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.     

Upregulation of ERK1/2-eNOS via AT2 Receptors Decreases the Contractile Response to Angiotensin II in Resistance Mesenteric Arteries from Obese Rats

It has been clearly established that mitogen-activated protein kinases (MAPKS) are important mediators of angiotensin II (Ang II) signaling via AT1 receptors in the vasculature. However, evidence for a role of these kinases in changes of Ang II-induced vasoconstriction in obesity is still lacking. Here we sought to determine whether vascular MAPKs are differentially activated by Ang II in obese animals. The role of AT2 receptors was also evaluated. Male monosodium glutamate-induced obese (obese) and non-obese Wistar rats (control) were used. The circulating concentrations of Ang I and Ang II, determined by HPLC, were increased in obese rats. Ang II-induced isometric contraction was decreased in endothelium-intact resistance mesenteric arteries from obese compared with control rats and exhibited a retarded AT1 receptor antagonist response. Blocking of AT2 receptors and inhibition of either endothelial nitric oxide synthase (eNOS) or extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) restored Ang II-induced contraction in obese rats. Western blot analysis revealed increased protein expression of AT2 receptors in arteries from obese rats. Basal and Ang II-induced ERK1/2 phosphorylation was also increased in obese rats. Blockade of either AT1 or AT2 receptors corrected the increased ERK1/2 phosphorylation in arteries from obese rats to levels observed in control preparations. Phosphorylation of eNOS was increased in obese rats. Incubation with the ERK1/2 inhibitor before Ang II stimulation did not affect eNOS phosphorylation in control rats; however, it corrected the increased phosphorylation of eNOS in obese rats. These results clearly demonstrate that enhanced AT2 receptor and ERK1/2-induced, NO-mediated vasodilation reduces Ang II-induced contraction in an endothelium-dependent manner in obese rats.     

Endothelium-dependent vasodilation of cerebral arteries is altered with simulated microgravity through nitric oxide synthase and EDHF mechanisms.

Cephalic elevations in arterial pressure associated with microgravity and prolonged bed rest alter cerebrovascular autoregulation in humans. Using the head-down tail-suspended (HDT) rat to chronically induce headward fluid shifts and elevate cerebral artery pressure, previous work has likewise shown cerebral perfusion to be diminished. The purpose of this study was to test the hypothesis that 2 wk of HDT reduces cerebral artery vasodilation. To test this hypothesis, dose-response relations for endothelium-dependent (2-methylthioadenosine triphosphate and bradykinin) and endothelium-independent (nitroprusside) vasodilation were determined in vitro in middle cerebral arteries (MCAs) from HDT and control rats. All in vitro measurements were done in the presence and absence of the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (10(-5) M) and cyclooxygenase inhibitor indomethacin (10(-5) M). MCA caveolin-1 protein content was measured by immunoblot analysis. Endothelium-dependent vasodilation to 2-methylthioadenosine triphosphate and bradykinin were both lower in MCAs from HDT rats. These lower vasodilator responses were abolished with N(G)-nitro-L-arginine methyl ester but were unaffected by indomethacin. In addition, HDT was associated with lower levels of MCA caveolin-1 protein. Endothelium-independent vasodilation was not altered by HDT. These results indicate that chronic cephalic fluid shifts diminish endothelium-dependent vasodilation through alterations in the endothelial nitric oxide synthase signaling mechanism. Such decrements in endothelium-dependent vasodilation of cerebral arteries could contribute to the elevations in cerebral vascular resistance and reductions in cerebral perfusion that occur after conditions of simulated microgravity in HDT rats.     

Mechanisms of endothelial dysfunction in resistance arteries from patients with end-stage renal disease

The study focuses on the mechanisms of endothelial dysfunction in the uremic milieu. Subcutaneous resistance arteries from 35 end-stage renal disease (ESRD) patients and 28 matched controls were studied ex-vivo. Basal and receptor-dependent effects of endothelium-derived factors, expression of endothelial NO synthase (eNOS), prerequisites for myoendothelial gap junctions (MEGJ), and associations between endothelium-dependent responses and plasma levels of endothelial dysfunction markers were assessed. The contribution of endothelium-derived hyperpolarizing factor (EDHF) to endothelium-dependent relaxation was impaired in uremic arteries after stimulation with bradykinin, but not acetylcholine, reflecting the agonist-specific differences. Diminished vasodilator influences of the endothelium on basal tone and enhanced plasma levels of asymmetrical dimethyl L-arginine (ADMA) suggest impairment in NO-mediated regulation of uremic arteries. eNOS expression and contribution of MEGJs to EDHF type responses were unaltered. Plasma levels of ADMA were negatively associated with endothelium-dependent responses in uremic arteries. Preserved responses of smooth muscle to pinacidil and NO-donor indicate alterations within the endothelium and tolerance of vasodilator mechanisms to the uremic retention products at the level of smooth muscle. We conclude that both EDHF and NO pathways that control resistance artery tone are impaired in the uremic milieu. For the first time, we validate the alterations in EDHF type responses linked to kinin receptors in ESRD patients. The association between plasma ADMA concentrations and endothelial function in uremic resistance vasculature may have diagnostic and future therapeutic implications.     

Decreased endothelial nitric-oxide synthase (eNOS) activity resulting from abnormal interaction between eNOS and its regulatory proteins in hypoxia-induced pulmonary hypertension

In the pulmonary artery isolated from 1-week hypoxia-induced pulmonary hypertensive rats, endothelial NO production stimulated by carbachol was decreased significantly in in situ visualization using diaminofluorescein-2 diacetate and also in cGMP content. This change was followed by the decrease in carbachol-induced endothelium-dependent relaxation. Protein expression of endothelial NO synthase (eNOS) and its regulatory proteins, caveolin-1 and heat shock protein 90, did not change in the hypoxic pulmonary artery, indicating that chronic hypoxia impairs eNOS activity at posttranslational level. In the hypoxic pulmonary artery, the increase in intracellular Ca(2+) level stimulated by carbachol but not by ionomycin was reduced. We next focused on changes in Ca(2+) sensitivity of the eNOS activation system. A morphological study revealed atrophy of endothelial cells and a peripheral condensation of eNOS in hypoxic endothelial cells preserving co-localization between eNOS and Golgi or plasma membranes. However, eNOS was tightly coupled with caveolin-1, and was dissociated from heat shock protein 90 or calmodulin in the hypoxic pulmonary artery in either the presence or absence of carbachol. Furthermore, eNOS Ser(1177) phosphorylation in both conditions significantly decreased without affecting Akt phosphorylation in the hypoxic artery. In conclusion, chronic hypoxia impairs endothelial Ca(2+) metabolism and normal coupling between eNOS and caveolin-1 resulted in eNOS inactivity.     

Increased pulmonary vascular resistance and defective pulmonary artery filling in caveolin-1-/- mice

Caveolin-1, the structural and signaling protein of caveolae, is an important negative regulator of endothelial nitric oxide synthase (eNOS). We observed that mice lacking caveolin-1 (Cav1(-/-)) had twofold increased plasma NO levels but developed pulmonary hypertension. We measured pulmonary vascular resistance (PVR) and assessed alterations in small pulmonary arteries to determine the basis of the hypertension. PVR was 46% greater in Cav1(-/-) mice than wild-type (WT), and increased PVR in Cav1(-/-) mice was attributed to precapillary sites. Treatment with NG-nitro-l-arginine methyl ester (l-NAME) to inhibit NOS activity raised PVR by 42% in WT but 82% in Cav1(-/-) mice, indicating greater NO-mediated pulmonary vasodilation in Cav1(-/-) mice compared with WT. Pulmonary vasculature of Cav1(-/-) mice was also less reactive to the vasoconstrictor thromboxane A2 mimetic (U-46619) compared with WT. We observed redistribution of type I collagen and expression of smooth muscle alpha-actin in lung parenchyma of Cav1(-/-) mice compared with WT suggestive of vascular remodeling. Fluorescent agarose casting also showed markedly decreased density of pulmonary arteries and artery filling defects in Cav1(-/-) mice. Scanning electron microscopy showed severely distorted and tortuous pulmonary precapillary vessels. Thus caveolin-1 null mice have elevated PVR that is attributed to remodeling of pulmonary precapillary vessels. The elevated basal plasma NO level in Cav1(-/-) mice compensates partly for the vascular structural abnormalities by promoting pulmonary vasodilation.     

Aging induces muscle-specific impairment of endothelium-dependent dilation in skeletal muscle feed arteries.

We tested the hypothesis that aging decreases endothelium-dependent vasodilation in feed arteries perfusing rat skeletal muscle. In addition, we tested the hypothesis that attenuated vasodilator responses are associated with decreased endothelial nitric oxide synthase (eNOS) and superoxide dismutase-1 (SOD-1) expression. Soleus feed arteries (SFA) and gastrocnemius feed arteries (GFA) were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats. Feed arteries from the right hindlimb were cannulated with two glass micropipettes for examination of endothelium-dependent [acetylcholine (ACh)] and endothelium-independent [adenosine (Ado) or sodium nitroprusside (SNP)] vasodilator function. Feed arteries from the left hindlimb were frozen and used to assess eNOS and SOD-1 protein and mRNA expression. In SFA, endothelium-dependent dilation to ACh was reduced in old rats (0.9 +/- 0.04 vs. 0.8 +/- 0.03), whereas dilator responses to Ado and SNP were similar in SFA of young and old rats. In GFA, vasodilator responses to ACh, Ado, and SNP were not altered by age. eNOS and SOD-1 protein expression declined with age in SFA (-71 and -54%, respectively) but not in GFA. eNOS and SOD-1 mRNA expression were not altered by age in SFA or GFA. Collectively, these data indicate aging induces muscle-specific impairment of endothelium-dependent vascular function in SFA.     

Endothelium-dependent vasorelaxation in inhibited by in vivo depletion of vascular thiol levels: role of endothelial nitric oxide synthase.

Thiols like glutathione may serve as reducing cofactors in the production of nitric oxide (NO) and protect NO from inactivation by radical oxygen species. Depletion of thiol compounds reduces NO-mediated vascular effects in vitro and in vivo. The mechanisms underlying these actions are not clear, but may involve decreased synthesis of NO and/or increased degradation of NO. This study investigates the effect of glutathione depletion on the response to NO-mediated vasodilation induced by acetylcholine (Ach, 10 micrograms/kg), endothelial NO synthase (eNOS) activity and potential markers of vascular superoxide anion (O2.-) production in conscious chronically catheterized rats. Thiol depletion induced by buthionine sulfoximine (BSO, 1 g i.p. within 24 h) decreased the hypotensive effect of Ach by 30% (MAP reduction before BSO 27 +/- 3 mmHg, 19 +/- 3 mmHg after BSO, (mean +/- SEM), p < .05, n = 8). The impaired effect of Ach was associated with a significant reduction in eNOS activity (control: 7.7 +/- 0.8, BSO: 3.9 +/- 0.4 pmol/min/mg protein (p < .05), n = 6). In contrast, neither NADH/NADPH driven membrane-associated oxidases nor lucigenin reductase activity were significantly (p < .05) affected by BSO (BSO: 4415 +/- 123, control: 4105 +/- 455 counts/mg; n = 6) in rat aorta. It is concluded that in vivo thiol depletion results in endothelial dysfunction and a reduced receptor-mediated vascular relaxation. This effect is caused by reduced endothelial NO formation.     

Impaired insulin-induced vasodilation in small coronary arteries of Zucker obese rats is mediated by reactive oxygen species

Insulin resistance (IR) and associated hyperinsulinemia are major risk factors for coronary artery disease. Mechanisms linking hyperinsulinemia to coronary vascular dysfunction in IR are unclear. We evaluated insulin-induced vasodilation in isolated small coronary arteries (SCA; approximately 225 microm) of Zucker obese (ZO) and control Zucker lean (ZL) rats. Vascular responses to insulin (0.1-100 ng/ml), ACh (10(-9)-10(-5) mol/l), and sodium nitroprusside (10(-8)-10(-4) mol/l) were assessed in SCA by measurement of intraluminal diameter using videomicroscopy. Insulin-induced dilation was decreased in ZO compared with ZL rats, whereas ACh and sodium nitroprusside elicited similar vasodilations. Pretreatment of arteries with SOD (200 U/ml), a scavenger of reactive oxygen species (ROS), restored the vasorelaxation response to insulin in ZO arteries, whereas ZL arteries were unaffected. Pretreatment of SCA with N-nitro-L-arginine methyl ester (100 micromol/l), an inhibitor of endothelial nitric oxide (NO) synthase (eNOS), elicited a vasoconstrictor response to insulin that was greater in ZO than in ZL rats. This vasoconstrictor response was reversed to vasodilation in ZO and ZL rats by cotreatment of the SCA with SOD or apocynin (10 micromol/l), a specific inhibitor of vascular NADPH oxidase. Lucigenin-enhanced chemiluminescence showed increased basal ROS levels as well as insulin (330 ng/ml)-stimulated production of ROS in ZO arteries that was sensitive to inhibition by apocynin. Western blot analysis revealed increased eNOS expression in ZO rats, whereas Mn SOD and Cu,Zn SOD expression were similar to ZL rats. Thus IR in ZO rats leads to decreased insulin-induced vasodilation, probably as a result of increased production of ROS by vascular NADPH oxidase, leading to decreased NO bioavailability, despite a compensatory increase in eNOS expression.     

Stimulated HSP90 binding to eNOS and activation of the PI3-Akt pathway contribute to globular adiponectin-induced NO production: vasorelaxation in response to globular adiponectin

The present study examined potential interactions between endothelial NO synthase (eNOS), heat shock protein (HSP)90, and Akt in vascular endothelial cells stimulated with globular adiponectin to produce nitric oxide (NO). Globular adiponectin-induced eNOS phosphorylation was accompanied by eNOS-HSP90-Akt complex formation, resulting in a dose-dependent increase in NO release. Globular adiponectin stimulated binding of HSP90 to eNOS, and inhibition of HSP90 significantly suppressed globular adiponectin-stimulated NO release. Globular adiponectin also caused Akt phosphorylation, and inhibition of PI3 kinase significantly suppressed globular adiponectin-stimulated NO release. This study also examined whether globular adiponectin really induces endothelial-dependent vasodilation using rings from rat thoracic aorta. It was observed that globular adiponectin caused dose-dependent vasorelaxation in the aorta. These results indicate that stimulated HSP90 binding to eNOS and activation of the PI3-Akt pathway contribute to globular adiponectin-induced eNOS phosphorylation and NO production, and to endothelium-dependent vasorelaxation.     

Chronic high blood flow potentiates shear stress-induced release of NO in arteries of aged rats

Aging impairs shear-stress-dependent dilation of arteries via increased superoxide production, decreased SOD activity, and decreased activation of endothelial nitric oxide (NO) synthase (eNOS). In the present study, we investigated whether chronic increases in shear stress, elicited by increases in blood flow, would improve vascular endothelial function of aged rats. To this end, second-order mesenteric arteries of young (6 mo) and aged (24 mo) male Fischer-344 rats were selectively ligated for 3 wk to elevate blood flow in a first-order artery [high blood flow (HF)]. An in vitro study was then conducted on first-order arteries with HF and normal blood flow (NF) to assess shear stress (1, 10, and 20 dyn/cm(2))-induced release of NO into the perfusate. In HF arteries of both age groups, shear stress-induced NO production increased significantly. In 24-mo-old rats, the reduced shear stress-induced NO production in NF arteries was normalized by HF to a level similar to that in NF arteries of 6-mo-old rats. The increased NO production in HF arteries of 24-mo-old rats was associated with increased shear stress-induced dilation, expression of eNOS protein, and shear stress-induced eNOS phosphorylation. Wortmannin, a phosphatidylinositol 3-kinase inhibitor, reduced shear stress-induced eNOS phosphorylation and vasodilation. Superoxide production decreased significantly in HF compared with NF arteries in 24-mo-old rats. The decreased superoxide production was associated with significant increases in CuZn-SOD and extracellular SOD protein expressions and total SOD activity. These results suggest that stimulation with chronic HF restores shear-stress-induced activation of eNOS and antioxidant ability in aged arteries.     

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.     

TRPV4 is involved in irisin-induced endothelium-dependent vasodilation

Irisin, an exercise-induced myokine, induces conversion of white into brown adipocytes, promoting mitochondrial biogenesis and energy expenditure. Irisin has a vascular protective effect on endothelial function in animals, including humans. Defects in irisin signaling pathways result in endothelial dysfunction in obesity and diabetes. However, the mechanisms underlying the effects of irisin on endothelial function have not been elucidated. Transient receptor potential vanilloid subtype 4 (TRPV4) channels are one of the most important Ca²⁺-permeable cation channels in vascular endothelial cells. In this study, we hypothesized that irisin may induce endothelium-dependent vasodilation by activating Ca²⁺ influx into endothelial cells via TRPV4 channels. In primary cultured rat mesenteric artery endothelial cells, irisin caused an increase in [Ca²⁺]_i due to extracellular Ca²⁺ influx rather than release from Ca²⁺ stores. Moreover, irisin-induced increases in [Ca²⁺]_i were completely abolished by a TRPV4 inhibitor. In addition, irisin induced endothelium-dependent vasodilation of rat mesenteric arteries. However, irisin had no effect on endothelium-independent vasodilation. Furthermore, irisin-induced vasodilation was fully abolished in the presence of a TRPV4 inhibitor, indicating the involvement of TRPV4 channels in endothelium-dependent vasodilation. This study provides the first evidence that irisin-induced endothelium-dependent vasodilation is related to the stimulation of extracellular Ca²⁺ influx via TRPV4 channels in rat mesenteric arteries.     

Upregulation of eNOS in pregnant ovine uterine arteries by chronic hypoxia

We tested the hypothesis that chronic high-altitude (3,820 m) hypoxia during pregnancy was associated with the upregulation of endothelial nitric oxide (NO) synthase (eNOS) protein and mRNA in ovine uterine artery endothelium and enhanced endothelium-dependent relaxation. In pregnant sheep, norepinephrine-induced dose-dependent contractions were increased by removal of the endothelium in both control and hypoxic uterine arteries. The increment was significantly higher in hypoxic tissues. The calcium ionophore A23187-induced relaxation of the uterine artery was significantly enhanced in hypoxic compared with control tissues. However, sodium nitroprusside- and 8-bromoguanosine 3',5'-cyclic monophosphate-induced relaxations were not changed. Accordingly, chronic hypoxia significantly increased basal and A23187-induced NO release. Chronic hypoxia increased eNOS protein and mRNA levels in the endothelium from uterine but not femoral or renal arteries. In nonpregnant animals, chronic hypoxia increased eNOS mRNA in uterine artery endothelium but had no effects on eNOS protein, NO release, or endothelium-dependent relaxation. Chronic hypoxia selectively augments pregnancy-associated upregulation of eNOS gene expression and endothelium-dependent relaxation of the uterine artery.     

Phenanthraquinone inhibits eNOS activity and suppresses vasorelaxation

Diesel exhaust particles cause an impairment of endothelium-dependent vasorelaxation and are associated with cardiopulmonary-related diseases and mortality, but the mechanistic details are poorly understood. Since we reported previously that phenanthraquinone, an environmental chemical contained in diesel exhaust particles, suppresses neuronal nitric oxide synthase (nNOS) activity by shunting electrons away from the normal catalytic pathway, it was hypothesized that phenanthraquinone inhibits endothelial NOS (eNOS) activity and affects vascular tone. Therefore, the effects of phenanthraquinone on eNOS activity, endothelium-dependent relaxation, and blood pressure were examined in the present study. Phenanthraquinone inhibited NO formation evaluated by citrulline formed by total membrane fraction of bovine aortic endothelial cells with an IC(50) value of 0.6 microM. A kinetic study revealed that phenanthraquinone is a competitive inhibitor with respect to NADPH and a noncompetitive inhibitor with respect to L-arginine. Endothelium-dependent relaxation of rat aortic rings by ACh was significantly inhibited by phenanthraquinone (5 microM), whereas the endothelium-independent relaxation by nitroglycerin was not. Furthermore, an intraperitoneal injection of phenanthraquinone (0.36 mmol/kg) to rats resulted in an elevation of blood pressure (1.4-fold, P < 0.01); under this condition, plasma levels of stable NO metabolites, nitrite/nitrate, in phenanthraquinone-treated rats was reduced to 68% of control levels. The present findings suggest that phenanthraquinone has a potent inhibitory action on eNOS activity via a similar mechanism reported for nNOS, thereby causing the suppression of NO-mediated vasorelaxation and elevation of blood pressure.     

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.     

Eicosapentaenoic acid (EPA) induces Ca(2+)-independent activation and translocation of endothelial nitric oxide synthase and endothelium-dependent vasorelaxation

Eicosapentaenoic acid (EPA), but not its metabolites (docosapentaenoic acid and docosahexaenoic acid), stimulated nitric oxide (NO) production in endothelial cells in situ and induced endothelium-dependent relaxation of bovine coronary arteries precontracted with U46619. EPA induced a greater production of NO, but a much smaller and more transient elevation of intracellular Ca(2+) concentration ([Ca(2+)]i), than did a Ca(2+) ionophore (ionomycin). EPA stimulated NO production even in endothelial cells in situ loaded with a cytosolic Ca(2+) chelator 1,2-bis-o-aminophenoxythamine-N',N',N'-tetraacetic acid, which abolished the [Ca(2+)]i elevations induced by ATP and EPA. The EPA-induced vasorelaxation was inhibited by N(omega)-nitro-L-arginine methyl ester. Immunostaining analysis of endothelial NO synthase (eNOS) and caveolin-1 in cultured endothelial cells revealed eNOS to be colocalized with caveolin in the cell membrane at a resting state, while EPA stimulated the translocation of eNOS to the cytosol and its dissociation from caveolin, to an extent comparable to that of the eNOS translocation induced by a [Ca(2+)]i-elevating agonist (10 microM bradykinin). Thus, EPA induces Ca(2+)-independent activation and translocation of eNOS and endothelium-dependent vasorelaxation.     

Plasma membrane-associated endothelial nitric oxide synthase and activity in aging rat aortic vascular endothelia markedly decline with age

The mechanisms leading to the age-related loss of endothelial nitric oxide (NO) and NO-dependent vasodilation remain largely unknown. Freshly isolated endothelium from young (6 months) and old (36 months) F344xBrN rats were analyzed for endothelial nitric oxide synthase (eNOS) protein, its subcellular distribution, and association with regulatory proteins. Results show that both vessel ring vasoreactivity and A23187-induced eNOS activity in isolated endothelial cells significantly (p < or = 0.05) declined with age. Levels of cGMP, a reliable marker for NO bioactivity also declined significantly (p < or = 0.01). However, no change in overall eNOS protein was evident. Subcellular fractionation studies revealed an age-related loss in active, plasma membrane-bound eNOS relative to eNOS in the Golgi/cytosol of the endothelium. Plasma membrane-associated eNOS in aged endothelium was also less complexed with the activating proteins Hsp90 and Akt and more associated with to caveolin-1, which inhibits eNOS activity. These results suggest that age-dependent loss of NO may be partly caused by differences in eNOS subcellular distribution and its association with inhibitory proteins.