Restoration of coronary endothelial function in obese Zucker rats by a low-carbohydrate diet

A popular diet used for weight reduction is the low-carbohydrate diet, which has most calories derived from fat and protein, but effects of this dietary regimen on coronary vascular function have not been identified. We tested the hypothesis that obesity-induced impairment in coronary endothelial function is reversed by a low-carbohydrate diet. We used four groups of male Zucker rats: lean and obese on normal and low-carbohydrate diets. Rats were fed ad libitum for 3 wk; total caloric intake and weight gain were similar in both diets. To assess endothelial and vascular function, coronary arterioles were cannulated and pressurized for diameter measurements during administration of acetylcholine or sodium nitroprusside or during flow. When compared with lean rats, endothelium-dependent acetylcholine-induced vasodilation was impaired by approximately 50% in obese rats (normal diet), but it was restored to normal by the low-carbohydrate diet. When the normal diet was fed, flow-induced dilation (FID) was impaired by >50% in obese compared with lean rats. Similar to acetylcholine, responses to FID were restored to normal by a low-carbohydrate diet. N(omega)-nitro-L-arginine methyl ester (10 microM), an inhibitor of nitric oxide (NO) synthase, inhibited acetylcholine- and flow-induced dilation in lean rats, but it had no effect on acetylcholine- or flow-induced vasodilation in obese rats on a low-carbohydrate diet. Tetraethylammonium, a nonspecific K(+) channel antagonist, blocked flow-dependent dilation in the obese rats, suggesting that the improvement in function was mediated by a hyperpolarizing factor independent of NO. In conclusion, obesity-induced impairment in endothelium-dependent vasodilation of coronary arterioles can be dramatically improved with a low-carbohydrate diet most likely through the production of a hyperpolarizing factor independent of NO.     

Impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type II diabetic rats

The goals of this study were to determine the effects of type II diabetes mellitus on nitric oxide synthase-dependent responses of cerebral arterioles and on endothelial nitric oxide synthase (eNOS) protein in cerebral arterioles. We examined dilatation of cerebral (pial) arterioles in 13-15 week old male lean and diabetic obese Zucker rats in response to nitric oxide synthase-dependent agonists (acetylcholine and adenosine diphosphate (ADP)) and a nitric oxide synthase-independent agonist (nitroglycerin). We found that acetylcholine (10 microM) increased cerebral arteriolar diameter by 10 +/- 3% (mean +/- SE) in lean Zucker rats, but by only 2 +/- 2% in diabetic obese Zucker rats (p<0.05). In addition, ADP (100 microM) increased cerebral arteriolar diameter by 20 +/- 2% in lean Zucker rats, but by only 8 +/- 2% in diabetic obese Zucker rats (p<0.05). In contrast, nitroglycerin produced similar vasodilatation in lean and diabetic obese Zucker rats. Thus, impaired dilatation of cerebral arterioles in diabetic obese Zucker rats is not related to non-specific impairment of vasodilatation. Following these functional studies, we harvested cerebral microvessels for Western blot analysis of eNOS protein. We found that eNOS protein was significantly higher in diabetic obese Zucker rats than in lean Zucker rats (p<0.05). Thus, type II diabetes mellitus impairs nitric oxide synthase-dependent responses of cerebral arterioles. In addition, eNOS protein from cerebral blood vessels is increased in diabetic obese Zucker rats.     

Impaired capsaicin-induced relaxation of coronary arteries in a porcine model of the metabolic syndrome

Recent studies implicate channels of the transient receptor potential vanilloid family (e.g., TRPV1) in regulating vascular tone; however, little is known about these channels in the coronary circulation. Furthermore, it is unclear whether metabolic syndrome alters the function and/or expression of TRPV1. We tested the hypothesis that TRPV1 mediates coronary vasodilation through endothelium-dependent mechanisms that are impaired by the metabolic syndrome. Studies were conducted on coronary arteries from lean and obese male Ossabaw miniature swine. In lean pigs, capsaicin, a TRPV1 agonist, relaxed arteries in a dose-dependent manner (EC50 = 116 +/- 41 nM). Capsaicin-induced relaxation was blocked by the TRPV1 antagonist capsazepine, endothelial denudation, inhibition of nitric oxide synthase, and K+ channel antagonists. Capsaicin-induced relaxation was impaired in rings from pigs with metabolic syndrome (91 +/- 4% vs. 51 +/- 10% relaxation at 100 microM). TRPV1 immunoreactivity was prominent in coronary endothelial cells. TRPV1 protein expression was decreased 40 +/- 11% in obese pigs. Capsaicin (100 microM) elicited divalent cation influx that was abolished in endothelial cells from obese pigs. These data indicate that TRPV1 channels are functionally expressed in the coronary circulation and mediate endothelium-dependent vasodilation through a mechanism involving nitric oxide and K+ channels. Impaired capsaicin-induced vasodilation in the metabolic syndrome is associated with decreased expression of TRPV1 and cation influx.     

Modulation of vasomotion in resistance arteries of JCR:LA-cp rats: a model of insulin resistance.

Obesity and insulin resistance are strongly associated with an increased risk of vascular disease. Vasomotion is the cyclic variation in the diameter of arteries and is a general feature of the vasculature that may have important physiological consequences. We tested the hypothesis that obesity - insulin resistance is associated with abnormal vasomotion by comparing obese, insulin-resistant JCR:LA-cp rats, known to develop vasculopathy, atherosclerosis, and ischemic lesions of the heart, with lean insulin-sensitive animals from the same strain. Vasomotion was assessed using isolated mesenteric arteries on a myograph system after preconstriction to 50% of maximal constriction with norepinephrine. The amplitude of vasomotion was enhanced by the presence of meclofenamate, a prostaglandin H synthase inhibitor, and was diminished by N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor. Removal of the endothelium essentially abolished vasomotion, and meclofenamate had no effect on de-endothelialized arteries. Frequency was not altered by either L-NAME or meclofenamate. Although pharmacological inhibition of nitric oxide and eicosanoid production clearly altered vasomotion, there was no difference in the amplitude or frequency of vasomotion in arteries from obese rats compared with lean rats. These results indicate that the endothelium plays a central role in modulating vasomotion, involving both enhancing and inhibiting effects, and that vasomotion is similar between obese, insulin-resistant and lean, insulin-sensitive rats.     

Vascular wall dysfunction in JCR:LA-cp rats: effects of age and insulin resistance

We tested thehypothesis that aging and insulin resistance interact to increasevascular dysfunction by comparing the function of isolated mesentericresistance arteries in obese, insulin-resistant JCR:LA-cp rats andlean, insulin-sensitive rats of the same strain at 3, 6, 9, and 12 moof age. The peak constrictor responses to norepinephrine,phenylephrine, and high potassium were elevated in arteries from obeserats. Responses to these agents increased with age in both obese andlean rats. An eicosanoid constrictor contributed substantially tovasoconstriction in the arteries from both lean and obese animals.Inhibition of nitric oxide synthase increased the vasoconstrictorresponse to norepinephrine in both obese and lean rats. This effectincreased with age in lean rats only. Vascular relaxation in responseto acetylcholine and sodium nitroprusside was impaired in the obeserats and did not alter with age. The results suggest that obeseJCR:LA-cp rats have enhanced maximal constriction, which originates inthe arterial smooth muscle and increases with age. There is evidencethat the ability of the arteries to compensate for the enhancedcontractility is impaired in obese rats, particularly with advanced age.

     

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.     

Modulation of noradrenaline-induced vasoconstriction in isolated perfused mesenteric arterial beds from obese Zucker rats in the presence and absence of insulin

The genetically obese Zucker rat (fa/fa) is an insulin-resistant animal model with early-onset severe hyperinsulinemia that eventually develops mild hypertension. Thus, it represents a model in which the effect of hyperinsulinemia - insulin resistance associated with hypertension on vascular reactivity can be examined. The purpose of this study was to investigate the contribution of endogenous nitric oxide (NO) and prostaglandins to reactivity to noradrenaline (NA) in the presence and absence of insulin in mesenteric arterial beds (MAB) from 25-week-old obese Zucker rats and their lean, gender-matched littermates. In the absence of insulin, bolus injection of NA (0.9-90 nmol) produced a dose-dependent increase in perfusion pressure in MAB from both lean and obese rats. Although there was no significant difference in NA pD2 (-log ED50) values, the maximum response of MAB from obese rats to NA was slightly but significantly reduced compared with that of MAB from lean rats. The nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 300 microM) enhanced and indomethacin (20 microM) inhibited pressor responses to NA in MAB from both obese and lean rats. Perfusion with insulin (200 mU/L, a level similar to that in obese rats in vivo) potentiated only the responses of the obese MAB to the two lowest doses of NA tested (0.9 and 3 nmol). In the presence of L-NMMA, insulin further potentiated the NA response in MAB from obese rats. Indomethacin, the prostaglandin H2/thromboxane A2 receptor antagonist SQ 29548 (0.3 microM), and the nonselective endothelin-1 (ET-1) receptor antagonist bosentan (3 microM) all abolished insulin potentiation of the NA response in obese MAB. These data suggest that concurrent release of NO and vasoconstrictor cyclooxygenase product(s) in MAB from both obese and lean Zucker rats normally regulates NA-induced vasoconstrictor responses. Furthermore, insulin increases the release of contracting cyclooxygenase product(s) and enhances reactivity to low doses of NA in MAB from obese rats. The effects of insulin may be partially mediated by ET-1 via ET receptors and are buffered to some extent by concomitant NO release. This altered action of insulin may play a role in hypertension in this hyperinsulinemic - insulin-resistant model.     

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.     

Increased vascular thromboxane generation impairs dilation of skeletal muscle arterioles of obese Zucker rats with reduced oxygen tension

This study determined if altered vascular prostacyclin (PGI(2)) and/or thromboxane A(2) (TxA(2)) production with reduced Po(2) contributes to impaired hypoxic dilation of skeletal muscle resistance arterioles of obese Zucker rats (OZRs) versus lean Zucker rats (LZRs). Mechanical responses were assessed in isolated gracilis muscle arterioles following reductions in Po(2) under control conditions and following pharmacological interventions inhibiting arachidonic acid metabolism and nitric oxide synthase and alleviating elevated vascular oxidant stress. The production of arachidonic acid metabolites was assessed using pooled arteries from OZRs and LZRs in response to reduced Po(2). Hypoxic dilation, endothelium-dependent in both strains, was attenuated in OZRs versus LZRs. Nitric oxide synthase inhibition had no significant impact on hypoxic dilation in either strain. Cyclooxygenase inhibition dramatically reduced hypoxic dilation in LZRs and abolished responses in OZRs. Treatment of arterioles from OZRs with polyethylene glycol-superoxide dismutase improved hypoxic dilation, and this improvement was entirely cyclooxygenase dependent. Vascular PGI(2) production with reduced Po(2) was similar between strains, although TxA(2) production was increased in OZRs, a difference that was attenuated by treatment of vessels from OZRs with polyethylene glycol-superoxide dismutase. Both blockade of PGH(2)/TxA(2) receptors and inhibition of thromboxane synthase increased hypoxic dilation in OZR arterioles. These results suggest that a contributing mechanism underlying impaired hypoxic dilation of skeletal muscle arterioles of OZRs may be an increased vascular production of TxA(2), which competes against the vasodilator influences of PGI(2). These results also suggest that the elevated vascular oxidant stress inherent in metabolic syndrome may contribute to the increased vascular TxA(2) production and may blunt vascular sensitivity to PGI(2).     

Pathophysiological correlation of arginase-1 in development of type 2 diabetes from obesity in adolescents

BackgroundThere is great interest to understand causal pathophysiological correlation between obesity and diabetes mellitus (DM). Vascular endothelial dysfunction is crucially involved in pathogenesis of vascular complications in DM. Recently, increased arginase expression and activity have been described as underlying mechanisms of endothelial dysfunction in DM and vascular inflammation in obesity. By limiting L-arginine bioavailability to endothelial nitric oxide synthase (NOS III), nitric oxide production is potentially impaired.MethodsWe investigated the impact of plasma from diabetic and obese adolescents on arginase and NOS III expression in cultured human endothelial cells (ECs). A total of 148 male adolescents participated in this study including 18 obese, 28 type 1-, 28 type 2-DM patients, and 74 age-matched healthy volunteers.ResultsA concurrent increase in arginase-1 (1.97-fold) and decrease in NOS III expression (1.45-fold) was observed in ECs exposed to type 2 diabetic plasma compared to control subjects. ECs incubated with type 1 DM plasma had a diminished NOS III level without impact on arginase-1 expression. Urea-assay featured an increased arginase activity in treated ECs with type 1- or 2-DM plasma. Despite increased pro-inflammatory cytokines and chemokines in obese plasma, arginase-1 expression/activity did not change in treated ECs. However, NOS III expression was significantly reduced. Pearson analysis revealed positive correlation between arginase-1, but not NOS III, expression with FBS in ECs treated with type 2-DM plasma.ConclusionsOur data demonstrate that increased arginase-1 expression/activity in ECs, as critical pathogenic factor is correlated with development of obesity-related type 2-DM and linked vascular disease.     

Role of nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) in the regulation of blood pressure by leptin in lean and obese rats

We investigated the role of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in hemodynamic action of leptin. The effect of leptin (1 mg/kg i.p.) on systolic blood pressure (SBP) was examined in lean rats and in rats made obese by feeding highly palatable diet for either 1 or 3 months. Separate groups received NO synthase inhibitor, L-NAME, or EDHF inhibitors, the mixture of apamin+charybdotoxin or sulfaphenazole, before leptin administration. Leptin increased NO production, as evidenced by increase in plasma and urinary NO metabolites and cyclic GMP. This effect was impaired in both obese groups. In lean rats either leptin or EDHF inhibitors had no effect on blood pressure. L-NAME increased blood pressure in lean animals and this effect was prevented by leptin. However, when leptin was administered to animals pretreated with both L-NAME and EDHF inhibitors, blood pressure increased even more than after L-NAME alone. In the 1-month obese group leptin had no effect on SBP, however, pressor effect of leptin was observed in animals pretreated with EDHF inhibitors. In the 3-month obese group leptin alone increased SBP, and EDHF inhibitors did not augment its pressor effect. The results suggest that leptin may stimulate EDHF when NO becomes deficient, e.g. after NOS blockade or in short-term obesity. Although the effect of leptin on NO production is impaired in the 1-month obese group, BP does not increase, probably because EDHF compensates for NO deficiency. In contrast, leptin increases BP in 3-month obesity because its effect on EDHF is also attenuated.     

Impaired pulmonary artery contractile responses in a rat model of microgravity: role of nitric oxide.

Vascular contractile hyporesponsiveness is an important mechanism underlying orthostatic intolerance after microgravity. Baroreceptor reflexes can modulate both pulmonary resistance and capacitance function and thus cardiac output. We hypothesized, therefore, that pulmonary vasoreactivity is impaired in the hindlimb-unweighted (HLU) rat model of microgravity. Pulmonary artery (PA) contractile responses to phenylephrine (PE) and U-46619 (U4) were significantly decreased in the PAs from HLU vs. control (C) animals. N(G)-nitro-L-arginine methyl ester (10(-5) M) enhanced the contractile responses in the PA rings from both C and HLU animals and completely abolished the differential responses to PE and U4 in HLU vs. C animals. Vasorelaxant responses to ACh were significantly enhanced in PA rings from HLU rats compared with C. Moreover, vasorelaxant responses to sodium nitroprusside were also significantly enhanced. Endothelial nitric oxide synthase (eNOS) and soluble guanlyl cyclase expression were significantly enhanced in PA and lung tissue from HLU rats. In marked contrast, the expression of inducible nitric oxide synthase was unchanged in lung tissue. These data support the hypothesis that vascular contractile responsiveness is attenuated in PAs from HLU rats and that this hyporesponsiveness is due at least in part to increased nitric oxide synthase activity resulting from enhanced eNOS expression. These findings may have important implications for blood volume distribution and attenuated stroke volume responses to orthostatic stress after microgravity exposure.     

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.     

Nitric oxide modulates vascular inflammation and intimal hyperplasia in insulin resistance and the metabolic syndrome

Type 2 diabetes mellitus (DM) and the metabolic syndrome, both characterized by insulin resistance, are associated with an accelerated form of atherosclerotic vascular disease and poor outcomes following vascular interventions. These vascular effects are thought to stem from a heightened inflammatory environment and reduced bioavailability of nitric oxide (NO). To better understand this process, we characterized the vascular injury response in the obese Zucker rat by examining the expression of adhesion molecules, the recruitment of inflammatory cells, and the development of intimal hyperplasia. We also evaluated the ability of exogenous NO to inhibit the sequela of vascular injury in the metabolic syndrome. Obese and lean Zucker rats underwent carotid artery balloon injury. ICAM-1 and P-selectin expression were increased following injury in the obese animals compared with the lean rats. The obese rats also responded with increased macrophage infiltration of the vascular wall as well as increased neointima formation compared with their lean counterparts (intima/media = 0.91 vs. 0.52, P = 0.001). After adenovirus-mediated inducible NO synthase (iNOS) gene transfer, ICAM-1, P-selectin, inflammatory cell influx, and oxidized low-density lipoprotein (LDL) receptor expression were all markedly reduced versus injury alone. iNOS gene transfer also significantly inhibited proliferative activity (54% and 73%; P < 0.05) and neointima formation (53% and 67%; P < 0.05) in lean and obese animals, respectively. The vascular injury response in the face of obesity and the metabolic syndrome is associated with increased adhesion molecule expression, inflammatory cell infiltration, oxidized LDL receptor expression, and proliferation. iNOS gene transfer is able to effectively inhibit this heightened injury response and reduce neointima formation in this proinflammatory environment.     

Estrogen replacement reduces PGHS-2-dependent vasoconstriction in the aged rat

The reduction in estrogen in postmenopausal women contributes to an increase in vascular dysfunction. Models of aging have shown that this is due, in part, to increased prostaglandin H synthase (PGHS)-dependent vasoconstriction. We showed previously that inducible PGHS-2-dependent vasoconstriction is increased with aging. In the present study, we hypothesized that estrogen suppresses PGHS-2-dependent constriction in the aged rat. Isolated mesenteric arteries from placebo- or estrogen-treated, ovariectomized aged (24 mo) Fisher rats were assessed for endothelium-dependent relaxation in the absence or presence of PGHS inhibitors. PGHS inhibition (meclofenamate, 1 micromol/l) enhanced methacholine-induced relaxation only in the placebo group. Specific PGHS-2 inhibition (NS-398, 10 micromol/l) increased arterial relaxation to a greater extent than PGHS-1 inhibition (valeryl salicylate, 3 mmol/l). Estrogen prevented the PGHS-dependent constrictor effect but did not enhance nitric oxide-dependent relaxation in this model. PGHS-1 and endothelial nitric oxide synthase were not altered by estrogen, whereas PGHS-2 expression was decreased in the estrogen-replaced rats (P < 0.05). In summary, estrogen replacement improved vasodilation in aged rats by decreasing PGHS-dependent constriction.     

Nitric oxide mediates hyperphagia of obese zucker rats: Relation to specific changes in the microstructure of feeding behavior

The presence of a nitric oxide synthetase (NOS) was demonstrated in the rat brain. It has been demonstrated recently that NOS-inhibitors reduce food intake in mammals and this suggest that nitric oxide (NO) might be a physiological mediator involved in the mechanisms controlling feeding behavior. Actually, there is no information about the acute central and peripheral effects of NOSinhibitors on feeding behavior in obese an lean Zucker rats. That is why we investigated the acute dose-dependent activity of N^G-Nitro-Arginine-Methyl-Ester (L-NAME) on food intake and feeding behavior in these rats. When given peripherally in the obese rats, L-NAME produced a dosedependent decrease in food intake (p < 0.001). The calculated MED and the ED 50 were 0.50 mg/kg IP and 3.46 mg/kg IP, respectively. These effects could not be reproduced in the lean Zucker rats whatever the dose used (p = 0.59). The anorectic properties of L-NAME were wery well translated into the microstructure of the feeding behavior. Time spent to eat (p < 0.001), meal duration (p < 0.01) and meal number (p < 0.001) were reduced in the obese rats. Interestingly, L-NAME produced the same effects in the lean rats, but meal size increased in a compensatory manner. Central administration of L-NAME reproduced the same effects in the obese rats, but lean rats still remained insensitive. Central aminergic and/or peptidergic defects associated with the expression of hyperphagia might explain the differences observed between these lean and the obese animals. These results indicate a role of nitric oxide in the expression of hyperphagia and show that it might be a physiological mediator involved in the mechanisms controlling feeding behavior.     

Endothelium-dependent vasorelaxation effect of rutin-free tartary buckwheat extract in isolated rat thoracic aorta

The aim of this study was to point out the potential of tartary buckwheat on vascular functions. A nonabsorbed fraction of hot-water extract of tartary buckwheat on a SP70 column (TBSP-T), which was free from rutin, was used for this aim. In a contractile experiment using Sprague-Dawley rat thoracic aorta rings contracted by 1.0 microM phenylephrine (PE) or 50 mM KCl, TBSP-T evoked a significant vasorelaxation [EC50 (mg/ml): PE; 2.2; KCl, 1.9]. By a further fractionation of TBSP-T by liquid-liquid partitioning into basic, neutral and acidic fractions, a marked enhancement of vasorelaxation effect was observed only for acidic fraction (EC50, 0.25 mg/ml). The action of acidic fraction was significantly attenuated in endothelium-denuded aortic rings and in the presence of nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (100 microM). The fraction also enhanced the cyclic guanosine monophosphate (cGMP) production in aortic rings contracted with PE [cGMP (pmol/mg protein): PE, 7.2+/-2.3; PE+Acidic fraction, 35+/-8]. These results indicate that acidic fraction could mediate NO/cGMP pathways, thereby exerting endothelium-dependent vasorelaxation action. In conclusion, tartary buckwheat was proven to regulate vascular tones and have latent acidic candidates except for rutin.     

Insulin resistance does not diminish eNOS expression, phosphorylation, or binding to HSP-90

Previously, using an animal model of syndrome X, the obese Zucker rat (OZR), we documented impaired endothelium-dependent vasodilation. The aim of this study was to determine whether reduced expression or altered posttranslational regulation of endothelial nitric oxide synthase (eNOS) underlies the vascular dysfunction in OZR rats. There was no significant difference in the relative abundance of eNOS in hearts, aortas, or skeletal muscle between lean Zucker rats (LZR) and OZR regardless of age. There was no difference in eNOS mRNA levels, as determined by real-time PCR, between LZR and OZR. The inability of insulin resistance to modulate eNOS expression was also documented in two additional in vivo models, the ob/ob mouse and the fructose-fed rat, and in vitro via adenoviral expression of protein tyrosine phosphatase 1B in endothelial cells. We next investigated whether changes in the acute posttranslational regulation of eNOS occurs with insulin resistance. Phosphorylation of eNOS at S632 (human S633) and T494 was not different between LZR and OZR; however, phosphorylation of S1176 was significantly enhanced in OZR. Phosphorylation of S1176 was not different in the ob/ob mouse or in fructose-fed rats. The association of heat shock protein 90 with eNOS, a key regulatory step controlling nitric oxide and aberrant O2- production, was not different between OZR and LZR. Taken together, these results suggest that changes in eNOS expression or posttranslation regulation do not underlie the vascular dysfunction seen with insulin resistance and that other mechanisms, such as altered localization, reduced availability of cofactors, substrates, and the elevated production of O2-, may be responsible.     

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.     

Obesity lowers hyperglycemic threshold for impaired in vivo endothelial nitric oxide function

Obesity is a risk for type II diabetes mellitus and increased vascular resistance. Disturbances of nitric oxide (NO) physiology occur in both obese animals and humans. In obese Zucker rats, we determined whether a protein kinase C-beta II (PKC-beta II) mechanism may lower the resting NO concentration ([NO]) and predispose endothelial NO abnormalities at lower glucose concentrations than occur in lean rats. NO was measured with microelectrodes touching in vivo intestinal arterioles. At rest, the [NO] in obese Zucker rats was 60 nm less than normal or about a 15% decline. After local blockade of PKC-beta II with LY-333531, the [NO] increased approximately 90 nm in obese rats but did not change in lean rats. In lean rats, administration of 300 mg/dl D-glucose for 45 min depressed endothelium-dependent dilation; only 200 mg/dl was required in obese animals. These various observations indicate that resting [NO] is depressed in obese rats by a PKC-beta II mechanism and the hyperglycemic threshold for endothelial NO suppression is reduced to 200 mg/dl D-glucose.