Effect of obesity and troglitazone on expression of two glutathione peroxidases: Cellular and extracellular types in serum,kidney and adipose tissue

To determine the effect of obesity on expression of cellular- (C-) and extracellular (EC-) glutathione peroxidase (GPX) in serum, kidney and adipose tissue, we measured GPX in serum, kidneys and adipose tissue of the obese Otsuka-Long-Evans-Tokushima Fatty (OLETF) rat and its lean counterpart (LETO). We also investigated the effect of troglitazone. Five each of OLETF and LETO rats were fed diet with or without 0.2% troglitazone for 10 days. Final body weight, kidney weight, blood glucose and serum tumor necrosis factor-α (TNF-α) level were higher in OLETF rats than in LETO rats. Serum and kidney GPX activities were higher, but adipose tissue GPX activity was lower, in OLETF rats than in LETO rats. Troglitazone treatment decreased adipose tissue GPX activity and abolished overproduction of TNF-α in OLETF rats. Immunoblot analysis, for the first time, revealed that both obesity and troglitazone suppressed the protein signals for C-GPX and EC-GPX in adipose tissue. Serum protein carbonyl groups were increased in OLETF rats and troglitazone completely blocked this increase. Increased serum GPX activity in obese rat was due to the increased secretion of EC-GPX from the kidney. Troglitazone protected against the enhanced oxidative stress induced by obesity independently of the serum GPX concentration.     

Differential expression of lipoprotein lipase gene in tissues of the rat model with visceral obesity and postprandial hyperlipidemia

Postprandial hyperlipidemia is frequently accompanied with intra-abdominal visceral accumulation in human subjects. We have found that the decreased lipoprotein lipase (LPL) mass and activity is negatively associated with the amount of visceral fat accumulation. Here, we studied the postprandial hyperlipidemia using the OLETF rat, a model with visceral obesity, in order to clarify the molecular mechanism causing postprandial hyperlipidemia accompanied with visceral obesity. At the same age of 32 weeks, the OLETF rats showed obviously higher plasma leptin, total cholesterol, triglyceride, and HDL-cholesterol levels than the control LETO rats, although the plasma glucose level was not significantly different. Fat-loading test revealed the delayed metabolism of exogenous fat in the OLETF rats compared to the LETO rats, similar to human subjects with visceral obesity. In the obese rats, plasma levels of LPL mass and activities were 60 and 49% of control rats. The expression of LPL gene was decreased in subcutaneous adipose tissues and skeletal muscle of OLETF rats to 40 and 52% compared to those of LETO rats. In OLETF rats, plasma tumor necrosis factor-alpha (TNF-alpha) and insulin levels were increased to 2.0- and 2.3-folds compared to those in control rats. Furthermore, plasma insulin and TNF-alpha levels in OLETF rats were negatively correlated with the expression levels of LPL gene in subcutaneous fat and muscle. These results indicate that decreased LPL mass and activity in the animal model with visceral obesity is possibly caused by decreased expression of LPL gene in tissues mediated by the increased levels of insulin and TNF-alpha. The different expression of LPL gene in tissues associated with the increased levels of insulin and TNF-alpha possibly elucidate the underlying mechanisms involving the postprandial hyperlipidemia observed in visceral obesity.     

Identification of genes specifically expressed in the accumulated visceral adipose tissue of OLETF rats

The Otsuka Long-Evans Tokushima fatty (OLETF) rat is an animal model of type 2 diabetes, characterized by abdominal obesity, insulin resistance, hypertension, and dyslipidemia. To elucidate the underlying molecular mechanism of obesity and its related complications, we used representational difference analysis and identified the genes more abundantly and specifically expressed in the visceral adipose tissue (VAT) of obese OLETF rats compared with the diabetes-resistant counterpart, that is, Long-Evans Tokushima Otsuka (LETO) rats. By Northern blot analysis, we confirmed the differential expression of 13 genes, including 3 novel genes. The upregulated expression of well-characterized lipid metabolic enzymes, such as lipoprotein lipase, phosphoenolpyruvate carboxykinase, and cholesterol esterase, were observed in VAT of OLETF rats. We demonstrated the differential expression of secreted proteins in VAT of OLETF rats, such as thrombospondin 1 and contrapsin-like protease inhibitor. In contrast to lipid enzymes, the secreted proteins revealed exclusive mRNA expression and they were not detected in VAT of LETO rats. Furthermore, the novel genes OL-16 and OL-64 were also expressed specifically in VAT of OLETF rats and were absent in that of LETO rats and other tissues, including subdermal and brown adipose tissues. The C-terminal partial amino acid sequence of OL-64 revealed that it showed approximately 40% homology with alpha(1)-antitrypsin and it seemed to be a new member of the serine proteinase inhibitor (SERPIN) gene family. VAT of OLEFT rats had a unique gene expression profile, and the accumulated VAT-specific known and novel secreted proteins may play a role(s) in the pathogenesis of obesity and its related complications.     

Dietary troglitazone decreases oxidative stress in early stage type II diabetic rats

Oxidative stress is involved in the initiation and development of atherosclerosis in diabetes. We tested the hypothesis that oxidative stress is already increased in early stage type II diabetes, and that troglitazone may prevent the increase. Three groups of 20 week old rats were studied: untreated Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as an animal model of type II diabetes, OLETF rats treated with troglitazone, and control Long-Evans Tokushima Otsuka (LETO) rats. Plasma lipid hydroperoxides (LOOH) concentration, as an indication of lipid peroxidation, and superoxide dismutase (SOD) activity in the thoracic aorta were measured. Plasma LOOH concentration was significantly higher in non-treated OLETF rats compared to LETO rats and treatment with troglitazone completely prevented this increase. SOD activity was significantly decreased in non-treated OLETF rats compared to LETO rats and troglitazone attenuated the diminution of it. These observations demonstrate oxidative stress is already increased in the early stage of type II diabetes and we confirmed troglitazone has the effect of an antioxidant in vivo.     

Calorie restriction improves whole-body glucose disposal and insulin resistance in association with the increased adipocyte-specific GLUT4 expression in Otsuka Long-Evans Tokushima fatty rats

Calorie restriction (CR) has been shown to improve peripheral insulin resistance and type 2 diabetes in animal models. However, the exact mechanism of CR on GLUT4 expression and translocation in insulin-sensitive tissues has not been well elucidated. In the present study, we examine the effect of CR on the expression of glucose transporter 4 (GLUT4), GLUT4 translocation, and glucose transport activity in adipose tissue from Otsuka Long-Evans Tokushima Fatty (OLETF) rat and control (LETO) rats. CR (70% of satiated group) ameliorated hyperglycemia and improved impaired glucose tolerance (IGT) in OLETF rats. In skeletal muscle, the expression levels of GLUT4 and GLUT1 were not significantly different between LETO and OLETF rats, and were not affected by CR. By contrast, the expression level of GLUT4 was markedly decreased in the adipose tissue of OLETF rats, but was dramatically increased by CR. The GLUT4 recruitment stimulated by insulin was also improved in OLETF rat adipocytes by CR. The insulin-stimulated 2-deoxyglucose (2DG) uptake was significantly increased in adipocytes from the CR OLETF rats, as compared with the satiated OLETF rats. Taken together, these results suggest that CR improves whole body glucose disposal and insulin resistance in OLETF rats, and that these effects may associate with the increased adipocyte-specific GLUT4 expression.     

Consumption of pork-liver protein hydrolysate reduces body fat in Otsuka Long-Evans Tokushima Fatty rats by suppressing hepatic lipogenesis

This study was performed to examine the effect of consumption of pork-liver protein hydrolysate (PLH) on body fat accumulation in Otsuka Long-Evans Tokushima Fatty (OLETF) rats as a non-insulin-dependent diabetes mellitus model and in Long-Evans Tokushima Otsuka (LETO) rats as a control. Male 20-week-old OLETF and LETO rats were pair-fed either PLH or casein containing diet for 14 weeks. In the OLETF rats, dietary PLH significantly reduced the growth and weight of fat pad including perirenal and epididymal adipose tissues. Consumption of PLH markedly suppressed hepatic activities of lipogenesis enzymes such as glucose-6-phosphate dehydrogenase and fatty acid synthase and slightly elevated fecal excretion of total fat. In the LETO rats, growth and adipose tissue weight were unaffected by dietary treatment. The results suggest that PLH is a novel ingredient suppressing body fat in genetically obese rats by reducing lipogenesis.     

Anti-Obesity Effects of Granulocyte-Colony Stimulating Factor in Otsuka-Long-Evans-Tokushima Fatty Rats

Granulocyte-colony stimulating factor (G-CSF) has molecular structures and intracellular signaling pathways that are similar to those of leptin and ciliary neurotropic factor (CNTF). It also has immune-modulatory properties. Given that leptin and CNTF play important roles in energy homeostasis and that obesity is an inflammatory condition in adipose tissue, we hypothesized that G-CSF could also play a role in energy homeostasis. We treated 12 38-week-old male Otsuka-Long-Evans-Tokushima fatty rats (OLETF, diabetic) and 12 age-matched male Long-Evans-Tokushima rats (LETO, healthy) with 200 µg/day G-CSF or saline for 5 consecutive days. Body weight reduction was greater in G-CSF-treated OLETF (G-CSF/OLETF) than saline-treated OLETF (saline/OLETF) following 8 weeks of treatment (−6.9±1.6% vs. −3.1±2.2%, p<0.05). G-CSF treatment had no effect on body weight in LETO or on food intake in either OLETF or LETO. Body fat in G-CSF/OLETF was more reduced than in saline/OLETF (−32.2±3.1% vs. −20.8±6.2%, p<0.05). Energy expenditure was higher in G-CSF/OLETF from 4 weeks after the treatments than in saline/OLETF. Serum levels of cholesterol, triglyceride, interleukin-6 and tumor necrosis factor-α were lower in G-CSF/OLETF than in saline/OLETF. Uncoupling protein-1 (UCP-1) expression in brown adipose tissue (BAT) was higher in G-CSF/OLETF than in saline/OLETF, but was unaffected in LETO. Immunofluorescence staining and PCR results revealed that G-CSF receptors were expressed in BAT. In vitro experiments using brown adipocyte primary culture revealed that G-CSF enhanced UCP-1 expression from mature brown adipocytes via p38 mitogen-activated protein kinase pathway. In conclusion, G-CSF treatment reduced body weight and increased energy expenditure in a diabetic model, and enhanced UCP-1 expression and decreased inflammatory cytokine levels may be associated with the effects of G-CSF treatment.     

Altered basal and stimulated accumbens dopamine release in obese OLETF rats as a function of age and diabetic status

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat lacking the CCK-1 receptor is hyperphagic, prefers palatable and high-calorie meals, and gradually develops obesity and type 2 diabetes. To determine dopamine levels in this strain, we used in vivo quantitative (no net flux) microdialysis at three different ages representing nondiabetic (8 wk), prediabetic (18 wk), and diabetic (56 wk) stages in OLETF and age-matched lean Long-Evans Tokushima Otsuka (LETO) controls. Results showed significantly elevated basal dopamine levels in the caudomedial nucleus accumbens of OLETF rats compared with LETO at younger ages (8 wk: 20.10 +/- 5.61 nM vs. 15.85 +/- 5.63 nM; 18 wk: 7.37 +/- 3.71 nM vs. 4.75 +/- 1.25 nM, means +/- SD). In contrast, at 56 wk of age, a profound decline in extracellular dopamine concentrations was seen in both strains with a tendency for a greater effect in OLETF rats (1.78 +/- 0.40 nM vs. 2.39 +/- 0.42 nM). Further, extracellular fraction, an index for reuptake, was higher in 56-wk-old OLETF compared with LETO (0.648 +/- 0.049 vs. 0.526 +/- 0.057). Potassium-stimulated dopamine efflux revealed an increased capacity of vesicular pool in OLETF rats compared with LETO across all age groups with an accentuated strain difference at 56 wk. These findings demonstrate altered striatal dopamine functions (i.e., increased stimulated release and uptake) in obese OLETF rat. This could be due to the lack of functional CCK-1 receptors, or metabolic and hormonal factors associated with the development of obesity and insulin resistance, or both.     

Troglitazone stimulates pancreatic growth in congenitally CCK-A receptor-deficient OLETF rats

We examined the effect of troglitazone treatment on pancreatic growth in the CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rat, an animal model for type 2 diabetes mellitus. A troglitazone-rich diet (0.2%) was given from 12 to 28 wk of age or from 12 or 28 wk of age to 72 wk of age. Fasting serum glucose concentrations in control OLETF rats increased progressively with age, which was almost completely prevented by troglitazone treatment. Insulin levels in serum and pancreatic content in the control rat markedly increased at 28 wk of age but significantly decreased at 72 wk of age compared with those at 12 wk of age, whereas those in troglitazone-treated rats were nearly the same at all ages and were similar to those in control rats at 12 wk of age. Pancreatic wet weight in control rats decreased with age irrespective of whether they were hyperinsulinemic (28 wk old) or hypoinsulinemic (72 wk old). Troglitazone treatment significantly increased pancreatic wet weight and protein, DNA, and enzyme contents compared with those in the control rats. Moreover, troglitazone treatment completely prevented or reversed histological alterations such as fibrosis, fatty replacement, and inflammatory cell infiltration. Our results indicate that troglitazone stimulates pancreatic growth in the congenitally CCK-A receptor-deficient OLETF rat not only by reducing insulin resistance and potentiating insulin action but also by suppressing inflammatory changes in the pancreas.     

A role for NPY overexpression in the dorsomedial hypothalamus in hyperphagia and obesity of OLETF rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors are hyperphagic, obese, and diabetic. We have previously demonstrated that these rats have a peripheral satiety deficit resulting in increased meal size. To examine the potential role of hypothalamic pathways in the hyperphagia and obesity of OLETF rats, we compared patterns of hypothalamic neuropeptide Y (NPY), proopiomelanocortin (POMC), and leptin receptor mRNA expression in ad libitum-fed Long-Evans Tokushima (LETO) and OLETF rats and food-restricted OLETF rats that were pair-fed to the intake of LETO controls. Pair feeding OLETF rats prevented their increased body weight and elevated levels of plasma insulin and leptin and normalized their elevated POMC and decreased NPY mRNA expression in the arcuate nucleus. In contrast, NPY expression was upregulated in the dorsomedial hypothalamus (DMH) in pair-fed OLETF rats. A similar DMH NPY overexpression was evident in 5-wk-old preobese OLETF rats. These findings suggest a role for DMH NPY upregulation in the etiology of OLETF hyperphagia and obesity.     

Troglitazone inhibits the expression of inducible nitric oxide synthase in adipocytes in vitro and in vivo study in 3T3-L1 cells and Otsuka Long-Evans Tokushima Fatty rats

The aim of this study was to determine the mechanism of troglitazone action on nitric oxide (NO) production via inducible NO synthase (iNOS) in adipocytes in vitro and in vivo. The treatment of 3T3-L1 adipocytes with the combination of lipopolysaccharide (LPS), tumor necrosis factor-alpha and interferon-gamma synergistically induced de novo iNOS expression leading to enhanced NO production. The NO production was inhibited by co-treatment with aminoguanidine or N-nitro-L-arginine methylester hydrochloride. Troglitazone inhibited the NO production in a dose dependent manner by the suppression of iNOS expression. In the 24 week-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats, the mean weight and the blood glucose were 21% and 30%, respectively, higher than in their lean counterparts. The serum nitrite concentration was increased after injection of LPS (4 mg/kg, i.p.), more markedly in OLETF rats than in the lean rats. The epididymal fats from LPS-injected groups, but not the ones from the non-injected groups, expressed mRNA and protein of iNOS. Troglitazone pre-treatment blocked the LPS-induced expression of iNOS in adipose tissue and the increase in serum nitrite concentration. These results suggest that troglitazone inhibits the cytokine-induced NO production in adipocytes by blocking iNOS expression both in vitro and in vivo.     

Conditioned preference for sweet stimuli in OLETF rat: effects of food deprivation

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an outbred strain of Long- Evans Tokushima Otsuka rat (LETO) that lacks CCK-1 receptor expression, is hyperphagic and develops obesity and type-2 diabetes. The present study sought to assess how OLETF rats alter intake, preference, and conditioned preference of palatable solutions after acute food deprivation. Our results show that after 24 h chow restriction, LETO rats increase both sucrose intake and two-bottle sucrose preference relative to their free-fed baseline, whereas OLETF rats do not increase sucrose intake (0.3 M or 1.0 M sucrose) or preference (1.0 M vs. 0.3 M sucrose) when they are food deprived. In contrast, OLETF rats exhibit a higher conditioned flavor preference when sucrose is used as unconditioned stimulus (US) relative to LETO rats, whether overnight food restricted (81% vs. 71% for OLETF and LETO rats, respectively) or free fed (82% vs. 54% for OLETF and LETO rats, respectively) during the test. When a noncaloric saccharin solution is used as US, OLETF rats show a higher preference for the saccharin-associated flavor relative to LETO rats when nondeprived (76% vs. 58% for OLETF and LETO rats, respectively); however, neither strain shows differential conditioned flavor preference for saccharin in the deprivation state during the test. These findings suggest that OLETF rats fail to integrate postabsorptive and orosensory effects of sucrose in a conditioning setting to influence intake. Thus, it appears that OLETF rats form preferences for sucrose based largely on orosensory and hedonic properties of the solution, rather than caloric value.     

UDP-induced relaxation is enhanced in aorta from female obese Otsuka Long–Evans Tokushima Fatty rats

Uridine 5′-diphosphate (UDP) plays an important role in controlling vascular tone; however, UDP-mediated response in metabolic syndromes, including obesity and type 2 diabetes in females, remains unclear. In this study, we investigated UDP-mediated response in the aorta of female obese Otsuka Long–Evans Tokushima Fatty (OLETF) rats and control Long–Evans Tokushima Otsuka (LETO) rats. In OLETF rat aortas precontracted by phenylephrine (PE) (vs. LETO), (1) UDP-induced relaxation was increased, whereas acetylcholine (ACh)-induced relaxation was decreased; (2) no UDP- or ACh-induced relaxations were observed in endothelial denudation, whereas UDP-induced small contraction was observed; and (3) N^G-nitro-L-arginine [L-NNA, a nitric oxide (NO) synthase inhibitor] eliminated UDP-induced relaxation and small contraction, whereas caused contrasting responses by ACh, including slight relaxations (LETO) and contractions (OLETF). Indomethacin, a cyclooxygenase inhibitor, eliminated the difference in UDP- and ACh-induced relaxations between the groups by increased UDP-induced relaxation in the LETO group and increased ACh-induced relaxation in the OLETF group. MRS2578, a P2Y₆ receptor antagonist, eliminated the difference in UDP-induced relaxations between the groups by decreasing UDP-induced relaxation in the OLETF group. MRS2578 had no effect on UDP-induced contraction in endothelium-denuded aortas. Therefore, these findings demonstrate opposite trends of relaxations by UDP and ACh in OLETF and LETO rat aortas. These differences may be attributed to the imbalance between NO and vasoconstrictor prostanoids upon stimulations. Increased UDP-induced relaxation in OLETF rat aorta may be caused by the activation of endothelial MRS2578-sensitive P2Y₆ receptor.     

Downregulation of the skeletal muscle pyruvate dehydrogenase complex in the Otsuka Long-Evans Tokushima Fatty rat both before and after the onset of diabetes mellitus

The pyruvate dehydrogenase complex (PDC) catalyzes the irreversible oxidative decarboxylation of pyruvate in mitochondria. The PDC activity is regulated by a phosphorylation/dephosphorylation cycle catalyzed by specific kinases (PDK) and phosphatases (PDP). In this study, the regulatory mechanisms of PDC were examined in skeletal muscle of the spontaneously diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rat before and after the onset of diabetes. The Long-Evans Tokushima Otsuka (LETO) rat was used as control. Plasma glucose and insulin concentrations were at normal levels in both groups at 8 weeks of age but were significantly higher in OLETF than in LETO rats at 25 weeks of age (1.2-fold for glucose and 15-fold for insulin), indicating development of diabetes in the former. Plasma free fatty acids were 1.6-fold concentrated and the skeletal muscle PDC activity state was significantly lower in OLETF than in LETO rats at both ages, suggesting suppression of pyruvate oxidation in OLETF rats even before the onset of diabetes. The PDK activity and the abundance of the PDK isoform 4 protein as well as mRNA were greater in OLETF rats at both ages. Conversely, the abundance of the PDP isoform 1 protein and mRNA was less in OLETF than in LETO rats at both ages. These results suggest that concomitant greater PDK4 and less PDP1 expression in skeletal muscle of OLETF rats before the onset of diabetes are responsible for the lowering of the PDC activity and may be related with the development of diabetes mellitus.     

ATP synthesis is impaired in isolated mitochondria from myotubes established from type 2 diabetic subjects

Leptin resistance associated with hyperleptinemia in high-fat-diet-induced obese rats and aged obese rats is well established, but it is not clear whether hyperphagia-induced obese rats also develop leptin resistance. We investigated whether Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which are a strain of hyperphagia-induced obese rats, develop leptin resistance and whether caloric restriction reversed this leptin resistance-induced leptin receptor (ObRb) deficit. Twenty male OLETF rats, 20 male Long-Evans Tokushima Otsuka (LETO) rats, and 10 male Sprague Dawley (SD) rats were used. All rats were initially studied at 10 weeks of age and were freely fed with standard rat chow and water until they were 38 weeks of age. Daily food intake, body weight, and plasma leptin levels of OLETF rats were remarkably increased compared to LETO or SD rats from 10 to 38 weeks of age. When they were 38 weeks of age, all OLETF rats were randomly divided into two groups. One group was freely fed with standard rat chow (FD, or free diet group), and the other group (RD, or restricted diet group) was fed with only 70% of the amount consumed by the FD group. The LETO and SD rats were dismissed from further study. After 4 weeks of caloric restriction, the average body weight (636 ± 33 g vs. 752 ± 24 g, P < 0.05) and abdominal adipose tissue weight (10.6 ± 3.2 g vs. 15.8 ± 1.5 g, P < 0.05) of the RD group were decreased compared with those of the FD group. Plasma leptin levels of the RD group were significantly decreased compared with those of the FD group (3.47 ± 1.40 ng/mL vs. 11.55 ± 1.16 ng/mL, P < 0.05). The mRNA expression of ObRb and leptin-related suppressor of cytokine signaling 3 (SOCS3) in the hypothalamus, liver, and skeletal muscles of the RD group were significantly decreased compared with those of the FD group. Caloric restriction did not improve leptin receptor (ObRb) deficit or the downstream signaling of leptin in the liver, skeletal muscles, and hypothalamus. Thus, we demonstrated that OLETF rats, which are a strain of hyperphagia-induced obese rats, did not develop central or peripheral leptin resistance. We suggest that hyperleptinemia in OLETF rats is a compensatory mechanism to overcome obesity induced by hyperphagia.     

Isomer-specific anti-obese and hypolipidemic properties of conjugated linoleic acid in obese OLETF rats

Conjugated linoleic acid (CLA), a mixture of positional and geometric isomers of linoleic acid, has attracted considerable attention because of its potentially beneficial biologic effects both in vitro and in vivo. Our results clearly show the specific action of the 10trans,12cis-CLA isomer against hyperlipidemia and obesity in obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats. After 2 weeks of feeding with 10t,12c-CLA, but not 9cis,11trans-CLA, abdominal adipose tissue weight and serum and hepatic lipid levels in OLETF rats were lower than those in linoleic acid-fed rats. These effects were attributable to suppressed fatty acid synthesis and enhanced fatty acid beta oxidation in the liver on a 10t,12c-CLA diet. Additionally, we showed that mRNA expression of fatty acid synthase, carnitine palmitoyltransferase, leptin, and sterol regulatory element binding protein-1 was also regulated by 10t,12c-CLA. We suppose that 10t,12c-CLA reveals hypolipidemic and anti-obese activity through the alteration of mRNA expressions in the liver and white adipose tissue.     

Independent ingestion and microstructure of feeding patterns in infant rats lacking CCK-1 receptors

Otsuka Long-Evans Tokushima fatty (OLETF) rats are a strain of Long-Evans Tokushima Otsuka (LETO) rats that do not express CCK-1 receptors, developing in adulthood, hyperphagia, obesity, and non-insulin-dependent diabetes mellitus (NIDDM). We examined weight gain and meal patterns during a 30-min independent ingestion test on postnatal days 2-4 and again on days 9-11 in OLETF and LETO rat pups. OLETF pups were significantly heavier compared with their LETO controls at both ages, and they consumed significantly more of the sweet milk diet. The difference in intake can be attributed to a significant increase in meal size and duration. Number of clusters and bursts of licking within a meal were greater in OLETF rat pups, with no difference between strains in burst and cluster size. Interlick interval (ILI) was not significantly different between OLETF and LETO pups. This measure decreased on days 9-11 compared with days 2-4 in both strains. Latency to start feeding was significantly shorter on days 2-4 in OLETF vs. LETO pups, but this difference disappeared at the second test at the older age. Two- to four-day-old OLETF pups consumed a larger volume of milk during the first minute of feeding, and their initial lick rate and decay of lick rate were significantly larger compared with their LETO controls. Lack of CCK-1 receptors, or other OLETF-related abnormalities, therefore, resulted in a satiation deficit, leading to increased meal size, hyperphagia, and increased weight gain as early as 2-4 postnatal days.     

DHEA administration increases brown fat uncoupling protein 1 levels in obese OLETF rats

We found that UCP-1 and UCP-3 mRNA expression levels and the UCP-1 protein content in brown adipose tissue (BAT) were reduced in prediabetic OLETF rats than the lean LETO rats. Administration of dehydroepiandrosterone (DHEA) for 17 days induced remarkable weight loss, which was in part attributed to an enhanced utilization of ingested energy. DHEA administration significantly increased the levels of BAT UCP-1 and UCP-3 mRNA expression. Among the upstream signals for UCP-1 regulation, expression levels of the beta 3 adrenergic receptor (beta(3)AR) and PPAR gamma coactivator-1 (PGC-1) were significantly decreased in the OLETF rats and increased by DHEA administration. The decreased expression levels of UCP-1 and its upstream regulators, beta(3)AR and PGC-1, in BAT may contribute to inefficient energy utilization and obesity in OLETF rats, which was corrected by DHEA treatment.     

Differential body weight and feeding responses to high-fat diets in rats and mice lacking cholecystokinin 1 receptors

Prior data demonstrated differential roles for cholecystokinin (CCK)1 receptors in maintaining energy balance in rats and mice. CCK1 receptor deficiency results in hyperphagia and obesity of Otsuka Long-Evans Tokushima Fatty (OLETF) rats but not in mice. To ascertain the role of CCK1 receptors in high-fat-diet (HFD)-induced obesity, we compared alterations in food intake, body weight, fat mass, plasma glucose, and leptin levels, and patterns of hypothalamic gene expression in OLETF rats and mice lacking CCK1 receptors in response to a 10-wk exposure to HFD. Compared with Long-Evans Tokushima Otsuka (LETO) control rats, OLETF rats on HFD had sustained overconsumption over the 10-wk period. High fat feeding resulted in greater increases in body weight and plasma leptin levels in OLETF than in LETO rats. In situ hybridization determinations revealed that, while HFD reduced neuropeptide Y (NPY) mRNA expression in both the arcuate nucleus (Arc) and the dorsomedial hypothalamus (DMH) of LETO rats, HFD resulted in decreased NPY expression in the Arc but not in the DMH of OLETF rats. In contrast to these results in OLETF rats, HFD increased food intake and induced obesity to an equal degree in both wild-type and CCK1 receptor(-/-) mice. NPY gene expression was decreased in the Arc in response to HFD, but was not detectable in the DMH in both wild-type and CCK1 receptor(-/-) mice. Together, these data provide further evidence for differential roles of CCK1 receptors in the controls of food intake and body weight in rats and mice.