Investigation of endothelial hyperreactivity in the obese Zucker rat in-situ: reversal by vitamin E

Protective effects of blueberries on vascular function: A narrative review of preclinical and clinical evidence

Blueberries are rich in nutrients and (poly)phenols, popular with consumers, and a major agricultural crop with year-round availability supporting their use in food-based strategies to promote human health. Accumulating evidence indicates blueberry consumption has protective effects on cardiovascular health including vascular dysfunction (i.e., endothelial dysfunction and arterial stiffening). This narrative review synthesizes evidence on blueberries and vascular function and provides insight into underlying mechanisms with a focus on oxidative stress, inflammation, and gut microbiota. Evidence from animal studies supports beneficial impacts on vascular function. Human studies indicate acute and chronic blueberry consumption can improve endothelial function in healthy and at-risk populations and may modulate arterial stiffness, but that evidence is less certain. Results from cell, animal, and human studies suggest blueberry consumption improves vascular function through improving nitric oxide bioavailability, oxidative stress, and inflammation. Limited data in animals suggest the gut microbiome mediates beneficial effects of blueberries on vascular function; however, there is a paucity of studies evaluating the gut microbiome in humans. Translational evidence indicates anthocyanin metabolites mediate effects of blueberries on endothelial function, though this does not exclude potential synergistic and/or additive effects of other blueberry components. Further research is needed to establish the clinical efficacy of blueberries to improve vascular function in diverse human populations in a manner that provides mechanistic information. Translation of clinical research to the community/public should consider feasibility, social determinants of health, culture, community needs, assets, and desires, barriers, and drivers to consumption, among other factors to establish real-world impacts of blueberry consumption.

Dietary acid load significantly predicts 10-years survival in patients underwent coronary artery bypass grafting (CABG) surgery

BACKGROUNDS

Numerous studies have revealed the role of dietary acid load as a potential risk factor for cardiovascular events and blood pressure. However, its role in predicting the mortality rate in patients underwent coronary artery bypass grafting surgery (CABG) has not been reported. In the current study we aimed to evaluate the relationship of dietary acid load and cardio-metabolic risk factors with ten year survival among patients underwent CABG.

METHODS

The current prospective cohort study comprises 454 patients underwent CABG. Anthropometric, clinical and biochemical measurements were performed. Dietary acid load was calculated as either potential renal acid load (PRAL) or net endogenous acid production (NEPA) using the data obtained from a semi-quantitative food frequency questionnaire (FFQ). Survival analysis was performed using Kaplan-Meier method followed by log-rank test. The association between all-cause mortality and study parameters was performed with Cox-proportional hazard model.

RESULTS

Patients in the higher PRAL and NEAP quartiles had lower BMI and lower ejection fraction rate (P <0.05). Moreover, lower hematocrit values were observed in patients of higher PRAL quartiles. Higher PRAL scores were associated with higher mortality rate and reduced survival days (adjusted hazard ratio: 1.023 (1.00-1.04; P-value = 0.01). However, there was no relationship between NEAP and survival.

CONCLUSIONS

We revealed that high PRAL scores are positive predictors of 10-year mortality in patients underwent CABG. The results of our study suggest that maintaining an adequate acid-base balance can contribute to longevity by reducing the risk of mortality.

Effect of combination treatment of S-amlodipine with peroxisome proliferator-activated receptor agonists on metabolic and cardiovascular parameters in Zucker fa/fa rats

BACKGROUND

Type 2 diabetes is a complex metabolic disorder characterized by hyperglycemia, impaired glucose tolerance and insulin resistance associated with dyslipidemia and hypertension. The available drugs are not sufficiently efficacious in reducing cardiovascular risk and restoring normal glucose metabolism associated with type 2 diabetes as a mono- or a combination therapy. The present study examined the combined effects of an antihypertensive (S-Amlodipine) and an insulin-sensitizing agent, peroxisome proliferator-activated receptor (PPAR) agonists (Pioglitazone and Ragaglitazar), on cardiovascular risk factors in aged diabetic and insulin-resistant Zucker fa/fa rats.

METHODS

Following combination treatment for 14 days, blood pressure (BP), serum glucose, total cholesterol and triglycerides were measured. Aortic ring study was conducted to determine the effect of combination treatments on phenylephrine-induced vasoconstriction and acetylcholine (Ach)-induced vasorelaxation.

RESULTS

In combination, S-Amlodipine and Pioglitazone significantly reduced blood glucose (115.1 ± 6.6 vs. 81.7 ± 4.2), BP (184.4 ± 5.0 vs. 155.1 ± 5.0), serum triglycerides (362.5 ± 47.5 vs. 211.1 ± 23.7) and glucose intolerance when compared with vehicle treated Zucker fa/fa rats. Similar results were observed with the combination of S-Amlodipine and Ragaglitazar (Triglycerides, 362.5 ± 47.5 vs. 252.34 ± 27.86; BP, 184.4 ± 5.0 vs. 159.0 ± 8.0) except for serum glucose. ACh-induced vasorelaxation in aortic rings was also superior with both of the combinations compared to individual treatment. Furthermore, there was less body weight gain and food intake with S-Amlodipine and Pioglitazone combination in Zucker fa/fa rats. S-Amlodipine itself caused significant reduction in glucose (115.1 ± 6.6 vs. 89.7 ± 2.7) and BP (184.4 ± 5.0 vs. 156.1 ± 4.0) with improvement in insulin sensitivity observed through oral glucose tolerance test.

CONCLUSIONS

The results suggest that a combination of PPAR agonists and S-Amlodipine has partial benefits in improving the cardiovascular risk factors such as reduction in triglyceride levels, associated with chronic type 2 diabetes, and therefore may be utilized as an approach for addressing some of these devastating metabolic syndrome complications.

Prevention of hyperglycemic signal pathways in metabolic syndrome carotid artery of rats

Obesity is the major risk factor for metabolic syndrome and atherosclerotic cardiocerebrovascular diseases and induces insulin resistance characterized by a dysfunction of insulin to activate insulin receptor /insulin receptor substrate 1(IRS-1)/phosphoinositide 3-kinase (PI3K)/Akt pathway. Zucker fatty rats (8 weeks) were treated with vehicle (0.5 % methyl cellulose in physiological saline, p.o.), amlodipine (3 mg/kg/day, p.o.), atorvastatin (10 mg/kg/day, p.o.), or the combination of amlodipine plus atorvastatin (3 + 10 mg/kg/day, p.o.) for 28 days, and anti-insulin-like growth factor 1 (IGF-1)/IRS-1/PI3K/Akt pathways were evaluated. Our present immunohistochemical study first demonstrated that a combination of amlodipine plus atorvastatin treatment prevented an arteriosclerotic process compared to the single treatment with amlodipine or atorvastatin with strong recoveries of pTyr IRS-1, pPI3K, and pAkt expressions and with remarkable restraints of IGF-1 and pSer IRS-1. As a result, combination therapy with amlodipine plus atorvastatin showed a strong synergistic effect to prevent atherosclerotic processes. The present study newly suggests a synergistic benefit of combination therapy with amlodipine plus atorvastatin for strong prevention of atherosclerotic processes, which could reduce the clinical risk of cerebrovascular events for obesity patients.

Wild blueberry consumption affects aortic vascular function in the obese Zucker rat

This study evaluates the effect of wild blueberry (WB) consumption on the biomechanical properties of the aorta in the obese Zucker rat (OZR), a model of the metabolic syndrome. Thirty-six OZRs and 36 lean controls (lean Zucker rats) were placed either on a WB-enriched or a control (C) diet for 8 weeks. Phenylephrine (Phe)-mediated vasoconstriction and acetylcholine (Ach)-mediated vasorelaxation in the aortic vessel were investigated, as well as the contribution of the nitric oxide synthase and cyclooxygenase (COX) pathways in each of the above responses by using specific inhibitors. Obese Zucker rats exhibited a reduced vasocontstrictor response to Phe and an exaggerated vasorelaxant response to Ach. The WB diet partially restored Phe-induced constrictor responses and attenuated Ach-induced relaxant responses in OZR. Plasma nitric oxide was significantly attenuated (22.1 ± 1.1 μmol·L(-1), WB vs 25.6 ± 1.4 μmol·L(-1), C, p ≤ 0.05) with the WB diet. Thromboxane A2 levels in the aortic effluent were not significantly affected in the WB diet group, while PGI2 concentration significantly increased (766.5 ± 92.2 pg·mg(-1) aorta in the WB vs 571.7 ± 37.8 pg·g(-1) aorta in the C group, p ≤ 0.05). Downregulation of inducible nitric oxide synthase and COX2 expression in the OZR aorta was observed in the WB diet group. In conclusion, WB consumption altered the biomechanical properties of the OZR aorta by partially restoring the impaired Phe-induced constrictor responses and attenuating the exaggerated response to Ach-induced vasorelaxation.

Microvascular function in younger adults with obesity and metabolic syndrome: role of oxidative stress

Older adults with cardiovascular disease exhibit microvascular dysfunction and increased levels of reactive oxygen species (ROS). We hypothesized that microvascular impairments begin early in the disease process and can be improved by scavenging ROS. Forearm blood flow (Doppler ultrasound) was measured in 45 young (32 ± 2 yr old) adults (n = 15/group) classified as lean, obese, and metabolic syndrome (MetSyn). Vasodilation in response to endothelial (ACh) and vascular smooth muscle [nitroprusside (NTP) and epoprostenol (Epo)] agonists was tested before and after intra-arterial infusion of ascorbic acid to scavenge ROS. Vasodilation was assessed as a rise in relative vascular conductance (ml·min(-1)·dl(-1)·100 mmHg(-1)). ACh and NTP responses were preserved (P = 0.825 and P = 0.924, respectively), whereas Epo responses were lower in obese and MetSyn adults (P < 0.05) than in lean controls. Scavenging of ROS via infusion of ascorbic acid resulted in an increase in ACh-mediated (P < 0.001) and NTP-mediated (P < 0.001) relative vascular conductance across all groups, suggesting that oxidative stress influences vascular responsiveness in adults with and without overt cardiovascular disease risk. Ascorbic acid had no effect on Epo-mediated vasodilation (P = 0.267). These results suggest that obese and MetSyn adults exhibit preserved endothelium-dependent vasodilation with reduced dependence on prostacyclin and are consistent with an upregulation of compensatory vascular control mechanisms.

Hypertension in metabolic syndrome: vascular pathophysiology

METABOLIC SYNDROME IS A CLUSTER OF METABOLIC AND CARDIOVASCULAR SYMPTOMS: insulin resistance (IR), obesity, dyslipemia. Hypertension and vascular disorders are central to this syndrome. After a brief historical review, we discuss the role of sympathetic tone. Subsequently, we examine the link between endothelial dysfunction and IR. NO is involved in the insulin-elicited capillary vasodilatation. The insulin-signaling pathways causing NO release are different to the classical. There is a vasodilatory pathway with activation of NO synthase through Akt, and a vasoconstrictor pathway that involves the release of endothelin-1 via MAPK. IR is associated with an imbalance between both pathways in favour of the vasoconstrictor one. We also consider the link between hypertension and IR: the insulin hypothesis of hypertension. Next we discuss the importance of perivascular adipose tissue and the role of adipokines that possess vasoactive properties. Finally, animal models used in the study of vascular function of metabolic syndrome are reviewed. In particular, the Zucker fatty rat and the spontaneously hypertensive obese rat (SHROB). This one suffers macro- and microvascular malfunction due to a failure in the NO system and an abnormally high release of vasoconstrictor prostaglandins, all this alleviated with glitazones used for metabolic syndrome therapy.

Daily physical activity enhances reactivity to insulin in skeletal muscle arterioles of hyperphagic Otsuka Long-Evans Tokushima Fatty rats

Insulin-mediated glucose disposal is dependent on the vasodilator effects of insulin. In type 2 diabetes, insulin-stimulated vasodilation is impaired as a result of an imbalance in NO and ET-1 production. We tested the hypothesis that chronic voluntary wheel running (RUN) prevents impairments in insulin-stimulated vasodilation associated with obesity and type 2 diabetes independent of the effects of RUN on adiposity by randomizing Otsuka Long Evans Tokushima Fatty (OLETF) rats, a model of hyperphagia-induced obesity and type 2 diabetes, to 1) RUN, 2) caloric restriction (CR; diet adjusted to match body weights of RUN group), or 3) sedentary control (SED) groups (n = 8/group) at 4 wk. At 40 wk, NO- and ET-1-mediated vasoreactivity to insulin (1-1,000 μIU/ml) was assessed in the presence of a nonselective ET-1 receptor blocker (tezosentan) or a NO synthase (NOS) inhibitor [N(G)-nitro-L-arginine methyl ester (L-NAME)], respectively, in second-order arterioles isolated from the white portion of the gastrocnemius muscle. Body weight, fasting plasma glucose, and hemoglobin A1c were lower in RUN and CR than SED (P < 0.05); however, the glucose area under the curve (AUC) following the intraperitoneal glucose tolerance test was lower only in the RUN group (P < 0.05). Vasodilator responses to all doses of insulin were greater in RUN than SED or CR in the presence of a tezosentan (P < 0.05), but group differences in vasoreactivity to insulin with coadministration of L-NAME were not observed. We conclude daily wheel running prevents obesity and type 2 diabetes-associated declines in insulin-stimulated vasodilation in skeletal muscle arterioles through mechanisms that appear to be NO mediated and independent of attenuating excess adiposity in hyperphagic rats.

Pioglitazone improves superoxide dismutase mediated vascular reactivity in the obese Zucker rat

OBJECTIVE

To test the hypothesis that the thiazolidinedione agent, pioglitazone, mediates its chronic BP lowering action via improving vascular reactivity.

METHODS AND RESULTS

Lean (Fa/fa) and obese (fa/fa) Zucker rats were treated with or without pioglitazone (20 mg/ kg/day) for 4 weeks (n=8 animals per group). Pioglitazone treatment was associated with a significant improvement in oral glucose tolerance in the obese animals (p<0.05 compared with untreated obese). Pioglitazone prevented the development of hypertension seen in obese untreated rats (SBP 126+/-1 versus 138+/-1 mmHg; p<0.0001). Aortic ring preparations from pioglitazone-treated obese rats showed improved relaxation responsiveness (ED(50) 0.28 versus 1.15 U/ ml, p<0.001) to SOD, a NO potentiator, compared with untreated obese animals.

CONCLUSIONS

SOD-mediated vasorelaxation may contribute to the chronic antihypertensive effect and/or the improvement in insulin sensitivity following pioglitazone treatment.

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.

Vitamins E and C in the prevention of cardiovascular disease in men: the Physicians' Health Study II randomized controlled trial

CONTEXT

Basic research and observational studies suggest vitamin E or vitamin C may reduce the risk of cardiovascular disease. However, few long-term trials have evaluated men at initially low risk of cardiovascular disease, and no previous trial in men has examined vitamin C alone in the prevention of cardiovascular disease.

OBJECTIVE

To evaluate whether long-term vitamin E or vitamin C supplementation decreases the risk of major cardiovascular events among men.

DESIGN, SETTING, AND PARTICIPANTS

The Physicians' Health Study II was a randomized, double-blind, placebo-controlled factorial trial of vitamin E and vitamin C that began in 1997 and continued until its scheduled completion on August 31, 2007. There were 14,641 US male physicians enrolled, who were initially aged 50 years or older, including 754 men (5.1%) with prevalent cardiovascular disease at randomization.

INTERVENTION

Individual supplements of 400 IU of vitamin E every other day and 500 mg of vitamin C daily.

MAIN OUTCOME MEASURES

A composite end point of major cardiovascular events (nonfatal myocardial infarction, nonfatal stroke, and cardiovascular disease death).

RESULTS

During a mean follow-up of 8 years, there were 1245 confirmed major cardiovascular events. Compared with placebo, vitamin E had no effect on the incidence of major cardiovascular events (both active and placebo vitamin E groups, 10.9 events per 1000 person-years; hazard ratio [HR], 1.01 [95% confidence interval {CI}, 0.90-1.13]; P = .86), as well as total myocardial infarction (HR, 0.90 [95% CI, 0.75-1.07]; P = .22), total stroke (HR, 1.07 [95% CI, 0.89-1.29]; P = .45), and cardiovascular mortality (HR, 1.07 [95% CI, 0.90-1.28]; P = .43). There also was no significant effect of vitamin C on major cardiovascular events (active and placebo vitamin E groups, 10.8 and 10.9 events per 1000 person-years, respectively; HR, 0.99 [95% CI, 0.89-1.11]; P = .91), as well as total myocardial infarction (HR, 1.04 [95% CI, 0.87-1.24]; P = .65), total stroke (HR, 0.89 [95% CI, 0.74-1.07]; P = .21), and cardiovascular mortality (HR, 1.02 [95% CI, 0.85-1.21]; P = .86). Neither vitamin E (HR, 1.07 [95% CI, 0.97-1.18]; P = .15) nor vitamin C (HR, 1.07 [95% CI, 0.97-1.18]; P = .16) had a significant effect on total mortality but vitamin E was associated with an increased risk of hemorrhagic stroke (HR, 1.74 [95% CI, 1.04-2.91]; P = .04).

CONCLUSIONS

In this large, long-term trial of male physicians, neither vitamin E nor vitamin C supplementation reduced the risk of major cardiovascular events. These data provide no support for the use of these supplements for the prevention of cardiovascular disease in middle-aged and older men.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00270647.

Endothelin stimulates vascular hydroxyl radical formation: effect of obesity

Reactive oxygen species (ROS) and endothelin-1 (ET-1) contribute to vascular pathophysiology in obesity. In this context, whether ET-1 modulates hydroxyl radical (•OH) formation and the function of ROS/•OH in obesity is not known. In the present study, formation and function of ROS, including •OH, were investigated in the aorta of lean and leptin-deficient obese ob/ob mice. Hydroxyl radical formation was detected ex vivo using terephthalic acid in intact aortic rings and the involvement of ROS in ET-1-mediated vasoreactivity was analyzed using the antioxidant EPC-K1, a combination of α-tocopherol and ascorbic acid. Generation of either •OH, •O2−, and H2O2was strongly inhibited by EPC-K1 (all P < 0.05). In obese mice, basal vascular •OH formation and ROS activity were reduced by 3-fold and 5-fold, respectively ( P < 0.05 vs. lean). ET-1 markedly enhanced •OH formation in lean (6-fold, P < 0.05 vs. untreated) but not in obese mice. Obesity increased ET-1-induced contractions ( P < 0.05 vs. lean), and ROS scavenging further enhanced the response ( P < 0.05 vs. untreated). Exogenous ROS, including •OH caused stronger vasodilation in obese animals ( P < 0.05 vs. lean), whereas endothelium-dependent relaxation was similar between lean and obese animals. In conclusion, we present a sensitive method allowing ex vivo measurement of vascular •OH generation and provide evidence that ET-1 regulates vascular •OH formation. The data indicate that in obesity, vascular formation of ROS, including •OH is lower, whereas the sensitivity to ROS is increased, suggesting a novel and important role of ROS, including •OH in the regulation of vascular tone in disease status associated with increased body weight.

Selective resistance to vasoactive effects of insulin in muscle resistance arteries of obese Zucker (fa/fa) rats

Obesity is related to insulin resistance and hypertension, but the underlying mechanisms are unclear. Insulin exerts both vasodilator and vasoconstrictor effects on muscle resistance arteries, which may be differentially impaired in obesity.

OBJECTIVES

To investigate whether vasodilator and vasoconstrictor effects of insulin are impaired in muscle resistance arteries of obese rats and the roles of Akt and endothelial NO synthase (eNOS).

METHODS/RESULTS

Effects of insulin were studied in resistance arteries isolated from cremaster muscles of lean and obese Zucker rats. In arteries of lean rats, insulin increased activity of both NO and endothelin (ET-1), resulting in a neutral effect under basal conditions. In arteries of obese rats, insulin induced endothelin-mediated vasoconstriction (-15 +/- 5% at 1 nM, P < 0.05 vs. lean). Insulin induced vasodilatation during endothelin receptor blockade in arteries of lean rats (20 +/- 5% at 1 nM) but not in those of obese rats. Inhibition of NO synthesis increased vascular tone (by 12 +/- 2%) and shifted insulin-mediated vasoreactivity to vasoconstriction (-25 +/- 1% at 1 nM) in lean rats but had no effect in arteries of obese rats, indicating reduced NO activity. Protein analysis of resistance arteries revealed that insulin-mediated activation of Akt was preserved in obese rats, whereas expression of eNOS was markedly decreased.

CONCLUSIONS

Vasodilator but not vasoconstrictor effects of insulin are impaired in muscle resistance arteries of obese rats, and this selective impairment is associated with decreased protein levels of eNOS. These findings provide a new mechanism linking obesity to insulin resistance and hypertension.

Bromocriptine reduces steatosis in obese rodent models

BACKGROUND/AIMS

Obesity is a risk factor for glucose intolerance, steatosis, and oxidative stress, characteristics of nonalcoholic fatty liver disease. Bromocriptine may have anti-obesity, insulin-sensitizing, lipolytic, and antioxidant properties. We, therefore, hypothesized that bromocriptine would improve markers of nonalcoholic fatty liver disease in obese rodent models.

METHODS

We performed a randomized, controlled experiment in genetically obese fatty Zucker rats and diet-induced obese rats to assess for behavioral and peripheral anti-obesity actions of bromocriptine (10mg/kg) that would improve nonalcoholic fatty liver disease.

RESULTS

Behaviorally, food intake decreased and locomotor activity increased in bromocriptine-treated fatty Zucker and dietary-induced obese rats. Peripherally, liver triglycerides were significantly reduced and hepatic manganese superoxide dismutase significantly increased in bromocriptine-treated fatty Zucker and diet-induced obese rats compared to controls. Blood glucose was significantly lower in bromocriptine-treated Zucker rats compared to fatty controls and was no different than that of lean controls.

CONCLUSIONS

Improvements in obesigenic behaviors, glucose tolerance, hepatic lipid accumulation, and mitochondrial oxidative stress observed in genetically obese and diet-induced obese rodents indicate that bromocriptine may be promising as a broad-based therapy for nonalcoholic fatty liver disease.

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 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.

Age-dependent changes in blood pressure and arterial reactivity in obese Zucker rats

The purpose of the present investigation was to determine whether there is an association between changes in arterial reactivity to vasoactive agents and the development of hypertension in obese Zucker rats. At 20 weeks of age, obese rats were mildly hypotensive compared to their lean littermate controls. Maximum contractile responses of endothelium-intact mesenteric arteries from these rats to noradrenaline, endothelin-1 and KCl were depressed, although there was no change in relaxation to acetylcholine. By 32 weeks of age, obese rats had developed hypertension compared to their lean littermate controls. Maximum contractile responses of mesenteric arteries from 32-week-old obese rats to noradrenaline and endothelin-1 were no longer significantly different than control, although contractile responses to KCl remained depressed. In addition, there was a small increase in sensitivity to endothelin-1, while endothelium-dependent relaxation to acetylcholine was impaired. In contrast, there were no changes in contractile responses of endothelium-intact aortas from either 20- or 32-week-old obese rats to noradrenaline, endothelin-1 or KCl, while endothelium-dependent relaxation of this artery to acetylcholine was slightly enhanced at both ages. Therefore, changes in the reactivity of the mesenteric artery but not the aorta from obese Zucker rats parallel changes in blood pressure in these animals.

Impaired dilation of skeletal muscle microvessels to reduced oxygen tension in diabetic obese Zucker rats

This study determined alterations to hypoxic dilation of isolated skeletal muscle resistance arteries (gracilis arteries; viewed via television microscopy) from obese Zucker rats (OZR) compared with lean Zucker rats (LZR). Hypoxic dilation was reduced in OZR compared with LZR. Endothelium removal and cyclooxygenase inhibition (indomethacin) severely reduced this response in both groups, although nitric oxide synthase inhibition (N(omega)-nitro-L-arginine methyl ester) reduced dilation in LZR only. Treatment of vessels with a PGH(2)-thromboxane A(2) receptor antagonist had no effect on hypoxic dilation in either group. Arterial dilation to arachidonic acid, iloprost, acetylcholine, and sodium nitroprusside was reduced in OZR versus LZR, although dilation to forskolin and aprikalim was unaltered. Treatment of arteries from OZR with oxidative radical scavengers increased dilation to hypoxia and agonists, with no effect on responses in LZR. The restored hypoxic dilation in OZR was abolished by indomethacin. These results suggest that hypoxic dilation of skeletal muscle microvessels from LZR represents the summated effects of prostanoid and nitric oxide release, whereas the impaired response of vessels in OZR may reflect scavenging of PGI(2) by superoxide anion.

Impaired NO-dependent dilation of skeletal muscle arterioles in hypertensive diabetic obese Zucker rats

This study determined alterations to nitric oxide (NO)-dependent dilation of skeletal muscle arterioles from obese (OZR) versus lean Zucker rats (LZR). In situ cremaster muscle arterioles from both groups were viewed via television microscopy, and vessel dilation was measured with a video micrometer. Arteriolar dilation to acetylcholine and sodium nitroprusside was reduced in OZR versus LZR, although dilation to aprikalim was unaltered. NO-dependent flow-induced arteriolar dilation (via parallel microvessel occlusion) was attenuated in OZR, impairing arteriolar ability to regulate wall shear rate. Vascular superoxide levels, as assessed by dihydroethidine fluorescence, were elevated in OZR versus LZR. Treatment of cremaster muscles of OZR with the superoxide scavengers polyethylene glycol-superoxide dismutase and catalase improved arteriolar dilation to acetylcholine and sodium nitroprusside and restored flow-induced dilation and microvascular ability to regulate wall shear rate. These results suggest that NO-dependent dilation of skeletal muscle microvessels in OZR is impaired due to increased levels of superoxide. Taken together, these data suggest that the development of diabetes and hypertension in OZR may be associated with an impaired skeletal muscle perfusion via an elevated vascular oxidant stress.

Oxidative stress in a rat model of obesity-induced hypertension

The mechanisms underlying the development of hypertension in obesity are not yet fully understood. We recently reported the development of hypertension in a rat model of diet-induced obesity. When Sprague-Dawley rats (n=60) are fed a moderately high fat diet (32 kcal% fat) for 10 to 16 weeks, approximately half of them develop obesity (obesity-prone [OP] group) and mild hypertension (158+/-3.4 mm Hg systolic pressure), whereas the other half (obesity-resistant [OR] group) maintains a body weight equivalent to that of a low fat control group and is normotensive (135.8+/-3.8 mm Hg). We examined the potential role of oxidative stress in the development of hypertension in this model. Lipid peroxides measured as thiobarbituric acid-reactive substances showed a significant increase in the LDL fraction of OP rats (2.8+/-0.32 nmol malondialdehyde/mg protein) compared with OR and control rats (0.9+/-0.3 nmol malondialdehyde/mg protein). Also, aortic and kidney thiobarbituric acid-reactive substances showed a significant (3- and 5- fold) increase in OP rats after 16 weeks of diet. In addition, superoxide generation by aortic rings, measured by lucigenin luminescence, showed a 2-fold increase in the OP group compared with both the OR and control groups. In addition, free isoprostane excretion and nitrotyrosine in the kidney showed an increase in OP rats only. The urine and plasma nitrate/nitrite measured by the LDH method showed a 1.8-fold decrease in OP rats compared with OR rats. However, endothelial NO synthase expression in the kidney cortex and medulla assessed by reverse transcriptase-polymerase chain reaction showed a strong increase in the OP rats versus OR and control rats (endothelial NO synthase/beta-actin ratio 1.3+/-0.04 in OP rats versus 0.44+/-0.02 in OR rats), suggesting a possible shift toward superoxide production by the enzyme. Collectively, the data show a decreased NO bioavailability in OP animals that is due in part to the increased oxidative stress.

Investigation of basal endothelial function in the obese Zucker rat in vitro

(a) We studied basal endothelial function in the insulin-resistant, obese Zucker rat, including the influence of superoxide anion on the regulation of contractile reactivity by nitric oxide (NO), following treatment in vivo with the antioxidant tiron or the pro-oxidant combination hydroquinone+buthionine sulfoximine. (b) The leftward shift in the contractile potency of phenylephrine due to NO synthase inhibition with N(G)-nitro-L-arginine methyl ester (L-NAME) was greater in the isolated aorta of the obese Zucker rat relative to its insulin-sensitive littermate, the lean Zucker rat. (c) Pretreatment with tiron depressed vasoconstriction to phenylephrine and comparably enhanced the L-NAME-mediated leftward shift in contractile reactivity in the obese and lean Zucker rats in hydroquinone+buthionine sulfoximine-sensitive manner. (d) Our data therefore indicate superior endothelial function in the obese relative to the lean Zucker rat, reflected by a greater regulation of vasoconstrictor reactivity by basal NO, while the regulation of NO bioavailability by superoxide anion is similar.

Endothelial dysfunction accompanies a pro-oxidant, pro-diabetic challenge in the insulin resistant, obese Zucker rat in vivo

We have recently made the novel observation that a pro-oxidant challenge with hydroquinone in combination with buthionine sulfoximine (each at 50 mg/kg i.p. daily for 7 days) provokes the onset of type II diabetes mellitus in a model of insulin resistance, the obese Zucker rat. Since endothelial dysfunction in oxidant stress may aggravate in vivo insulin resistance, we have now investigated endothelium-dependent and nitric oxide (NO)-mediated vascular responses in the obese Zucker rat in vivo following this pro-oxidant insult. Pro-oxidant-treated animals exhibited defective vasodepression to the endothelium-dependent agent acetylcholine and to a lesser extent, the NO donor glyceryl trinitrate, together with a reduction in circulating levels of cGMP. Our data therefore suggest that the progression to type II diabetes mellitus in the obese Zucker rat mediated by a pro-oxidant insult is associated with impairments in agonist-stimulated, endothelium-dependent vasodilation and vascular NO signalling.