Effect of lower limb exercise on forearm vascular function: contribution of nitric oxide

We examined vascular function in an inactive muscle bed, the forearm, during lower limb exercise and determined the contribution of endothelium-derived nitric oxide (NO) to the hyperemic response. Eight young males were randomized to participate in two studies, each consisting of two bouts of lower limb exercise, separated by a 30-min recovery. Peak forearm blood flow (PFBF) and mean blood flow (MFBF) were continuously recorded at baseline and during exercise using continuous high-resolution vascular ultrasound and Doppler flow velocity measurement. During one session, the brachial artery was cannulated to allow continuous infusion of saline or N(G)-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase. The alternate session was performed to control for possible effects of repeated exercise. At 60, 100, and 160 W, L-NMMA significantly decreased both PFBF and MFBF compared with the saline infusion. These results suggest that systemic production of NO occurs during exercise in resting vessel beds, which do not feed metabolically active tissue. This finding provides a plausible explanation for the antiatherogenic benefits of exercise.     

Interaction between nitric oxide signaling and gap junctions: Effects on vascular function

Nitric oxide signaling, through eNOS (or possibly nNOS), and gap junction communication are essential for normal vascular function. While each component controls specific aspects of vascular function, there is substantial evidence for cross-talk between nitric oxide signaling and the gap junction proteins (connexins), and more recently, protein-protein association between eNOS and connexins. This review will examine the evidence for interaction between these pathways in normal and diseased arteries, highlight the questions that remain about the mechanisms of their interaction, and explore the possible interaction between nitric oxide signaling and the newly discovered pannexin channels. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.     

Effects of nitric oxide on mitochondrial permeability transition pore and thiol-mediated responses in cardiac myocytes

Nitric oxide (NO) alters the opening of mitochondrial permeability transition pore (mPTP). However, the signaling pathways of NO on mPTP remain elusive. We aimed to clarify the contribution of thiol-mediated responses to the effects of NO on mPTP in permeabilized myocytes. We found that (1) a high concentration of spermine NONOate (an NO donor; 500 μM) opened mPTP and depolarized ΔΨ(m). (2) A low concentration of NONOate (5 μM) prevented atractyloside (an mPTP opener)-induced mPTP opening. (3) Mn(III) tetrakis (4-benzoic acid) porphyrin (Mn-TBAP, ONOO(-) scavenger) attenuated the effect of high-concentration NONOate on mPTP opening, but did not inhibited the preventive effects of low-concentration NONOate. (4) When the interaction of NO with thiol was inhibited by N-ethylmaleimide, the opening (by high-concentration NONOate) and preventive effects (by low-concentration NONOate) of NONOate on mPTP were blocked. (5) Dithiothreitol (an inhibitor of disulfide bonds formation) prevented high-concentration NONOate-induced mPTP opening. (6) Ascorbic acid (an inhibitor of S-nitrosylation) prevented the preventive effects of low-concentration NONOate on mPTP. We conclude that opening of mPTP by high-concentration NO is related to disulfide bonds formation and oxidizing effects of ONOO(-). In contrast, the inhibitory effect of physiological concentrations of NO on mPTP is related to S-nitrosylation.     

Effect of chronic social stress on nitric oxide synthesis and vascular function in rats with family history of hypertension

Genetic predisposition and psychosocial stress are known risk factors in the aetiology of hypertension. The aim of this study was to investigate the as yet unknown role of nitric oxide (NO) in mechanisms of social stress-induced hypertension in rats with a family history of hypertension. Male adult rats used in the study were offspring of normotensive (Wistar) dams and spontaneously hypertensive sires. The rats were exposed to 6-week crowding stress (5 rats/cage, 200 cm2/rat). Control rats were kept four per cage (480 cm2/rat). Blood pressure was determined non-invasively on the tail. Basal blood pressure of all rats was 131 +/- 2 mm Hg. Crowding stress increased significantly blood pressure (p < 0.02 vs. basal value). Crowding had no influence on NO synthase activity in the left ventricle, adrenal glands and kidney. However, crowding stress reduced significantly NO synthase activity in the aorta by 37% (p < 0.01 vs. control). Acetylcholine-induced relaxation and noradrenaline-induced vasoconstriction of the femoral artery were reduced in stressed rats by 58% (p < 0.001) and 41% (p < 0.003), respectively. On balance then, the results indicate that chronic social stress produced by crowding was associated with reduced vascular NO synthesis and altered vascular function in adult borderline hypertensive rats of normotensive mothers.     

Effect of nitric oxide donors on oxygen-dependent cytotoxic responses mediated by neutrophils

We analyzed the effect of nitric oxide (NO) on oxygen-dependent cytotoxic responses mediated by neutrophils against unopsonized erythrocytes using three NO donors: S-nitrosoglutathione (GSNO), S-nitroso-N-acetylpenicillamine (SNAP), and sodium nitroprusside (SNP). Neutrophils were treated with these compounds for 1-2 min at 37 degrees C and cytotoxicity was then triggered in the presence of NO donors by precipitating immune complexes, aggregated IgG, the chemotactic peptide FMLP, or opsonized zymosan. GSNO induced, in all cases, a marked increase in cytotoxic responses, while SNAP moderately increased cytotoxicity triggered by immune complexes, aggregated IgG, or Z, opsonized zymosen, without modifying those responses induced by FMLP. By contrast, SNP dramatically suppressed cytotoxicity triggered by all of the stimuli assessed. The enhancing effects mediated by GSNO and SNAP did not depend on the stimulation of guanylyl cyclase and were prevented by the NO scavengers hemoglobin and PTIO (2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide). The inhibitory activity of SNP, on the other hand, was not prevented by NO scavengers, suggesting that it cannot be ascribed to the release of NO. In another set of experiments, neutrophils were pretreated with GSNO or SNAP for different times. Then cells were washed to remove NO donors from the culture medium, and cytotoxicity was triggered by different stimuli. It was found that neutrophils must be pretreated with NO donors for at least 4 h to increase cytotoxic responses, and pretreatment for longer periods (i.e., 8 or 18 h) further increased cytotoxicity. Not only cytotoxic responses, but also the production of O2- and H2O2, and the release of myeloperoxidase were increased under these conditions.     

Effect of endogenous nitric oxide on the nerve-muscle synapse function]

The nitric oxide (NO) precursor L-arginine was found to decrease the amplitude and the quantum content of the EPPs and to increase the amplitude of the AP third deflection in the frog neuromuscular junction of the m. cutaneous pectoris preparation. Inhibitor of the NO synthase NG-nitro-L-arginine methylester exerted opposite effects. The data obtained suggest that endogenous NO is produced in the neuromuscular synapse area and can modify the work of potassium ion channels.     

一氧化氮对心肌缺血/再灌注损伤细胞凋亡和心功能的影响

目的:采取促进或抑制NO的方法,了解在重复可逆性心肌缺血/再灌注所致的心肌顿抑时,血液中一氧化氮(NO)的动态变化与细胞顿抑及心功能的影响.方法:新西兰兔15只,随机分为3组(n=5):对照组、在静脉内注射NO合成底物L-精氨酸为L-Arg组、静脉注射一氧化氮合酶抑制剂L-硝基-精氨酸为L-NNA组.用戊巴比妥钠静脉注射麻醉后,结扎前降支制成心肌缺血/再灌注模型,用电子自旋共振法测定血液中NO含量,同时记录左心室最大上升速率dp/dtmax.将兔心肌缺血10 min,共3次,第1、2次缺血后再灌注10 min,第3次缺血后再灌注120 min.结果:第1次缺血/再灌注5 min时NO升高的顺序依次为L-Arg组最大、对照组次之,而L-NNA组较缺血前降低.而dp/dtmax明显下降的是L-Arg组最大、对照组次之、L-NNA组最小.细胞凋亡指数:L-Arg组最大,对照组次之、L-NNA组最小.结论:再灌注早期NO的大量生成及细胞凋亡参与加重心肌顿抑的过程.     

The diversity of nitric oxide function in plant responses to metal stress

Nitric oxide (NO) emerges as signalling molecule, which is involved in diverse physiological processes in plants. High mobility metal interferes with NO signaling. The exogenous NO alleviates metal stress, whereas endogenous NO contributes to metal toxicity in plants. Owing to different cellular localization and concentration, NO may act as multifunctional regulator in plant responses to metal stress. It not only plays a crucial role in the regulation of gene expression, but serves as a long-distance signal. Through tight modulation of redox signaling, the integration among NO, reactive oxygen species and stress-related hormones in plants determines whether plants stimulate death pathway or activate survival signaling.     

一氧化氮在吲哚昔酚抑制血管平滑肌细胞增殖中的作用

目的：观察吲哚昔酚（ldoxifene,ldo）对大鼠血管平滑肌细胞增殖的影响,并探讨平滑肌源性一氧化氮（NO）在其中的作用。方法：血管平滑肌细胞培养、NO释放的测定、细胞计数和MTT测定。结果：吲哚昔酚可剂量依赖性的促使血管平滑肌细胞NO的释放,10μmol／L吲哚昔酚明显抑制10％胎牛血清（FCS）和10^-7mol／L的ET-1诱导的细胞增殖,吲哚昔酚的抑制作用可被一氧化氮合酶抑制剂L-NAME（100μmol／L）和鸟苷酸环化酶（guanylate cyclase,GC）抑制剂美蓝（methylene blue,MB）（10μmol／L）明显减轻。结论：吲哚昔酚抑制血管平滑肌细胞增殖的作用与其NO释放密切相关,其中可能有NO-GC-cGMP通路的参与。     

Effect of nitric oxide synthase inhibition on cardiorespiratory responses in the conscious rat

Gozal, David, José E. Torres, Yair M. Gozal, andSanford M. Littwin. Effect of nitric oxide synthase inhibition on cardiorespiratory responses in the conscious rat. J. Appl. Physiol. 81(5): 2068-2077, 1996.Nitricoxide synthase (NOS) blockade was used to test the cardioventilatoryresponses to hypercapnia and hypoxia in freely behaving animals.Chronically instrumented adult Sprague-Dawley rats were studied beforeand after intravenous administration of either 100 mg/kg ofN^G-nitro-L-arginine methylester (L-NAME), a nonspecificNOS blocker, or 10 mg/kg ofS-methyl-L-thiocitrulline(SMTC), a selective neural NOS inhibitor.L-NAME injection inducedsustained blood pressure (BP) elevation with transient tachycardia andincreased minute ventilation (E), whichreturned to baseline within minutes. SMTC elicited similar, althoughtransient, BP increases; however, heart rate andE decreased.L-NAME and SMTC did not modifyoverall steady-state hypercapnic responses. In controlconditions, hypoxia induced early Eincreases with further E enhancementsat 30 min. L-NAME increased theearly E response to 10%O₂ but induced lateE reductions in hypoxia. SMTC did notchange early E responses but inducedmarked reductions in the later Ehypoxic responses. In control animals, hypoxia induced a significantheart rate increase. This increase was absent during the early response after SMTC and was followed in bothL-NAME- and SMTC-treated animals by significant heart rate reductions to values below room air. Similarly, the sustained BP response to hypoxia in control animals wasabsent after administration of NOS inhibitors. These findings suggestthat NOS activity exerts excitatory influences on respiration andcardiac chronotropy and sustained vasomotor tone during hypoxia. Wespeculate that NOS-mediated mechanisms may play an important role inhypoxia-induced ventilatory roll-off during wakefulness.

     

Segmental pulmonary vascular responses to ATP in rat lungs: role of nitric oxide

Hakim, Tawfic S., Lara Ferrario, Jeffrey C. Freedman, RobertE. Carlin, and Enrico M. Camporesi. Segmental pulmonary vascularresponses to ATP in rat lungs: role of nitric oxide. J. Appl. Physiol. 82(3): 852-858, 1997.ATP exhibits vascular pressor and depressor responses in a dose-and tone-dependent manner. The vascular site of ATP-induced contractionor dilation has not previously been characterized. Using the vascularocclusion technique, we investigated the effects of ATP in isolated rat lungs perfused with autologous blood (hematocrit = 20%) and described its action during resting and elevated tone in terms of changes inresistances of the small and large arteries and veins. During restingtone, ATP (10⁵M)

     

Effect of nitric oxide synthase inhibitor on diaphragmatic function after resistive loading

We studied the effect of a nitric oxide synthase inhibitor, Nomega-Nitro-L-arginine-methyl-ester (L-NAME), on in vitro diphragmatic function both at rest (control) or after inspiratory resistive loading (IRL). Sprague-Dawley rats were anesthetized, instrumented, and then the following experimental groups: (1) controls; (2) L-NAME (100 mg/kg/body weight intravenously alone); (3) IRL alone; and (4) L-NAME + IRL. The IRL protocol consisted of applying a variable resistor to the inspiratory limb of a two-way valve at 70% of maximal airway pressure until apnea. After the experiment, the animals were sacrificed and diaphragmatic strips were obtained for activity of constitutive nitric oxide synthase (cNOS) and measurements of in vitro contractile properties: tetanic (Po) and twitch tensions (Pt). cNOS activity was significantly decreased in the L-NAME and L-NAME + IRL groups (P < or = 0.05) as compared with control and IRL groups. L-NAME alone did not affect Po or Pt. However, in both IRL groups, with and without was a significant decrease in Po and Pt. This reduction was comparable in both groups. In summary, our data showed that L-NAME resulted in a significant decrease cNOS activity, but in vitro contractility was impaired.     

Lack of nitric oxide synthase depresses ion transporting enzyme function in cardiac muscle

Nitric oxide (NO*) is produced endogenously from NOS isoforms bound to sarcolemmal (SL) and sarcoplasmic reticulum (SR) membranes. To investigate whether locally generated NO* directly affects the activity of enzymes mediating ion active transport, we studied whether knockout of selected NOS isoforms would affect the functions of cardiac SL (Na+ + K+)-ATPase and SR Ca2+-ATPase. Cardiac SL and SR vesicles containing either SL (Na+ + K+)-ATPase or SR Ca2+-ATPase were isolated from mice lacking either nNOS or eNOS, or both, and tested for enzyme activities. Western blot analysis revealed that absence of single or double NOS isoforms did not interrupt the protein expression of SL (Na+ + K+)-ATPase and SR Ca2+-ATPase in cardiac muscle cells. However, lack of NOS isoforms in cardiac muscle significantly altered both (Na+ + K+)-ATPase activity and SR Ca2+-ATPase function. Our experimental results suggest that disrupted endogenous NO* production may change local redox conditions and lead to an unbalanced free radical homeostasis in cardiac muscle cells which, in turn, may affect key enzyme activities and membrane ion active transport systems in the heart.     

Nitric oxide and cardiac function

Nitric oxide (NO) participates in the control of contractility and heart rate, limits cardiac remodeling after an infarction and contributes to the protective effect of ischemic pre- and postconditioning. Low concentrations of NO, with production of small amounts of cGMP, inhibit phosphodiesterase III, thus preventing the hydrolysis of cAMP. The subsequent activation of a protein-kinase A causes the opening of sarcolemmal voltage-operated and sarcoplasmic ryanodin receptor Ca(2+) channels, thus increasing myocardial contractility. High concentrations of NO induce the production of larger amounts of cGMP which are responsible for a cardiodepression in response to an activation of protein kinase G (PKG) with blockade of sarcolemmal Ca(2+) channels. NO is also involved in reduced contractile response to adrenergic stimulation in heart failure. A reduction of heart rate is an evident effect of NO-synthase (NOS) inhibition. It is noteworthy that the direct effect of NOS inhibition can be altered if baroreceptors are stimulated by increases in blood pressure. Finally, NO can limit the deleterious effects of cardiac remodeling after myocardial infarction possibly via the cGMP pathway. The protective effect of NO is mainly mediated by the guanylyl cyclase-cGMP pathway resulting in activation of PKG with opening of mitochondrial ATP-sensitive potassium channels and inhibition of the mitochondrial permeability transition pores. NO acting on heart is produced by vascular and endocardial endothelial NOS, as well as neuronal and inducible synthases. In particular, while in the basal control of contractility, endothelial synthase has a predominant role, the inducible isoform is mainly responsible for the cardiodepression in septic shock.     

Effect of nitric oxide and putrescine on antioxidative responses under NaCl stress in chickpea plants

Chickpea plants were subjected to salt stress for 48 h with 100 mM NaCl, after 50 days of growth. Other batches of plants were simultaneously treated with 0.2 mM sodium nitroprusside (NO donor) or 0.5 mM putrescine (polyamine) to examine their antioxidant effects. Sodium chloride stress adversely affected the relative water content (RWC), electrolyte leakage and lipid peroxidation in leaves. Sodium nitroprusside and putrescine could completely ameliorate the toxic effects of salt stress on electrolyte leakage and lipid peroxidation and partially on RWC. No significant decline in chlorophyll content under salt stress as well as with other treatments was observed. Sodium chloride stress activated the antioxidant defense system by increasing the activities of peroxidase (POX), catalase (CAT) superoxide dismutase (SOD) and ascorbate peroxidase (APX). However no significant effect was observed on glutathione reductase (GR) and dehydro ascorbate reductase (DHAR) activities. Both putrescine and NO had a positive effect on antioxidant enzymes under salt stress. Putrescine was more effective in scavenging superoxide radical as it increased the SOD activity under salt stress whereas nitric oxide was effective in hydrolyzing H₂O₂ by increasing the activities of CAT, POX and APX under salt stress.