Stimulatory Effect of Leptin on Nitric Oxide Production Is Impaired in Dietary‐Induced Obesity

Objective: We investigated the effect of leptin on nitric oxide production in lean and rats made obese by a high‐calorie diet. Research Methods and Procedures: The animals were placed in metabolic cages, and urine was collected in 2‐hour periods after leptin (1 mg/kg intraperintoneally) or vehicle administration. Blood was obtained 0.5, 1, 2, 4, or 6 hours after injection. Results: Leptin had no effect on systolic blood pressure in either lean or obese animals. Plasma concentration of NO metabolites (nitrites + nitrates, NO_x) increased in lean rats by 31.5%, 58.0%, and 27.9% at 1, 2, and 4 hours after leptin injection, respectively. In the obese group, plasma NO_x increased only at 2 hours (+36.5%). Leptin increased urinary NO_x excretion by 31.8% in the first 2‐hour period after injection in lean but not in obese rats. In lean animals, leptin elevated plasma cyclic 3′, 5′‐guanosine monophosphate (cGMP) at 1, 2, and 4 hours by 35.3%, 96.3%, and 57.3%, respectively. In the obese group, plasma cGMP was higher only at 2 and 4 hours (+44.6% and +32.1%, respectively). Urinary excretion of cGMP increased in lean animals by 67.1% in the first period and by 50.4% in the second period. In the obese group, leptin induced a 53.9% increase in urinary cGMP excretion only in the first 2‐hour period. Discussion: The stimulatory effect of leptin on NO production is impaired in dietary‐induced obesity; however, leptin does not increase blood pressure in obese animals, suggesting that other NO—independent depressor mechanisms are stimulated.     

Leptin-Induced Endothelium-Dependent Vasorelaxation of Peripheral Arteries in Lean and Obese Rats: Role of Nitric Oxide and Hydrogen Sulfide

Adipose tissue hormone leptin induces endothelium-dependent vasorelaxation mediated by nitric oxide (NO) and endothelium-derived hyperpolarizing factors (EDHF). Previously it has been demonstrated that in short-term obesity the NO-dependent and the EDHF-dependent components of vascular effect of leptin are impaired and up-regulated, respectively. Herein we examined the mechanism of the EDHF-dependent vasodilatory effect of leptin and tested the hypothesis that alterations of acute vascular effects of leptin in obesity are accounted for by chronic hyperleptinemia. The study was performed in 5 groups of rats: (1) control, (2) treated with exogenous leptin for 1 week to induce hyperleptinemia, (3) obese, fed highly-palatable diet for 4 weeks, (4) obese treated with pegylated superactive rat leptin receptor antagonist (PEG-SRLA) for 1 week, (5) fed standard chow and treated with PEG-SRLA. Acute effect of leptin on isometric tension of mesenteric artery segments was measured ex vivo. Leptin relaxed phenylephrine-preconstricted vascular segments in NO- and EDHF-dependent manner. The NO-dependent component was impaired and the EDHF-dependent component was increased in the leptin-treated and obese groups and in the latter group both these effects were abolished by PEG-SRLA. The EDHF-dependent vasodilatory effect of leptin was blocked by either the inhibitor of cystathionine γ-lyase, propargylglycine, or a hydrogen sulfide (H₂S) scavenger, bismuth (III) subsalicylate. The results indicate that NO deficiency is compensated by the up-regulation of EDHF in obese rats and both effects are accounted for by chronic hyperleptinemia. The EDHF-dependent component of leptin-induced vasorelaxation is mediated, at least partially, by H₂S.     

Protein kinase betaII in Zucker obese rats compromises oxygen and flow-mediated regulation of nitric oxide formation

In severe obesity, microvascular endothelial regulation of nitric oxide (NO) formation is compromised in response to muscarinic stimulation, and major arteries have suppressed flow-mediated dilation. Because normal microvessels are highly dependent on flow-mediated stimulation of NO generation and are responsive to intra- and extravascular oxygen availability, they are likely a major site of impaired endothelial regulation. This study evaluated the blood flow and oxygen-dependent aspects of intestinal microvascular regulation and NO production in Zucker obese rats just before the onset of hyperglycemia. Ruboxistaurin (LY-333531) was used to inhibit PKC-betaII to determine whether flow or oxygen-related NO regulation was improved. Blood flow velocity was increased by forcing arterioles to perfuse approximately 50% larger tissue areas by occlusion of nearby arterioles, and oxygen tension in the bath was lowered to create a modest oxygen depletion. When compared with lean Zucker rats, the periarteriolar NO concentration ([NO]) for obese rats was approximately 30% below normal. At elevated shear rates, the [NO] for arterioles of obese animals was 20-30% below those in the arterioles of lean rats, and the NO response to decreased oxygen was about half normal in obese rats. All of these regulatory problems were essentially corrected in obese rats by PKC blockade with only minor changes in the microvascular behavior in lean rats. Therefore, activation of PKC-betaII in endothelial cells during obesity suppressed NO regulation both at rest and in response to increased flow velocity and decreased oxygen availability.     

Sex Differences in Renal Nitric Oxide Synthase,NAD(P)H Oxidase,and Blood Pressure in Obese Zucker Rats

Background: By increasing renal oxidative stress, obesity may alter the protective effect of female sex on blood pressure (BP).Objectives: The aim of this study was to determine whether female rats had altered expression and activity of renal nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase and nitric oxide synthase (NOS), enzymes important in superoxide and nitric oxide generation, respectively, and whether this relationship was altered in obesity.Methods: Male and female, lean and obese Zucker rats were fed progressively higher levels of NaCl over 54 days while BP was measured by radiotelemetry. Kidneys were harvested after euthanization.Results: A total of 32 (n = 8/body type/sex) Zucker rats were examined. On a high-salt diet (4% NaC1), male and obese rats had significantly higher mean arterial blood pressure relative to female and lean rats (mm Hg: lean male = 108, lean female = 99, obese male = 129, and obese female = 123) and reduced renal cortical NOS activity (determined by 2-way analysis of variance; P < 0.05 for sex and body type). Immunoblotting revealed that cortical endothelial NOS protein abundance was reduced in obese but not in male rats. Surprisingly, lean female rats had the highest outer medullary protein levels of several NADPH oxidase subunits, including gp91phox, p47phox, and p67phox (% of lean male: 207, 196, and 151, respectively; P < 0.01 for all). However, renal NADPH activity was not increased in lean females, but was significantly increased in obese rats of both sexes (P < 0.05).Conclusions: High-NaCl diet increased BP modestly in obese females, but not at all in lean females, suggesting some loss of protection with obesity in female rats. Reduced cortical NOS activity (both in male and obese rats) and/or increased NADPH oxidase activity (obese rats) may have contributed to increased salt sensitivity of BP.     

Activation of the central melanocortin system contributes to the increased arterial pressure in obese Zucker rats

We have previously demonstrated that leptin-mediated activation of the central nervous system (CNS) melanocortin system reduces appetite and increases sympathetic activity and blood pressure (BP). In the present study we examined whether endogenous melanocortin system activation, independent of leptin's actions, contributes to the regulation of BP and metabolic functions in obese Zucker rats, which have mutated leptin receptors. The long-term cardiovascular and metabolic effects of central melanocortin-3/4 receptor (MC3/4R) antagonism with SHU-9119 were assessed in lean (n = 6) and obese (n = 8) Zucker rats. BP and heart rate (HR) were measured 24-h/day by telemetry and an intracerebroventricular cannula was placed in the brain lateral ventricle. After stable control measurements, SHU-9119 was infused intracerebroventricularlly (1 nmol/h) for 10 days followed by a 10-day recovery period. Chronic CNS MC3/4R antagonism significantly increased food intake and body weight in lean (20 ± 1 to 45 ± 2 g and 373 ± 11 to 432 ± 14 g) and obese (25 ± 2 to 35 ± 2 g and 547 ± 10 to 604 ± 11 g) rats. No significant changes were observed in plasma glucose levels in lean or obese rats, whereas plasma leptin and insulin levels markedly increased in lean Zucker rats during CNS MC3/4R antagonism. Chronic SHU-9119 infusion in obese Zucker rats reduced mean arterial pressure (MAP) and HR by 6 ± 1 mmHg and 24 ± 5 beats/min, whereas in lean rats SHU-9119 infusion reduced HR by 31 ± 9 beats/min while causing only a transient decrease in MAP. These results suggest that in obese Zucker rats the CNS melanocortin system contributes to elevated BP independent of leptin receptor activation.     

Single intracerebroventricular bolus injection of a recombinant adenovirus expressing leptin results in reduction of food intake and body weight in both lean and obese Zucker fa/fa rats

Leptin acts as a satiety factor within the central nervous system by binding to its receptor located in the hypothalamus. A missense mutation of the leptin receptor induces hyperphagia and obesity in the obese Zucker fa/fa rat. Since the CNS is an important target of leptin action, we hypothesized that leptin gene transfer into the lateral cerebral ventricle could efficiently lead to inhibition of food intake and reduction of body weight in obese fa/fa rats as well as in lean animals. A single intracerebroventricular injection of an adenoviral vector containing a cDNA encoding leptin resulted in the expression of leptin in the ependymal cells lining the ventricle and the secretion of leptin into the cerebrospinal fluid (CSF). During the first week after injection, when high concentrations of leptin were produced in the CSF, the reducing effects of leptin on food intake and body weight were comparable in lean and in obese fa/fa rats. The subsequent decline in CSF leptin levels, that was similar in lean and obese fa/fa rats, resulted in the faster resumption of food intake and body weight gain in obese than in lean animals, confirming a reduced sensitivity to leptin in the obese group. The results of this study show that leptin gene delivery into the cerebral ventricles allows for the production of elevated leptin concentrations in CSF, and they support the hypothesis that the impaired sensitivity to leptin may be overcome in obese fa/fa rats.     

Enhanced AT1 receptor-mediated vasocontractile response to ANG II in endothelium-denuded aorta of obese Zucker rats

In the present study, we tested the hypothesis that ANG II causes a greater vasoconstriction in obese Zucker rats, a model of type 2 diabetes, with mild hypertension. Measurement of isometric tension in isolated aortic rings with intact endothelium revealed a modest but not significantly greater ANG II-induced contraction in obese than lean rats. Removal of endothelium or inhibition of nitric oxide (NO) synthase by N(G)-nitro-L-arginine methyl ester (L-NAME) enhanced 1) ANG II-induced contraction in both lean and obese rats, being significantly greater in obese rats (E(max) g/g tissue, denuded: lean 572 +/- 40 vs. obese 664 +/- 16; L-NAME: lean 535 +/- 14 vs. obese 818 +/- 23) and 2) ANG II sensitivity in obese compared with lean rats, as revealed by the pD(2) values. Endothelin-1 and KCl elicited similar contractions in the aortic rings of lean and obese rats. ACh, a NO-dependent relaxing hormone, produced greater relaxation in the aortic rings of obese than lean rats, whereas sodium nitroprusside, an NO donor, elicited similar relaxations in both rat strains. The expression of the ANG type 1 (AT(1)) receptor protein and mRNA in the endothelium-intact aorta was significantly greater in obese than lean rats, whereas the endothelium-denuded rings expressed modest but not significantly greater levels of AT(1) receptors in obese than lean rats. The endothelial NO synthase protein and mRNA expression levels were higher in the aorta of obese than lean animals. We conclude that, although ANG II produces greater vasoconstriction in obese rat aortic rings, enhanced endothelial AT(1) receptor-mediated NO production appears to counteract the increased ANG II-induced vasoconstriction, suggesting that arterial AT(1) receptor may not be a contributing factor to hypertension in this model of obesity.     

Reduced constrictor reactivity balances impaired vasodilation in the mesenteric circulation of the obese Zucker rat

Obesity causes whole body insulin resistance and impaired vasodilation to nitric oxide (NO). Because NO is a major contributor to the regulation of mesenteric blood flow, the mesenteric circulation of obese animals is faced with reduced capacity to increase flow and increased demand for flow associated with elevated consumption of food. This study hypothesized that insulin resistance impairs NO-mediated dilation but that constrictor reactivity would be reduced to compensate in obese animals. We further hypothesized that elevated superoxide levels caused impaired responses to NO in insulin resistance. Vasodilator reactivity and vasoconstrictor reactivity of mesenteric resistance arteries from lean (LZR) and obese (OZR) Zucker rats were examined in vitro using videomicroscopy. Insulin resistance independent of obesity was induced via fructose feeding in LZR (FF-LZR). Endothelium-dependent NO-mediated dilation was reduced in OZR and FF-LZR compared with LZR. Impairments in NO-mediated dilation were reversed with 1 mM tempol, a SOD mimetic. Constrictor reactivity to norepinephrine was reduced in OZR but not in FF-LZR relative to LZR. Basal mesenteric vascular resistance was similar in LZR and OZR despite impaired NO-dependent dilation in OZR. Mesenteric vascular resistance was increased in FF-LZR relative to LZR. These data indicate that there is reduced constrictor reactivity in OZR that may offset the impaired NO-mediated dilation and preserve mesenteric blood flow in hyperphagic, obese animals.     

Association between Serum Leptin Levels and 24‐Hour Blood Pressure in Obese Women

Objective: To assess the relationship between serum leptin and 24‐hour blood pressure (BP) in obese women, according to body fat distribution. Research Methods and Procedures: A cross‐sectional study was carried out in a population of 70 nondiabetic, normotensive, obese women (40 with android and 30 with gynoid type of obesity) and 20 nonobese healthy women as a control group. All subjects underwent 24‐hour ambulatory BP monitoring. Blood samples were collected for serum leptin and plasma insulin measurements. Total cholesterol and high‐density lipoprotein cholesterol were also measured. Results: Serum leptin levels were significantly higher in obese subjects than in controls, and they were more elevated in android obese women than in gynoid ones. Leptin levels were positively related to body mass index (BMI), insulin, and waist and hip circumferences in the android group. Among gynoid subjects, leptin levels showed positive associations with BMI and insulin. In women with android obesity, strong positive correlations (p < 0.001) were found between leptin levels and 24‐hour systolic BP (SBP), daytime SBP, nighttime SBP, 24‐hour diastolic BP (DBP), and daytime DBP. Multiple regression analyses, including age, insulin and leptin concentrations, BMI, and waist and hip circumferences on 24‐hour and daytime SBP and DBP, showed that only leptin levels contributed to the variability of BP. Conclusions: Our study shows that serum leptin levels are directly related to 24‐hour BP levels in normotensive women with android fat distribution, independently of BMI.     

Efficiency of NO donors in substituting impaired endogenous NO production: a functional and morphological study

Two exogenous NO donors were used to act as substitutes for impaired endogenous nitric oxide (NO) production due to inhibition of NO synthase in rats. Six weeks' lasting inhibition of NO synthase by NG-nitro-L-arginine methyl ester (L-NAME) induced stabilized hypertension. Simultaneously administered isosorbide-5-mononitrate did not prevent the development of hypertension. Molsidomine, administered concomitantly with L-NAME, significantly attenuated the BP increase. However, BP was still found to be moderately increased compared to the initial values. Remarkable alterations in the geometry of the aorta, carotid and coronary artery found in NO-deficient hypertension were prevented in rats administered L-NAME plus molsidomine at the same time. In spite of 6 weeks' lasting inhibition of NOS, the NOS activators acetylcholine and bradykinin induced BP decrease; the maximum hypotensive value did not differ from the values recorded in the controls or in animals treated with L-NAME plus molsidomine. Notably enough, the hypotension was similar to that found in rats administered L-NAME alone for six weeks. After NO synthase inhibition, Isosorbide-5-mononitrate does not substitute and molsidomine substitute only partially the impaired endogenous NO production.     

Leptin and Its Relation to Obesity and Insulin in the SHR/N-corpulent Rat,A Model of Type II Diabetes Mellitus

The spontaneously hypertensive/NIH-corpulent (SHR/N-cp) rat is a genetic animal model that exhibits obesity, metabolic features of hyperinsulinemia, hyperglycemia, and hyperlipidemia, which are characteristic of type II diabetes and mild hypertension. To determine the role of leptin, the protein product of the ob gene, in the development of obesity and diabetes in this model, we measured steady-state circulating levels of leptin in obese and lean SHR/N-cp rats and examined the relation between plasma leptin levels and metabolic variables at the stage of established obesity in these animals. Mean fasting plasma leptin concentration was 8-fold higher in obese than in lean rats (p<0.01). This was associated with a 6-fold elevation in plasma insulin in the obese group. Fasting levels of plasma glucose, cholesterol, and triglyceride were all significantly higher in obese rats than in lean controls. Spearman correlation analysis showed a significant positive correlation between plasma leptin concentration and body weight among the animals (r=0.73, p<0.01). Similarly, plasma insulin concentration was significantly correlated with BW in all animals (r=0.54, p<0.05). There was also a significant positive.correlation between plasma leptin and plasma insulin in the entire group (r=0.70, p<0.01). However, this relationship was significant only for lean rats but not for obese rats (r=0.59, p<0.05 for lean rats, and r=0.23, p=NS, for obese rats). Plasma leptin also correlated positively with fasting plasma glucose (r=0.75, p<0.05), total cholesterol (r=0.63, p<0.05), and triglyceride (r=0.67, p <0.05). The marked elevation of plasma leptin in obese SHR/N-cp rats suggests that obesity in this animal model is related to up-regulation of the ob gene. Circulating leptin appears to be one of the best biological markers of obesity and that hyperleptinemia is closely associated with several metabolic risk factors related to insulin resistance in the diabesity syndrome.     

Effect of nitric oxide inhibition on blood pressure and corticosterone responses in adult rats neonatally treated with glutamate

The role of nitric oxide (NO) in the regulation of blood pressure and hypothalamic-pituitary-adrenal function of adult rats treated with monosodium glutamate (MSG) during the neonatal period was investigated. Blood pressure and the heart rate were registered by a computerized system of direct blood pressure measurement through an indwelling cannula in the femoral artery. The inhibition of the activity of NO synthase by acute injection of Nomega-nitro-L-argininemethylester (L-NAME, 30 mg/kg, i.v.) to control rats produced a rise of blood pressure and a fall of heart rate. Both responses were reduced in MSG-treated rats. Repeated administration of L-NAME (50 mg/kg, i.p, two times daily for 4 days) increased BP in both groups of animals. Corticosterone concentrations in the plasma were significantly increased in response to repeated L-NAME administration in MSG-treated rats, while ACTH levels were similar in both groups of animals. These data suggest that some of the cardiovascular and endocrine changes in rats treated with MSG may be due to the abnormal function of the NO system.     

Gender-dependent response in blood pressure changes following the inhibition of nitric oxide synthase

Many studies employed L-NAME (N(G)-nitro-L-arginine methyl ester), an L-arginine antagonist and nitric oxide (NO) synthase (NOS) inhibitor, to produce hypertension experimentally in male animals. It is not known whether females respond similarly. We thus examined the effect of long-term oral administration of L-NAME on body weight (BW), blood pressure (BP), and heart rate (HR) of both female and male rats. We found that L-NAME induced significant increase in mean BP (MAP) in both genders, however, L-NAME-treated females (F*) exhibited a significantly higher elevation than males (M*) did. This difference persisted for 5 wks and then diminished. L-NAME was thus withdrawn and a rapid decrease of MAP was observed. MAP of F* decreased less and thus remained higher than M* for 5 wks. MAP of control rats (F and M) remained unchanged during the period. Systolic BP (SBP) altered in a similar pattern. We also found that HR decreased immediately after L-NAME administration and that HR of F* was significantly less reduced. These findings indicate that L-NAME induced a more pronounced response in females than males, consistent with the view that females are more dependent on NOS activity for their regulation of BP.     

Serum leptin, lipids, free fatty acids, and fat pads in long-term dehydroepiandrosterone-treated Zucker rats

The obese Zucker rat has a genetically flawed leptin system and is a model of hyperphagia, obesity, hyperlipidemia, and markedly elevated leptin levels. Dehydroepiandrosterone (DHEA) administration reduces hyperphagia, hyperlipidemia, and obesity in Zucker rats. Since serum leptin levels are associated with body fat, we wondered what the effects of fat pad weight reduction from DHEA administration would have on leptin levels. This experiment investigated the effects of DHEA on intra-abdominal fat pads, serum lipids, and peripheral leptin in male lean and obese Zucker rats that were administered DHEA in their food from 4 weeks of age to 20 weeks. Lean and obese rats received plain chow or chow containing DHEA. Additional chow-fed groups of lean and obese weight-matched controls and obese pair-fed rats helped to control for the reduced body weight, food intake, and fat pad weights seen with DHEA administration. DHEA administration to lean Zucker rats reduced body weight and fat pad weights, but leptin levels showed a lower trend. Among obese rats, both DHEA treatment and pair-feeding reduced body weight and fat pad weights, but only DHEA lowered leptin levels. The weight-matched controls had reductions in fat pad weights similar to the DHEA-treated group, but with increased leptin levels. Thus, DHEA may exert a small, independent effect on leptin levels in this animal model, but the reduction is less than what would be expected.     

Acute effects of exercise on circulating leptin in lean and genetically obese fa/fa rats

Mechanisms of regulation of plasma leptin in lean and genetically obese animals are not completely understood. In particular a relation has been proposed between energy metabolism and leptin. However, it is not clear how energy expenditure and leptin are related under exercise in lean and obese animals. To clarify these aspects we investigated lean and genetically obese (fa/fa) Zucker rats undergoing a single bout (30 min) of swimming and measured several biochemical and hormonal parameters of energy metabolism and leptin changes throughout the study. Moreover ob-gene expression in adipose tissue was also measured. Our results showed that plasma leptin is decreased by 30% at the end of exercise in lean animals while resulting unaffected in obese animals. Leptin changes in lean rats are concomitant with the peak of NEFA and glycerol release from adipose tissue rather than with the reduction of plasma insulin. Ob-gene expression in adipose tissue was markedly increased in fa/fa compared to lean rats, but was not modified by exercise both in lean and obese animals. In conclusion our data show that leptin changes during exercise are related to lipolytic events in adipose tissue and support a link between leptin and energy expenditure.     

Diazoxide down-regulates leptin and lipid metabolizing enzymes in adipose tissue of Zucker rats.

We have previously reported that attenuation of hyperinsulinemia by diazoxide (DZ), an inhibitor of glucose-mediated insulin secretion, increased insulin sensitivity and reduced body weight in obese Zucker rats. These findings prompted us to investigate the effects of DZ on key insulin-sensitive enzymes regulating adipose tissue metabolism, fatty acid synthase (FAS), and lipoprotein lipase (LPL), as well as on circulating levels of leptin. We also determined the direct effects of diazoxide on FAS in 3T3-L1 adipocytes. Seven-week-old female obese and lean Zucker rats were treated with DZ (150 mg/kg/d) or vehicle (C, control) for a period of 6 wk. Changes in plasma parameters by DZ include significant decreases in triglycerides, free fatty acids, glucose, and insulin, consistent with our previous reports. DZ obese rats exhibited lower plasma leptin levels (P<0.03) compared to their C animals. DZ significantly reduced adipose tissue FAS activity in both lean (P<0.0001) and obese (P<0.01) animals. LPL mRNA content was also decreased significantly in DZ-treated obese animals (P<0.009) as compared to their respective controls without a significant effect on lean animals. The possibility that DZ exerted a direct effect on adipocytes was further tested in cultured 3T3-L1 adipocytes. Although diazoxide (5 microM) alone did not change FAS activity in cultured 3T3-L1 adipocytes, it significantly attenuated insulin's effect on FAS activity (P<0.001). We demonstrate that DZ regulates key insulin-sensitive enzymes involved in regulation of adipose tissue metabolism. These findings suggest that modification of insulin-sensitive pathways can be therapeutically beneficial in obesity management.     

Leptin resistance of adipocytes in obesity: role of suppressors of cytokine signaling

Liver-derived hyperleptinemia induced in normal rats by adenovirus-induced gene transfer causes rapid disappearance of body fat, whereas the endogenous adipocyte-derived hyperleptinemia of obesity does not. Here we induce liver-derived hyperleptinemia in rats with adipocyte-derived hyperleptinemia of acquired obesity caused by ventromedial hypothalamus lesioning (VMH rats) or by feeding 60% fat (DIO rats). Liver-derived hyperleptinemia in obese rats caused only a 5-7% loss of body weight, compared to a 13% loss in normoleptinemic lean animals; but in actual grams of weight lost there was no significant difference between obese and lean groups, suggesting that a subset of cells remain leptin-sensitive in obesity. mRNA and protein of a putative leptin-resistance factor, suppressor of cytokine signaling (SOCS)-1 or -3, were both increased in white adipose tissues (WAT) of VMH and DIO rats. Since transgenic overexpression of SOCS-3 in islets reduced the lipopenic effect of leptin by 75%, we conclude that the increased expression of SOCS-1 and -3 in WAT of rats with acquired obesity could have blocked leptin's lipopenic action in the leptin-resistant WAT population.     

Dietary obesity increases NO and inhibits BKCa-mediated, endothelium-dependent dilation in rat cremaster muscle artery: association with caveolins and caveolae

Obesity is a risk factor for hypertension and other vascular disease. The aim of this study was to examine the effect of diet-induced obesity on endothelium-dependent dilation of rat cremaster muscle arterioles. Male Sprague-Dawley rats (213 ± 1 g) were fed a cafeteria-style high-fat or control diet for 16-20 wk. Control rats weighed 558 ± 7 g compared with obese rats 762 ± 12 g (n = 52-56; P < 0.05). Diet-induced obesity had no effect on acetylcholine (ACh)-induced dilation of isolated, pressurized (70 mmHg) arterioles, but sodium nitroprusside (SNP)-induced vasodilation was enhanced. ACh-induced dilation of arterioles from control rats was abolished by a combination of the K(Ca) blockers apamin, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), and iberiotoxin (IBTX; all 0.1 μmol/l), with no apparent role for nitric oxide (NO). In arterioles from obese rats, however, IBTX had no effect on responses to ACh while the NO synthase (NOS)/guanylate cyclase inhibitors N(ω)-nitro-L-arginine methyl ester (L-NAME; 100 μmol/l)/1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 μmol/l) partially inhibited ACh-induced dilation. Furthermore, NOS activity (but not endothelial NOS expression) was increased in arteries from obese rats. L-NAME/ODQ alone or removal of the endothelium constricted arterioles from obese but not control rats. Expression of caveolin-1 and -2 oligomers (but not monomers or caveolin-3) was increased in arterioles from obese rats. The number of caveolae was reduced in the endothelium of arteries, and caveolae density was increased at the ends of smooth muscle cells from obese rats. Diet-induced obesity abolished the contribution of large-conductance Ca(2+)-activated K(+) channel to ACh-mediated endothelium-dependent dilation of rat cremaster muscle arterioles, while increasing NOS activity and inducing an NO-dependent component.     

Exercise-induced increase in skeletal muscle vasodilatory responses in obese Zucker rats

The purpose of this study was to test the hypothesis that exercise training improves microvascular function in obese Zucker rats, a model of obesity and type II diabetes. Animals were divided into four age-matched groups: lean sedentary (LS), lean exercise (LE), obese sedentary (OS), and obese exercise (OE). The exercise groups were treadmill-exercised from 5 to 11 wk of age, including a 2-wk acclimation period. Mean arterial pressure (MAP) was not significantly different between any of the groups. The OS had significantly higher mean body weight, blood glucose, insulin, IL-6, and leptin levels compared with the LS, whereas the OE had significantly lower blood glucose, insulin, and IL-6 levels compared with the OS. Functional hyperemia and endothelial-dependent vasodilation were tested in the spinotrapezius muscle using intravital microscopy. Functional hyperemia and acetylcholine (0.1 microM, 1 microM, and 10 microM) responses were significantly attenuated in OS compared with the LS, while the contraction and ACh-induced (1 microM and 10 microM) vasodilation were significantly increased in both LE and OE compared with the sedentary animals. These results suggest that exercise training can improve vascular function in this model of type II diabetes. Moreover, the impaired vasodilation observed in 11-wk-old OZR suggests that the microvascular dysfunction is not likely due to an elevated blood pressure.