L-arginine Nitric Oxide Pathway Research Articles

Effects of L-arginine on impaired blood fluidity after high-intensity exercise: An in vitro evaluation.

Exercise-induced impairment of blood fluidity is considered to be associated with thrombosis development. However, the effects of L-arginine on blood fluidity after exercise remain unclear. We investigated the mechanisms of impaired blood fluidity after high-intensity exercise, and examined whether L-arginine improves exercise-induced blood fluidity impairment in vitro. Ten healthy male participants performed 15 minutes of ergometer exercise at 70% of their peak oxygen uptake levels. Blood samples were obtained before and after exercise. L-arginine and NG-monomethyl-L-arginine acetate (L-NMMA)-a nitric oxide (NO) synthase inhibitor-were added to the post-exercise blood samples. Using Kikuchi's microchannel method, we measured the blood passage time, percentage of obstructed microchannels, and the number of adherent white blood cells (WBCs) on the microchannel terrace. Exercise increased the hematocrit levels. The blood passage times, percentage of obstructed microchannels, and the number of adherent WBCs on the microchannel terrace increased after exercise; however, they decreased in a dose-dependent manner after the addition of L-arginine. L-NMMA inhibited the L-arginine-induced decrease in blood passage time. High-intensity exercise impairs blood fluidity by inducing hemoconcentration along with increasing platelet aggregation and WBC adhesion. The L-arginine-NO pathway improves blood fluidity impairment after high-intensity exercise in vitro.

Arginine and Arginine/ADMA Ratio Predict 90-Day Mortality in Patients with Out-of-Hospital Cardiac Arrest-Results from the Prospective, Observational COMMUNICATE Trial.

(1) Background: In patients with shock, the L-arginine nitric oxide pathway is activated, causing an elevation of nitric oxide, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels. Whether these metabolites provide prognostic information in patients after out-of-hospital cardiac arrest (OHCA) remains unclear. (2) Methods: We prospectively included OHCA patients, recorded clinical parameters and measured plasma ADMA, SDMA and Arginine levels by liquid chromatography tandem mass spectrometry (LC-MS). The primary endpoint was 90-day mortality. (3) Results: Of 263 patients, 130 (49.4%) died within 90 days after OHCA. Compared to survivors, non-survivors had significantly higher levels of ADMA and lower Arginine and Arginine/ADMA ratios in univariable regression analyses. Arginine levels and Arginine/ADMA ratio were significantly associated with 90-day mortality (OR 0.51 (95%CI 0.34 to 0.76), p < 0.01 and OR 0.40 (95%CI 0.26 to 0.61), p < 0.001, respectively). These associations remained significant in several multivariable models. Arginine/ADMA ratio had the highest predictive value with an area under the curve (AUC) of 0.67 for 90-day mortality. Results for secondary outcomes were similar with significant associations with in-hospital mortality and neurological outcome. (4) Conclusion: Arginine and Arginine/ADMA ratio were independently associated with 90-day mortality and other adverse outcomes in patients after OHCA. Whether therapeutic modification of the L-arginine-nitric oxide pathway has the potential to improve outcome should be evaluated.

The possible protective effect of L-arginine against 5-fluorouracil-induced nephrotoxicity in male albino rats.

5-fluorouracil (5-FU) is a potent antineoplastic agent used for the treatment of various malignancies. The L-arginine nitric oxide (NO) pathway involved in the pathogenesis of chemotherapy induced kidney damage. This work investigated the beneficial mechanism of L-arginine supplementation in 5-FU induced nephropathy. Eighty male Wistar rats were divided into four equal groups: control group; L-arginine group (378 mg/rat/day for 4 weeks); 5-FU group (189 mg/rat/week for 4 weeks) and L-arginine for 1 week before and 4 weeks concomitant with 5-FU group. At the end of experiment, the kidney functions were assessed and kidneys specimens were processed for paraffin sections and stained with haematoxylin and eosin (H&E), Masson's trichome (MT) and periodic acid-Schiff (PAS) stains. Other sections were processed for immunohistochemical demonstration of caspase-3 and inducible NO synthase (iNOS). Image analyser was used to analyse the results morphometrically and statistically. L-arginine administration to 5-FU treated animals elicited significant reduction in serum urea and creatinine levels, urine volume, urinary protein excretion and kidney/body weight ratio in comparison to fluorouracil treated group. L-arginine improved glomeruloscelerosis, degeneration of convoluted tubules and interstitial fibrosis in 5-FU treated animals. L-arginine attenuated effectively some biochemical and histological changes in 5-FU nephrotoxicity.

Asymmetric Dimethylarginine Predicts Long-Term Outcome in Patients with Acute Exacerbation of Chronic Obstructive Pulmonary Disease.

In chronic obstructive pulmonary disease (COPD), there is an activation of the L-arginine nitric oxide pathway. Pulmonary obstruction causes to elevated nitric oxide (NO) levels, which lead to higher production of the NO-inhibiting metabolites asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). We investigated the association of L-arginine, ADMA, and SDMA with clinical outcomes in a well-defined observational cohort of 150 patients with acute exacerbation of COPD. We measured L-arginine, ADMA, and SDMA by mass spectrometry in patients with pneumonic or non-pneumonic exacerbation of COPD included in a Swiss multicenter trial. We used Cox regression models to investigate the associations between blood marker levels and disease severity as well as all-cause mortality over a follow-up of 6.1years. Six-year all-cause mortality was 54%. Admission levels of ADMA and SDMA (μmolL-1) were increased in 6-year non-survivors compared to survivors' median (0.60 vs. 0.46, p=0.004; and 1.05 vs. 0.85, p=0.012). In a multivariate Cox regression analysis, ADMA was associated with long-term mortality resulting in an age- and comorbidity-adjusted hazard ratio (HR) of 4.55 (95% confidence interval 1.02-20.43, p=0.048). SDMA was only associated in univariate models and no association of L-arginine with outcome was found. ADMA was found to be an independent risk factor for long-term all-cause mortality in patients with acute exacerbation of COPD. Whether therapeutic modification of the L-arginine-nitric oxide pathway has the potential to improve outcome should be evaluated in future interventional trials.

Involvement of l-arginine-nitric oxide pathway in anxiolytic-like effects of zinc chloride in rats.

Zinc is crucial for normal development of the brain, and Zinc deficiency has been shown to associate with neurological disorders (e.g. anxiety) through interactions with several neurotransmitter systems such as nitric oxide (NO). In this regard, our study aimed to evaluate the possible involvement of l-arginine NO pathway on anxiolytic effects of zinc in adult male rats. Zinc chloride at doses of 2.5 and 10mg/kg (intraperitoneal or ip) or saline (1ml/kg, ip) were injected 30min before the anxiety test. Zinc administrated rats (10mg/kg) were pre-treated with intra-CA1 microinjection of l-arginine in sub-effective dose of 1μg/rat (dorsal hippocampus, vehicle: saline1μl/rat). In addition, zinc chloride and NG-nitro-l-arginine methyl ester (l-NAME) were intraperitoneally co-administrated in sub-effective doses of 2.5mg/kg and 80mg/kg, respectively. The percentage of open arm time (OAT%), percentage of open arm entry (OAE%), as measures of anxiety, and total number of arm entries, as measures of locomotor activity, were recorded. Treatment with zinc (10mg/kg) markedly produced an increase in OAT% and OAE% in the Elevated plus maze test (EPM). A decrease of OAT% and OAE% was shown in groups which received zinc (10mg/kg) and l-arginine (1μg/rat) concomitantly as compared to the control group. Moreover, an increase of OAE% was revealed in the group exposed to Zinc (2.5mg/kg) and l-NAME (80mg/kg) co-administration. Although, Two-way ANOVA showed no significant differences of anxiety indices in rats received drug+zinc chloride in compare to the zinc pretreated with saline group. Anxiolytic- like effect of zinc reversed by nitric oxide precursor l-arginine. Additionally, the synergistic effects of l-NAME and ZnCl2 were shown in the EPM. Thus our findings suggest that at least in part the anxiolytic effects of zinc can be mediated through the nitric oxide system.

Hyperaggregability and impaired nitric oxide production in platelets from postmenopausal women

ObjectiveCardiovascular mortality increases after menopause in women. Nitric oxide is essential for proper platelet function inhibiting its aggregation and maintaining vascular haemostasis. Here, we investigated whether platelet function and intraplatelet l-arginine–nitric oxide pathway are impaired in postmenopausal women. Study designCross-sectional. Main outcomes measuresBlood was collected from 16 premenopausal and 12 postmenopausal women without any additional risk factor for cardiovascular disease. Platelet reactivity was measured by light transmission aggregometry. l-Arginine–nitric oxide pathway was assessed measuring transmembrane l-[3H]-arginine transport, nitric oxide synthase activity by the citrulline assay, and arginase activity by the conversion of l-[14C]arginine to l-[14C]-urea. The activity of antioxidant enzymes was measured by spectrophotometric assays. Protein expression was determined by Western blotting. ResultsPlatelet aggregation was increased in postmenopausal compared to premenopausal women. Postmenopausal women demonstrated reduced plasma levels of l-arginine, a lower nitric oxide synthase activity, similar endothelial and inducible nitric oxide synthase expression, and a compensatory increase in l-arginine transmembrane transport. Arginase expression and activity did not differ between groups. In regard to oxidative stress, no differences between groups were observed NAPDH oxidase subunits expression and protein carbonylation. However, the activity of the antioxidant enzyme superoxide dismutase and catalase protein levels in platelets were higher in postmenopausal women. ConclusionPostmenopausal women present increased platelet reactivity, which may be due to a reduction in intraplatelet nitric oxide synthesis. Platelet hyperaggregability is known to be associated with arterial and venous thromboembolic event; therefore, it may contribute to the heightened risk of cardiovascular adverse events in this population.

Nitric oxide mediates the anticonvulsant effects of thalidomide on pentylenetetrazole-induced clonic seizures in mice

Thalidomide is an old glutamic acid derivative which was initially used as a sedative medication but withdrawn from the market due to the high incidence of teratogenicity. Recently, it has reemerged because of its potential for counteracting number of diseases, including neurodegenerative disorders.Other than the antiemetic and hypnotic aspects, thalidomide exerts some anticonvulsant properties in experimental settings. However, the underlying mechanisms of thalidomide actions are not fully realized yet. Some investigations revealed that thalidomide could elicit immunomodulatory or neuromodulatory properties by affecting different targets, including cytokines (such as TNF α), neurotransmitters, and nitric oxide (NO). In this regard, we used a model of clonic seizure induced by pentylenetetrazole (PTZ) in male NMRI mice to investigate whether the anticonvulsant effect of thalidomide is affected through modulation of the l-arginine–nitric oxide pathway or not.Injection of a single effective dose of thalidomide (10mg/kg, i.p. or higher) significantly increased the seizure threshold (P<0.05). On the one hand, pretreatment with low and per se noneffective dose of l-arginine [NO precursor] (10, 30 and 60mg/kg) prevented the anticonvulsant effect of thalidomide. On the other hand, NOS inhibitors [l-NAME and 7-NI] augmented the anticonvulsant effect of a subeffective dose of thalidomide (1 and 5mg/kg, i.p.) at relatively low doses. Meanwhile, several doses of aminoguanidine [an inducible NOS inhibitor] (20, 50 and 100mg/kg) failed to alter the anticonvulsant effect of thalidomide significantly. In summary, our findings demonstrated that the l-arginine–nitric oxide pathway can be involved in the anticonvulsant properties of thalidomide, and the role of constitutive nNOS is prominent in the reported neuroprotective feature.

Effects of Acute and Chronic Stress on the L-Arginine Nitric Oxide Pathway in Black and White South Africans

This study investigated the impact of stress on effectors of the L-arginine/nitric oxide (NO) system including the endogenous inhibitor asymmetric dimethylarginine (ADMA). Black (n = 168) and white (n = 206) South African teachers were exposed to a mental and a physical stressor for 1 minute, respectively. Serum samples for determination of l-arginine, NO metabolites, ADMA, and symmetric dimethylarginine (SDMA) were obtained at rest and during stress exposure. Perception of task stressfulness was assessed on a 7-point Likert scale, and psychological distress was estimated by the General Health Questionnaire. Black South Africans exhibited higher resting levels of NO metabolites (adjusted mean [standard error of the mean] = 11.3 [1.3] versus 3.9 [1.1] μmol/l, p < .001) but lower circulating ADMA (0.62 [0.02] versus 0.70 [0.02] μmol/l, p = .004) and SDMA (0.41 [0.01] versus 0.53 [0.01] μmol/l, p < .001) than did white South Africans. Ethnicity-by-psychological distress interaction was observed for resting levels of ADMA (p = .002), SDMA (p = .038), and L-arginine (p = .048). Ethnic differences in responses to experimental stress were evident for NO metabolites (blacks versus whites: 5.94 [1.55] versus -0.74 [1.25] μmol/l, p = .004) and SDMA (blacks versus whites: -0.02 [0.01] versus 0.02 [0.01] μmol/l, p = .004). Ethnicity-by-psychological distress interaction for stress responses was found for l-arginine/ADMA ratio (p = .027). The l-arginine/NO system is affected by psychosocial distress with higher susceptibility in black South Africans. This interaction may contribute to the higher cardiovascular disease risk in black South Africans.

Intermedin modulates hypoxic pulmonary vascular remodeling by inhibiting pulmonary artery smooth muscle cell proliferation

BackgroundHypoxic pulmonary arterial hypertension (PAH) is a disabling disease with limited treatment options. Hypoxic pulmonary vascular remodeling is a major cause of hypoxic PAH. Pharmacological agents that can inhibit the remodeling process may have great therapeutic value. ObjectiveTo examine the effect of intermedin (IMD), a new calcitonin gene-related peptide family of peptide, on hypoxic pulmonary vascular remodeling. MethodsRats were exposed to normoxia or hypoxia (∼10% O2), or exposed to hypoxia and treated with IMD, administered by an implanted mini-osmotic pump (6.5 μg/rat/day), for 4 weeks. The effects of IMD infusion on the development of hypoxic PAH and right ventricle (RV) hypertrophy, on pulmonary vascular remodeling, on pulmonary artery smooth muscle cell (PASMC) proliferation and apoptosis, and on the activations of l-arginine nitric oxide (NO) pathway and endoplasmic reticulum stress apoptotic pathway were examined. ResultsRats exposed to hypoxia developed PAH and RV hypertrophy. IMD treatment alleviated PAH and prevented RV hypertrophy. IMD inhibited hypoxic pulmonary vascular remodeling as indicated by reduced wall thickness and increased lumen diameter of pulmonary arterioles, and decreased muscularization of distal pulmonary vasculature in hypoxia-exposed rats. IMD treatment inhibited PASMC proliferation and promoted PASMC apoptosis. IMD treatment increased tissue level of constitutive NO synthase activity and tissue NO content in lungs, and enhanced l-arginine uptake into pulmonary vascular tissues. IMD treatment increased cellular levels of glucose-regulated protein (GRP) 78 and GRP94, two major markers of endoplasmic reticulum (ER) stress, and increased caspase-12 expression, the ER stress-specific caspase, in lungs and cultured PASMCs. ConclusionsThese results demonstrate that IMD treatment attenuates hypoxic pulmonary vascular remodeling, and thereby hypoxic PAH mainly by inhibiting PASMC proliferation. Promotion of PASMC apoptosis may also contribute to the inhibitory effect of IMD. Activations l-arginine–NO pathway and of ER stress-specific apoptosis pathway could be the mechanisms mediating the anti-proliferative and pro-apoptotic effects of IMD.

Inhibition of the l-arginine–nitric oxide pathway mediates the antidepressant effects of ketamine in rats in the forced swimming test

Converging evidence shows that the acute administration of a sub-anaesthetic dose ketamine produces fast-acting and robust antidepressant properties in patients suffering from major depressive disorder. However, the underlying mechanisms have not been fully elucidated. The present study aimed to investigate the role of the l-arginine–nitric oxide pathway in the antidepressant effects of ketamine in rats performing the forced swimming test (FST). Ketamine (10mg/kg) significantly decreased immobility times in the FST and the activities of total nitric oxide synthases (T-NOS), inducible NOS (iNOS), and endothelial NOS (eNOS) in the rat hippocampus. Interestingly, the plasma activities of T-NOS, iNOS, and eNOS increased after administration of ketamine. Furthermore, the activities of neuronal NOS (nNOS) did not change significantly in either the hippocampus or plasma after ketamine administration. The antidepressant effects of ketamine were prevented by pre-treatment with l-arginine (750mg/kg). Pre-treatment with the NOS inhibitor l-NG–nitroarginine methyl ester at a sub-antidepressant dose of 50mg/kg and ketamine at a sub-antidepressant dose of 3mg/kg reduced immobility time in the FST compared to treatment with either drug alone. None of the drugs affected crossing and rearing scores in the open field test. These results suggest that the l-arginine–nitric oxide pathway is involved in the antidepressant effects of ketamine observed in rats in the FST and this involvement is characterised by the inhibition of brain T-NOS, iNOS, and eNOS activities.

Insulin-Mediated Activation of the L-Arginine Nitric Oxide Pathway in Man, and Its Impairment in Diabetes

Aims/HypothesisImpaired L-arginine transport has been reported in cardiovascular diseases, providing a possible mechanism for reduced nitric oxide (NO) production. Given that cardiovascular diseases are also associated with insulin resistance, and insulin is known to induce vasodilation via a NO-dependent pathway, we hypothesised that abnormal insulin modulation of L-arginine transport may contribute to vascular dysfunction in diabetes.MethodsForearm blood flow (FBF) responses to insulin and sodium nitroprusside (SNP) were measured in control and type 2 diabetic volunteers using venous occlusion plethysmography. Effects of intra-arterial insulin on the forearm veno-arterial flux of arginine and related amino acids were determined by HPLC. The effect of locally delivered insulin on arginine transport was assessed during an intra-arterial infusion of [4,5-3H] L-arginine.ResultsIn controls, intrabrachial infusion of 5 mUnits/min insulin lead to a progressive rise in FBF (p<0.001) while this was not evident in diabetics. In support of this observation, we observed a concomitant, significant increase in the flux of N-hydroxy-L-arginine (the NO precursor) in controls (baseline vs. 60 mins insulin: 16.2±12.2 vs. 33.0±13.1 nmol/100 ml tissue/min; p<0.01), whilst no increase was observed in diabetics. Moreover, insulin augmented the clearance of [3H]L-arginine from the forearm circulation in controls (baseline vs insulin: 123±22 vs. 150±28 ml/min; p<0.05) but not in diabetics.ConclusionThese findings suggest that insulin resistance may contribute substantially to the onset and development of cardiovascular disease in type 2 diabetics via abnormal insulin-mediated regulation of L-arginine transport.

Evaluation of mechanisms involved in the antinociception of the ethanol extract from the inner bark of Caesalpinia pyramidalis in mice

Ethnopharmacological relevanceCaesalpinia pyramidalis Tul. (Fabaceae) is an endemic tree of the Northeast region of Brazil, mainly in the Caatinga region. More commonly, inner bark or flowers are traditionally used to treat many painful and inflammatory processes. A common use of this plant is made by macerating a handful of its stem bark in a liter of wine or sugarcane brandy. It is drunk against stomachache, dysenteries, and diarrheas. Materials and methodsThe ethanol extract of Caesalpinia pyramidalis inner bark was used in mice via oral route, at the doses of 10, 30, and 100mg/kg, in behavioral models of nociception and investigates some of the mechanisms underlying this effect. ResultsThe ethanol extract (30 and 100mg/kg, P<0.001), given orally, produced dose dependent inhibition of acetic acid-induced visceral pain. The ethanol extract also caused significant and dose-dependent inhibition of capsaicin-(100mg/kg, P<0.001) and glutamate-(10, 30, and 100mg/kg, P<0.01) induced pain. The antinociception caused by the ethanol extract (30mg/kg) in the abdominal constriction test was significantly attenuated (P<0.001) by intraperitoneal treatment of mice with l-arginine (600mg/kg). ConclusionsCollectively, the present results suggest that the ethanol extract of Caesalpinia pyramidalis produced dose-related antinociception in several models of pain through mechanisms that involved both glutamatergic system and/or the l-arginine–nitric oxide pathway, supporting the folkloric usage of the plant to treat various painful processes.

Influence of the AT2 receptor on the L-arginine–nitric oxide pathway and effects of (-)-epicatechin on HUVECs from women with preeclampsia

Pregnancy is a state of vasodilation mediated by nitric oxide (NO). This vasodilation is impaired in women with preeclampsia, and an alteration in the L-arginine-NO pathway may be a causal factor. The production of NO and arginase activity were investigated in plasma and human umbilical vein endothelial cells (HUVECs) from women with preeclampsia, which were associated with arginase II, eNOS, caveolin, angiotensin 1 and 2 receptor expression (AT1R and AT2R, respectively). The effect of (-)-epicatechin on arginase activity and production of anion superoxide in HUVEC also were investigated. Healthy volunteer non-pregnant (HV), normal pregnant (NP) and preeclamptic (PE) women were recruited for this study. Higher values of nitrite/nitrate (NO(2)/NO(3)) were detected in the plasma from PE women as opposed to HV and NP. Lower arginase activity in PE versus HV or NP women was observed. HUVECs from PE women showed lower values of NO(2)/NO(3), higher activity of arginase and higher expression of AT(1)R and AT(2)R than HUVECS from NP women. Interestingly, arginase activity was associated with AT(2)R stimulation; indeed this activity and the high NADPH (nicotinamide adenine dinucleotide phosphate) oxidase activity in HUVECs from PE women can uncouple the production or inactivation of NO. However, we demonstrated that (-)-epicatechin could lead to a decrease in the activity of both enzymes.

Resolution of nebivolol-induced coronary vasospasm by intracoronary nitroglycerin during a coronary angiogram

Nebivolol is a novel beta1-selective beta-blocker with vasodilator properties mediated through activation of the l-arginine–nitric oxide pathway. There is no published report of coronary artery spasm associated with nebivolol. We describe a 64-year-old female patient who developed unstable angina secondary to nebivolol-induced vasospastic angina which was also visible during coronary angiography.

Resolution of nebivolol-induced coronary vasospasm by intracoronary nitroglycerin during a coronary angiogram

Nebivolol is a novel beta1-selective beta-blocker with vasodilator properties mediated through activation of the l-arginine–nitric oxide pathway. There is no published report of coronary artery spasm associated with nebivolol. We describe a 64-year-old female patient who developed unstable angina secondary to nebivolol-induced vasospastic angina which was also visible during coronary angiography.

Nitric oxide activity in platelets of dengue haemorrhagic fever patients: the apparent paradoxical role of ADMA and l-NMMA

Dengue haemorrhagic fever (DHF) is a prevalent acute disease that occurs in patients infected by an arbovirus in tropical and subtropical regions. We have previously shown increased intraplatelet nitric oxide (NO) production in patients with dengue fever associated with reduced platelet aggregation. In this study, l-arginine transport as well as expression and activity of nitric oxide synthase (NOS) isoforms in the presence or absence of l-arginine analogues were examined in 23 DHF patients. l-arginine transport and NOS activity in platelets were increased in patients with DHF compared with controls. However, platelet endothelial NOS (eNOS) and inducible (iNOS) protein levels did not differ between healthy controls and DHF patients. Endogenous or exogenous analogues did not inhibit platelet NOS activity from DHF patients. In contrast, endogenous l-arginine analogues [NG-monomethyl-l-arginine (l-NMMA) and asymmetric dimethylarginine (ADMA)] inhibited NOS activity in platelets from healthy subjects. These results show the first evidence that the intraplatelet l-arginine–NO pathway is activated in DHF patients. The lack of inhibition of NO formation in vitro by all l-arginine analogues tested in DHF platelets may suggest another mechanism by which NOS activity can be regulated.

396 Early Endothelium-Dependent Vasodilatory Dysfunction Innormotensive, Intra-Uterine Growth Restricted Rats is Restored by L-Arginine and Inhibition of Arginases

Increasing clinical and experimental evidence demonstrates that fetalprogrammed hypertension in adulthood is associated with altered endotheliumdependent vasodilation. However, it is debated whether decreased endothelium-dependent vasodilation precedes or is a consequence of elevated arterial pressure. We studied endotheliumdependent vasodilating capacity and the L-argininenitric oxide pathway in intra-uterine growthrestricted (IUGR), 5-week-old, male rats, before the development of elevated arterial pressure. We furthermore tested the hypothesis that alteration in endothelial vasodilation may be due to a reduction in L-arginine bioavailability. Methods- Pregnant rats were fed either a control or protein restricted diet during gestation. Endothelium-intact aortic rings of 5-week-old male offspring of the control and IUGR groups were isolated and preconstricted with phenylephrine (PE) to test vascularreactivity to acetylcholine (Ach) and sodium nitroprusside (SNP), respectively endothelium-dependent and -independent vasodilators. Other experiments were conducted with L-arginine supplementation or with S-(2-boronoethyl)-L-cysteine (BEC), a specific endothelial arginase inhibitor. Arginase enzymatic activity was measured in aorta. Results- Systolic blood pressure was not different between groups, and increased later in IUGR rats. While the vasodilatory response to SNP was similar in the two groups, a decreased vasodilatory response to Ach (- 20 %, p< 0.05) was observed in the IUGR group. Moreover, L-arginine supplementation and arginases inhibition restored the altered vasodilating capacity of aortic rings of IUGR animals. Arginase activity is enhanced in aorta of young IUGR rats. Conclusions- Reduced endothelium-dependent vascular relaxation precedes the developmentof fetal programmed hypertension in IUGR rats and involves the L-arginine-NO pathway. L-arginine supplementation and inhibition of arginases restore endothelium-dependent vasodilation in IUGR, prehypertensive rats.

NO-synthase independent NO generation in mammals

Inorganic nitrate ( NO 3 - ) and nitrite ( NO 2 - ) are part of the nitrogen cycle in nature. To the general public these anions are generally known as undesired residues in the food chain with potentially carcinogenic effects. Among biologists, these inorganic anions have merely been viewed as inert oxidative end products of endogenous nitric oxide (NO) metabolism. However, recent studies surprisingly show that nitrate and nitrite can be metabolized in vivo to form nitric oxide (NO) and other bioactive nitrogen oxides. This represents an important alternative source of NO especially during hypoxia when the oxygen-dependent l-arginine–NO pathway can be altered. A picture is now emerging suggesting important biological functions of the nitrate–nitrite–NO pathway with profound implications in relation to the diet and cardiovascular homeostasis. Moreover, an increasing number of studies suggest a therapeutic potential for nitrate and nitrite in diseases such as myocardial infarction, stroke, hypertension, renal failure and gastric ulcers.

No arguments for increased endothelial nitric oxide synthase activity in migraine based on peripheral biomarkers

To assess whether migraine patients display a chronic nitric oxide synthase (NOS) hyperactivity by comparing the nitric oxide (NO) production before and following a loading dose of L-arginine between migraine patients (interictally) and matched healthy control subjects. In addition, we evaluated whether a loading dose of L-arginine triggers an acute migraine headache in migraineurs. Twenty healthy subjects and 20 migraine patients participated in a 2-period, randomised, double-blind, placebo-controlled study. Each subject received a 30-min infusion, by peripheral vein, of 30 g L-arginine hydrochloride or placebo (i.e. an equal volume of 0.9% saline solution). Meanwhile, biomarkers associated with the L-arginine-NO pathway (i.e. exhaled NO/nasal NO), plasma citrulline and urinary excretion of nitrite/nitrate and cGMP were assessed before and for 6 h following the start of the infusion. At baseline, exhaled NO and nasal NO were higher in migraineurs compared to healthy subjects (mean±95% confidence interval): 15.9 (8.8, 23.0) parts per billion (ppb) versus 10.8 (7.0, 14.5) ppb for exhaled NO (P=0.04) and 76.3 (61.2, 91.4) versus 61.6 (51.2, 72.0) ppb for nasal NO (P=0.03), respectively. The AUC0-6 in ppb for exhaled NO and nasal NO following L-arginine or saline infusion did not differ between both groups. The increase in L-citrulline, following L-arginine infusion, was smaller in migraine patients (15 (13, 18) µmol/l) compared to healthy volunteers (19 (16, 23) µmol/l; P=0.046). In healthy subjects, both nitrate and cGMP excretion were higher following L-arginine compared to placebo infusion: 132.63 (100.24, 165.02) versus 92.07 (66.33, 117.82) µmol/mmol creatinine for nitrate (P=0.014) and 50.53 (42.19, 58.87) versus 39.64 (33.94, 45.34) nmol/mmol creatinine for cGMP (P=0.0003), respectively. In migraineurs, excretion of these biomarkers was comparable following L-arginine or saline infusion. The results of the present study do not support the idea of a generalised increase in NO synthase activity in migraine patients outside of a migraine attack. The smaller increase in plasma L-citrulline, urinary nitrate and cGMP excretion following L-arginine infusion in migraine patients might indicate dysfunction of endothelial NO synthase.

Exercise training in doxorubicin-induced heart failure: effects on the L-arginine–NO pathway and vascular reactivity

Heart failure (HF) is the end-stage of cardiovascular disease and is associated with a high incidence of thrombotic events. Nitric oxide (NO) mediates vasodilation and prevents platelet activation, providing an important antithrombotic effect. The aim of this study was to investigate the effects of aerobic training on survival, platelet L-arginine–NO pathway, and vasodilator properties in doxorubicin (DOX)-induced HF. Sprague Dawley rats were randomly assigned to saline/sedentary (SAL/SED), saline/exercise (SAL/EX), DOX/sedentary (DOX/SED), and DOX/exercise (DOX/EX) groups. Four weeks after intraperitoneal DOX injection (1 mg/kg -1/d -1; 10 days), shortening fraction in DOX/SED and DOX/EX was significantly reduced. Treadmill exercise was performed during 6 weeks, 5 days/week -1, 30 minutes/day -1, 50% to 60% of maximum velocity. Survival was higher in DOX/EX (67%) than DOX/SED (33%). No differences were observed in intraplatelet L-arginine transport assessed by incubation with L- [ 3H]-arginine, nor in NOS activity measured by the conversion of L- [ 3H]-arginine into L- [ 3H]-citrulline among the groups. Vasodilation response to acetylcholine was impaired in DOX/SED and DOX/EX; in nitroglycerine, it was limited to DOX/SED. Aerobic training reduced mortality in DOX-induced HF animals and restored vascular smooth muscle relaxation properties. However, it did not ameliorate intraplatelet NO bioavailability and endothelial function during the period studied.