Constitutive Nitric Oxide Production Research Articles

Ethylene mediates salicylic-acid-induced stomatal closure by controlling reactive oxygen species and nitric oxide production in Arabidopsis

Both salicylic acid (SA) and ethylene induce stomatal closure and positively regulate stomatal immunity, but their interactions in guard cell signaling are unclear. Here, we observed that SA induced the expression of ethylene biosynthetic genes; the production of ethylene, reactive oxygen species (ROS) and nitric oxide (NO); and stomatal closure in Arabidopsis thaliana. However, SA-induced stomatal closure was inhibited by an ethylene biosynthetic inhibitor and mutations in ethylene biosynthetic genes, ethylene-signaling genes [RESPONSE TO ANTAGONIST 1 (RAN1), ETHYLENE RESPONSE 1 (ETR1), ETHYLENE INSENSITIVE 2 (EIN2), EIN3 and ARABIDOPSIS RESPONSE REGULATOR 2 (ARR2)], NADPH oxidase genes [ATRBOHD and ATRBOHF], and nitrate reductase genes (NIA1 and NIA2). Furthermore, SA-triggered ROS production in guard cells was impaired in ran1, etr1, AtrbohD and AtrbohF, but not in ein2, ein3 or arr2. SA-triggered NO production was impaired in all ethylene-signaling mutants tested and in nia1 and nia2. The stomata of mutants for CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) showed constitutive ROS and NO production and closure. These results indicate that ethylene mediates SA-induced stomatal closure by activating ATRBOHD/F-mediated ROS synthesis in an RAN1-, ETR1- and CTR1-dependent manner. This in turn induces NIA1/2-mediated NO production and subsequent stomatal closure via the ETR1, EIN2, EIN3 and ARR2-dependent pathway(s).

Ischemic Preconditioning Preserves Liver Energy Charge and Function on Hepatic Ischemia/Reperfusion Injury in Rats

Cell energy during ischemia/reperfusion depends on mechanisms including adenosine diphosphate degradation, oxygen species and cytokine liberation, neutrophil infiltration, and endothelial dysfunction. Preconditioning-a brief ischemic episode that confers a state of protection against subsequent ischemia-reperfusion injury-involves NO and adenosine production, reduction in oxygen species liberation, and preservation of microcirculation. During hypoxia, constitutive NO production assures adequate oxygen delivery and reduced energy loss. The aim was to determine the role of ischemic preconditioning in the stimulation of constitutive endothelial nitric oxide (NO) production and its effect on energy charge, radical oxygen species generation, cytokine liberation, and neutrophil infiltration during reperfusion. Rats were assigned to one of four groups depending on the preconditioning protocol: hepatic ischemia/reperfusion, or hepatic ischemia/reperfusion and ischemic preconditioning, for 5, 10, or 20min. A portosystemic shunt was established between the portal and left jugular veins during ischemia. Preconditioning produced rises in plasma nitrites, but no rise in inducible nitric oxide synthase gene expression. A 5 or 10min preconditioning period allowed for higher energy charge, bile production, and glutathione levels, with less lipoperoxide, alanine aminotransferase, tumor necrosis factor-α, and interleukin-1 production and neutrophil infiltration, compared with 20min or control. Survival was 80% in the G10 group, 70 in G5, 10 in GC, and 0% in the G20 group. Ten-min liver preconditioning improves survival and prevents energy loss during hepatic ischemia/reperfusion by stimulating constitutive NO production, maintaining glutathione concentrations and reducing oxygen species and proinflammatory cytokine generation as well as neutrophil infiltration.

Increased constitutive nitric oxide production by whole body periodic acceleration ameliorates alterations in cardiomyocytes associated with utrophin/dystrophin deficiency

Duchenne Muscular Dystrophy (DMD) cardiomyopathy is a progressive lethal disease caused by the lack of the dystrophin protein in the heart. The most widely used animal model of DMD is the dystrophin-deficient mdx mouse; however, these mice exhibit a mild dystrophic phenotype with heart failure only late in life. In contrast, mice deficient for both dystrophin and utrophin (mdx/utrn−/−, or dKO) can be used to model severe DMD cardiomyopathy where pathophysiological indicators of heart failure are detectable by 8–10weeks of age. Nitric oxide (NO) is an important signaling molecule involved in vital functions of regulating rhythm, contractility, and microcirculation of the heart, and constitutive NO production affects the function of proteins involved in excitation-contraction coupling. In this study, we explored the efficacy of enhancing NO production as a therapeutic strategy for treating DMD cardiomyopathy using the dKO mouse model of DMD. Specifically, NO production was induced via whole body periodic acceleration (pGz), a novel non-pharmacologic intervention which enhances NO synthase (NOS) activity through sinusoidal motion of the body in a headward-footward direction, introducing pulsatile shear stress to the vascular endothelium and cardiomyocyte plasma membrane. Male dKO mice were randomized at 8weeks of age to receive daily pGz (480cpm, Gz±3.0m/s2, 1h/d) for 4weeks or no treatment, and a separate age-matched group of WT animals (pGz-treated and untreated) served as non-diseased controls. At the conclusion of the protocol, cardiomyocytes from untreated dKO animals had, respectively, 4.3-fold and 3.5-fold higher diastolic resting concentration of Ca2+ ([Ca2+]d) and Na+ ([Na+]d) compared to WT, while pGz treatment significantly reduced these levels. For dKO cardiomyocytes, pGz treatment also improved the depressed contractile function, decreased oxidative stress, blunted the elevation in calpain activity, and mitigated the abnormal increase in [Ca2+]d upon mechanical stress. These improvements culminated in a significant reduction in circulating cardiac troponin T (cTnT) and an extension of the median lifespan of dKO mice from 16 to 31weeks. Treatment with L-NAME (NOS inhibitor) significantly decreased overall lifespan and abolished the cardioprotective properties elicited by pGz. Our results provide evidence that enhancement of NO synthesis by pGz can ameliorate cellular dysfunction in dKO cardiomyocytes and may represent a novel therapeutic intervention in DMD cardiomyopathy patients.

Constitutive production of nitric oxide leads to enhanced drought stress resistance and extensive transcriptional reprogramming in Arabidopsis.

Nitric oxide (NO) is involved in plant responses to many environmental stresses. Transgenic Arabidopsis lines that constitutively express rat neuronal NO synthase (nNOS) were described recently. In this study, it is reported that the nNOS transgenic Arabidopsis plants displayed high levels of osmolytes and increased antioxidant enzyme activities. Transcriptomic analysis identified 601 or 510 genes that were differentially expressed as a consequence of drought stress or nNOS transformation, respectively. Pathway and gene ontology (GO) term enrichment analyses revealed that genes involved in photosynthesis, redox, stress, and phytohormone and secondary metabolism were greatly affected by the nNOS transgene. Several CBF genes and members of zinc finger gene families, which are known to regulate transcription in the stress response, were changed by the nNOS transgene. Genes regulated by both the nNOS transgene and abscisic acid (ABA) treatments were compared and identified, including those for two ABA receptors (AtPYL4 and AtPYL5). Moreover, overexpression of AtPYL4 and AtPYL5 enhanced drought resistance, antioxidant enzyme activity, and osmolyte levels. These observations increase our understanding of the role of NO in drought stress response in Arabidopsis.

Increased Ornithine-Derived Polyamines Cause Airway Hyperresponsiveness in a Mouse Model of Asthma

Up-regulation of arginase contributes to airways hyperresponsiveness (AHR) in asthma by reducing L-arginine bioavailability for the nitric oxide (NO) synthase isozymes. The product of arginase activity, L-ornithine, can be metabolized into polyamines by ornithine decarboxylase. We tested the hypothesis that increases in L-ornithine-derived polyamines contribute to AHR in mouse models of allergic airways inflammation. After measuring significantly increased polyamine levels in sputum samples from human subjects with asthma after allergen challenge, we used acute and subacute ovalbumin sensitization and challenge mouse models of allergic airways inflammation and naive mice to investigate the relationship of AHR to methacholine and polyamines in the lung. We found that spermine levels were elevated significantly in lungs from the acute model, which exhibits robust AHR, but not in the subacute murine model of asthma, which does not develop AHR. Intratracheal administration of spermine significantly augmented airways responsiveness to methacholine in both naive mice and mice with subacute airways inflammation, and reduced nitrite/nitrate levels in lung homogenates, suggesting that the AHR developed as a consequence of inhibition of constitutive NO production in the airways. Chronic inhibition of polyamine synthesis using an ornithine decarboxylase inhibitor significantly reduced polyamine levels, restored nitrite/nitrate levels to normal, and abrogated the AHR to methacholine in the acute model of allergic airways inflammation. We demonstrate that spermine increases airways responsiveness to methacholine, likely through inhibition of constitutive NO synthesis. Thus, inhibition of polyamine production may represent a new therapeutic target to treat airway obstruction in allergic asthma.

Therapeutic use of eNOS/Caveolin‐1 antagonistic peptides for endothelial dysfunction and atherogenesis

RationaleEndothelial dysfunction, which is characterized by a reduction in nitric oxide (NO) bioavailability, is an early pro‐atherogenic step. Endothelial nitric oxide synthase (eNOS), the enzyme responsible for the constitutive production of NO, is negatively regulated by its association to Caveolin‐1 (Cav‐1), the major coat protein of caveolae. Whether antagonizing the eNOS/Cav‐1 interaction is an anti‐atherosclerotic drug target is unknown.ObjectiveWe have recently shown that a mutant Cav‐1 derived peptide (CavNoxin) can increase NO release by antagonizing eNOS binding to Cav‐1 (Bernatchez, Sharma et al., JCI 2011). Since upregulating NO production is therapeutically relevant in atherosclerosis we hypothesized that CavNoxin can attenuate atherosclerotic progression in vivo.Methods & ResultsApoE knockout mice were placed on a high fat diet for 12 weeks and were injected with either CavNoxin (2.5mg/kg) or vehicle peptide every 3 days. At the end of the 12 weeks, atherosclerotic lesions were analysed. CavNoxin treatment attenuated atherosclerotic lesions in the aorta and aortic sinuses by 42% and 21% respectively, as compared to vehicle controls. In addition, Cavnoxin reduced VCAM‐1 (adhesion molecule) expression and oxidative stress (measured by DHE and nitrotyrosine staining) in vivo.ConclusionThese data are the first to show an effect of the eNOS/Cav‐1 antagonism in atherosclerosis.

Nitric oxide and geriatrics: Implications in diagnostics and treatment of the elderly

The nation's aging population is growing rapidly. By 2030, the number of adults age 65 and older will nearly double to 70 million. Americans are living longer and older adults can now live for many years with multiple chronic illnesses but with a substantial cost to health care. Twenty percent of the Medicare population has at least five chronic conditions i.e., hypertension, diabetes, arthritis, etc. Studies in experimental models and even humans reveal that constitutive production of nitric oxide (NO) is reduced with aging and this circumstance may be relevant to a number of diseases that plague the aging population. NO is a multifunctional signaling molecule, intricately involved with maintaining a host of physiological processes including, but not limited to, host defense, neuronal communication and the regulation of vascular tone. NO is one of the most important signaling molecules in our body, and loss of NO function is one of the earliest indicators or markers of disease. Clinical studies provide evidence that insufficient NO production is associated with all major cardiovascular risk factors, such as hyperlipidemia, diabetes, hypertension, smoking and severity of atherosclerosis, and also has a profound predictive value for disease progression including cardiovascular and Alzheimers disease. Thirty plus years after its discovery and over 13 years since a Nobel Prize was awarded for its discovery, there have been no hallmark therapeutic breakthroughs or even NO based diagnostics. We will review the current state of the science surrounding NO in the etiology of a number of different diseases in the geriatric patient. From these observations, it can be concluded that enzymatic production of NO declines steadily with increasing age in healthy human subjects. Implementing strategies to diagnose and treat NO insufficiency may provide enormous benefit to the geriatric patient.

Pulmonary Microvascular Constriction and Oxidative Stress in the Intact‐ventilated Mouse Lung during Acute Inhibition of Nitric Oxide Synthase

Constitutive nitric oxide (NO) synthesis contributes to maintain low pulmonary vascular resistance in mice, but less is known about its effects on microvasculature at the alveolar level. Given its role in regulating microvascular responsiveness in various species, we determined the effects of acute NO synthesis inhibition on pulmonary arteriolar diameter and oxidative stress in anesthetized, open chest mice with ventilated lungs. NO synthesis was inhibited acutely by injecting L-NAME (0.1 mg/g body wt) into the pulmonary circulation via the right jugular vein. We examined subpleural microvessels (less than 50 μm in diameter) in the right lung, during brief periods when the lungs were statically inflated with O2. NADPH oxidase subunit, p47-phox translocation to the membrane, suggestive of NADPH oxidase activation, was assessed in lung lysates by immunoblot. L-NAME decreased arteriolar diameter by about 14% and increased the translocation of p47-phox compared to saline controls. Our data suggest that constitutive NO production decreases microvascular tone and inhibits NADPH oxidase in the ventilated mouse lung during physiological conditions. This study presents a reliable model for examining the role of NO synthesis in the responses of individual pulmonary microvessels in-vivo, and may provide valuable information on pulmonary microvascular responses to various pathophysiological circumstances.

Nitric Oxide as the Main Mediator of Adaptation to Physical Training

Intensive constitutive production of nitric oxide (NO) during physical training improves vasodilatation and heart function. However it reminds unclear how NO takes part in myocardial adaptation to workload, which accompanied with increased heart inflow and intra- cellular calcium content. Using isolated rat heart by Langendorf preparation we studied myo- cardial response to gradually increased left ventricular volume (Frank-Starling low) and in- creasing concentration of Ca 2+ in perfusion solution (from 1.7 mM to 12.5 mM) in trained and untrained rats. It was shown that 4 weeks swimming course improved heart function: heart rate was decreased; contractile activity (dP/dt max) and coronary flow were increased by 20% and 33% respectively. Equal volume of balloon stretching in left ventricle provoked greater con- traction in trained comparing to untrained hearts, demonstrating extended functional reserves of myocardium after swimming course. Furthermore, physical training significantly increased mitochondrial membrane potential (-176.5 ± 8.4 mV vs -156 ± 3.5 mV in control), that points to improved efficiency of oxidative phosphorylation. Heart contracture and increase of end diastolic pressure during calcium upload were much prevented in trained rat hearts. Mitochon- drial factor release due to opening of mitochondrial permeability transition (MPT) pore in trained heart was detected at higher concentration of calcium that reveals extended calcium capacity of mitochondria and lesser sensitivity of MPTP to its inductor - calcium. Pretreatment with NO synthesis inhibitor - L-NAME - in dose of 10 -4 M for 15 min abolished reaction of trained heart during Frank-Starling and calcium upload. Thus, heart adaptation to physical training and extend of functional reserves of heart are provided by endogenous NO production.

Роль оксиду азоту у розвитку скоротливих реакцій міокарда тренованих тварин

Intensive constitutive production of nitric oxide (NO) during physical training improves vasodilatation and heart function. However, it remains unclear how NO takes part in myocardial adaptation to workload, which is accompanied by an increased heart inflow and intracellular calcium content. Using isolated rat heart by Langendorf preparation, we studied myocardial response to gradually increased left ventricular volume (Frank-Starling low) and increasing concentration of Ca2+ in the perfusion solution (from 1.7 mM to 12.5 mM) in trained and untrained rats. It was shown that 4 weeks swimming course improved heart function: heart rate was decreased; contractile activity (dP/dt max) and coronary flow were increased by 20% and 33%, respectively. Equal volume stretching of balloon in left ventricle provoked greater contraction in trained comparing to untrained hearts, demonstrating extended functional reserves after swimming course. Mitochondrial membrane potential was significantly increased in hearts of trained rats. Furthermore, training prevented fast increase of the end diastolic pressure during calcium upload. Mitochondrial factor release due to opening of mitochondrial permeability transition pore (MPTP) in trained hearts was detected at higher concentrations of calcium that reveals extended calcium capacity of mitochondria and lesser sensitivity of MPTP to its inductor-calcium. Blockade of NO synthesis with L-NAME application of (10(-4) M for 15 min) abolished reaction of trained heart during Frank-Starling and calcium upload. Thus, heart adaptation to physical training and extension of functional reserves in heart are provided by endogenous NO production. Key words: nitric oxide, Frank-Starling low, physical training, calcium upload, mitochondrial permeability transition, membrane potential.

Nitric Oxide and the Ryanodine Receptor Ca-Release Channel

To the Editor: I have read with interest the recent review on the role of S -nitrosylation in cardiovascular signaling, in which Lima et al1 provide a very useful digest on the current status of research in this important but burgeoning field of cardiovascular physiology. On the other hand, I believe that one of the many functions of a scientific review, especially when summarizing the status of a field with a certain degree of ambiguity, is to promote further progress. This is, perhaps, best achieved if all the available data relevant to the field are summarized and discussed, even those that seem to be contradictory to the intended conclusion of the review. Although the review in question cites almost 200 works, it …

ORIGINAL ARTICLE: Role of Inflammatory Cytokines and eNOS Gene Polymorphism in Pathophysiology of Pre‐Eclampsia

Citation Singh A, Sharma D, Raghunandan C, Bhattacharjee J. Role of inflammatory cytokines and eNOS gene polymorphism in pathophysiology of pre‐eclampsia. Am J Reprod Immunol 2010; 63: 244–251Problem Pre‐eclampsia involves endothelial vascular dysfunction. The aim of this study was to test the hypothesis that (i) endothelial nitric oxide (NO) synthase Glu298Asp gene polymorphism limits constitutive NO production causing endothelial dysfunction and (ii) inflammatory cytokines impairs endothelium dependent relaxation in pre‐eclampsia.Method of study This cross‐sectional study included 50 women with pre‐eclampsia and 50 healthy pregnant women. Their blood samples were analyzed for NO, inflammatory cytokines and endothelial NO synthase (eNOS) gene polymorphism.Result Decreased NO levels whereas increased tumor necrosis factor‐α, interleukin (IL)‐6 and interleukin‐2 were found in pre‐eclampsia (P < 0.001). No significant differences were found in genotype/allele distribution between two groups. Significant negative correlation was observed between NO and IL‐6 in pre‐eclamptic group (P = 0.001).Conclusion An IL‐6‐mediated endothelium dependent NO‐cyclic guanine monophosphate‐mediated relaxation pathway may be inhibited in systemic vessels in pre‐eclampsia. As observed in this study Glu298Asp eNOS gene polymorphism did not showed significant association with pre‐eclampsia.

MECHANICAL STRETCH INDUCES ENDOTHELIAL NITRIC OXIDE SYNTHASE GENE EXPRESSION IN NEONATAL RAT CARDIOMYOCYTES

1. Mechanical stretch leads to cardiac hypertrophy and may ultimately cause heart failure. However, the effect of mechanical stretch on gene induction in cardiomyocytes remains to be determined. 2. In the present study, we compared transcript profiles of mechanically stretched neonatal rat cardiomyocytes with those of unstretched cells using cDNA microarrays. The microarrays contained probes for 480 known genes, including those involved in signal transduction, cell cycle regulation, the cytoskeleton and cell motility. Eighteen genes, including the eNOS gene, were identified as having significantly differential expression in response to mechanical stretch in cardiomyocytes. 3. Northern and western blot analysis further quantified the expression of the eNOS gene. Mechanical stretch increased constitutive NOS activity and nitric oxide (NO) production. The NO donor s-nitroso-N-acetylpenicillamine (SNAP) inhibited mechanical stretch-stimulated protein synthesis, as measured by [3H]-leucine uptake. In addition, cardiomyocytes were infected with adenoviral vectors encoding cDNA for eNOS (Ad-eNOS) and a phosphoglycerate kinase (PGK) empty vector (Ad-PGK). In contrast with Ad-PGK-infected cells, in cardiomyocytes infected with Ad-eNOS, there was increased calcium-dependent NOS activity and nitrite production. Cardiomyocytes infected with Ad-eNOS exhibited diminished mechanical stretch-stimulated protein synthesis. In contrast, in eNOS-knockdown cells, the increased eNOS protein levels and NOS activity induced by mechanical stretch were abolished, but protein synthesis was enhanced. 4. The results of the present study indicate that eNOS gene expression is induced by mechanical stretch, leading to increased constitutive NOS activity and NO production, which may be a negative regulator in cardiomyocyte hypertrophy.

Enzyme-Independent NO Stores in Human Skin: Quantification and Influence of UV Radiation

Nitric oxide (NO) has many functions in the skin, including the mediation of inflammation and antimicrobial defense, wound healing, regulation of keratinocyte homeostasis, and regulation of apoptosis following UV radiation. NO is synthesized by a family of NO synthase enzymes, but its rapid release following UV exposure suggests the existence of preformed stores. NO can be converted into nitrite or nitrosothiols that are stable until cleaved by UV to release NO. Using dermal microdialysis, suction blister epidermal samples, and sweat collection, we demonstrated cutaneous concentrations of total NO-related products of 12+/-5.97 microM, 0.03+/-0.03 micromol mg(-1) epidermal protein, and 22+/-9.34 microM, respectively. The predominant oxyanion was nitrate (60-75%) followed by nitrite. S-Nitrosothiols were barely detectable. Serum total NO-related products correlated directly with those of the upper dermis and sweat (R(2)=0.62 and 0.3, respectively). UVA irradiation (10 mW cm(-2)) increased the yield of NO-related products by microdialysis, peaking after 30 minutes. Dialysis with noradrenaline abrogated this rise. Both the skin and the dermal vasculature contain biologically significant stores of NO, particularly nitrite, which can be directly mobilized by UVA irradiation. The level of circulating NO-related products probably determines skin-bound stores.

The Presence of Endogenous Morphine Signaling in Animals

Recent empirical findings have contributed valuable mechanistic information in support of a regulated de novo biosynthetic pathway for chemically authentic morphine and related morphinan alkaloids within animal cells. Importantly, we and others have established that endogenously expressed morphine represents a key regulatory molecule effecting local circuit autocrine/paracrine cellular signaling via a novel mu(3) opiate receptor coupled to constitutive nitric oxide production and release. The present report provides an integrated review of the biochemical, pharmacological, and molecular demonstration of mu(3) opiate receptors in historical linkage to the elucidation of mechanisms of endogenous morphine production by animal cells and organ systems. Ongoing research in this exciting area provides a rare window of opportunity to firmly establish essential biochemical linkages between dopamine, a morphine precursor, and animal biosynthetic pathways involved in morphine biosynthesis that have been conserved throughout evolution.

Highlights From The Literature

Highlights From The Literature

Constitutive intracellular production of iNOS and NO in human melanoma: possible role in regulation of growth and resistance to apoptosis

Human melanoma tumors cells are known to express the enzyme, inducible nitric oxide synthase (iNOS), which is responsible for cytokine induced nitric oxide (NO) production during immune responses. This constitutive expression of iNOS in many patients’ tumor cells, as well as its strong association with poor patient survival, have led to the consideration of iNOS as a molecular marker of poor prognosis, as well as a possible target for therapy. The expression of iNOS in patient tumors was found to associate with nitrotyrosine, COX2, pSTAT3, and arginase. Using human melanoma patients’ samples as well as cell lines, we have further evidence supporting intracellular NO production by detection of nitrotyrosine and also by use of DAF-2DA staining. Experiments were performed to scavenge the endogenous NO (with c-PTIO) resulting in melanoma cell growth inhibition; this was restored with SIN-1 (NO and O2-donor) providing data to support a functional role of this gas. Our goal is to understand the aberrant biology leading to this curious phenomenon, and to regulate it in favor of patient treatments.

Effects of propofol on the leukocyte nitric oxide pathway: in vitro and ex vivo studies in surgical patients

This study was designed to evaluate the mechanism by which propofol modifies leukocyte production of nitric oxide (NO) in humans. In vitro experiments used whole blood from healthy volunteers (n = 10 samples/experiment). Ex vivo experiments studied the effects of an intravenous dose of 2.5 mg propofol per kilogram body weight followed by intravenous infusion of 4 mg kg(-1) h(-1) in surgical patients in ASA class I or II (n = 20). In whole blood, neutrophils and plasma, we measured NO production and the activities of the enzymes nitric oxide synthase [inducible (iNOS) and constitutive (cNOS)] and cyclooxygenase [constitutive (COX-1) and inducible (COX-2)]. Concentrations of interleukins (IL-1beta, IL-6, and IL-10) and tumor necrosis factor-alpha (TNFalpha) were measured in plasma. In blood from healthy donors, propofol increased NO production and cNOS activity. The concentration of propofol that increased NO production by 50% (EC(50)) was 23.5 microM, and the EC(50) of propofol for cNOS was 18.6 microM. In blood from surgical patients, propofol increased NO production by 52% and cNOS activity by 57%. Propofol inhibited iNOS activity in vitro; the concentration that reduced activity by 50% (IC(50)) was 19.9 microM. In surgical patients propofol inhibited iNOS activity by 53%. COX-1 and COX-2 activities were inhibited in vitro (IC(50) 32.6 and 187 microM, respectively) and in surgical patients (53 and 81% inhibition, respectively). Plasma concentrations of IL-1beta, IL-6, and TNFalpha were significantly reduced in surgical patients (32, 23, and 21% inhibition, respectively). None of these parameters were modified in a group of patients (n = 10) anesthetized with sevoflurane. We conclude that propofol stimulated constitutive NO production and inhibited inducible NO production, possibly by curtailing the stimulation of iNOS by inflammatory mediators in surgical patients.

Melatonin ameliorates hippocampal nitric oxide production and large conductance calcium‐activated potassium channel activity in chronic intermittent hypoxia

Melatonin protects against hippocampal injury induced by intermittent hypoxia (IH). IH-induced oxidative stress is associated with decreases in constitutive production of nitric oxide (NO) and in the activity of large conductance calcium-activated potassium (BK) channels in hippocampal neurons. We tested the hypothesis that administration of melatonin alleviates the NO deficit and impaired BK channel activity in the hippocampus of IH rats. Sprague-Dawley rats were injected with melatonin (10 mg/kg, i.p.) or vehicle before daily IH exposure for 8 hr for 7 days. The NO and intracellular calcium ([Ca2+]i) levels in the CA1 region of hippocampal slices were measured by electrochemical microsenor and spectrofluorometry, respectively. The activity of BK channels was recorded by patch-clamping electrophysiology in dissociated CA1 neurons. Malondialdehyde levels were increased in the hippocampus of hypoxic rats and were lowered by the melatonin treatment. Levels of NO under resting and hypoxic conditions, and the protein expression of neuronal NO synthase (nNOS) were significantly reduced in the CA1 neurons of hypoxic animals compared with the normoxic controls. These deficits were mitigated in the melatonin-treated hypoxic rats with an improved [Ca2+]i response to acute hypoxia. The open probability of BK channels was decreased in the hypoxic rats and was partially restored in the melatonin-treated animals, without alterations in the expression of channel subunits and unitary conductance. Acute treatment of melatonin had no significant effects on the BK channel activity or on the [Ca2+]i response to hypoxia. Collectively, these results suggest that melatonin ameliorates the constitutive NO production and BK channel activity via an antioxidant mechanism against an IH-induced down-regulation of nNOS expression in hippocampal neurons.

Nitric oxide release from a single cell affects filopodial motility on growth cones of neighboring neurons

Nitric oxide (NO), a gaseous messenger, has been reported to be involved in a variety of functions in the nervous system, ranging from neuronal pathfinding to learning and memory. We have shown previously that the application of NO via NO donors to growth cones of identified Helisoma buccal neurons B5 in vitro induces an increase in filopodial length, a decrease in filopodial number, and a slowing in neurite advance. It is unclear, however, whether NO released from a physiological source would affect growth cone dynamics. Here we used cell bodies of identified neurons known to express the NO synthesizing enzyme nitric oxide synthase (NOS) as a source of constitutive NO production and tested their effect on growth cones of other cells in a sender-receiver paradigm. We showed that B5 cell bodies induced a rapid increase in filopodial length in NO-responsive growth cones, and that this effect was blocked by the NOS inhibitor 7-NI, suggesting that the effect was mediated by NO. Inhibition of soluble guanylyl cyclase (sGC) with ODQ blocked filopodial elongation induced by B5 somata, confirming that NO acted via sGC. We also demonstrate that the effect of NO was reversible and that a cell releasing NO can affect growth cones over a distance of at least 100 microm. Our results suggest that NO released from a physiological source can affect the motility of nearby growth cones and thus should be considered a signaling molecule with the potential to affect the outcome of neuronal pathfinding in vivo.