Neuronal nitric oxide synthase and its interaction with soluble guanylate cyclase is a key factor for the vascular dysfunction of experimental sepsis

Blockade of sympathetic ganglia improves vascular dysfunction in septic shock

Sepsis/septic shock activates the sympathetic nervous system (SNS) to deal with the infection stress. However, an imbalanced or maladaptive response due to excessive or uncontrolled activation characterizes autonomic dysfunction. Our hypothesis was that reducing this excessive activation of the autonomic nervous system would impact positively in sepsis. Using ganglionic blockers as a pharmacological approach, the main aim of the present report was to assess the role of ganglionic transmission in the vascular dysfunction associated with sepsis.Sepsis was induced in rats by cecal ligation and puncture (CLP). One hour after CLP surgery, rats were treated subcutaneously with hexamethonium (15 mg/kg; ganglionic blocker), pentolinium (5 mg/kg; a blocker with a higher selectivity for sympathetic ganglia compared to hexamethonium), or vehicle (PBS). Basal blood pressure and the response to adrenergic agonists were evaluated at 6 and 24 h after CLP surgery. Reactivity to vasoconstrictors, nitric oxide (NO) synthase 2 (NOS-2) expression, IL-1 and TNF plasma levels, and density of α1 adrenergic receptors were evaluated in the aorta 24 h after CLP.Septic shock resulted in hypotension and hyporesponsiveness to norepinephrine and phenylephrine, increased plasma cytokine levels and NOS-2 expression in the aorta, and decreased α1 receptor density in the same vessel. Pentolinium but not hexamethonium recovered responsiveness and α1 adrenergic receptor density in the aorta. Both blockers normalized the in vivo response to vasoconstrictors, and reduced plasma IL-1 and NOx levels and NOS-2 expression in the aorta.Blockade of ganglionic sympathetic transmission reduced the vascular dysfunction in experimental sepsis. This beneficial effect seems to be, at least in part, due to the preservation of α1 adrenergic receptor density and to reduced NOS-2 expression and may lead to adjuvant ways to treat human sepsis.

Pharmacokinetics, biodistribution, and in vivo toxicity of 7-nitroindazole loaded in pegylated and non-pegylated nanoemulsions in rats

Sepsis is a life-threatening condition caused by a dysregulated host response to infection. The development of sepsis is associated with excessive nitric oxide (NO) production, which plays an important role in controlling vascular homeostasis. 7-nitroindazole (7-NI) is a selective inhibitor of neuronal nitric oxide synthase (NOS-1) with potential application for treating NO imbalance conditions. However, 7-NI exhibits a low aqueous solubility and a short plasma half-life. To circumvent these biopharmaceutical limitations, pegylated (NEPEG7NI) and non-pegylated nanoemulsions (NENPEG7NI) containing 7-NI were developed. This study evaluates the pharmacokinetic profiles and toxicological properties of 7-NI loaded into the nanoemulsions. After a single intravenous administration of the free drug and the nanoemulsions at a dose of 10 mg.kg-1 in Wistar rats, 7-NI was widely distributed in the organs. The pharmacokinetic parameters of Cmax, t1/2, and AUC0-t were significantly increased after administration of the NEPEG7NI, compared to both free 7-NI and NENPEG7NI (p < 0.05). No observable adverse effects were observed after administering the free 7-NI, NEPEG7NI, or NENPEG7NI in the animals after a single dose of up to 3.0 mg.kg-1. The results indicated that 7-NI-loaded nanoemulsions are safe, constituting a promising approach to treating sepsis.

Research Progress on the Mechanism and Management of Septic Cardiomyopathy: A Comprehensive Review

Sepsis is defined as a kind of life-threatening organ dysfunction due to a dysregulated host immune response to infection and is a leading cause of mortality in the intensive care unit. Sepsis-induced myocardial dysfunction, also called septic cardiomyopathy, is a common and serious complication in patients with sepsis, which may indicate a bad prognosis. Although efforts have been made to uncover the pathophysiology of septic cardiomyopathy, a number of uncertainties remain. This article sought to review available literature to summarize the existing knowledge on current diagnostic tools and biomarkers, pathogenesis, and treatments for septic cardiomyopathy.

The expanding roles of neuronal nitric oxide synthase (NOS1)

The nitric oxide synthases (NOS; EC 1.14.13.39) use L-arginine as a substrate to produce nitric oxide (NO) as a by-product in the tissue microenvironment. NOS1 represents the predominant NO-producing enzyme highly enriched in the brain and known to mediate multiple functions, ranging from learning and memory development to maintaining synaptic plasticity and neuronal development, Alzheimer's disease (AD), psychiatric disorders and behavioral deficits. However, accumulating evidence indicate both canonical and non-canonical roles of NOS1-derived NO in several other tissues and chronic diseases. A better understanding of NOS1-derived NO signaling, and identification and characterization of NO-metabolites in non-neuronal tissues could become useful in diagnosis and prognosis of diseases associated with NOS1 expression. Continued investigation on the roles of NOS1, therefore, will synthesize new knowledge and aid in the discovery of small molecules which could be used to titrate the activities of NOS1-derived NO signaling and NO-metabolites. Here, we address the significance of NOS1 and its byproduct NO in modifying pathophysiological events, which could be beneficial in understanding both the disease mechanisms and therapeutics.

Machine learning applied to serum and cerebrospinal fluid metabolomes revealed altered arginine metabolism in neonatal sepsis with meningoencephalitis

Background

Neonatal sepsis with meningoencephalitis is a common complication of sepsis, which is a leading cause of neonatal death and neurological dysfunction. Early identification of neonatal sepsis with meningoencephalitis is particularly important for reducing brain damage. We recruited 70 patients with neonatal sepsis, 42 of which were diagnosed as meningoencephalitis, and collected cerebrospinal fluid (CSF) and serum samples. The purpose of this study was to find neonatal sepsis with meningoencephalitis-related markers using unbiased metabolomics technology and artificial intelligence analysis based on machine learning methods.

Results

We found that the characteristics of neonatal sepsis with meningoencephalitis were manifested mainly as significant decreases in the concentrations of homo-l-arginine, creatinine, and other arginine metabolites in serum and CSF, suggesting possible changes in nitric oxide synthesis. The antioxidants taurine and proline in the serum of the neonatal sepsis with meningoencephalitis increased significantly, suggesting abnormal oxidative stress. Potentially harmful bile salts and aromatic compounds were significantly increased in the serum of the group with meningoencephalitis. We compared different machine learning methods and found that the lasso algorithm performed best. Combining the lasso and XGBoost algorithms was successful in predicting the concentration of homo-l-arginine in CSF per the concentrations of metabolite markers in the serum.

Conclusions

On the basis of machine learning combined with analysis of the serum and CSF metabolomes, we found metabolite markers related to neonatal sepsis with meningoencephalitis. The characteristics of neonatal sepsis with meningoencephalitis were manifested mainly by changes in arginine metabolism and related changes in creatinine metabolism.

Perivascular adipose tissue phenotype and sepsis vascular dysfunction: Differential contribution of NO, ROS and beta 3-adrenergic receptor

AIMS

Vascular dysfunction plays a key role in sepsis but the role of perivascular adipose tissue (PVAT) in this condition is relatively unknown.

MAIN METHODS

Sepsis was induced by cecal ligation and puncture (CLP). The responses of the aorta and superior mesenteric artery to norepinephrine in the presence or absence of PVAT were evaluated. Fluorescent probes measured the production of nitric oxide (NO) and reactive oxygen species (ROS). NO synthases (NOS) and β3-adrenoceptor expression were detected by immunofluorescence and S-nitrosylation by the biotin switch assay.

KEY FINDINGS

Aorta and superior mesenteric arteries from septic animals with intact PVAT showed a worsened response to the vasoconstrictor compared to vessels without PVAT. PVAT from the aorta (APVAT) produced NO and ROS whereas PVAT from the superior mesenteric artery (MPVAT) produced only ROS. Septic APVAT exhibited a higher density of NOS-1 and NOS-3. S-nitrosylation was found in APVAT. Donor (PVAT obtained from normal or septic rats):Host (normal vessel without PVAT) experiments showed that L-NAME, ODQ and β3-adrenergic receptor antagonist blocked the septic APVAT anti-contractile effect. None of these compounds affected MPVAT; tempol, but not apocynin, blocked its anti-contractile effect.

SIGNIFICANCE

PVAT contributes to the anti-contractile effect in the aorta and mesenteric artery of septic rats through different pathways. β3-Adrenergic receptor and NO appear to be key mediators of this effect in APVAT, but not in MPVAT where ROS seem to be a relevant mediator. Therefore, PVAT is a relevant player of sepsis vascular dysfunction.

Effects of plane of nutrition and arginine on ovarian follicles in non-pregnant sheep: Cell proliferation, and expression of endothelial nitric oxide and its receptor

The aim of this study was to investigate the role of the nitric oxide (NO) system in ovarian function, by determining if arginine (Arg) supplementation impacts follicle number, cell proliferation, and expression of the NO system members in nutritionally compromised ewes. Ewes were randomly assigned into maintenance (C, 100% requirements), excess (O; 2xC), or restricted (U; 0.6xC) diets 8 weeks prior to Arg treatment. Ewes were individually fed twice daily with pelleted diets. Ewes from each nutritional group were randomly assigned to one of two treatments: saline or Arg, which was initiated on day 0 of the estrous cycle and administered 3 times per day. Ovaries were collected at the early-luteal, mid-luteal and late-luteal/follicular phases of the estrous cycle to determine 1) the number of surface follicles, 2) follicle cell proliferation marked by Ki67 protein expression, and 3) expression of endothelial nitric oxide (eNOS; NOS3) and soluble guanylyl cyclase beta (sGC; GUCY1B3) protein and mRNA in granulosa (G) and theca (T) layers using immunohistochemistry followed by image analysis and qPCR, respectively. During nutritional treatment, C maintained body weight, O gained 6±1.2 kg, and U lost 14±1.3 kg. Our data show that: 1) Ki67 was expressed in all ovarian compartments, eNOS protein was detected in blood vessels of T and stroma, and sGC protein was detected in T cells, and blood vessels of T layer and other ovarian compartments; 2) plane of nutrition affected the number of surface follicles, and thus folliculogenesis, cell proliferation in the T layer, eNOS and sGC protein expression in T, and NOS3 and GUCY1B3 mRNA expression in G; 3) Arg treatment affected cell proliferation in G and T, eNOS and sGC protein expression in T, mRNA expression of NOS3 in T in all groups, and GUCY1B3 in G depending on the stage of the estrous cycle; and 4) G and T cell proliferation, and expression of eNOS and sGC protein in T was affected by the stage of the estrous cycle. Our data demonstrated that plane of nutrition and Arg are involved in the regulation of follicular functions in non-pregnant sheep.

7-nitroindazol-loaded nanoemulsions: Preparation, characterization and its improved inhibitory effect on nitric oxide synthase-1

Nitric oxide (NO) participates in several physiological processes such as maintenance of blood pressure, host defense, neurotransmission, inhibition of platelet aggregation and learning and memory. NO is also involved in several diseases or dysfunctions in the cardiovascular, central nervous and musculoskeletal systems. NO also has been shown to be a major player in sepsis. NOS-1-derived NO has been shown to be a relevant species in physiology but also is an important element in pathology. There exist some NOS-1 inhibitors and among of them, 7-nitroindazole has been used for its in vivo selectivity. However, 7-NI has a very short half-life (∼2 h) and a poor water solubility. In this study, we describe the preparation and characterization of 7-NI-loaded nanoemulsions (NE_7-NI). The chemical stability of 7-NI was greatly increased and the drug release rate could be controlled after nanoemulsification. NE_7-NI reduced NO production in a long-lasting manner in vascular smooth muscle cells and skeletal muscle, without cytotoxicity. Our results evidenced that nanoemulsification approach increases the effective action time of 7-NI, rendering a suitable dosage form, which may be an interesting tool to study the role of NOS-1 in physiology and disease.

Inhibition of neuronal nitric oxide synthase activity does not alter vasopressin secretion in septic rats

BACKGROUND/PURPOSE

During the early phase of sepsis, hypotension is accompanied by increase of plasma vasopressin hormone (AVP) levels, which decline during the late phase. This hypotension is due in part to increase of nitric oxide (NO) synthesis by nitric oxide synthase (NOS) enzyme. Neuronal isoform of this enzyme (nNOS) is present in vasopressinergics neurons of hypothalamus, but its role in vasopressin secretion during sepsis is unknown.

METHODS

We evaluated the role of nNOS in NO production and vasopressin secretion during sepsis. Wistar rats received 7-nitroindazole (50 mg/kg, i.p.), an inhibitor of nNOS activity, or vehicle and were submitted to septic stimulus by cecal ligation and puncture (CLP). At the time points 0, 4, 6, 18 and 24 h after sepsis induction the animals were decapitated and neurohypophysis and hypothalamus were removed for analysis of vasopressin content and NOS activity, respectively. Hematocrit, serum sodium, osmolality, proteins and plasmatic AVP were quantified.

RESULTS

Mortality was not affected by 7-nitroindazole (7-NI). Sodium and plasma proteins levels decreased after CLP and the treatment anticipated the protein loss, and delayed serum sodium decrease. Septic animals treated with 7-NI showed decrease of osmolality 4 h after CLP. Nitric oxide synthase activity in hypothalamus increased at 4 and 24 h after CLP and was reduced with 7-NI. Neurohypophysis content of AVP diminished after CLP and 7-NI did not alter this parameter. Plasma AVP levels increased at 6 h and decreased 18 and 24 h after CLP. Treatment with 7-NI did not alter plasma vasopressin levels.

CONCLUSION

We concluded that nNOS does not have a substantial role in vasopressin secretion during experimental sepsis.

Protective role of cGMP in early sepsis

Septic shock, which is triggered by microbial products, is mainly characterised by inadequate tissue perfusion, which can lead to multiple organ dysfunction and death. An intense release of vasoconstrictors agents occurs in the early stages of shock, which can lead to ischemic injury. In this scenario, cGMP could play a key role in counterbalancing these agents and preventing tissue damage. Sildenafil, which is a phosphodiesterase-5 inhibitor, increases cGMP in smooth muscle cells and promotes vasodilation. Thus, the purpose of this study was to investigate the effect of treatment with sildenafil in the early stages of sepsis. Male rats were submitted to either cecal ligation and puncture (CLP) or a sham procedure. Eight h after the procedure, the CLP and sham groups were randomly assigned to receive sildenafil (10mg/kg, gavage) or vehicle, and twelve or twenty-four h later the inflammatory, biochemical and haemodynamic parameters were evaluated. Sepsis significantly increased levels of plasma nitrate/nitrite (NOx), aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea, creatinine, creatine kinase and lactate. Additionally, sepsis led to hypotension, hyporesponsiveness to vasoconstrictor, renal blood flow reduction and also increased lung and kidney myeloperoxidase. Sildenafil increased renal blood flow and reduced the plasma levels of creatinine, lactate and creatine kinase, as well as reducing lung myeloperoxidase. Thus, phosphodiesterase inhibition may be a useful therapeutic strategy if administered at the proper time.

C-Type Natriuretic Peptide Induces Anti-contractile Effect Dependent on Nitric Oxide, Oxidative Stress, and NPR-B Activation in Sepsis

AIMS

To evaluate the role of nitric oxide, reactive oxygen species (ROS), and natriuretic peptide receptor-B activation in C-type natriuretic peptide-anti-contractile effect on Phenylephrine-induced contraction in aorta isolated from septic rats.

METHODS AND RESULTS

Cecal ligation and puncture (CLP) surgery was used to induce sepsis in male rats. Vascular reactivity was conducted in rat aorta and resistance mesenteric artery (RMA). Measurement of survival rate, mean arterial pressure (MAP), plasma nitric oxide, specific protein expression, and localization were evaluated. Septic rats had a survival rate about 37% at 4 h after the surgery, and these rats presented hypotension compared to control-operated (Sham) rats. Phenylephrine-induced contraction was decreased in sepsis. C-type natriuretic peptide (CNP) induced anti-contractile effect in aortas. Plasma nitric oxide was increased in sepsis. Nitric oxide-synthase but not natriuretic peptide receptor-B expression was increased in septic rat aortas. C-type natriuretic peptide-anti-contractile effect was dependent on nitric oxide-synthase, ROS, and natriuretic peptide receptor-B activation. Natriuretic peptide receptor-C, protein kinase-Cα mRNA, and basal nicotinamide adenine dinucleotide phosphate (NADPH)-dependent ROS production were lower in septic rats. Phenylephrine and CNP enhanced ROS production. However, stimulated ROS production was low in sepsis.

CONCLUSION

CNP induced anti-contractile effect on Phenylephrine contraction in aortas from Sham and septic rats that was dependent on nitric oxide-synthase, ROS, and natriuretic peptide receptor-B activation.

Differential Role of Neurohypophysial Hormones in Hypotension and Nitric Oxide Production During Endotoxaemia

Besides their well-established endocrine roles, vasopressin and oxytocin are also important regulators of immune function, participating in a complex neuroendocrine-immune network. In the present study, we investigated whether and how vasopressin and oxytocin could modulate lipopolysaccharide (LPS)-induced nitric oxide (NO) production in a well-established model of experimental endotoxaemia. Male Wistar rats were previously treated i.v. with vasopressin V1 or oxytocin receptor antagonists and then received either an i.v. LPS injection to induce endotoxaemia or a saline imjection as a control. The animals were divided into two groups: in the first group, blood was collected at 2, 4 and 6 h after LPS injection; in the second group, mean arterial blood pressure (MABP) and heart rate (HR) were recorded over 6 h. Plasma vasopressin and oxytocin values were higher in LPS- compared to saline-injected animals at 2 and 4 h but returned to basal levels at 6 h. NO levels exhibited an opposite pattern, showing a progressive increase over the entire period. The previous administration of a vasopressin V1 receptor antagonist significantly reduced NO plasma concentrations at 2 and 4 h but not at 6 h. By contrast, oxytocin receptor agonist pre-treatment had no effect on the NO plasma concentration. In relation to MABP, previous treatment with vasopressin V1 receptor antagonist reversed the LPS-induced hypotension at 4 h, although this was not the case for oxytocin antagonist-treated animals. None of the antagonists affected HR. Our findings indicate that vasopressin (but not oxytocin) has effects on NO production during endotoxaemia in rats, although they do not lend support to the proposed anti-inflammatory actions of vasopressin during endotoxaemia.

Sex-dichotomous effects of NOS1AP promoter DNA methylation on intracranial aneurysm and brain arteriovenous malformation

The goal of this study was to investigate the contribution of NOS1AP-promoter DNA methylation to the risk of intracranial aneurysm (IA) and brain arteriovenous malformation (BAVM) in a Han Chinese population. A total of 48 patients with IAs, 22 patients with BAVMs, and 26 control individuals were enrolled in the study. DNA methylation was tested using bisulfite pyrosequencing technology. We detected significantly higher DNA methylation levels in BAVM patients than in IA patients based on the multiple testing correction (CpG4-5 methylation: 5.86±1.04% vs. 4.37±2.64%, P=0.006). In women, CpG4-5 methylation levels were much lower in IA patients (3.64±1.97%) than in BAVM patients (6.11±1.20%, P<0.0001). However, in men, CpG1-3 methylation levels were much higher in the controls (6.92±0.78%) than in BAVM patients (5.99±0.70%, P=0.008). Additionally, there was a gender-based difference in CpG1 methylation within the controls (men vs. women: 5.75±0.50% vs. 4.99±0.53%, P=0.003) and BAVM patients (men vs. women: 4.70±0.74% vs. 5.50±0.87%, P=0.026). A subgroup analysis revealed significantly higher CpG3 methylation in patients who smoked than in those who did not (P=0.041). Our results suggested that gender modulated the interaction between NOS1AP promoter DNA methylation in IA and BAVM patients. Our results also confirmed that regular tobacco smoking was associated with increased NOS1AP methylation in humans. Additional studies with larger sample sizes are required to replicate and extend these findings.

Skeletal muscle atrogene expression and insulin resistance in a rat model of polytrauma

Polytrauma is a combination of injuries to more than one body part or organ system. Polytrauma is common in warfare, and in automobile and industrial accidents. The combination of injuries can include burn, fracture, hemorrhage, and trauma to the extremities or specific organ systems. Resistance to anabolic hormones, loss of muscle mass, and metabolic dysfunction can occur following injury. To investigate the effects of combined injuries, we have developed a highly reproducible rodent model of polytrauma. This model combines burn injury, soft tissue trauma, and penetrating injury to the gastrointestinal (GI) tract. Adult, male Sprague–Dawley rats were anesthetized with pentobarbital and subjected to a 15–20% total body surface area scald burn, or laparotomy and a single puncture of the cecum with a G30 needle, or the combination of both injuries (polytrauma). In the current studies, the inflammatory response to polytrauma was examined in skeletal muscle. Changes in skeletal muscle mRNA levels of the proinflammatory cytokines TNF‐α, IL‐1β, and IL‐6 were observed following single injuries and polytrauma. Increased expression of the E3 ubiquitin ligases Atrogin‐1/FBX032 and TRIM63/MuRF‐1 were measured following injury, as was skeletal muscle insulin resistance, as evidenced by decreased insulin‐inducible insulin receptor (IR) and AKT/PKB (Protein Kinase B) phosphorylation. Changes in the abundance of IR and insulin receptor substrate‐1 (IRS‐1) were observed at the protein and mRNA levels. Additionally, increased TRIB3 mRNA levels were observed 24 h following polytrauma, the same time when insulin resistance was observed. This may suggest a role for TRIB3 in the development of acute insulin resistance following injury.

Cecal inoculum peritonitis: An alternative model for sepsis vascular dysfunction study

AIMS

Sepsis is a life threatening condition that is characterized by the loss of vascular reactivity. The factor(s) responsible for the diminished vascular function seen in sepsis are not well understood. The purpose of this study was to characterize the vascular dysfunction from the rat cecal inoculum (CI) sepsis model using cecal ligation and puncture (CLP), and lipopolysaccharide (LPS) sepsis as reference models.

MATERIALS AND METHODS

Experiments were performed on isolated aorta from CI, CLP and LPS treated rats using a combination of pharmacological approaches.

KEY FINDINGS

Phenylephrine (PE)-induced aortic contraction was significantly decreased in each model (p<0.05) and not normalized by L-NAME or indomethacin. The vascular response elicited in the CI model for acetylcholine (Ach) was more similar to that seen in the CLP than the LPS model. The removal of the endothelial layer increased sensitivity to L-NAME (p<0.05) in aortae from CI group. Inhibition of the large conductance Ca(2+)/voltage sensitive K(+) (BKCa) channel did not normalize PE hyporesponsiveness but did abolish sepsis-induced contractile oscillation. Inhibition of the voltage dependent Kv1.5 channel was not able to reverse the vascular hyporesponsiveness, however, inhibition of the ATP dependent (KATP) channel inhibition partially restored the contractile response (p<0.05). Elevation of VCAM expression and aortic structural alternation were observed in each model.

SIGNIFICANCE

These results suggest that the CI model may be an additional tool that could be used to investigate the mechanisms of vascular hyporesponsiveness in sepsis.

Separation of flavonoids from Millettia griffithii with high-performance counter-current chromatography guided by anti-inflammatory activity

Millettia griffithii is a unique Chinese plant located in the southern part of Yunnan Province. Up to now, there is no report about its phytochemical or related bioactivity research. In our previous study, the n-hexane crude extract of Millettia griffithii revealed significant anti-inflammatory activity at 100 μg/mL, inspiring us to explore the anti-inflammatory constituents. Four fractions (I, II, III, and A) were fractionated from n-hexane crude extract by high-performance counter-current chromatography with solvent system composed of n-hexane/ethyl acetate/methanol/water (8:9:8:9, v/v) and then were investigated for the potent anti-inflammatory activity. Fraction A, with the most potent inhibitory activity was further separated to give another four fractions (IV, V, VI, and B) with solvent system composed of n-hexane/ethyl acetate/methanol/water (8:4:8:4, v/v). Compound V and fraction B exhibited remarkable anti-inflammatory activity with nitric oxide inhibitory rate of 80 and 65%, which was worth further fractionation. Then, three fractions (VII, VIII, and IX) were separated from fraction B with a solvent system composed of n-hexane/ethyl acetate/methanol/water (8:1:8:1, v/v), with compound VIII demonstrating the most potent inhibitory activity (80%). Finally, the IC50 values of compound V and VIII were tested as 38.2 and 14.9 μM. The structures were identified by electrospray ionization mass spectrometry and(1)H and (13)C NMR spectroscopy.

Anti-peroxynitrite treatment ameliorated vasorelaxation of resistance arteries in aging rats: involvement with NO-sGC-cGKs pathway

Declined vasorelaxation function in aging resistance arteries is responsible for aging-related multiple organ dysfunctions. The aim of the present study is to explore the role of peroxynitrite (ONOO-) in aging resistance arterial vasorelaxation dysfunction and the possible mechanism. In the present study, young (3-4 months olds) and aging (20 months olds) male SD rats were randomized to receive vehicle (Saline) or FeTMPyP (ONOO- scavenger) for 2 weeks. The vasorelaxation of resistance arteries was determined in vitro; NOx level was tested by a colorimetric assay; the expression of nitrotyrosine (NT), soluble Guanylate Cyclase (sGC), vasodilator-stimulated phosphoprotein (VASP), phosphorylated VASP (P-VASP) and cGMP in resistance arteries were detected by immunohistochemical staining. In the present study, endothelium-dependent dilation in aging resistance arteries was lower than in those from young rats (young vs. aging: 68.0% ± 4.5% vs. 50.4% ± 2.9%, P<0.01). And the endothelium-independent dilation remained constant. Compared with young rats, aging increased nitrative stress in resistance arteries, evidenced by elevated NOx production in serum (5.3 ± 1.0 nmol/ml vs. 3.3 ± 1.4 nmol/ml, P<0.05) and increased NT expression (P<0.05). ONOO- was responsible for the vasorelaxation dysfunction, evidenced by normalized vasorelaxation after inhibit ONOO- or its sources (P<0.05) and suppressed NT expression after FeTMPyP treatment (P<0.05). The expression of sGC was not significantly different between young and aging resistance arteries, but the cGMP level and P-VASP/VASP ratio (biochemical marker of NO-sGC-cGKs signaling) decreased, which was reversed by FeTMPyP treatment in vivo (P<0.05). The present study suggested that ONOO- mediated the decline of endothelium-dependent vasorelaxation of aging resistance arteries by induction of the NO-sGC-cGKs pathway dysfunction.