Chronic Nitric Oxide Inhibition Research Articles

Kaempferol protects against cardiovascular abnormalities induced by nitric oxide deficiency in rats by suppressing the TNF-α pathway

Kaempferol is a natural flavonoid compound that exhibits various pharmacological actions. However, there are few reports regarding the role of kaempferol in cardiovascular abnormalities. This study aimed to assess whether kaempferol could prevent cardiovascular malfunction and hypertrophy provoked by chronic inhibition of nitric oxide (NO) formation in rats. Rats (180–200 g) were treated daily with Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME) (40 mg/kg, in drinking water) for five weeks concomitant with kaempferol (oral administration) at a dose of 20 mg/kg or 40 mg/kg or lisinopril (5 mg/kg). Kaempferol partially prevented the progression of hypertension provoked by NO inhibition (p < 0.05). Left ventricular malfunction and hypertrophy present in hypertensive rats were alleviated by concurrent administration of kaempferol (p < 0.05). Furthermore, L-NAME rats had increased sympathetic nerve-mediated vasoconstriction and decreased acetylcholine-induced vasorelaxation and aortic wall thickening, which were resolved by kaempferol treatment (p < 0.05). Kaempferol restored tissue superoxide formation, malondialdehyde, catalase activity, plasma nitric oxide metabolites, tumor necrosis factor-alpha (TNF-α) and interleukin-6 in L-NAME rats (p < 0.05). Overexpression of tumor necrosis factor receptor 2 (TNFR2), phosphatidylinositol 3-kinases (PI3K), AKT serine/threonine kinase 1 (Akt1) and smad2/3 in heart tissue and upregulation of tumor necrosis factor receptor 1 (TNFR1), phosphorylated nuclear factor-kappaB (p–NF–κB) and transforming growth factor beta 1 (TGF-β1) in vascular tissue were suppressed by kaempferol (p < 0.05). In conclusion, kaempferol exerts antihypertensive, cardioprotective, antioxidant, and anti-inflammatory effects in NO-dependent hypertensive rats. The underlying mechanisms of kaempferol in preventing cardiovascular changes induced by L-NAME were due to the suppression of the TNF-α pathway.

Chronic environmental hypoxia attenuates innate immunity activation and renal injury in two CKD models.

Tissue hypoxia has been pointed out as a major pathogenic factor in chronic kidney disease (CKD). However, epidemiological and experimental evidence inconsistent with this notion has been described. We have previously reported that chronic exposure to low ambient Po2 promoted no renal injury in normal rats and in rats with 5/6 renal ablation (Nx) unexpectedly attenuated renal injury. In the present study, we investigated whether chronic exposure to low ambient Po2 would also be renoprotective in two additional models of CKD: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. In both models, normobaric ambient hypoxia attenuated the development of renal injury and inflammation. In addition, renal hypoxia limited the activation of NF-κB and NOD-like receptor family pyrin domain containing 3 inflammasome cascades as well as oxidative stress and intrarenal infiltration by angiotensin II-positive cells. Renal activation of hypoxia-inducible factor (HIF)-2α, along with other adaptive mechanisms to hypoxia, may have contributed to these renoprotective effects. The present findings may contribute to unravel the pathogenesis of CKD and to the development of innovative strategies to arrest its progression.NEW & NOTEWORTHY Hypoxia is regarded as a major pathogenic factor in chronic kidney disease (CKD). In disagreement with this view, we show here that sustained exposure to low ambient Po2 lessened kidney injury and inflammation in two CKD models: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. Together with our previous findings in the remnant kidney, these observations indicate that local changes elicited by hypoxia may exert renoprotection in CKD, raising the prospect of novel therapeutic strategies for this disease.

Pathogenic role of innate immunity in a model of chronic NO inhibition associated with salt overload.

Nitric oxide inhibition with Nω-nitro-l-arginine methyl ester (l-NAME), along with salt overload, leads to hypertension, albuminuria, glomerulosclerosis, glomerular ischemia, and interstitial fibrosis, characterizing a chronic kidney disease (CKD) model. Previous findings of this laboratory and elsewhere have suggested that activation of at least two pathways of innate immunity, Toll-like receptor 4 (TLR4)/NF-κB and nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 3 (NLRP3) inflammasome/IL-1β, occurs in several experimental models of CKD and that progression of renal injury can be slowed with inhibition of these pathways. In the present study, we investigated whether activation of innate immunity, through either the TLR4/NF-κB or NLRP3/IL-1β pathway, is involved in the pathogenesis of renal injury in chronic nitric oxide inhibition with the salt-overload model. Adult male Munich-Wistar rats that received l-NAME in drinking water with salt overload (HS + N group) were treated with allopurinol (ALLO) as an NLRP3 inhibitor (HS + N + ALLO group) or pyrrolidine dithiocarbamate (PDTC) as an NF-κB inhibitor (HS + N + PDTC group). After 4 wk, HS + N rats developed hypertension, albuminuria, and renal injury along with renal inflammation, oxidative stress, and activation of both the NLRP3/IL-1β and TLR4/NF-κB pathways. ALLO lowered renal uric acid and inhibited the NLRP3 pathway. These effects were associated with amelioration of hypertension, albuminuria, and interstitial inflammation/fibrosis but not glomerular injury. PDTC inhibited the renal NF-κB system and lowered the number of interstitial cells staining positively for NLRP3. PDTC also reduced renal xanthine oxidase activity and uric acid. Overall, PDTC promoted a more efficient anti-inflammatory and nephroprotective effect than ALLO. The NLRP3/IL-1β and TLR4/NF-κB pathways act in parallel to promote renal injury/inflammation and must be simultaneously inhibited for best nephroprotection.

Gender Differences in the Progression of Experimental Chronic Kidney Disease Induced by Chronic Nitric Oxide Inhibition.

Chronic kidney disease (CKD) is considered a public health problem, assuming epidemic proportions worldwide. In this context, the preponderance of CKD prevalence in male over age-matched female patients is of note. In the present study, we investigated the impact of the gender on the development of experimental CKD induced by chronic nitric oxide (NO) inhibition in Wistar male and female rats through the administration of L-NAME. CKD model induced by L-NAME is characterized by systemic vasoconstriction, resulting in severe hypertension, albuminuria, renal ischemia, glomerulosclerosis, interstitial expansion, and macrophage infiltration. After 30 days of CKD induction, male NAME rats exhibited remarkable albuminuria, augmented cortical histological damage, interstitial inflammation, and fibrosis. Age-matched female NAME rats showed significantly lower albuminuria, diminished glomerular ischemia, and glomerulosclerosis, as well as a significant reduction in the expression of α-smooth muscle actin renal interstitial Ang II+ cells. Thus, the present study demonstrated that female rats submitted to the NAME model developed less severe CKD than males. Female renoprotection could be promoted by both the estrogen anti-inflammatory activity and/or by the lack of testosterone, related to renin-angiotensin-aldosterone system hyperactivation and fibrogenesis. However, the influence of sex hormones on the progression of CKD needs to be further investigated.

Chronic NOS inhibition accelerates NAFLD progression in an obese rat model.

The progression in nonalcoholic fatty liver disease (NAFLD) to nonalcoholic steatohepatitis is a serious health concern, but the underlying mechanisms remain unclear. We hypothesized that chronic inhibition of nitric oxide (NO) synthase (NOS) via N(ω)-nitro-L-arginine methyl ester (L-NAME) would intensify liver injury in a rat model of obesity, insulin resistance, and NAFLD. Obese Otsuka Long-Evans Tokushima fatty (OLETF) and lean Long-Evans Tokushima Otsuka (LETO) rats received control or L-NAME (65-70 mg·kg(-1)·day(-1))-containing drinking water for 4 wk. L-NAME treatment significantly (P < 0.05) reduced serum NO metabolites and food intake in both groups. Remarkably, despite no increase in body weight, L-NAME treatment increased hepatic triacylglycerol content (+40%, P < 0.05) vs. control OLETF rats. This increase was associated with impaired (P < 0.05) hepatic mitochondrial state 3 respiration. Interestingly, the opposite effect was found in LETO rats, where L-NAME increased (P < 0.05) hepatic mitochondrial state 3 respiration. In addition, L-NAME induced a shift toward proinflammatory M1 macrophage polarity, as indicated by elevated hepatic CD11c (P < 0.05) and IL-1β (P = 0.07) mRNA in OLETF rats and reduced expression of the anti-inflammatory M2 markers CD163 and CD206 (P < 0.05) in LETO rats. Markers of total macrophage content (CD68 and F4/80) mRNA were unaffected by L-NAME in either group. In conclusion, systemic NOS inhibition in the obese OLETF rats reduced hepatic mitochondrial respiration, increased hepatic triacylglycerol accumulation, and increased hepatic inflammation. These findings suggest an important role for proper NO metabolism in the hepatic adaptation to obesity.

Can Chronic Nitric Oxide Inhibition Improve Liver and Renal Dysfunction in Bile Duct Ligated Rats?

The aims of the present work were to study the effects of chronic NO inhibition on liver cirrhosis and to analyze its relationship with liver and kidney damage markers. Two inhibitors of NO synthesis (inducible NO synthase (iNOS) inhibitor, aminoguanidine (AG), and nonselective NOS inhibitor, L-nitroarginine methyl ester (L-NAME)) were administered for 6 weeks to bile duct ligated (BDL) rats 3 days after surgery. The present study showed that BDL was associated with liver injury and renal impairment. BDL increased liver NO content and myeloperoxidase (MPO) activity. This was corroborated by increased oxidative stress, TNF-α, TGF-1β, and MMP-13 genes overexpression. Although both drugs reduced NO synthesis and TNF-α gene overexpression, only AG improved renal dysfunction and liver damage and reduced liver oxidative stress. However, L-NAME exacerbated liver and renal dysfunction. Both drugs failed to modulate TGF-1β and MMP-13 genes overexpression. In conclusion, inhibition of NO production by constitutive nitric oxide synthase (cNOS) plays a crucial role in liver injury and renal dysfunction while inhibition of iNOS by AG has beneficial effect. TNF-α is not the main cytokine responsible for liver injury in BDL model. Nitric oxide inhibition did not stop the progression of cholestatic liver damage.

Nox1 upregulates the function of vascular T-type calcium channels following chronic nitric oxide deficit.

Cardiovascular disease is characterised by reduced nitric oxide bioavailability resulting from oxidative stress. Our previous studies have shown that nitric oxide deficit per se increases the contribution of T-type calcium channels to vascular tone through increased superoxide from NADPH oxidase (Nox). The aim of the present study was therefore to identify the Nox isoform responsible for modulating T-type channel function, as T-type channels are implicated in several pathophysiological conditions involving oxidative stress. We evaluated T-channel function in skeletal muscle arterioles in vivo, using a novel T-channel blocker, TTA-A2 (3 μmol/L), which demonstrated no cross reactivity with L-type channels. Wild-type and Nox2 knockout (Nox2ko) mice were treated with the nitric oxide synthase inhibitor L-NAME (40 mg/kg/day) for 2 weeks. L-NAME treatment significantly increased systolic blood pressure and the contribution of T-type calcium channels to arteriolar tone in wild-type mice, and this was not prevented by Nox2 deletion. In Nox2ko mice, pharmacological inhibition of Nox1 (10 μmol/L ML171), Nox4 (10 μmol/L VAS2870) and Nox4-derived hydrogen peroxide (500 U/mL catalase) significantly reduced the effect of chronic nitric oxide inhibition on T-type channel function. In contrast, in wild-type mice, ML171 and VAS2870, but not catalase, reduced the contribution of T-type channels to vascular tone, suggesting a role for Nox1 and non-selective actions of VAS2870. We conclude that Nox1, but not Nox2 or Nox4, is responsible for the upregulation of T-type calcium channels elicited by chronic nitric oxide deficit. These data point to an important role for this isoform in increasing T-type channel function during oxidative stress.

Chronic deficit in nitric oxide elicits oxidative stress and augments T-type calcium-channel contribution to vascular tone of rodent arteries and arterioles

As cardiovascular disease is characterized by reduced nitric oxide bioavailability, our aim was to determine the impact of this change on the mechanism underlying vascular tone of pressurized arteries in vitro and in vivo. We used pressurized cerebral and mesenteric arteries in vitro and skeletal muscle arterioles in vivo to study the contribution of L-type (1 µmol/L nifedipine) and T-type (1 µmol/L mibefradil, 3 µmol/L NNC 55-0396) calcium channels to vascular tone, following acute or chronic inhibition of nitric oxide. Acute inhibition with l-NAME (10 µmol/L) significantly increased the T-type, but not the L-type, channel contribution to vascular tone in vitro and in vivo, and altered the smooth muscle expression of the Cav3.1 and Cav3.2 T-type channels. In pressurized mesenteric arteries of Cav3.1ko and Cav3.2ko mice, acutely treated with l-NAME, the contribution of T-type channels relative to L-type channels was significantly reduced, compared with arteries from wild-type mice.Chronic l-NAME treatment (40 mg/kg/day; 14-18 days) increased blood pressure, vascular superoxide, and the contribution of T-type channels to vascular tone in vivo. The latter was reversed by acute scavenging of superoxide with tempol (1 mmol/L), or inhibition of NADPH oxidase with apocynin (500 µmol/L) or DPI (5 µmol/L). We conclude that nitric oxide deficit produces a significant increase in the contribution of Cav3.1 and Cav3.2 T-type calcium channels to vascular tone, by regulating the bioavailability of reactive oxygen species produced by NADPH oxidase. Our data provide evidence for a novel causal link between nitric oxide deficit, oxidative stress, and T-type calcium channel function.

Different Natriuretic Responses in Obese and Lean Rats in Response to Nitric Oxide Reduction

Nitric oxide (NO) is an important regulator of renal sodium transport and participates in the control of natriuresis and diuresis. In obesity, the nitric oxide bioavailability was reportedly reduced, which may contribute to the maintenance of hypertension. The aim of this study was to determine the effect of NO depletion on renal sodium handling in a model of diet-induced obesity hypertension. Obese hypertensive (obesity-prone (OP)) and lean normotensive (obesity-resistant (OR)) Sprague-Dawley rats were treated with 1.2 mg/kg/day N(G)-nitro-L-arginine-methyl ester (L-NAME) for 4 weeks to inhibit NO synthesis. Acute pressure natriuresis and diuresis were measured in response to an increase in perfusion pressure. NHE3 and Na(+), K(+)-ATPase protein expression were measured by Western blot and NHE3 activity was determined as the rate of pH change in brush border membrane vesicles. NHE3 membrane localization was determined by confocal microscopy. L-NAME did not significantly attenuate the natriuretic and diuretic responses to increases in renal perfusion pressure (RPP) in OP rats while inducing a significant reduction in OR rats. Following chronic NO inhibition, NHE3 protein expression and activity and Na(+), K(+)-ATPase protein expression were significantly increased in the OR but not in the OP group. Immunofluorescence studies indicated that the increase in NHE3 activity could be, at least in part, due to NHE3 membrane trafficking. Obese hypertensive rats have a weaker natriuretic response in response to NO inhibition compared to lean rats and the mechanism involves different regulation of the apical sodium exchanger NHE3 expression, activity, and trafficking.

Cytosolic Phospholipase A 2 α Contributes to Blood Pressure Increases and Endothelial Dysfunction Under Chronic NO Inhibition

Nitric oxide (NO) is an important modulator of cardiovascular function. In this study, we examined whether cytosolic phospholipase A2α (cPLA2α), an initial enzyme in the arachidonic acid pathway, is involved in blood pressure (BP) elevation in a murine model of chronic NO inhibition. cPLA2α gene-deficient mice (cPLA2α-/-) and wild-type mice (WT) were administered the NO synthesis inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) for 4 weeks. Before treatment, BP was comparable in both groups; it increased significantly in the WT but not in the cPLA2α-/- after treatment. Bone marrow transplantation experiments showed that cPLA2α in blood cells and plasma eicosanoid concentrations were not involved in BP elevation by L-NAME treatment. Activation of cPLA2α and subsequent production of eicosanoids in the aortic endothelium but not in aortic smooth muscle cell, heart, or kidney was observed after L-NAME treatment. Aortic ring assays revealed that endothelial function was comparable in both groups of mice before treatment. L-NAME treatment disturbed endothelial function in WT but not in cPLA2α-/-. These results suggest that endothelial cPLA2α may play a principal role in L-NAME-induced hypertension and may be a target molecule for maintaining endothelial function under NO inhibition.

Adrenomedullin Gene Delivery is Cardio-protective in a Model of Chronic Nitric Oxide Deficiency Combining Pressure Overload, Oxidative Stress and Cardiomyocyte Hypertrophy

Background/aims: Chronic inhibition of nitric oxide (NO) synthesis is associated with hypertension, myocardial ischemia, oxidative stress and hypertrophy; expression of the vasodilator peptide, adrenomedullin (AM) and its receptors is augmented in cardiomyocytes, indicating that the myocardial AM system may be activated in response to pressure loading and ischemic insult to serve a counter-regulatory, cardio-protective role. The study examined the hypothesis that oxidative stress and hypertrophic remodeling in NO-deficient cardiomyocytes are attenuated by adenoviral vector-mediated delivery of the human adrenomedullin (hAM) gene in vivo. Methods: The NO synthesis inhibitor, N^G-nitro-L-arginine methyl ester (L-NAME, 15mg · kg^-1 · day^-1) was given to rats for 4 weeks following systemic administration via the tail vein of a single injection of either adenovirus harbouring hAM cDNA under the control of the cytomegalovirus promoter-enhancer (Ad.CMV-hAM-4F2), or for comparison, adenovirus alone (Ad.Null) or saline. Cardiomyocytes were subsequently isolated for assessment of the influence of each intervention on parameters of oxidative stress and hypertrophic remodelling. Results: Cardiomyocyte expression of the transgene persisted for ≧4 weeks following systemic administration of adenoviral vector. In L-NAME treated rats, relative to Ad.Null or saline administration, Ad.CMV-hAM-4F2 (i) reduced augmented cardiomyocyte membrane protein oxidation and mRNA expression of pro-oxidant (p22phox) and anti-oxidant (SOD-3, GPx) genes; (ii) attenuated increased cardiomyocyte width and mRNA expression of hypertrophic (sk-α-actin) and cardio-endocrine (ANP) genes; (iii) did not attenuate hypertension. Conclusions: Adenoviral vector mediated delivery of hAM resulted in attenuation of myocardial oxidative stress and hypertrophic remodelling in the absence of blood pressure reduction in this model of chronic NO-deficiency. These findings are consistent with a direct cardio-protective action in the myocardium of locally-derived hAM which is not dependant on NO generation.

Effect of orchiectomy on renal function in control and diabetic rats with chronic inhibition of nitric oxide

1. Male gender is associated with higher blood pressure (BP) and more rapid loss of renal function in a spectrum of clinical and experimental renal diseases, including diabetic nephropathy. Consequently, modulation of testosterone levels could exert beneficial effects in the diabetic kidney. 2. The aim of the present study was to determine whether testosterone deficiency (orchiectomy) could influence BP and renal function in streptozotocin-diabetic rats, with or without accelerated endothelial dysfunction achieved by chronic inhibition of nitric oxide (NO) synthesis using N(G)-nitro-L-arginine methyl ester (l-NAME; 40-100 mg/L in the drinking water for 2 weeks), as well as in age-matched non-diabetic rats subjected to the same interventions. 3. Orchiectomy did not affect L-NAME-induced increases in BP in non-diabetic or diabetic rats. In non-diabetic rats, orchiectomy prevented L-NAME-induced increases in proteinuria. These effects on proteinuria were not observed in diabetic rats. In non-diabetic rats, orchiectomy had no effect on renal haemodynamics in animals receiving vehicle and did not affect L-NAME-induced changes in renal haemodynamics, characterized by reductions in renal plasma flow (RPF) and higher filtration fractions (FF). In intact diabetic rats, L-NAME treatment resulted in lower RPF. This difference was not observed in diabetic rats subjected to orchiectomy, although L-NAME-treated diabetic orchiectomized rats had lower RPF and higher FF compared with vehicle-treated intact diabetic rats. 4. In conclusion, we report modest beneficial effects of orchiectomy on proteinuria in normal, but not in diabetic, rats with inhibition of NO production. This suggests that testosterone reduction does not attenuate the deleterious impact of the diabetic metabolic milieu in the kidney.

Effect of Targeting Mitogen-Activated Protein Kinase on Cardiac Remodeling in Rats

Increasing evidence suggests that the activation of p38 mitogen-activated protein kinase (p38MAPK) plays a role in cardiac remodeling. Targeting p38MAPK using drugs reported to interfere with its phosphorylation, namely statins and all-trans retinoic acid (atRA), might play a role in ameliorating this remodeling. Cardiac remodeling was induced in male albino rats by chronic inhibition of nitric oxide (NO) synthesis by N-nitro L-arginine methyl ester (L-NAME). Daily oral administration of L-NAME for 4 weeks resulted in the elevation of mean arterial blood pressure (MABP) together with cardiac remodeling evidenced by an increase in left ventricular-body weight ratio together with an increase in cardiac hydroxyproline concentration and a decrease in left ventricular papillary muscle-developed tension. An elevation in cardiac phosphorylated p38MAPK concentration, tumor necrosis factor alpha concentration and in cardiac caspase 3 activity was also observed. Administration of either rosuvastatin or all-trans retinoic acid (atRA), starting 4 weeks after L-NAME administration, ameliorated remodeling and improved all studied parameters. Targeting MAPK might represent a useful therapeutic avenue to ameliorate cardiac remodeling and support the notion that atRA and statins are potential candidates for the prevention and therapy of cardiac remodeling.

Counter-regulation by atorvastatin of gene modulations induced by L-NAME hypertension is associated with vascular protection

Statins, 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, protect against deleterious effects of chronic nitric oxide inhibition. We aimed at determining the genes and pathways involved in the protective effect of statin treatment during hypertension. Chronic inhibition of nitric oxide synthesis by Nω-nitro- l-arginine methyl ester (L-NAME) induced accelerated hypertension which was slightly reduced by cotreatment with atorvastatin (100 mg/kg/day). Gene expression profile of aortic media was strongly modified by atorvastatin cotreatment which prevented modulation of many genes regulated by L-NAME administration (described in Dupuis, M., Soubrier, F., Brocheriou, I., Raoux, S., Haloui, M., Louedec, L., Michel, J.B., Nadaud, S., 2004. Profiling of aortic smooth muscle cell gene expression in response to chronic inhibition of nitric oxide synthase in rats. Circulation 110, 867–873). The functional classification of these genes highlighted several major biological pathways modulated in aortic media by atorvastatin: effectors involved in smooth muscle tone; extracellular matrix; intracellular mediators of cell proliferation. Moreover, atorvastatin partially prevented arterial wall thickening, TGF-β pathway activation, MCP-1 induction and smooth muscle cell proliferation induced by L-NAME treatment although blood pressure was only slightly reduced, suggesting mechanisms independent of blood pressure levels. The induction of PPARalpha mRNA expression by atorvastatin in L-NAME treated rats also suggests that this pathway could participate in the protective effect. In conclusion, our data show that atorvastatin specifically antagonizes a set of genes modulated by L-NAME-induced accelerated hypertension.

Effect of Chronic Inhibition of Nitric Oxide on Hypertension, Insulin Resistance, and Cardiovascular Remodeling in Glucose-fed Rats

To determine the contribution of nitric oxide (NO) in cardiovascular remodeling associated to hypertension and insulin resistance, male Sprague-Dawley rats received tap water supplemented or not (control), with 10% D-glucose (G) and/or 50 mg x kg(-1) x d(-1) L-NAME to inhibit NO synthase (G-LN or LN) for 4 weeks. Systolic blood pressure increased by 12%, 26%, and 39% with G, LN, and G-LN treatments, respectively. Hyperinsulinemia and insulin resistance (homeostasis model assessment index) occurred in G-treated rats (P < 0.05) and were further increased in G-LN (P < 0.01). Plasma adrenaline concentrations were markedly increased in all treated groups, especially in G-LN (P < 0.01), whereas noradrenaline was increased in G-treated rats only. Whereas no cardiac hypertrophy or fibrosis was detected, aortic hypertrophy occurred in LN and G-LN rats (P < 0.001) without smooth muscle hyperplasia. Superoxide anion formation was increased in the aorta of all treated groups (P < 0.01) and in the heart of LN (P < 0.05), but reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase activity was not affected. In conclusion, the loss of the wide-range protective effects of NO, the increased vascular oxidative stress, and the sympathoadrenal hyperactivity are among the contributing factors leading to the exacerbation of hypertension and insulin resistance in G-LN. These factors were sufficient to cause vascular but not cardiac hypertrophy.

S31-1 Blockade of Aldosterone Receptors Prevents Atrial Structural and Electrical Remodeling in Rats with Hypertension by Chronic Nitric Oxide Inhibition

S31-1 Blockade of Aldosterone Receptors Prevents Atrial Structural and Electrical Remodeling in Rats with Hypertension by Chronic Nitric Oxide Inhibition

I030 Young spontaneously hypertensive rats (SHR) with chronic inhibition of nitric oxide exhibit similar aortic stiffness to old SHR

The old spontaneously hypertensive rat (SHR) is known to be a good experimental model that is highly analogous to essential hypertension in man but is costly and time consuming. Chronic inhibition of nitric oxide (NO) production in young adult SHR is an experimental model of malignant hypertension and chronic renal disease, very similar to old SHR1. Considering that acute or chronic decreases in NO production in normotensive rats increase arterial stiffness, we aimed to compare the aortic stiffness between SHR/L-NAME and old SHR. Male SHR (18 weeks old) received N-Nitro-L-Arginine Methyl Ester (L-NAME) 6 mg/kg/d in drinking water (SHR/L-NAME) for 2 weeks and were compared to SHR and Wistar Kyoto rats (WKY). Moreover, two groups are composed of 55 weeks aged SHR (Old SHR) and WKY (Old WKY). Under anesthesia, two catheters were introduced in the left common carotid artery and the left femoral artery to measure central and peripheral blood pressure and assess aortic stiffness with pulse wave velocity (PWV= distance between the tips of the two catheters / transit time), β-index (2.11×(PWV2/Diastolic blood pressure)), amplification and pulse pressure (PP). At 20 weeks, although SHR have higher central systolic blood pressure (SBP) than WKY (201±7 mmHg vs. 154±4 mmHg), no significant difference in PWV, PP, amplification and β-index was observed between these two groups. With age, old WKY have higher SBP (181±8 mmHg) and higher PWV (6.7±0.5 m/s) and β-index (0.70±0.08) than young WKY. Old SHR exhibit higher SBP (252±13 mmHg), PWV (9.3±0.7 m/s), PP (71±7 mmHg), β-index (1.08±0.16) than old WKY and young SHR (PWV=6.3±0.2 m/s, PP=39±3 mmHg and β-index=0.50±0.03). Young SHR, after 2 weeks of L-NAME administration, have higher SBP (238±10 mmHg) and aortic stiffness (PWV=8.6±0.6 m/s, PP=54±6 mmHg and β-index=0.89±0.14) than young SHR and possess the aortic stiffness observed in old SHR. In conclusion, our results indicate a close analogy in arterial stiffness between SHR/L-NAME and old SHR. Thus, this experimental model shows similarities to hypertensive humans and appears relevant to test new anti-hypertensive treatments.

Effects of hypertension on vasorelaxation to endocannabinoids in vitro

The hypotensive actions of methanandamide are enhanced in anaesthetised spontaneously hypertensive rats (SHR), which may be due to increased sensory nerve activity. We have now investigated in vitro the role of sensory nerves and other vasorelaxant mechanisms of anandamide in this model of hypertension, and in rats made hypertensive by chronic inhibition of nitric oxide (NO) synthase. Male SHR and Sprague-Dawley rats (given ~ 10 mg/kg/day N G nitro- l-arginine methyl ester (L-NAME) to drink for 4 weeks) were used. Vasorelaxant responses to anandamide and capsaicin were determined in perfused mesenteric arterial beds and thoracic aortic rings. The contributions of sensory nerves, NO, prostanoids, cannabinoid receptors and the endothelium in these responses were investigated. In mesenteric arterial beds from SHR, anandamide was less potent as a vasorelaxant, but in aortae caused greater maximal relaxations compared to controls. The reduced potency in the mesenteric arterial bed was accompanied by impaired NO-dependent relaxation. Pre-treatment with capsaicin prevented the enhancement of vasorelaxation by anandamide in mesenteric arterial beds from rats with L-NAME-induced hypertension. The reduced potency of anandamide in mesenteric arterial beds from SHR was due to reduced NO-dependent vasorelaxation, and provides no evidence for increased sensory nerve activity. The enhanced responses in the SHR aortae were endothelium-dependent. However, in L-NAME-induced hypertension the enhanced vasorelaxation to anandamide in the mesenteric vasculature was due to increased sensory nerve-mediated activity. In conclusion, the alterations in responses to anandamide in hypertension are dependent on the vessels studied and the model of hypertension.

Abstract 5425: Nuclear Shuttling of Sirt1 Is Associated with Caloric Restriction-Induced Cardioprotection

Ischemic tolerance decreases with ageing and the cardioprotective effect of ischemic preconditioning (PC) is impaired in middle-aged animals. We have demonstrated that short-term caloric restriction (CR) improves myocardial ischemic tolerance via the activation of adiponectin-AMPK-mediated signaling. However, it is unknown whether prolonged CR confers cardioprotection in a similar manner. Furthermore, little is known regarding the myocardial expression of sirt1 (which reportedly mediates various aspects of the CR response) with ageing and prolonged CR. Thus, 6-month-old Fischer344 rats were randomly divided into ad libitum (AL) and CR groups. Six months later, isolated perfused hearts were subjected to 25 min of global ischemia followed by 30 min of reperfusion with or without ischemic PC. CR improved the recovery of LV developed pressure (A) and restored the cardioprotective effect of ischemic PC. Serum adiponectin levels increased but myocardial levels of total and phosphorylated AMPK did not change with prolonged CR. Total levels of sirt1 did not change with ageing and CR; however, in the nuclear fraction, CR significantly increased sirt1 (B) and decreased acetyl-histone H3. Eight rats from each group were given L-NAME in the drinking water for 4 weeks before sacrifice. In these hearts, chronic inhibition of nitric oxide (NO) synthase prevented the nuclear shuttling of sirt1 by CR (B) and abrogated CR-induced cardioprotection (A). These results demonstrate that prolonged CR improves myocardial ischemic tolerance and restores ischemic PC in middle-aged rats, and that CR-induced cardioprotection is associated with NO-dependent nuclear shuttling of sirt1.

Vasopressin response and shunting modulation in cirrhotic rats by chronic nitric oxide inhibition

Nitric oxide (NO) plays a significant role in the vascular hyposensitivity to vasoconstrictors in cirrhosis. Chronic NO inhibition improves the portal-systemic collateral responsiveness to arginine(8)-vasopressin (AVP) and ameliorates shunting degree in rats with prehepatic portal hypertension. This study investigated whether long-term NO inhibition by N(G)-nitro-L-arginine methyl ester (L-NAME) enhances the collateral vascular responsiveness to AVP and alleviates the severity of shunting in cirrhotic rats. Bile duct-ligated (BDL) rats received L-NAME in tap water (25 mg/kg/day) or tap water only (control) for 1 week from the 36th day after BDL. On the 43rd day, the mean arterial pressure and portal pressure were measured. With an in situ perfusion model of portal-systemic collateral vasculature, different concentrations of AVP (10(-10)-10(-7) mol/L) with a constant flow rate (12 mL/min) were applied to assess the perfusion pressure changes of collaterals. In addition, flow pressure curves were obtained with different flow rates (6-18 mL/min): the slopes serve as indices of collateral vascular resistance and the higher resistance indicates less collateral. The mean arterial pressure was significantly increased after L-NAME treatment (P < 0.05), whereas the heart rate and portal pressure were not significantly modified. As compared with the controls, the L-NAME group exerted significantly higher perfusion pressure changes to AVP at the concentrations of 3 x 10(-8), 10(-7) and 3 x 10(-7) mol/L. In addition, chronic L-NAME administration induced collateral vascular resistance elevation, suggesting the attenuation of portal-systemic shunting. Chronic NO inhibition improves the collateral vascular responsiveness to AVP and ameliorates portal-systemic shunting in BDL cirrhotic rats.