich cafeteria diet (plus chow). Following 6 or 15 weeks, half of each group was switched to the opposing diet. Rats were culled 48-h later. We measured fat mass, plasma hormones, and assessed brains for mRNA expression of several genes. Cafeteria-fed rats consumed more kilojoules, weighed more and had elevated leptin (plus reduced CORT at 15 weeks) relative to chow-fed rats. Fifteen weeks of cafeteria diet suppressed μ-opioid and CB1 receptor mRNA in the VTA, but elevated amygdala GR, and 6 weeks of cafeteria diet reduced BDNF, compared to chow-fed rats. Rats switched to the cafeteria diet ate similar amounts as rats maintained on the diet, and switching to cafeteria diet after 15 weeks reduced amygdala GR expression. Rats switched to chow ate less than rats maintained on chow, and switching to chow following 15 weeks of cafeteria diet increased hypothalamic CRH mRNA. Therefore, 15 weeks of cafeteria diet produced changes in brain regions implicated in reward processes. Switching these rats to chow activated the HPA axis, while switching chow-fed rats to the cafeteria diet decreased GR expression in the amygdala, a region associated with stress. These findings have implications for dieting in humans.

Grape-Seed Procyanidins Prevent the Cafeteria-Diet-Induced Decrease of Glucagon-Like Peptide-1 Production

Grape-seed procyanidin extract (GSPE) has been reported to improve insulin resistance in cafeteria rats. Because glucagon-like peptide-1 (GLP-1) is involved in glucose homeostasis, the preventive effects of GSPE on GLP-1 production, secretion, and elimination were evaluated in a model of diet-induced insulin resistance. Rats were fed a cafeteria diet for 12 weeks, and 25 mg of GSPE/kg of body weight was administered concomitantly. Vehicle-treated cafeteria-fed rats and chow-fed rats were used as controls. The cafeteria diet decreased active GLP-1 plasma levels, which is attributed to a decreased intestinal GLP-1 production, linked to reduced colonic enteroendocrine cell populations. Such effects were prevented by GSPE. In the same context, GSPE avoided the decrease on intestinal dipeptidyl-peptidase 4 (DPP4) activity and modulated the gene expression of GLP-1 and its receptor in the hypothalamus. In conclusion, the preventive treatment with GSPE abrogates the effects of the cafeteria diet on intestinal GLP-1 production and DPP4 activity.

Prevention of metabolic disorders and reproductive performance deficits by the blockade of Angiotensin II AT1 receptor in female rats fed with cafeteria diet

Besides the well-known detrimental effects of obesity on cardiovascular and metabolic function, studies have shown that obesity is also associated with impaired reproductive function in women. Alterations in Angiotensin II (Ang II) have been associated with obesity and with female reproduction. The aim of the present study was to evaluate the reproductive and metabolic effects of Ang II AT1 receptor blockade with losartan in an animal model of obesity, in which female rats were offered a palatable, high calorie diet from weaning to adulthood. Sexual behavior, ovulation rates and preovulatory levels of the hormones estradiol, progesterone, LH and prolactin were analyzed. Retroperitoneal and perigonadal fat pads, triglycerides and cholesterol (total, HDL and LDL), and insulin resistance were analyzed. Losartan prevented increases in fat pad storage, insulin resistance, as well as triglycerides and LDL levels induced by cafeteria diet intake. Losartan also prevented ovulatory deficits and loss of preovulatory surges of progesterone and LH in cafeteria-fed female rats probably through the prevention of the increase in body weight and body fat. No alterations in sexual behavior were observed. These results suggest, for the first time, that Ang II contributes to the development of the deleterious effects of obesity on preovulatory surges of LH and progesterone and on the reduction of ovulation in obese female rats.

Altered feeding patterns in rats exposed to a palatable cafeteria diet: increased snacking and its implications for development of obesity.

BackgroundRats prefer energy-rich foods over chow and eat them to excess. The pattern of eating elicited by this diet is unknown. We used the behavioral satiety sequence to classify an eating bout as a meal or snack and compared the eating patterns of rats fed an energy rich cafeteria diet or chow.MethodsEight week old male Sprague Dawley rats were exposed to lab chow or an energy-rich cafeteria diet (plus chow) for 16 weeks. After 5, 10 and 15 weeks, home-cage overnight feeding behavior was recorded. Eating followed by grooming then resting or sleeping was classified as a meal; whereas eating not followed by the full sequence was classified as a snack. Numbers of meals and snacks, their duration, and waiting times between feeding bouts were compared between the two conditions.ResultsCafeteria-fed rats ate more protein, fat and carbohydrate, consistently ingesting double the energy of chow-fed rats, and were significantly heavier by week 4. Cafeteria-fed rats tended to take multiple snacks between meals and ate fewer meals than chow-fed rats. They also ate more snacks at 5 weeks, were less effective at compensating for snacking by reducing meals, and the number of snacks in the majority of the cafeteria-fed rats was positively related to terminal body weights.ConclusionsExposure to a palatable diet had long-term effects on feeding patterns. Rats became overweight because they initially ate more frequently and ultimately ate more of foods with higher energy density. The early increased snacking in young cafeteria-fed rats may represent the establishment of eating habits that promote weight gain.

Peripheral blood mononuclear cells: a potential source of homeostatic imbalance markers associated with obesity development

Peripheral blood mononuclear cells (PBMC) have a great potential for nutrition and obesity studies. PBMC reflect the nutritional response of key organs involved in energy homeostasis maintenance, which is altered in the obese state. Here, we aimed to determine the usefulness of PBMC as a source of early markers of obesity. To that purpose, we analysed whether PBMC could reflect the insensitivity to changes in feeding conditions associated with obesity during the development of this pathology. Expression of key genes central to energy metabolism was measured by Q-PCR in PBMC samples of normoweight (control) and cafeteria-fed (obese) rats in feeding, fasting and refeeding conditions. Samples were obtained monthly from 2 (beginning of cafeteria diet-feeding) to 6 months of age. In general terms, expression of genes related to fatty acid synthesis (Fasn, Srebp1) and adipogenesis (Pparg) decreased with fasting and increased with refeeding. Conversely, the expression of a key gene regulating beta-oxidation (Cpt1a) and the gene for an orexigenic neuropeptide (Npy)-in accordance with their metabolic role-increased with fasting and decreased with refeeding. This expression pattern disappeared in obese rats, in which insensitivity to feeding conditions was observed after only 1 month of cafeteria diet-feeding. Thus, during development, PBMC accurately reflect nutritional regulation of energy homeostasic genes and the insensitivity to feeding associated with obesity, even in the earlier stages with a low degree of overweight. For this reason, this set of blood cells could constitute a potential source of biomarkers of early homeostatic imbalance which would be useful in nutrition studies that could help prevent the occurrence of obesity.

Catabolism of amino acids in livers from cafeteria-fed rats

Most studies using a hypercaloric diet to induce obesity have focused on the metabolism of fat and carbohydrates. Less concern has been given to the metabolism of amino acids, despite evidence of modifications in nitrogen metabolism during obesity. The aim of this study was to evaluate amino acid metabolism in livers from cafeteria diet-induced obese rats. Blood parameters were analysed, and histological sections of livers were stained with Sudan III. The enzymatic activities of some enzymes were determined in liver homogenates. Gluconeogenesis, ureagenesis, and oxygen consumption were evaluated in rat livers perfused with glutamine, alanine, or ammonium chloride. Compared to control rats, cafeteria-fed rats demonstrated higher levels of triacylglycerol and glucose in the blood and greater accumulation of fat in livers. Gluconeogenesis and urea production in livers perfused with glutamine and alanine at higher concentrations showed a substantial reduction in cafeteria-fed rats. However, no significant difference was observed among groups perfused with ammonium chloride. The activities of the enzymes alanine aminotransferase, glutaminase, and aspartate aminotransferase in the livers were reduced in cafeteria-fed rats. Taken together, these data are consistent with the hypothesis that livers from cafeteria diet-induced obese rats exhibit a limitation in their maximal capacity to metabolise glutamine and alanine to glucose, ammonia, and urea, not because of an impairment in gluconeogenesis and/or ureagenesis, but rather due to a depression in the activities of enzymes that catalyse the initial steps of amino acid metabolism.

Grape seed procyanidins improve β-cell functionality under lipotoxic conditions due to their lipid-lowering effect

Procyanidins have positive effects on glucose metabolism in conditions involving slightly disrupted glucose homeostasis, but it is not clear how procyanidins interact with β-cells. In this work, we evaluate the effects of procyanidins on β-cell functionality under an insulin-resistance condition. After 13 weeks of cafeteria diet, female Wistar rats were treated with 25 mg of grape seed procyanidin extract (GSPE)/kg of body weight (BW) for 30 days. To determine the possible mechanisms of action of procyanidins, INS-1E cells were separately incubated in high-glucose, high-insulin and high-oleate media to reproduce the conditions the β-cells were subjected to during the cafeteria diet feeding. In vivo experiments showed that chronic GSPE treatment decreased insulin production, since C-peptide levels and insulin protein levels in plasma were lower than those of cafeteria-fed rats, as were insulin and Pdx1 mRNA levels in the pancreas. GSPE effects observed in vivo were reproduced in INS-1E cells cultured with high oleate for 3 days. GSPE treatment significantly reduces triglyceride content in β-cells treated with high oleate and in the pancreas of cafeteria-fed rats. Moreover, gene expression analysis of the pancreas of cafeteria-fed rats revealed that procyanidins up-regulated the expression of Cpt1a and down-regulated the expression of lipid synthesis-related genes such as Fasn and Srebf1. Procyanidin treatment counteracted the decrease of AMPK protein levels after cafeteria treatment. Procyanidins cause a lack of triglyceride accumulation in β-cells. This counteracts its negative effects on insulin production, allowing for healthy levels of insulin production under hyperlipidemic conditions.

A cafeteria‐style diet induces obesity and increases lumbar sympathetic nerve activity in rats

Obesity is a primary cause of essential hypertension. Despite the importance of this link, little is known about how weight gain causes increases in arterial blood pressure (BP). A leading hypothesis suggests that obesity may activate long‐term elevations in sympathetic nerve activity (SNA) that increase peripheral resistance. We therefore predicted that a cafeteria‐style diet would chronically increase body weight and lumbar SNA in rats. To test this, we implanted Telemetry Research (Auckland, New Zealand) radio‐telemetry devices into female Wistar rats. Starting at 5 days following surgery, rats were divided into a Control group (n = 4) that received rat chow and water for 16 days and a Cafeteria group (n = 3) that received crackers, vanilla wafers, buttered popcorn, cheetos, chocolate, salami, smoked fish, condensed milk, and soda pop also for 16 days. At study completion, body weight gains were lower in Controls (from 257±21g to 284±16 g) than in Cafeteria (from 254±21 g to 306±28 g) rats. Whereas lumbar SNA remained at baseline levels in Control rats after 16 days, it increased by 20% in Cafeteria‐fed rats. A testing of lumbar SNA quality revealed that the nerves responded appropriately to sodium nitroprusside (from 100% baseline to 128±14%) and to hexamethonium bromide (100% to 16±6%). These data show, for the first time, that the high‐fat cafeteria‐style diet stimulates chronic increases in lumbar SNA in rats.

Slc27a2 expression in peripheral blood mononuclear cells as a molecular marker for overweight development

Peripheral blood mononuclear cells (PBMC) can be collected easily and repeatedly. Their potential use to reflect the individual's biological status is increasingly explored. Obesity is becoming the most common health problem of the 21st century, being dietary intake an important determinant of this pathology and numerous chronic health conditions. The aim of this study is to identify PBMC genes involved in energy homeostasis, which could be good markers of overweight development. Using whole-genome microarray analysis, we evaluated the gene expression in PBMC of normoweight and diet-induced obese (cafeteria-fed) Wistar rats. Microarray analysis showed 566 genes differentially expressed between normoweight and cafeteria-fed rats. Of these, 35 genes were particularly involved in energy homeostasis. The gene with the biggest fold change was the 'solute carrier family 27 (fatty acid transporter), member 2' (slc27a2), which is implicated in lipid biosynthesis and fatty acid degradation. Scl27a2 was 33-fold overexpressed in cafeteria-fed rats compared with normoweight rats. This result was confirmed by quantitative PCR, although the overexpression was smaller (sixfold). Moreover, the increase in slc27a2 expression in PBMC of cafeteria-fed rats from 2 to 6 months of age paralleled the increase in body weight. The progressive overexpression of slc27a2 in PBMC of cafeteria-fed rats as the body weight increases suggests this gene as an early marker of overweight development related to the intake of a hyperlipidic diet.

Effects of eicosapentaenoic acid ethyl ester on visfatin and apelin in lean and overweight (cafeteria diet-fed) rats

Previous studies have demonstrated that the n-3 fatty acid EPA improves insulin resistance induced by high-fat diets. The aim of the present study was to investigate the potential role of visfatin and apelin in the insulin-sensitising effects of EPA ethyl ester. The effects of EPA on muscle and adipose GLUT mRNA, as well as on liver glucokinase (GK) and glucose-6-phosphatase (G6Pase) activity, were investigated. Male Wistar rats fed on a standard diet or a high-fat cafeteria diet were daily treated by oral administration with EPA ethyl ester (1 g/kg) for 5 weeks. A significant decrease (P < 0.01) in white adipose tissue (WAT) visfatin mRNA levels was found in the cafeteria-fed rats, which was reversed by EPA administration (P < 0.05). Moreover, a negative relationship was observed between homeostatic model assessment (HOMA) and the visfatin:total WAT ratio. In contrast, cafeteria-diet feeding caused a significant increase (P < 0.01) in apelin mRNA in visceral WAT. EPA increased (P < 0.01) apelin gene expression, and a negative relationship between HOMA index with visceral apelin mRNA and serum apelin:total WAT ratio was also observed. EPA treatment did not induce changes in skeletal muscle GLUT1, GLUT4 or insulin receptor mRNA levels. Neither liver GK and G6Pase activity nor the GK:G6Pase ratio was modified by EPA. These data suggest that somehow the insulin-sensitising effects of EPA could be related to its stimulatory action on both visfatin and apelin gene expression in visceral fat, while changes in skeletal muscle GLUT, as well as in hepatic glucose production, are not likely to be the main contributing factors in the improvement in insulin resistance induced by EPA.

Effects of diet energy level and tomato powder consumption on antioxidant status in rats

Evaluate the influence of tomato powder in diets differing in energy level on antioxidant status in blood and liver of rats. Twenty-four adult male Wistar rats weighing 150-180 g were placed four groups (n=6). For 28 days, animals were fed a diet that was either hyper energetic or hypo energetic. Some diets were supplemented with tomato powder. Liver and blood were collected for analysis of antioxidant enzymes, non-enzymatic antioxidants, thiobarbituric acid reactive species, ubiquinol 9, alpha-tocopherol, lycopene and beta-carotene. Data were analysed by two-way ANOVA. Food intake and thiobarbituric acid-reactive substances contents in liver and plasma were significantly decreased by tomato powder at both energy levels. After tomato powder supplementation, the hepatic levels of ubiquinol 9, alpha-tocopherol, lycopene and beta-carotene were significantly enhanced. In plasma, only the contents of lycopene and beta-carotene were enhanced. The erythrocytic and hepatic activities of catalase were lower, while those of glutathione peroxidase were higher after the ingestion of tomato powder. Total and reduced glutathione contents in liver showed lower levels in cafeteria-fed rats compared to the hypo energetic diet. The data suggest that the lycopene and beta-carotene component in the tomato power supplement might be beneficial for the prevention of oxidative damage in rats fed both types of energetic diets.

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.

Hypercaloric cafeteria-like diet induced UCP3 gene expression in skeletal muscle is impaired by hypothyroidism.

The uncoupling protein UCP3 belongs to a family of mitochondrial carriers located in the inner mitochondrial membrane of certain cell types. It is expressed almost exclusively at high levels in skeletal muscle and its physiological role has not been fully determined in this tissue. In the present study we have addressed the possible interaction between a hypercaloric diet and thyroid hormone (T3), which are strong stimulators of UCP3 gene expression in skeletal muscle. Male Wistar rats weighing 180 +/- 20 g were rendered hypothyroid by thyroidectomy and the addition of methimazole (0.05%; w/v) to drinking water after surgery. The rats were fed a hypercaloric cafeteria diet (68% carbohydrates, 13% protein and 18% lipids) for 10 days and sacrificed by decapitation. Subsequently, the gastrocnemius muscle was dissected, total RNA was isolated with Trizol and UCP3 gene expression was determined by Northern blotting using a specific probe. Statistical analysis was performed by one-way analysis of variance (ANOVA) followed by the Student-Newman-Keuls post-test. Skeletal muscle UCP3 gene expression was decreased by 60% in hypothyroid rats and UCP3 mRNA expression was increased 70% in euthyroid cafeteria-fed rats compared to euthyroid chow-fed animals, confirming previous studies. Interestingly, the cafeteria diet was unable to stimulate UCP3 gene expression in hypothyroid animals (40% lower as compared to euthyroid cafeteria-fed animals). The results show that a hypercaloric diet is a strong stimulator of UCP3 gene expression in skeletal muscle and requires T3 for an adequate action.