Failure of L-nitroarginine to inhibit the activity of aortic inducible nitric oxide synthase

Nitric oxide synthase inhibition abolishes exercise-mediated protection against isoproterenol-induced cardiac hypertrophy in female mice

OBJECTIVE

Exercise training (ET) provides a cardioprotective effect against pathological cardiac hypertrophy. Nitric oxide (NO) plays an important role in modulating cardiac hypertrophy. However, few studies explore the relationship between NO signaling and the inhibitory effect of ET on pathological cardiac remodeling.

METHODS

In this study, we evaluated ET effects on isoproterenol (ISO)-induced cardiac hypertrophy in female mice. Moreover, L-NAME (Nω-nitro-L-arginine methyl ester), a nonselective NO synthase (NOS) inhibitor, was used to assess the involvement of NO signaling in cardiac hypertrophy. Morphological and echocardiographic variables were assessed. Cardiac hypertrophy-related gene expression was detected by real-time PCR and the protein levels of NOS signaling molecules were determined by Western blot.

RESULTS

L-NAME treatment prevented the beneficial effects of ET against the increase in heart weight (HW)/body weight (BW), HW/tibia length and lung weight/BW and echocardiographic variables following ISO injection. Also, L-NAME co-administration reversed ET-induced inhibition of myocardial fibrosis and fetal gene reactivation in ISO-treated mice. Furthermore, L-NAME treatment prevented ET-mediated up-regulation of phosphorylated endothelial NOS and plasma NO in ISO-treated mice.

CONCLUSIONS

Our findings demonstrate that L-NAME treatment could abolish ET-induced cardioprotection against pathological cardiac hypertrophy and that NOS modulation may be involved in the antihypertrophic effects induced by ET.

L-NAME treatment enhances exercise-induced content of myocardial heat shock protein 72 (Hsp72) in rats

BACKGROUND/AIM

Nitric oxide (NO) modulates the expression of the chaperone Hsp72 in the heart, and exercise stimulates both NO production and myocardial Hsp72 expression. The main purpose of the study was to investigate whether NO interferes with an exercise-induced myocardial Hsp72 expression.

METHODS

Male Wistar rats (70-100 days) were divided into control (C, n=12), L-NAME-treated (L, n=12), exercise (E, n=13) and exercise plus L-NAME-treated (EL, n=20) groups. L-NAME was given in drinking water (700 mg·L(-1)) and the exercise was performed on a treadmill (15-25 m·min(-1), 40-60 min.day(-1)) for seven days. Left ventricle (LV) protein Hsp content, NOS and phosphorylated-NOS (p-NOS) isoforms were measured using Western blotting. The activity of NOS was assayed in LV homogenates by the conversion of [(3)H]L-arginine to [(3)H]L-citrulline.

RESULTS

Hsp72 content was increased significantly (223%; p < 0.05) in the E group compared to the C group, but exercise alone did not alter the NOS content, p-NOS isoforms or NOS activity. Contrary to our expectation, L-NAME enhanced (p < 0.05) the exercise-induced Hsp72 content (EL vs. C, L and E groups = 1019%, 548% and 457%, respectively). Although the EL group had increased stimulatory p-eNOS(Ser1177) (over 200%) and decreased inhibitory p-nNOS(Ser852) (ñ50%) compared to both the E and L groups (p < 0.05), NOS activity was similar in all groups.

CONCLUSIONS

Our results suggest that exercise-induced cardiac Hsp72 expression does not depend on NO. Conversely, the in vivo L-NAME treatment enhances exercise-induced Hsp72 production. This effect may be due to an increase in cardiac stress.

The estrogen effects on endothelial repair and mitogen-activated protein kinase activation are abolished in endothelial nitric-oxide (NO) synthase knockout mice, but not by NO synthase inhibition by N-nitro-L-arginine methyl ester

We have previously shown that estrogen exerts a vasoprotective effect by accelerating reendothelialization after perivascular artery injury through activation of the estrogen receptor alpha. Because 17beta-estradiol (E2) is known to increase the bioavailability of nitric oxide, in this study, we used the same perivascular model to characterize the role of the endothelial nitric oxide synthase (eNOS) pathway in reendothelialization. Surprisingly, we found that the stimulatory effect of E2 on reendothelialization was not altered following pharmacological inhibition of nitric-oxide synthase enzymatic activity by N-nitro-L-arginine methyl ester, whereas it was abolished in eNOS-deficient (eNOS-/-) mice. This discrepancy between eNOS gene inactivation and the pharmacological inhibition of eNOS was confirmed in a classical model of endovascular injury. When assessing the involvement of eNOS in short-term membrane-associated signaling events induced by E2, we found that E2 stimulated phosphorylation of extracellular signal-regulated kinase 1/2 in isolated perfused carotid arteries from wild-type mice in the absence or presence of N-nitro-l-arginine methyl ester, whereas this stimulation was abolished in carotid arteries from eNOS-/- mice. Similar results were obtained in primary cultures of mouse aortic endothelial cells. These data reveal an original and unexpected role of eNOS, in which its presence but not its enzymatic activity appears to be a determinant for estrogen signaling in the endothelium. The consequences of this novel function of eNOS with respect to vascular diseases should be explored.

In silico analysis of arginine catabolism as a source of nitric oxide or polyamines in endothelial cells

We use a modeling and simulation approach to carry out an in silico analysis of the metabolic pathways involving arginine as a precursor of nitric oxide or polyamines in aorta endothelial cells. Our model predicts conditions of physiological steady state, as well as the response of the system to changes in the control parameter, external arginine concentration. Metabolic flux control analysis allowed us to predict the values of flux control coefficients for all the transporters and enzymes included in the model. This analysis fulfills the flux control coefficient summation theorem and shows that both the low affinity transporter and arginase share the control of the fluxes through these metabolic pathways.

Intrarenal detection of nitric oxide using electron spin resonance spectroscopy in hypertensive lipopolysaccharide-treated rats

The inhibition of nitric oxide (NO) synthesis by chronic administration of NG-nitro-l-arginine methyl ester (l-NAME) in rats is responsible for systemic hypertension. However, the mechanisms involved in this hypertension remain unclear. The effects of chronic l-NAME on kidney and blood NO production were studied in rats in a state of endotoxic shock due to lipopolysaccharide (LPS). A nitric oxide spin trapping technique using electron spin resonance (ESR) spectroscopy has been used to identify and measure the production of NO in the kidney. This method is based on the trapping of nitric oxide by a metal-chelator complex consisting of N-methyl-d-glucamine dithiocarbamate (MGD) and reduced iron (Fe2+) forming a water-soluble NO-FeMGD complex detected by ESR. After LPS injection (14 mg/kg, IV, 6 h before the sacrifice) to rats pretreated with l-NAME (10 mg/kg/d over 14 days), the NO-FeMGD complex was evaluated in the kidney (arbitrary units [AU]/g of kidney) and the density of polynuclear neutrophils was counted by light microscopy. Chronic inhibition of NO synthase by l-NAME, a nonspecific inhibitor, was responsible for a decrease of the NO-FeMGD complex levels in the kidney (24.9 +/- 1.6 AU versus 13.8 +/- 1.3 AU). LPS administration was responsible for a large increase in both NO-FeMGD complex and neutrophil levels in the kidney of normotensive rats (332.6 +/- 12.8 AU versus 24.9 +/- 1.6 AU for NO-FeMGD complex and 1.36 +/- 0.41 versus 0.11 +/- 0.03 for neutrophils). Conversely, LPS administration in hypertensive, l-NAME-pretreated rats was linked to a smaller increase in the NO-FeMGD complex (85.1 +/- 7.9 AU versus 332.6 +/- 12.8 AU) and a larger increase in glomerular neutrophils (2.48 +/- 0.36 versus 1.36 +/- 0.41) compared with normotensive rats. These results are in agreement with a direct implication of NO during LPS-and l-NAME-induced kidney injuries.