Leptin resistance before and after obesity: evidence that tissue glucose uptake underlies adipocyte enlargement and liver steatosis/steatohepatitis in Zucker rats from early-life stages.

BACKGROUND: Leptin resistance occurs in obese patients, but its independent contribution to adiposity and the accompanying metabolic diseases, i.e., diabetes, liver steatosis, and steatohepatitis, remains to be established. This study was conducted in an extreme model of leptin resistance to investigate mechanisms initiating diabetes, fat expansion, liver steatosis, and inflammatory disease, focusing on the involvement of glucose intolerance and organ-specific glucose uptake in brown and subcutaneous adipose tissues (BAT, SAT) and in the liver. METHODS: We studied preobese and adult Zucker rats (fa/fa, fa/+ ) during fasting or glucose loading to assess glucose tolerance. Relevant pancreatic and intestinal hormonal levels were measured by Milliplex. Imaging of 18F-fluorodeoxyglucose by positron emission tomography was used to quantify glucose uptake in SAT, BAT, and liver, and evaluate its relationship with adipocyte size and biopsy-proven nonalcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH). RESULTS: Preobese fa/fa pups showed impaired glucose tolerance, adipocyte enlargement, hepatic microsteatosis, and lobular inflammation, with elevated hepatic post-glucose load glucose uptake and production. Adult fa/fa rats had more severe glucose intolerance, fasting hyperglycemia, hormonal abnormalities, elevated glucose uptake in SAT and BAT, and more markedly in the liver, together with macrosteatosis, and highly prevalent hepatic inflammation. Organ glucose uptake was proportional to the degree of fat accumulation and tissue inflammation and was able to dissect healthy from NAFLD and NAFLD/NASH livers. Most severe NASH livers showed a decline in glucose uptake and liver enzymes. CONCLUSIONS: In fa/fa Zucker rats, leptin resistance leads to glucose intolerance, mainly due to hepatic glucose overproduction, preceding obesity, and explaining pancreatic and intestinal hormonal changes and fat accumulation in adipocytes and hepatocytes. Our data support the involvement of liver glucose uptake in the pathogenesis of liver inflammatory disease. Its potential as more generalized biomarker or diagnostic approach remains to be established outside of our leptin-receptor-deficient rat model.

Utilization of the Zucker Diabetic Fatty (ZDF) Rat Model for Investigating Hypoglycemia-related Toxicities.

Glucokinase (GK) catalyzes the initial step in glycolysis and is a key regulator of glucose homeostasis. Therefore, glucokinase activators (GKa) have potential benefit in treating type 2 diabetes. Administration of a Bristol-Myers Squibb GKa (BMS-820132) to healthy euglycemic Sprague-Dawley (SD) rats and beagle dogs in 1 mo toxicology studies resulted in marked and extended hypoglycemia with associated clinical signs of toxicity and degenerative histopathological changes in the stomach, sciatic nerve, myocardium, and skeletal muscles at exposures comparable to those expected at therapeutic clinical exposures. To investigate whether these adverse effects were secondary to exaggerated pharmacology (prolonged hypoglycemia), BMS-820132 was administered daily to male Zucker diabetic fatty (ZDF) rats for 1 mo. ZDF rats are markedly hyperglycemic and insulin resistant. BMS-820132 did not induce hypoglycemia, clinical signs of hypoglycemia, or any of the histopathologic adverse effects observed in the 1 mo toxicology studies at exposures that exceeded those observed in SD rats and dogs. This indicates that the toxicity observed in euglycemic animals was secondary to the exaggerated pharmacology of potent GK activation. This study indicates that ZDF rats, with conventional toxicity studies, are a useful disease model for testing antidiabetic agents and determining toxicities that are independent of prolonged hypoglycemia.

Vitamin A and feeding statuses modulate the insulin-regulated gene expression in Zucker lean and fatty primary rat hepatocytes.

Unattended hepatic insulin resistance predisposes individuals to dyslipidemia, type 2 diabetes and many other metabolic complications. The mechanism of hepatic insulin resistance at the gene expression level remains unrevealed. To examine the effects of vitamin A (VA), total energy intake and feeding conditions on the insulin-regulated gene expression in primary hepatocytes of Zucker lean (ZL) and fatty (ZF) rats, we analyze the expression levels of hepatic model genes in response to the treatments of insulin and retinoic acid (RA). We report that the insulin- and RA-regulated glucokinase, sterol regulatory element-binding protein-1c and cytosolic form of phosphoenolpyruvate carboxykinase expressions are impaired in hepatocytes of ZF rats fed chow or a VA sufficient (VAS) diet ad libitum. The impairments are partially corrected when ZF rats are fed a VA deficient (VAD) diet ad libitum or pair-fed a VAS diet to the intake of their VAD counterparts in non-fasting conditions. Interestingly in the pair-fed ZL and ZF rats, transient overeating on the last day of pair-feeding regimen changes the expression levels of some VA catabolic genes, and impairs the insulin- and RA-regulated gene expression in hepatocytes. These results demonstrate that VA and feeding statuses modulate the hepatic insulin sensitivity at the gene expression level.

Evaluation of the Zucker diabetic fatty (ZDF) rat as a model for human disease based on urinary peptidomic profiles.

Representative animal models for diabetes-associated vascular complications are extremely relevant in assessing potential therapeutic drugs. While several rodent models for type 2 diabetes (T2D) are available, their relevance in recapitulating renal and cardiovascular features of diabetes in man is not entirely clear. Here we evaluate at the molecular level the similarity between Zucker diabetic fatty (ZDF) rats, as a model of T2D-associated vascular complications, and human disease by urinary proteome analysis. Urine analysis of ZDF rats at early and late stages of disease compared to age- matched LEAN rats identified 180 peptides as potentially associated with diabetes complications. Overlaps with human chronic kidney disease (CKD) and cardiovascular disease (CVD) biomarkers were observed, corresponding to proteins marking kidney damage (eg albumin, alpha-1 antitrypsin) or related to disease development (collagen). Concordance in regulation of these peptides in rats versus humans was more pronounced in the CVD compared to the CKD panels. In addition, disease-associated predicted protease activities in ZDF rats showed higher similarities to the predicted activities in human CVD. Based on urinary peptidomic analysis, the ZDF rat model displays similarity to human CVD but might not be the most appropriate model to display human CKD on a molecular level.

Effects of a diabetes-specific enteral nutrition on nutritional and immune status of diabetic, obese, and endotoxemic rats: interest of a graded arginine supply.

OBJECTIVE: Obese and type 2 diabetic patients present metabolic disturbance-related alterations in nonspecific immunity, to which the decrease in their plasma arginine contributes. Although diabetes-specific formulas have been developed, they have never been tested in the context of an acute infectious situation as can be seen in intensive care unit patients. Our aim was to investigate the effects of a diabetes-specific diet enriched or not with arginine in a model of infectious stress in a diabetes and obesity situation. As a large intake of arginine may be deleterious, this amino acid was given in graded fashion. DESIGN: Randomized, controlled experimental study. SETTING: University research laboratory. SUBJECTS: Zucker diabetic fatty rats. INTERVENTIONS: Gastrostomized Zucker diabetic fatty rats were submitted to intraperitoneal lipopolysaccharide administration and fed for 7 days with either a diabetes-specific enteral nutrition without (G group, n=7) or with graded arginine supply (1-5 g/kg/day) (GA group, n=7) or a standard enteral nutrition (HP group, n=10). MEASUREMENTS AND MAIN RESULTS: Survival rate was better in G and GA groups than in the HP group. On day 7, plasma insulin to glucose ratio tended to be lower in the same G and GA groups. Macrophage tumor necrosis factor-α (G: 5.0±1.1 ng/2×106 cells·hr⁻¹; GA: 3.7±0.8 ng/2×106 cells·hr⁻¹; and HP: 1.7±0.6 ng/2×106 cells·hr⁻¹; p<.05 G vs. HP) and nitric oxide (G: 4.5±1.1 ng/2×106 cells·hr⁻¹; GA: 5.1±1.0 ng/2×106 cells·hr⁻¹; and HP: 1.0±0.5 nmol/2×106 cells·hr⁻¹; p<.05 G and GA vs. HP) productions were higher in the G and GA groups compared to the HP group. Macrophages from the G and GA groups exhibited increased arginine consumption. CONCLUSIONS: In diabetic obese and endotoxemic rats, a diabetes-specific formula leads to a lower mortality, a decreased insulin resistance, and an improvement in peritoneal macrophage function. Arginine supplementation has no additional effect. These data support the use of such disease-specific diets in critically ill diabetic and obese patients.

Bromocriptine administration reduces hyperphagia and adiposity and differentially affects dopamine D2 receptor and transporter binding in leptin-receptor-deficient Zucker rats and rats with diet-induced obesity.

BACKGROUND: The dopamine (DA) D(2) receptor (D2R) agonist bromocriptine (BC) decreases body fat in animal and human models and increases lean muscle mass, improves glucose intolerance and insulin resistance, and reduces triglycerides and free fatty acids. We have previously shown a negative correlation between D2R and body weight in obese individuals and in rodents, and that chronic food restriction increases D2R binding in genetically obese rats. The purpose of this study was to assess whether the antiobesity and metabolic effects of BC are related to changes in midbrain DA and D2R activity by measuring D2R and DA transporter (DAT) binding in a genetic (leptin-receptor-deficient) and environmental (diet-induced) rodent obesity model. METHODS: Obese (fa/fa) (leptin-receptor-deficient), lean (FA/FA) Zucker rats and rats with diet-induced obesity (DIO) were treated with 10 mg/kg BC for 4 weeks. Body weight, food intake, locomotor activity and blood glucose levels were measured along with D2R- and DAT-binding levels using in vitro receptor autoradiography. RESULTS: BC decreased food intake and body fat and increased locomotor activity in both the (fa/fa) and DIO rats. Furthermore, BC increased D2R binding in (fa/fa) but not in DIO rats. Finally, BC increased DAT binding in DIO rats but not in the (fa/fa) rats. CONCLUSION: These observations are all consistent with the existence of unique leptin-DA interactions and the hypothesis that there is hyposensitivity of the DA system in obesity.

Ratas Zucker como modelo experimental para el estudio de diferentes enfermedades / Zucker rats as an experimental model for the study of various diseases

Las ratas Zucker obesas son el modelo animal mejor conocido de obesidad genética. La obesidad en estos animales se hereda como carácter autosómico recesivo. Las ratas afectadas presentan una mutación en el receptor de leptina y acusan hiperfagia y otras alteraciones semejantes a las que aparecen en el síndrome metabólico humano. Estos animales presentan hiperinsulinemia, por lo que se los puede considerar también un modelo de resistencia a la insulina. Su utilidad como modelo de diabetes mellitus tipo 2, sin embargo, es cuestionable, pues presentan sólo ligera intolerancia a la glucosa. El perfil lipídico de estos animales también está alterado. Hay aumento de lipoproteínas de muy baja densidad (VLDL) y de alta densidad (HDL), pero no aumenta el colesterol de las lipoproteínas de baja densidad y no se los puede utilizar como modelo de aterogénesis. Tampoco se los considera un modelo de hipertensión, aunque pueden presentar valores altos de presión arterial sistólica a partir de las 28 semanas de vida (AU)

Zucker fatty rats are the best known animal model of genetic obesity. Obesity in these animals is inherited as an autosomal recessive trait. Affected rats have a mutation in the leptin receptor and show hyperphagia and other alterations similar to those that appear in human metabolic syndrome. These animals have hyperinsulinemia and can also be considered a model of insulin resistance. Nevertheless, the usefulness of Zucker fatty rats as a model of type 2 diabetes is questionable, since these animals have only mild glucose intolerance. The lipid profile in these animals is also altered. These rats show an increase in both very low density lipoproteins (VLDL) and high density lipoproteins (HDL) but no increase in LDL cholesterol and these animals cannot be used as a model for atherogenesis. Zucker obese rats are not a model for hypertension either, even though they show high systolic blood pressure values after 28 weeks of life (AU)

Discordance between intramuscular triglyceride and insulin sensitivity in skeletal muscle of Zucker diabetic rats after treatment with fenofibrate and rosiglitazone.

AIM: Intramyocellular triglyceride (IMTG) correlates with insulin resistance, but there is no clear causal relationship. Insulin resistance and associated hyperinsulinaemia may increase IMTG, via the insulin-regulated transcription factor, sterol regulatory element-binding protein 1 (SREBP-1). PPAR agonists may also affect IMTG via changes in insulin sensitivity, SREBP-1 or other factors. METHODS: We examined skeletal muscle IMTG and SREBP-1 expression, and metabolic parameters in Zucker diabetic fatty rats (ZDF) after 25 weeks of PPAR-gamma or PPAR-alpha administration. RESULTS: Compared with Zucker lean rats (ZL), untreated ZDF had significantly higher weights, serum glucose, insulin, free fatty acids, total cholesterol and triglycerides. IMTG and SREBP-1c messenger RNA (mRNA) were also higher in untreated ZDF; both were decreased by fenofibrate (FF). Rosiglitazone (Rosi), despite marked improvement in glycaemia, hyperinsulinaemia and hyperlipidaemia, failed to affect SREBP-1 expression, and increased body weight and IMTG. Rosi/FF combination caused less weight gain and no IMTG increase, despite metabolic effects similar to Rosi alone. CONCLUSIONS: IMTG and SREBP-1c mRNA are high in the ZDF. FF and Rosi both improved insulin sensitivity but had opposite effects on IMTG. Thus, there was a clear discordance between insulin sensitivity and IMTG with PPAR agonists, indicating that IMTG and insulin sensitivity do not share a simple relationship.

A metabonomic study of strain- and age-related differences in the Zucker rat.

Ultra-performance liquid chromatography (UPLC) coupled to orthogonal acceleration time-of-flight mass spectrometry (oa-TOFMS) in positive electrospray ionization mode was used to obtain metabolite profiles for urine obtained from three strains of Zucker rat. These were the Zucker lean, the Zucker (fa/fa) obese and the Zucker lean/(fa) cross. Clear age- and strain-related differences were noted with the leptin-deficient (fa/fa) obese animal showing significant differences from both the other Zucker rat strains with respect to metabolite profiles.

Fluoxetine alters mu opioid receptor expression in obese Zucker rat extrahypothalamic regions.

The aim of this article was to describe the effects of chronic fluoxetine on mu opioid receptor expression in obese Zucker rat extrahypothalamic regions. Male obese Zucker (fa/fa) rats were administered with fluoxetine (10 mg/kg; i.p.) daily for two weeks. Brain regional immunostaining for mu opioid receptor was carried out. An increase in the numbers of neural cells immunostained for mu opioid receptor in caudatus-putamen, dentate gyrus, lateral septum, amygdala, and frontal, parietal, and piriform cortices was observed. Increased mu opioid receptor expression in the central amygdaloid nuclei suggests a decreased opioidergic tone at this level that could be involved in fluoxetine anorectic action.

Differences in the pharmacokinetics of peroxisome proliferator-activated receptor agonists in genetically obese Zucker and sprague-dawley rats: implications of decreased glucuronidation in obese Zucker rats.

Genetically obese Zucker rats exhibit symptoms similar to those of obese patients with insulin-resistance or Type II diabetes; therefore, they have been used as a genetic model to study obesity, as well as a pharmacological model for the discovery of new drugs for the treatment of Type II diabetes and hyperlipidemia. In the present study, we compared the pharmacokinetics of two novel peroxisome proliferator-activated receptor (PPAR) agonists, MRL-I [(2R)-7-[3-[2-chloro-4-(4-fluorophenoxy)phenoxy]propoxy]-2-ethyl-3,4-dihydro-2H-benzopyran-2-carboxylic acid] and MRL-II [(2R)-7-[3-[2-chloro-4-(2,2,2-trifluoroethoxy)phenoxy]propoxy]-3,4-dihydro-2-methyl-2H-benzopyran-2-carboxylic acid], in obese Zucker and lean Sprague-Dawley rats following a single intravenous administration. The plasma clearance of both MRL-I and MRL-II was significantly lower in obese Zucker rats (4- and 2-fold, respectively) compared with Sprague-Dawley rats, but without any significant change in the volume of distribution, which resulted in a dramatic increase in the half-life (7- and 3-fold, respectively). The reversible in vitro plasma protein binding of [(14)C]MRL-I and [(14)C]MRL-II was comparable in the two strains, approximately 96% bound. The expression levels of uridine diphosphate-glucuronosyltransferases 1A1, 1A6, 2B1, and CYP2C11 and 3A1 mRNA in liver were lower (30-50%) in Zucker compared with Sprague-Dawley rats, as were the liver glutathione S-transferases (70%), quinone reductase (30%), organic anion-transporting protein 2 (80%), and multidrug resistance-associated protein 2 (Mrp2) (50%) mRNA levels. However, Mrp3 mRNA levels were similar in both strains. Consistent with these observations, the intrinsic clearance (CL(int)), calculated from the V(max)/K(m) of glucuronidation of [(14)C]MRL-I and [(14)C]MRL-II in liver microsomes, was approximately 2-fold lower in obese Zucker rats; the K(m) values were comparable in the two strains for both compounds. In conclusion, differences in the pharmacokinetics of two novel PPAR agonists, both cleared, predominantly, by conjugation, were evident in genetically obese Zucker rats compared with Sprague-Dawley rats. These differences were consistent with changes in the mRNA levels of hepatic drug-metabolizing enzymes and transporters. This information should be considered when comparing pharmacokinetic and efficacious doses in the obese Zucker rats, used as a pharmacological model, with those in Sprague-Dawley rats, which are used widely for drug metabolism and toxicology studies.

Galanin-like peptide mRNA alterations in arcuate nucleus and neural lobe of streptozotocin-diabetic and obese zucker rats. Further evidence for leptin-dependent and independent regulation.

Galanin-like peptide (GALP) is a 60-amino-acid peptide with structural similarities to galanin and a high affinity for galanin receptors. GALP is expressed by a discrete population of neurons in the arcuate nucleus (ARC) and median eminence of the hypothalamus of several species, including the rat. GALP neurons express leptin receptors and GALP mRNA levels are decreased slightly in fasted rats and stimulated significantly by acute leptin treatment in combination with fasting. In studies to further explore the leptin dependence of GALP expression, we examined GALP mRNA levels in the hypothalamus of obese Zucker and streptozotocin-induced diabetic (STZ-DM) rats. In leptin receptor-deficient obese Zucker rats, with 75% higher body weight than lean littermates, GALP mRNA levels in the ARC were decreased by 75%, while neuropeptide Y (NPY) mRNA levels were increased 7-fold (n = 5, p < 0.001), consistent with earlier reports. In hypoleptinemic diabetic rats with 4.5-fold higher blood glucose and 15% lower body weight than controls, GALP mRNA levels in the ARC were decreased by 90%, while NPY mRNA levels were increased 9-fold (n = 5, p < 0.001). GALP is also expressed by pituicytes in the neural lobe of the rat pituitary gland and GALP expression is increased by osmotic stimulation such as dehydration and salt loading. Thus, in STZ-DM rats that are in a hyperosmotic state with elevated plasma vasopressin levels, GALP mRNA levels were increased by approximately 20-fold in the neural lobe relative to control (n = 4, p < 0.001). The current findings are consistent with a strong tonic influence of leptin receptor signalling on hypothalamic GALP expression under normal conditions, and possible abnormalities in GALP neuronal signalling and their putative targets, thyrotropin-releasing hormone and gonadotropin hormone-releasing hormone neurons, under pathophysiological conditions such as diabetes and obesity. Our data in STZ-DM rats also clearly demonstrate that GALP gene expression is differentially regulated in neurons and pituicytes.

Defect in glucokinase translocation in Zucker diabetic fatty rats.

Hepatic glucose fluxes and intracellular movement of glucokinase (GK) in response to increased plasma glucose and insulin were examined in 10-wk-old, 6-h-fasted, conscious Zucker diabetic fatty (ZDF) rats and lean littermates. Under basal conditions, plasma glucose (mmol/l) and glucose turnover rate (GTR; micromol.kg(-1).min(-1)) were slightly higher in ZDF (8.4 +/- 0.3 and 53 +/- 7, respectively) than in lean rats (6.2 +/- 0.2 and 45 +/- 4, respectively), whereas plasma insulin (pmol/l) was higher in ZDF (1,800 +/- 350) than in lean rats (150 +/- 14). The ratio of hepatic uridine 5'-diphosphate-glucose 3H specific activity to plasma glucose 3H specific activity ([3H]UDP-G/[3H]G; %), total hepatic glucose output (micromol.kg(-1).min(-1)), and hepatic glucose cycling (micromol.kg(-1).min(-1)) were higher in ZDF (35 +/- 5, 87 +/- 16, and 33 +/- 10, respectively) compared with lean rats (18 +/- 3, 56 +/- 6, and 11 +/- 2, respectively). [3H]glucose incorporation into glycogen (micromol glucose/g liver) was similar in lean (1.0 +/- 0.7) and ZDF (1.6 +/- 0.8) rats. GK was predominantly located in the nucleus in both rats. With elevated plasma glucose and insulin, GTR (micromol.kg(-1).min(-1)), [3H]UDP-G/[3H]G (%), and [3H]glucose incorporation into glycogen (micromol glucose/g liver) were markedly higher in lean (191 +/- 22, 62 +/- 3, and 5.0 +/- 1.4, respectively) but similar in ZDF rats (100 +/- 6, 37 +/- 3, and 1.4 +/- 0.4, respectively) compared with basal conditions. GK translocation from the nucleus to the cytoplasm occurred in lean but not in ZDF rats. The unresponsiveness of hepatic glucose flux to the rise in plasma glucose and insulin seen in prediabetic ZDF rats was associated with impaired GK translocation.

Leptin-receptor gene transfer into the arcuate nucleus of female Fatty zucker rats using recombinant adeno-associated viral vectors stimulates the hypothalamo-pituitary-gonadal axis.

Fatty fa/fa Zucker rats with a missense mutation in the leptin receptor (OB-R) are obese and infertile with prolonged estrous cycles. To determine whether their reproductive deficits could be corrected by OB-R installation, we employed viral vectors to introduce the OB-R gene into either the arcuate nucleus (ARC) or the paraventricular nucleus (PVN) of the hypothalamus, sites of OB-R expression in wild-type rats. Recombinant adeno-associated viral (rAAV) vectors encoding the human leptin-receptor gene (rAAV-OB-Rb) were microinjected intraparenchymally to produce doxycycline-regulatable OB-R gene expression. Expression of the OB-R gene in the ARC and PVN was verified using reverse transcription-polymerase chain reaction. Expression of OB-R in the ARC, but not in the PVN, resulted in normalization of estrous cycle length, increased ovarian follicular development, and decreased serum progesterone levels. Compared to saline-injected rats, hypothalamic expression of neuropeptide Y (NPY) and pro-opiomelanocortin were decreased in ARC rAAV-OB-Rb-injected rats. Parallel decreases were noted in NPY and beta-endorphin (beta-END) concentrations in the hypothalamus, whereas luteinizing hormone-releasing hormone (LHRH) levels increased. These studies showed that rAAV vectors can be successfully used to install functional OB-R in the hypothalamus for extended periods. The resultant stimulation of the hypothalamo-pituitary-gonadal (HPG) axis in ARC-injected rats was probably brought about by the observed decreases in NPY and beta-END, which inhibit hypothalamic LHRH. Because these changes were seen in ARC-injected, but not in PVN-injected, rats, the results suggest that the ARC may be the primary site where leptin acts to regulate the HPG axis.

Strain variability in Zucker rats affects their response to oral oleoyl-estrone.

There is a considerable variability in the responses of Zucker fa/fa rats in metabolic studies, which could not be solely attributed to the leprfa mutation. In order to fathom the extent of this variability, we compared the response to oleoyl-estrone (OE), a powerful lipid-mobilising agent, of two strains of Zucker lean and obese rats: Harlan (H) and Charles River (CR). Rats were given an oral gavage of 10 micromol/day/kg of OE in sunflower oil, and were compared with oil-receiving controls. Body composition, energy and water balances, and plasma parameters were studied after 10 days of treatment. H rats showed a higher water turnover than CR rats; OE treatment reduced water intake, partly compensated by metabolic water, and decreased stool water. H rats accrued more cholesterol than CR animals, which showed higher cholesterolaemia. OE facilitated cholesterol disposal in lean (CR and H) and H obese rats. CR rats had higher body and liver lipids than H animals. No differences in energy balance were found. Insulin decrease following OE treatment was greater in lean CR than in H rats, but this trend was reversed in the obese rats, lacking effective responses to leptin. The red cell glucose compartment was smaller in H than in CR rats; the higher insulin levels in H rats may be partly responsible for that difference. Obese H maintained glycaemia (and liver glycogen) with higher insulin levels than CR animals. The extent to which the leprfa mutation affects the responses of Zucker fa/fa rats could not be singled out unless the metabolic environment of the batch used is known. This variability must be taken into account when developing a metabolic or hormonal study in which this model of obesity is used.

Impaired nitric oxide function in the basilar artery of the obese Zucker rat.

The effect of insulin-resistance syndrome on vascular function has been examined in isolated basilar arteries using the obese Zucker rat (OZR) and age-matched lean littermate controls (lean Zucker rat; LZR) at 36 weeks of age. The OZR showed significantly reduced oral glucose tolerance and increased body weight, blood pressure, proteinuria, plasma levels of triglycerides, cholesterol, and insulin compared with the LZR. The contractile response to serotonin was significantly increased in the OZR. Furthermore, contractions to serotonin in LZR but not OZR were enhanced in the presence of the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (NAME). Relaxations to acetylcholine (ACh), histamine, and A23187 were significantly reduced in precontracted arteries from the OZR. In the presence of NAME, histamine responses were significantly reduced whereas ACh and A23187 responses were almost abolished. Relaxations to free-radical nitric oxide (NO) and papaverine were not different in arteries from the OZR, even though responses to sodium nitroprusside were reduced in the OZR. Western blot and immunofluorescent quantitative analyses of eNOS content in cerebral microvessel fractions and basilar artery preparations, respectively, were not significantly different between OZR and LZR. The results suggest impairment in endothelial function resulting in reduced NO function in the basilar artery from the OZR.

Anti-hyperlipidemic action of a newly synthesized benzoic acid derivative, S-2E.

A newly synthesized benzoic acid derivative, (+)-(S)-p-[1-(p-tert-butylphenyl)-2-oxo-4-pyrrolidinyl]methoxybenzoic acid (S-2E), has the capacity to inhibit the biosynthesis of both sterol and fatty acids. Here, we report the mechanism by which S-2E lowers blood cholesterol and triglyceride levels. In the liver, S-2E was converted into its active metabolite, S-2E-CoA. S-2E-CoA noncompetitively inhibited the enzymatic activities of both 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase and acetyl-CoA carboxylase at K(i)=18.11 microM and K(i)=69.2 microM, respectively. Interestingly, pharmacokinetic experiments in rats showed that the concentration of S-2E-CoA in the liver was sufficient to inhibit the activities of HMG-CoA reductase and acetyl-CoA carboxylase, for example, when orally given to rats at 10 mg/kg. Indeed, S-2E (3-30 mg/kg) given orally suppressed the secretion rate of very-low-density lipoprotein (VLDL)-cholesterol and triglyceride in Triton WR-1339-injected rats. Furthermore, S-2E lowered the blood total cholesterol and triglyceride levels simultaneously in Zucker fatty rats. Collectively, S-2E may be useful in the treatment of familial hypercholesterolemia and mixed hyperlipidemia.

The rat arcuate nucleus integrates peripheral signals provided by leptin, insulin, and a ghrelin mimetic.

The hypothalamic circuits controlling food intake and body weight receive and integrate information from circulating satiety signals such as leptin and insulin and also from ghrelin, the only known circulating hormone that stimulates appetite following systemic injection. Activation of arcuate neurons by ghrelin and ghrelin mimetics (the growth hormone secretagogues) is augmented in 48-h-fasted rats compared with fed rats, as reflected by a greater number of cells expressing Fos protein in response to administration of the same maximally effective dose. Here we sought to determine whether this increased responsiveness in fasting might reflect or be influenced by low levels of circulating satiety factors such as leptin or insulin. Chronic central infusion of insulin or leptin during a 48-h fast suppressed the threefold increase in the Fos response to intravenous injection of a maximally effective dose of growth hormone-releasing peptide (GHRP)-6, a synthetic growth hormone secretagogue. This appears to be a direct central action of insulin and leptin because the marked decrease in plasma levels of insulin, leptin, and glucose during fasting were unaffected by central administration of either hormone. Furthermore, the GHRP-6-induced Fos response was twofold greater in obese leptin- and insulin-resistant Zucker rats compared with lean controls. These data provide evidence that the ghrelin-sensitive circuits in the hypothalamus are dynamically regulated by central insulin and leptin action.

Potenciación de la respuesta insulínica a una sobrecarga oral de glucosa en ratas zucker obesas tratadas con oleoil-estrona / Potentiation of insulin response to an oral glucose load in obese zucker rats treated with oleoyl-estrone

Antecedentes. La administración de oleoil-estrona induce la pérdida de peso en ratas preservando la glucemia y disminuyendo los valores de insulina. Métodos. Se utilizaron ratas Zucker connormopeso y obesas tratadas crónicamente con 3,5 µmol/kg/día de oleoil-estrona i.v. comparadas con controles que sólo recibieron el excipiente. Se administró (tras 12 h de ayuno) a todos los animales unasobrecarga oral de 3,5 g/kg de glucosa, valorándose acto seguido las concentraciones de glucosa e insulina durante 1 h. También se midieron los valores basales de leptina y estrona total plasmática. Resultados. En las ratas con normopeso, el efecto del tratamiento previo con oleoil-estrona se tradujo en una mayor elevación de la insulinemia y una más rápida recuperación de la glucemia en comparación con los controles. En ratas obesas, la oleoil-estrona indujo una más rápida recuperación de laglucemia y un fuerte incremento de la insulina como respuesta a la sobrecarga de glucosa. Conclusiones. Estos datos sugieren que la oleoil-estrona potencia la respuesta insulínica a la glucosa (AU)

Adipose tissue-specific increase in angiotensinogen expression and secretion in the obese (fa/fa) Zucker rat.

We investigated angiotensinogen (AGT) expression in adipose tissue and liver of Zucker rats during the onset of obesity. The developmental pattern of AGT expression (protein and mRNA) in liver was similar in both genotypes. In inguinal adipose tissue, AGT cell content was similar in suckling and weaned pups in lean rats, whereas it continuously increased with age in obese rats. AGT amount in adipocytes was unaffected by the genotype until weaning. Thereafter, adipocytes from obese rats displayed a significant increase in AGT content that was strengthened with age. Compared with the cell content, the amount of secreted AGT over 24 h was higher, and a genotype effect was observed as early as 14 days of age. Using fat cell populations differing by size, we showed that this AGT oversecretion was not solely related to adipocyte hypertrophy. Our results demonstrate that the fa genotype exerts a control on the production of AGT in a tissue-specific manner, suggesting a local role of AGT in the overdevelopment of adipose tissue.