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.     

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.     

Effect of leptin on insulin sensitivity in the Otsuka Long-Evans Tokushima Fatty rat

Leptin has been proposed to be a sensor of energy storage in adipose tissues, and is capable of mediating a feedback signal to the hypothalamus, which is involved in the regulation of energy homeostasis and body weight. In order to investigate the issue of whether resistance to the activity of leptin on insulin sensitivity is observed in young Otsuka Long-Evans Tokushima Fatty (OLETF) rats at 8 weeks of age, leptin (50 nmol/kg/h) was administered intravenously for 16 h to OLETF and Long-Evans Tokushima Otsuka (LETO) (lean controls) rats, followed by a measurement of insulin-stimulated glucose uptake in hindlimb muscles during hyperinsulinemic euglycemic clamp technique. In the case of LETO rats, the administration of leptin significantly decreased plasma insulin levels prior to the clamp test, but did not change plasma glucose levels. Furthermore, leptin led to an increase in insulin-stimulated glucose uptake in hindlimb muscles. However, in the case of OLETF rats, leptin administration changed neither plasma insulin levels nor insulin-stimulated glucose uptake. These data demonstrate that OLETF rats at 8 weeks of age have already become resistant to high concentration of peripheral leptin.     

OLETF (Otsuka Long-Evans Tokushima Fatty) rats that lack the CCK 1 (A) receptor develop less behavioral sensitization to repeated cocaine treatment than wild type LETO (Long Evans Tokushima Otsuka) rats.

OLETF (Otsuka Long-Evans Tokushima Fatty) lacking the CCK 1 (A) receptor have similar spontaneous activity and locomotor response (horizontal and vertical activity) in response to a single injection of cocaine as the wild type LETO (Long Evans Tokushima Otsuka) rats. In contrast, the OLETF rats display more stereotypy in response to the first dose of cocaine than the LETO rats. Tested at 7 and 14 days after a one week daily treatment with cocaine, the LETO rats display robust behavioral sensitization to cocaine while the OLETF rats did not. These results support the hypothesis that endogenous CCK released by cocaine treatment and acting at CCK 1 receptors is required for the development and/or expression of this behavior.     

Cholecystokinin-8 (CCK-8) has no effect on heart rate in rats lacking CCK-A receptors.

Heart rate responses to i.v. administration of cholecystokinin-8 (CCK-8) were investigated in Otsuka Long-Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors and control Long-Evans Tokushima Otsuka (LETO) rats. The heart rate decreased after i.v. administration of 3 nmol.kg(-)(1) of CCK-8 in LETO rats, but not in OLETF rats. Bradycardia in the LETO rats disappeared after treatment with MK-329, but not after treatment with L-365,260. The expression of CCK-A receptor precursor mRNA was found exclusively in the atrium in LETO rats. These results suggest that CCK-8 decreases heart rate via CCK-A receptors located in the atrium of the rats.     

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.     

Effect of AOB, a fermented-grain food supplement, on oxidative stress in type 2 diabetic rats

Reactive oxygen species (ROS) play an important role in the pathogenesis of diabetic complications. Antioxidant Biofactor (AOB) is a mixture of commercially available fermented grain foods and has strong antioxidant activity. This study investigated the effect of AOB supplementation of standard rat food on markers of oxidative stress and inflammation in Otsuka Long-Evans Tokushima Fatty (OLETF) rats with type 2 diabetes. Blood glucose, hemoglobin A1c, plasma free fatty acid, triacylglycerol and plasminogen activator inhibitor-1 (PAI-1) were significantly higher in OLETF rats than in non-diabetic control Long-Evans Tokushima Otsuka (LETO) rats at 29 weeks. AOB (6.5% of diet) was given to rats during 29-33 weeks of diabetic phase in OLETF rats. OLETF rats with AOB supplementation showed decreased blood glucose, hemoglobin A1c, triacyglycerol, low density lipoprotein, cholesterol and PAI-1. Mitochondrial ROS production was significantly increased in heart, aorta, liver and renal artery of OLETF rats. Uncoupling protein 2 (UCP2) is known to regulate ROS production. We found aortic UCP2 protein expression increased in OLETF rats, and AOB returned UCP2 expression to normal. Aortic endothelial NO synthase (eNOS) was also increased in OLETF rats more than in LETO rats at 33 weeks. In contrast, phosphorylated vasodilator-stimulated phosphoprotein, an index of the NO-cGMP pathway, was significantly diminished. AOB increased eNOS proteins in LETO and OLETF rats. In conclusion, AOB significantly improved the NO-cGMP pathway via normalizing ROS generation in OLETF rats. The data suggest that dietary supplementation with AOB contributes to nutritional strategies for the prevention and treatment of type 2 diabetes mellitus.     

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.     

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.     

Supplementation of alpha-tocopherol improves cardiovascular risk factors via the insulin signalling pathway and reduction of mitochondrial reactive oxygen species in type II diabetic rats

This study determined the effects of alpha- and gamma-tocopherol supplementation on metabolic control and oxidative stress in type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Blood glucose, haemoglobin A1c (HbA1c), urinary protein, plasma free fatty acid, triacylglycerol and plasminogen activator inhibitor-1 (PAI-1) levels in OLETF rats were significantly higher than in non-diabetic control Long-Evans Tokushima Otsuka (LETO) rats. Alpha-tocopherol inhibited the increase in urinary protein, blood glucose, HbA1c and PAI-1 levels, but gamma-tocopherol did not. Plasma and hepatic lipid peroxidation and hepatic steatosis were increased in OLETF rats. alpha-Tocopherol decreased lipid peroxidation. Mitochondrial reactive oxygen species production and uncoupling protein 2 (UCP2) expression were significantly increased in the heart and aorta of OLETF rats compared with LETO rats. Endothelial NO synthase and aortic nitrotyrosine were increased in OLETF rats. In contrast, the expression of phosphorylated vasodilator-stimulated phosphoprotein and glucose transporter 4 in the aorta was significantly decreased in OLETF rats. These abnormalities were reversed by alpha-tocopherol. These findings suggest that alpha-tocopherol may prevent cardiovascular tissues from oxidative stress and insulin signalling disorder resulting from diabetes mellitus.     

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.     

Daily exercise vs. caloric restriction for prevention of nonalcoholic fatty liver disease in the OLETF rat model

The maintenance of normal body weight either through dietary modification or being habitually more physically active is associated with reduced incidence of nonalcoholic fatty liver disease (NAFLD). However, the means by which weight gain is prevented and potential mechanisms activated remain largely unstudied. Here, we sought to determine the effects of obesity prevention by daily exercise vs. caloric restriction on NAFLD in the hyperphagic, Otsuka Long-Evans Tokushima Fatty (OLETF) rat. At 4 wk of age, male OLETF rats (n = 7-8/group) were randomized to groups of ad libitum fed, sedentary (OLETF-SED), voluntary wheel running exercise (OLETF-EX), or caloric restriction (OLETF-CR; 70% of SED) until 40 wk of age. Nonhyperphagic, control strain Long-Evans Tokushima Otsuka (LETO) rats were kept in sedentary cage conditions for the duration of the study (LETO-SED). Both daily exercise and caloric restriction prevented obesity and the development of type 2 diabetes observed in the OLETF-SED rats, with glucose tolerance during a glucose tolerance test improved to a greater extent in the OLETF-EX animals (30-50% lower glucose and insulin areas under the curve, P < 0.05). Both daily exercise and caloric restriction also prevented excess hepatic triglyceride and diacylglycerol accumulation (P < 0.001), hepatocyte ballooning and nuclear displacement, and the increased perivenular fibrosis and collagen deposition that occurred in the obese OLETF-SED animals. However, despite similar hepatic phenotypes, OLETF-EX rats also exhibited increased hepatic mitochondrial fatty acid oxidation, enhanced oxidative enzyme function and protein content, and further suppression of hepatic de novo lipogenesis proteins compared with OLETF-CR. Prevention of obesity by either daily exercise or caloric restriction attenuates NAFLD development in OLETF rats. However, daily exercise may offer additional health benefits on glucose homeostasis and hepatic mitochondrial function compared with restricted diet alone.     

Rare sugar d-psicose improves insulin sensitivity and glucose tolerance in type 2 diabetes Otsuka Long-Evans Tokushima Fatty (OLETF) rats

A rare sugar, d-psicose has progressively been evaluated as a unique metabolic regulator of glucose and lipid metabolism, and thus represents a promising compound for the treatment of type 2 diabetes mellitus (T2DM). The present study was undertaken to examine the underlying effector organs of d-psicose in lowering blood glucose and abdominal fat by exploiting a T2DM rat model, Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Rats were fed 5% d-psicose or 5% d-glucose supplemented in drinking water, and only water in the control for 13 weeks and the protective effects were compared. A non-diabetic Long-Evans Tokushima Otsuka (LETO), fed with water served as a counter control of OLETF. After 13 weeks feeding, d-psicose treatment significantly reduced the increase in body weight and abdominal fat mass. Oral glucose tolerance test (OGTT) showed the reduced blood glucose and insulin levels suggesting the improvement of insulin resistance in OLETF rats. Oil-red-O staining elucidated that d-psicose significantly reduced lipid accumulation in the liver. Immunohistochemical analysis showed d-psicose induced glucokinase translocation from nucleus to cytoplasm of the liver which enhances glucokinase activity and subsequent synthesis of glycogen in the liver. d-psicose also protected the pathological change of the β-cells of pancreatic islets. These data demonstrate that d-psicose controls blood glucose levels by reducing lipotoxicity in liver and by preserving pancreatic β-cell function.     

Cholecystokinin-8 increases Fos-like immunoreactivity in the brainstem and myenteric neurons of rats through CCK1 receptors

To examine the role of cholecystokinin1 receptor (CCK1) in the activation of brainstem and myenteric neurons by CCK, we compared the ability of exogenous CCK-8 to induce Fos-like immunoreactivity (Fos-LI) in these neurons in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, lacking CCK1 receptors, and Long-Evans Tokushima Otsuka (LETO) controls. Five groups (n=4 rats per group) of OLETF rats, and five LETO control groups, were injected intraperitoneally (IP) with 5, 10, 20, and 40 microg/kg CCK-8 or saline. Forty-micrometer brainstem sections containing the area postrema, nucleus of the solitary tract, and the dorsal motor nucleus of the vagus, and myenteric neurons of the duodenum, jejunum, and ileum underwent a diaminobenzidine reaction enhanced with nickel to reveal Fos-LI. CCK-8 did not increase Fos-LI in any of the tested neurons in the OLETF rats. CCK-8 increased Fos-LI in the brainstem of the LETO rats in a dose dependent manner. In the LETO rats only 40 microg/kg CCK-8 increased Fos-LI in the myenteric plexus of the jejunum. This study demonstrates that CCK-8 activates the brainstem and myenteric neurons through the CCK1 receptor.     

Neuronal nitric oxide synthase and cyclooxygenase-2 in diabetic nephropathy of type 2 diabetic OLETF rats.

Neuronal nitric oxide synthase (nNOS) and cyclooxygenase-2 (COX-2) regulate the tubuloglomerular feedback (TGF) and renin-angiotensin system (RAS) in the kidney. In type 1 diabetic rats, renal overproduction of these enzymes and their relationship to the pathogenesis of diabetic nephropathy has been demonstrated. In the present study, we histologically and immunohistochemically investigated the kidneys of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as a model of type 2 diabetes, at 62 weeks of age (chronic phase of diabetes). The kidneys of OLETF rats showed typical diabetic nephropathy. Quantitative scores for glomerulosclerosis and interstitial fibrosis in OLETF rats were significantly higher than those of age-matched control Long-Evans Tokushima Otsuka (LETO) rats. nNOS- and COX-2-positive immunoreactions were observed in the distal tubules and collecting ducts. These reactions appeared to be more widely distributed in OLETF, and the number of nNOS-and COX-2-positive sites in the OLETF were significantly more than those in LETO rats. Expression of renin, angiotensin II, and inducible nitric oxide synthase (iNOS) were also examined immunohistochemically, and no differences between OLETF and LETO rats were observed in the distributions and the number of immunoreactive-sites. In conclusion, the overproduction of nNOS and COX-2 in the kidney of OLETF rats was confirmed, suggesting that the overproduction of nNOS and/or COX-2 does not affect the intrarenal RAS or iNOS production but does affect TGF.     

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.     

Increased oral and decreased intestinal sensitivity to sucrose in obese, prediabetic CCK-A receptor-deficient OLETF rats

CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rats are hyperphagic and develop obesity and Type 2 diabetes. In this strain, taste preference functions have not been investigated. Therefore, a series of short-access, two-bottle tests were performed in age-matched prediabetic OLETF and nonmutant Long-Evans Tokushima Otsuka (LETO) rats to investigate preference for sucrose (0.03, 0.1, 0.3, or 1.0 M) presented with a choice of water. To discern orosensory from postgastric factors that may contribute to this preference, in a separate experiment, rats were allowed to sham feed sucrose in the absence or presence of duodenal sucrose infusion (0.3, 0.6, or 1.0 M). In the two-bottle real-feeding tests, OLETF rats exhibited a greater preference for 0.3 M sucrose (91.2 +/- 1.7 and 78.5 +/- 3.4% for OLETF and LETO, respectively; P < 0.01) and 1.0 M sucrose (65.3 +/- 1.2 and 57.5 +/- 2.7% for OLETF and LETO, respectively; P < 0.05) than LETO rats. OLETF rats also sham fed less of the lowest (0.03 M; 33.8 +/- 4.8 and 58.3 +/- 7.3 ml for OLETF and LETO, respectively; P < 0.05) and more of the highest (1.0 M; 109.9 +/- 6.5 and 81.0 +/- 3.9 ml for OLETF and LETO, respectively; P < 0.01) concentration of sucrose relative to LETO rats. Finally, intraduodenal sucrose infusions (0.6 and 1.0 M) produced a smaller reduction of 0.3 M sham sucrose intake [14.1 +/- 8.1 vs. 52.5 +/- 3.3 ml and 49.4 +/- 8.0 vs. 82.4 +/- 3.2 ml for 0.6 M (P < 0.01) and 1.0 M (P < 0.05) infusions in OLETF and LETO, respectively]. These findings demonstrate that OLETF rats display an increased preference for sucrose, an effect that is at least partially influenced by the orosensory stimulating effect of sucrose. This enhanced responsiveness to oral stimulation, coupled with the deficit in responding to the postingestive feedback of intestinal sucrose, may contribute additively to the development of hyperphagia and weight gain in OLETF rats.     

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.     

Imbalance between endothelium-derived relaxing and contracting factors in mesenteric arteries from aged OLETF rats, a model of Type 2 diabetes

We investigated whether the balance between endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs) might be altered in mesenteric arteries from aged Otsuka Long-Evans Tokushima Fatty (OLETF) rats (a Type 2 diabetic model) [vs. age-matched control Long-Evans Tokushima Otsuka (LETO) rats]. ACh-induced relaxation was impaired in the OLETF group, and a tendency for the relaxation to reverse at high ACh concentrations was observed in both groups. This tendency was abolished by indomethacin. Nitric oxide- and/or endothelium-derived hypolarizing factor-mediated relaxation and the protein expressions of phospho-endothelial nitric oxide synthase (Ser1177) and extracellular superoxide dismutase were also reduced in OLETF. An ACh-induced contraction was observed at higher ACh concentrations in the presence of N(G)-nitro-L-arginine (L-NNA) but was greater in OLETF rats. This contraction in OLETF rats was reduced by cyclooxygenase (COX) inhibitors and by prostanoid-receptor antagonists. The ACh-induced productions of thromboxane A(2) and PGE(2) were greater in OLETF than LETO rats, as were the mesenteric artery COX-1 and COX-2 protein expressions. Moreover, tert-butyl hydroperoxide (t-BOOH) (membrane-permeant oxidant) induced a concentration-dependent contraction that was greater in OLETF rats. The t-BOOH-mediated contraction was increased both by L-NNA and by endothelium removal in LETO but not OLETF rats, suggesting that a negative modulatory role of the endothelium was lost in OLETF rats. These results suggest that an imbalance between EDRFs and EDCFs may be implicated in the endothelial dysfunction seen in aged OLETF mesenteric arteries, and may be attributable to increased oxidative stress.     

Attenuated satiation response to intestinal nutrients in rats that do not express CCK-A receptors.

Pharmacological experiments suggest that satiation associated with intestinal infusion of several nutrients is mediated by CCK-A receptors. Otsuka Long-Evans Tokushima Fatty, (OLETF), rats do not express CCK-A receptors and are insensitive to the satiation-producing effects of exogenous CCK. To further evaluate the role of CCK-A receptors in satiation by intestinal nutrient infusion, we examined intake of solid (pelleted rat chow) or liquid (12.5% glucose) food intake, following intestinal infusions of fats (oleic acid or fat emulsion), sugars (maltotriose or glucose), or peptone in OLETF rats and Long Evans Tokushima Otsuka control rats (LETO). Intestinal infusion of glucose or maltotriose reduced solid food intake more in LETO than in OLETF rats from 30 min through 4 h post infusion. Reduction of solid food intake by intestinal infusions of fat or peptone did not differ between OLETF and LETO rats during the first 30 min post infusion, but reduction of intake by these infusates was attenuated in OLETF rats over the ensuing 4h post infusion. Intestinal infusion of glucose, oleate, fat emulsion and peptone reduced 30-min intake of 12.5% glucose more in LETO than OLETF rats. Furthermore, pretreatment with the CCK-A receptor antagonist, devazepide, attenuated intestinal nutrient-induced reduction of food intake only in LETO, but not OLETF rats. Our results confirm pharmacological results, indicating that CCK-A receptors participate in satiation by nutrients that elevate plasma CCK concentrations, as well as by nutrients that do not stimulate secretion of endocrine CCK. In addition, our results indicate: 1) that OLETF rats have deficits in the satiation response to a variety of intestinal nutrient infusions; 2) that the temporal pattern for CCK-A receptor participation in satiation by intestinal nutrients is different during ingestion of liquid and solid foods and 3) that intestinal nutrients provide some satiation signals that are CCK-A receptor mediated and some that are not.