NG-nitro L-arginine methyl ester and other alkyl esters of arginine are muscarinic receptor antagonists

Significance of nitric oxide derived from the nitric oxide synthases system in cardiovascular interorgan crosstalk

Interorgan crosstalk contributes to the pathogenesis of various disorders, and drug development based on interorgan crosstalk is attracting attention. The roles of nitric oxide (NO) derived from the NO synthases system (NOSs) in interorgan crosstalk remain unclear. We have investigated this issue by using our mice deficient in all 3 NOSs (triple n/i/eNOSs-/- mice). We reported that 2/3 nephrectomized triple n/i/eNOSs-/- mice die suddenly because of the early onset of myocardial infarction, suggesting the protective role of NO derived from NOSs in the crosstalk between the kidney and the heart. We studied the role of NO derived from NOSs expressed in the bone marrow in vascular lesion formation. Constrictive arterial remodeling and neointimal formation following unilateral carotid artery ligation were prominently aggravated in wild-type mice transplanted with triple n/i/eNOSs-/- bone marrow cells as compared with those with wild-type bone marrow cells, suggesting the protective role of NO derived from NOSs in the crosstalk between the bone marrow and the blood vessel. We further investigated the role of NO derived from NOSs expressed in the bone marrow in pulmonary hypertension. The extent of pulmonary hypertension after chronic hypoxic exposure was markedly exacerbated in wild-type mice that underwent triple n/i/eNOSs-/- bone marrow transplantation as compared with those that underwent wild-type bone marrow transplantation, suggesting the protective role of NO derived from NOSs in the crosstalk between the bone marrow and the lung. These lines of evidence demonstrate that systemic and myelocytic NOSs could be novel therapeutic targets for myocardial infarction, vascular disease, and pulmonary hypertension. SIGNIFICANCE STATEMENT: This study demonstrated partial nephrectomy accelerates the occurrence of myocardial infarction induced by systemic NOSs deficiency in triple n/i/eNOSs-/- mice, that myelocytic NOSs deficiency aggravates vascular lesion formation after unilateral carotid artery ligation, and that myelocytic NOSs deficiency exacerbates chronic hypoxia-induced pulmonary hypertension. These results suggest that NO derived from NOSs plays a protective role in cardiovascular interorgan crosstalk, indicating that systemic and myelocytic NOSs could be important therapeutic targets for myocardial infarction, vascular disease, and pulmonary hypertension.

Vasorelaxant mechanisms of the antidiabetic anagliptin in rabbit aorta: roles of Kv channels and SERCA pump

AIMS

The present study investigated the vasorelaxant mechanisms of an oral antidiabetic drug, anagliptin, using phenylephrine (Phe)-induced pre-contracted rabbit aortic rings.

METHODS

Arterial tone measurement was performed in rabbit thoracic aortic rings.

RESULTS

Anagliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the classical voltagedependent K+ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly decreased the vasorelaxant effect of anagliptin, whereas pre-treatment with the inwardly rectifying K+ (Kir) channel inhibitor Ba2+, the ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, and the large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline did not attenuate the vasorelaxant effect. Furthermore, the vasorelaxant response of anagliptin was effectively inhibited by pre-treatment with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid. Neither cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) nor cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) reduced the vasorelaxant effect of anagliptin. Similarly, the anagliptin-induced vasorelaxation was independent of the endothelium.

CONCLUSIONS

Based on these results, we suggest that anagliptin-induced vasorelaxation in rabbit aortic smooth muscle occurs by activating Kv channels and the SERCA pump, independent of other vascular K+ channels, cAMP/PKA- or cGMP/PKG-related signaling pathways, and the endothelium.

Role of Nitric Oxide Synthases in Respiratory Health and Disease: Insights from Triple Nitric Oxide Synthases Knockout Mice

The system of nitric oxide synthases (NOSs) is comprised of three isoforms: nNOS, iNOS, and eNOS. The roles of NOSs in respiratory diseases in vivo have been studied by using inhibitors of NOSs and NOS-knockout mice. Their exact roles remain uncertain, however, because of the non-specificity of inhibitors of NOSs and compensatory up-regulation of other NOSs in NOS-KO mice. We addressed this point in our triple-n/i/eNOSs-KO mice. Triple-n/i/eNOSs-KO mice spontaneously developed pulmonary emphysema and displayed exacerbation of bleomycin-induced pulmonary fibrosis as compared with wild-type (WT) mice. Triple-n/i/eNOSs-KO mice exhibited worsening of hypoxic pulmonary hypertension (PH), which was reversed by treatment with sodium nitrate, and WT mice that underwent triple-n/i/eNOSs-KO bone marrow transplantation (BMT) also showed aggravation of hypoxic PH compared with those that underwent WT BMT. Conversely, ovalbumin-evoked asthma was milder in triple-n/i/eNOSs-KO than WT mice. These results suggest that the roles of NOSs are different in different pathologic states, even in the same respiratory diseases, indicating the diversity of the roles of NOSs. In this review, we describe these previous studies and discuss the roles of NOSs in respiratory health and disease. We also explain the current state of development of inorganic nitrate as a new drug for respiratory diseases.

MECHANISMS OF CARDIAC DYSFUNCTION IN SEPSIS

ABSTRACT

Studies in animal models of sepsis have elucidated an intricate network of signaling pathways that lead to the dysregulation of myocardial Ca 2+ handling and subsequently to a decrease in cardiac contractile force, in a sex- and model-dependent manner. After challenge with a lethal dose of LPS, male animals show a decrease in cellular Ca 2+ transients (ΔCa i ), with intact myofilament function, whereas female animals show myofilament dysfunction, with intact ΔCa i . Male mice challenged with a low, nonlethal dose of LPS also develop myofilament desensitization, with intact ΔCa i . In the cecal ligation and puncture (CLP) model, the causative mechanisms seem similar to those in the LPS model in male mice and are unknown in female subjects. ΔCa i decrease in male mice is primarily due to redox-dependent inhibition of sarco/endoplasmic reticulum Ca 2+ ATP-ase (SERCA). Reactive oxygen species (ROS) are overproduced by dysregulated mitochondria and the enzymes NADPH/NADH oxidase, cyclooxygenase, and xanthine oxidase. In addition to inhibiting SERCA, ROS amplify cardiomyocyte cytokine production and mitochondrial dysfunction, making the process self-propagating. In contrast, female animals may exhibit a natural redox resilience. Myofilament dysfunction is due to hyperphosphorylation of troponin I, troponin T cleavage by caspase-3, and overproduction of cGMP by NO-activated soluble guanylate cyclase. Depleted, dysfunctional, or uncoupled mitochondria likely synthesize less ATP in both sexes, but the role of energy deficit is not clear. NO produced by NO synthase (NOS)-3 and mitochondrial NOSs, protein kinases and phosphatases, the processes of autophagy and sarco/endoplasmic reticulum stress, and β-adrenergic insensitivity may also play currently uncertain roles.

Mechanisms underlying the vasodilatory effects of canagliflozin in the rabbit thoracic aorta: Involvement of the SERCA pump and Kv channels

AIMS

Canagliflozin is an anti-diabetic agent and sodium glucose co-transporter-2 inhibitor. Despite numerous clinical trials demonstrating its beneficial effects on blood pressure, the cellular mechanisms underlying the effects of canagliflozin on vascular reactivity have yet to be clarified. We investigated the vasodilatory effect of canagliflozin on aortic rings isolated from rabbits.

MAIN METHODS

We used rabbit thoracic aortic rings and its arterial tone was tested by using wire myography system.

KEY FINDINGS

Canagliflozin caused concentration-dependent vasodilation in aortic rings pre-constricted with phenylephrine or high K⁺. However, the degree of canagliflozin-induced vasodilation of the aortic rings pre-constricted with high K⁺ was less than that of rings pre-constricted with phenylephrine. Application of 4-aminopyridine, a voltage-dependent K⁺ (Kv) channel inhibitor, reduced canagliflozin-induced vasodilation. However, pre-incubation of an inwardly rectifying K⁺ channel inhibitor, a large-conductance Ca²⁺-activated K⁺ channel inhibitor, and an ATP-sensitive K⁺ inhibitor did not modulate the vasodilatory effects of canagliflozin. Indeed, canagliflozin increased Kv currents in aortic smooth muscle cells. Pre-treatment with thapsigargin or cyclopiazonic acid, a sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors, reduced the vasodilatory effects of canagliflozin. Conversely, pre-treatment with a Ca²⁺ channel inhibitor, adenylyl cyclase/PKA inhibitors, and guanylyl cyclase/PKG inhibitors did not modulate the vasodilatory effects of canagliflozin. Endothelium removal, and pre-treatment with the nitric oxide synthase inhibitor L-NAME, and small- and intermediate-conductance Ca²⁺-activated K⁺ channel inhibitor apamin and TRAM-34, did not diminish the vasodilatory effects of canagliflozin.

SIGNIFICANCE

Our results indicate that canagliflozin induces vasodilation, which is dependent on the robust SERCA activity and Kv channel activation.

Spontaneous pulmonary emphysema in mice lacking all three nitric oxide synthase isoforms

The roles of endogenous nitric oxide (NO) derived from the entire NO synthases (NOSs) system have yet to be fully elucidated. We addressed this issue in mice in which all three NOS isoforms were deleted. Under basal conditions, the triple n/i/eNOSs^−/− mice displayed significantly longer mean alveolar linear intercept length, increased alveolar destructive index, reduced lung elastic fiber content, lower lung field computed tomographic value, and greater end-expiratory lung volume as compared with wild-type (WT) mice. None of single NOS^−/− or double NOSs^−/− genotypes showed such features. These findings were observed in the triple n/i/eNOSs^−/− mice as early as 4 weeks after birth. Cyclopaedic and quantitative comparisons of mRNA expression levels between the lungs of WT and triple n/i/eNOSs^−/− mice by cap analysis of gene expression (CAGE) revealed that mRNA expression levels of three Wnt ligands and ten Wnt/β-catenin signaling components were significantly reduced in the lungs of triple n/i/eNOSs^−/− mice. These results provide the first direct evidence that complete disruption of all three NOS genes results in spontaneous pulmonary emphysema in juvenile mice in vivo possibly through down-regulation of the Wnt/β-catenin signaling pathway, demonstrating a novel preventive role of the endogenous NO/NOS system in the occurrence of pulmonary emphysema.

Dysregulation of TRPV4, eNOS and caveolin-1 contribute to endothelial dysfunction in the streptozotocin rat model of diabetes

Endothelial dysfunction is a common complication in diabetes in which endothelium-dependent vasorelaxation is impaired. The aim of this study was to examine the involvement of the TRPV4 ion channel in type 1 diabetic endothelial dysfunction and the possible association of endothelial dysfunction with reduced expression of TRPV4, endothelial nitric oxide synthase (eNOS) and caveolin-1. Male Wistar rats (350-450 g) were injected with 65 mg/kg i.p. streptozotocin (STZ) or vehicle. Endothelial function was investigated in aortic rings and mesenteric arteries using organ bath and myograph, respectively. TRPV4 function was studied with fura-2 calcium imaging in endothelial cells cultured from aortas from control and STZ treated rats. TRPV4, caveolin-1 and eNOS expression was investigated in these cells using immunohistochemistry. STZ-treated diabetic rats showed significant endothelial dysfunction characterised by impaired muscarinic-induced vasorelaxation (aortic rings: STZ-diabetics: Emax = 29.6 ± 9.3%; control: Emax = 77.2 ± 2.5% P˂0.001), as well as significant impairment in TRPV4-induced vasorelaxation (aortic rings, 4αPDD STZ-diabetics: Emax = 56.0 ± 5.5%; control: Emax = 81.1 ± 2.1% P˂0.001). Furthermore, STZ-diabetic primary aortic endothelial cells showed a significant reduction in TRPV4-induced intracellular calcium elevation (P˂0.05) compared with the control group. This was associated with significantly lower expression of TRPV4, caveolin-1 and eNOS and this was reversed by insulin treatment of the endothelial cultures from STZ -diabetic rats. Taken together, these data are consistent with the hypothesis that signalling through TRPV4, caveolin-1, and eNOS is downregulated in STZ-diabetic aortic endothelial cells and restored by insulin treatment.

NO-mediated activation of KATP channels contributes to cutaneous thermal hyperemia in young adults

Local skin heating to 42°C causes cutaneous thermal hyperemia largely via nitric oxide (NO) synthase (NOS)-related mechanisms. We assessed the hypothesis that ATP-sensitive K⁺ (K_ATP) channels interact with NOS to mediate cutaneous thermal hyperemia. In 13 young adults (6 women, 7 men), cutaneous vascular conductance (CVC) was measured at four intradermal microdialysis sites that were continuously perfused with 1) lactated Ringer solution (control), 2) 5 mM glibenclamide (K_ATP channel blocker), 3) 20 mM N^G-nitro-l-arginine methyl ester (NOS inhibitor), or 4) a combination of K_ATP channel blocker and NOS inhibitor. Local skin heating to 42°C was administered at all four treatment sites to elicit cutaneous thermal hyperemia. Thirty minutes after the local heating, 1.25 mM pinacidil (K_ATP channel opener) and subsequently 25 mM sodium nitroprusside (NO donor) were administered to three of the four sites (each 25-30 min). The local heating-induced prolonged elevation in CVC was attenuated by glibenclamide (19%), but the transient initial peak was not. However, glibenclamide had no effect on the prolonged elevation in CVC in the presence of NOS inhibition. Pinacidil caused an elevation in CVC, but this response was abolished at the glibenclamide-treated skin site, demonstrating its effectiveness as a K_ATP channel blocker. The pinacidil-induced increase in CVC was unaffected by NOS inhibition, whereas the increase in CVC elicited by sodium nitroprusside was partly (15%) inhibited by glibenclamide. In summary, we showed an interactive effect of K_ATP channels and NOS for the plateau of cutaneous thermal hyperemia. This interplay may reflect a vascular smooth muscle cell K_ATP channel activation by NO.

Diet-induced obesity in young mice: Consequences on the pancreatic intrinsic nervous system control of insulin secretion

INTRODUCTION

Obesity has become a pandaemic even in children. We aimed to investigate the impact of obesity in youth on later pancreatic intrinsic nervous system (PINS) phenotype and control of insulin secretion.

METHODS

Young mice (5-week-old, T0 group) were fed either a normal diet (ND group) or a Western diet (WD group) for 12 weeks. Pancreas nervous system density, PINS phenotype and pancreas anatomy were analysed by immunohistochemistry at T0 and in adulthood (ND and WD groups). Insulin secretion was also studied in these 3 groups using a new model of ex vivo pancreatic culture, where PINS was stimulated by nicotinic and nitrergic agonists with and without antagonists. Insulin was assayed in supernatants by ELISA.

RESULTS

Pancreas nervous system density decreased with age in ND (P < .01) but not in WD mice (P = .08). Western diet decreased the PINS nitrergic component as compared to normal diet (P < .01) but it did not modify its cholinergic component (P = .50). Nicotinic PINS stimulation induced greater insulin secretion in ND compared to WD mice (P < .001) whereas nitrergic stimulation significantly decreased insulin secretion in ND mice (P < .001) and tended to increase insulin secretion in WD mice (P = .08). Endocrine pancreas anatomy was not modified by the Western diet as compared to the normal diet (P = .93).

CONCLUSIONS

Early Western diet induced neuronal density and phenotype changes in PINS that might be involved in the pancreas insulin secretion dysfunctions associated with obesity.

Shear Stress Attenuates Inward Remodeling in Cultured Mouse Thoracodorsal Arteries in an eNOS-Dependent, but Not Hemodynamic Manner, and Increases Cx37 Expression

BACKGROUND

Arteries chronically constricted in culture remodel to smaller diameters. Conversely, elevated luminal shear stress (SS) promotes outward remodeling of arteries in vivo and prevents inward remodeling in culture in a nitric oxide synthase (NOS)-dependent manner.

OBJECTIVES

To determine whether SS-induced prevention of inward remodeling in cultured arteries is specifically eNOS-dependent and requires dilation, and whether SS alters the expression of eNOS and other genes potentially involved in remodeling.

METHODS

Female mouse thoracodorsal arteries were cannulated, pressurized to 80 mm Hg, and cultured for 2 days with low SS (<7 dyn/cm2), high SS (≥15 dyn/cm2), high SS + L-NAME (NOS inhibitor, 10-4 M), or high SS in arteries from eNOS-/- mice. In separate arteries cultured 1 day with low or high SS, eNOS and connexin (Cx) 37, Cx40, and Cx43 mRNA were assessed with real-time PCR.

RESULTS

High SS caused little change in passive diameters after culture (-4.7 ± 2.0%), which was less than low SS (-18.9 ± 1.4%; p < 0.0001), high SS eNOS-/- (-18.0 ± 1.5; p < 0.001), or high SS + L-NAME (-12.0 ± 0.6%; nonsignificant) despite similar constriction during culture. Cx37 mRNA expression was increased (p < 0.05) with high SS, but other gene levels were not different.

CONCLUSIONS

eNOS is involved in SS-induced prevention of inward remodeling in cultured small arteries. This effect does not require NO-mediated dilation. SS increased Cx37.

Urinary dysfunction in transgenic sickle cell mice: model of idiopathic overactive bladder syndrome

Voiding abnormalities are common among the sickle cell disease (SCD) population, among which overactive bladder (OAB) syndrome is observed at rates as high as 39%. Although detrusor overactivity is the most common cause of OAB, its molecular pathophysiology is not well elucidated. The nitric oxide (NO) signaling pathway has been implicated in the regulation of lower genitourinary tract function. In the present study, we evaluated the role of the NO signaling pathway in voiding function of transgenic SCD mice compared with combined endothelial and neuronal NO synthase gene-deficient mice, both serving as models of NO deficiency. Mice underwent void spot assay and cystometry, and bladder and urethral specimens were studied using in vitro tissue myography. Both mouse models exhibited increased void volumes; increased nonvoiding and voiding contraction frequencies; decreased bladder compliance; increased detrusor smooth muscle contraction responses to electrical field stimulation, KCl, and carbachol; and increased urethral smooth muscle relaxation responses to sodium nitroprusside compared with WT mice. In conclusion, our comprehensive behavioral and functional study of the SCD mouse lower genitourinary tract, in correlation with that of the NO-deficient mouse, reveals NO effector actions in voiding function and suggests that NO signaling derangements are associated with an OAB phenotype. These findings may allow further study of molecular targets for the characterization and evaluation of OAB.

Endogenous nitric oxide inhibits spinal NMDA receptor activity and pain hypersensitivity induced by nerve injury

The role of nitric oxide (NO) in nociceptive transmission at the spinal cord level remains uncertain. Increased activity of spinal N-methyl-d-aspartate (NMDA) receptors contributes to development of chronic pain induced by peripheral nerve injury. In this study, we determined how endogenous NO affects NMDA receptor activity of spinal cord dorsal horn neurons in control and spinal nerve-ligated rats. Bath application of the NO precursor l-arginine or the NO donor S-nitroso-N-acetylpenicillamine (SNAP) significantly inhibited NMDA receptor currents of spinal dorsal horn neurons in both sham control and nerve-injured rats. Inhibition of neuronal nitric oxide synthase (nNOS) or blocking the S-nitrosylation reaction with N-ethylmaleimide abolished the inhibitory effects of l-arginine on NMDA receptor currents recorded from spinal dorsal horn neurons in sham control and nerve-injured rats. However, bath application of the cGMP analog 8-bromo-cGMP had no significant effects on spinal NMDA receptor currents. Inhibition of soluble guanylyl cyclase also did not alter the inhibitory effect of l-arginine on spinal NMDA receptor activity. Furthermore, knockdown of nNOS with siRNA abolished the inhibitory effects of l-arginine, but not SNAP, on spinal NMDA receptor activity in both groups of rats. Additionally, intrathecal injection of l-arginine significantly attenuated mechanical or thermal hyperalgesia induced by nerve injury, and the l-arginine effect was diminished in rats treated with a nNOS inhibitor or nNOS-specific siRNA. These findings suggest that endogenous NO inhibits spinal NMDA receptor activity through S-nitrosylation. NO derived from nNOS attenuates spinal nociceptive transmission and neuropathic pain induced by nerve injury.

Crucial roles of nitric oxide synthases in β-adrenoceptor-mediated bladder relaxation in mice

The specific roles of nitric oxide (NO) synthases (NOSs) in bladder smooth muscle remain to be elucidated. We examined the roles of NOSs in β-adrenoceptor (AR)-mediated bladder relaxation. Male mice (C57BL6) deficient of neuronal NOS [nNOS-knockout (KO)], endothelial NOS (eNOS-KO), neuronal/endothelial NOS (n/eNOS-KO), neuronal/endothelial/inducible NOS (n/e/iNOS-KO), and their controls [wild-type (WT)] were used. Immunohistochemical analysis was performed in the bladder. Then the responses to relaxing agents and the effects of several inhibitors on the relaxing responses were examined in bladder strips precontracted with carbachol. Immunofluorescence staining showed expressions of nNOS and eNOS in the urothelium and smooth muscle of the bladder. Isoproterenol-induced relaxations were significantly reduced in nNOS-KO mice and were further reduced in n/eNOS-KO and n/e/iNOS-KO mice compared with WT mice. The relaxation in n/e/iNOS-KO mice was almost the same as in n/eNOS-KO mice. Inhibition of Ca2+-activated K+ (KCa) channel with charybdotoxin and apamin abolished isoproterenol-induced bladder relaxation in WT mice. Moreover, direct activation of KCa channel with NS1619 caused comparable extent of relaxations among WT, nNOS-KO, and n/eNOS-KO mice. In contrast, NONOate (a NO donor) or hydrogen peroxide (H2O2) (another possible relaxing factor from eNOS) caused minimal relaxations, and catalase (H2O2 scavenger) had no inhibitory effects on isoproterenol-induced relaxations. These results indicate that both nNOS and eNOS are substantially involved in β-AR-mediated bladder relaxations in a NO- or H2O2-independent manner through activation of KCa channels.

Amlodipine, Nitric Oxide, and Platelet Aggregation

This study examined the effect of a single dose of 0.4 mg·kg−1 amlodipine on platelet aggregation with and without the nitric oxide synthase inhibitor, Nw-nitro-L-arginine. Blood samples were collected from rhesus monkeys at 0, 1, 2, and 6 hours after administration of amlodipine. Aggregation in platelet-rich plasma was stimulated by 10 μM adenosine diphosphate, 20 μM epinephrine, or 2 μg·mL−1 collagen. Administration of Nw-nitro-L-arginine alone significantly increased platelet aggregation for up to 2 hours. This effect was antagonized by amlodipine administered 30 minutes after Nw-nitro-L-arginine. The findings suggest that in platelet-rich plasma, the inhibition of platelet aggregation by amlodipine might be mediated by nitric oxide, a potent endogenous inhibitor of aggregation.

Hypertension potentiates cataractogenesis in rat eye through modulation of oxidative stress and electrolyte homeostasis

Purpose

To evaluate modes of cataractogenesis in the hypertensive state by using different hypertensive animal models, including fructose, cadmium chloride (CdCl₂), N_ω-nitro-l-arginine methyl ester (l-NAME), and two-kidney, one clip (2K1C) method.

Methods

Male Sprague–Dawley albino rats (150–180 g) were divided into different groups, each group containing six animals. Hypertension was induced in animals via six weeks administration of fructose (10% solution in drinking water), CdCl₂ (0.5 mg/kg/day, i.p.), and l-NAME (20 mg/kg/day, p.o.) in their respective groups and NaCl (0.9% solution in drinking water) in the 2K1C group. The Ramipril-treated group (2 mg/kg/day, orally) served as a standard group for the 2K1C animal model. Blood pressure was measured biweekly using non-invasive blood pressure system. The biochemical parameters in serum and eye lenses were evaluated after six weeks of the experimental protocol.

Results

Hypertensive animal models showed significant induction of systolic and diastolic blood pressure and modulation of oxidative stress through depletion of antioxidants, including glutathione peroxidase, catalase, superoxide dismutase, glutathione, and elevation of malondialdehyde in serum and eye lenses. A significant elevation of ionic contents (Na⁺ and Ca²⁺) and reduction of total protein and Ca²⁺ ATPase activity in eye lenses were observed in all hypertensive animal models except l-NAME when compared with the normal group. The significant restoration of the antioxidants, Malondialdehyde (MDA) total protein, and ionic contents in the eye lenses concomitant with reduction of blood pressure were observed in the ramipril-treated group as compared to the 2K1C animal model. The results indicate that the fructose, CdCl_2, and 2K1C models showed pronounced cataractogenic effects in the rat eye lenses.

Conclusion

Based on our findings, it can be concluded that systemic hypertension significantly increases the risk of cataract formation in the rat eyes via modulation of the antioxidant defense mechanism and electrolyte homeostasis.

Role of NO in arterial vascular function of intertidal fish (Girella laevifrons) and marine fish (Isacia conceptionis)

Abstract Previous studies performed in intertidal fish (Girella laevifrons),as well as marine fish (Isacia conceptionis), showed that acetylcholine (ACh) produced contractions mediated by cyclooxygenases that were dependent on the area and potency of contraction in several arterial vessels. Given that the role of nitric oxide is poorly understood in fish, the objective of our study was to evaluate the role of nitric oxide in branchial afferent (ABA), branchial efferent (ABE), dorsal (DA) and mesenteric (MA) arterial vessels from both Girella laevifrons and Isacia conceptionis. We studied afferent and efferent branchial, dorsal and mesenteric arteries that were dissected from 6 juvenile specimens. Isometric tension studies were done using dose response curves (DRC) for Ach (10–13 to 10–3 M) and blockade with L-NAME (10–5 M), and DRC for sodium nitroprusside (SNP, a donor of NO). L-NAME produced an attenuation of the contractile response in the dorsal, afferent and efferent branchial arteries and a potentiation of the contraction in the MA. SNP caused 70% dilation in the mesenteric artery and 40% in the dorsal artery. Our results suggest that Ach promotes precarious dilatation in MA mediated by NO; data that is supported by the use of sodium nitroprusside. In contrast, in the vessels DA, ABA and EBA our results support that the pathway Ach-NO-relaxation is absent in both species.

Endothelial-derived hyperpolarization contributes to acetylcholine-mediated vasodilation in human skin in a dose-dependent manner

Cutaneous acetylcholine (ACh)-mediated dilation is commonly used to assess microvascular function, but the mechanisms of dilation are poorly understood. Depending on dose and method of administration, nitric oxide (NO) and prostanoids are involved to varying extents and the roles of endothelial-derived hyperpolarizing factors (EDHFs) are unclear. In the present study, five incremental doses of ACh (0.01-100 mM) were delivered either as a 1-min bolus (protocol 1, n = 12) or as a ≥20-min continuous infusion (protocol 2, n = 10) via microdialysis fibers infused with 1) lactated Ringer, 2) tetraethylammonium (TEA) [a calcium-activated potassium channel (KCa) and EDHF inhibitor], 3) L-NNA+ketorolac [NO synthase (NOS) and cyclooxygenase (COX) inhibitors], and 4) TEA+L-NNA+Ketorolac. The hyperemic response was characterized as peak and area under the curve (AUC) cutaneous vascular conductance (CVC) for bolus infusions or plateau CVC for continuous infusions, and reported as %maximal CVC. In protocol 1, TEA, alone and combined with NOS+COX inhibition, attenuated peak CVC (100 mM Ringer 59 ± 6% vs. TEA 43 ± 5%, P < 0.05; L-NNA+ketorolac 35 ± 4% vs. TEA+L-NNA+ketorolac 25 ± 4%, P < 0.05) and AUC (Ringer 25,414 ± 3,528 vs. TEA 21,403 ± 3,416%·s, P < 0.05; L-NNA+ketorolac 25,628 ± 3,828%(.)s vs. TEA+L-NNA+ketorolac 20,772 ± 3,711%·s, P < 0.05), although these effects were only significant at the highest dose of ACh. At lower doses, TEA lengthened the total time of the hyperemic response (10 mM Ringer 609 ± 78 s vs. TEA 860 ± 67 s, P < 0.05). In protocol 2, TEA alone did not affect plateau CVC, but attenuated plateau in combination with NOS+COX inhibition (100 mM 50.4 ± 6.6% vs. 30.9 ± 6.3%, P < 0.05). Therefore, EDHFs contribute to cutaneous ACh-mediated dilation, but their relative contribution is altered by the dose and infusion procedure.

Role of nitric oxide in murine conventional outflow physiology

Elevated intraocular pressure (IOP) is the main risk factor for glaucoma. Exogenous nitric oxide (NO) decreases IOP by increasing outflow facility, but whether endogenous NO production contributes to the physiological regulation of outflow facility is unclear. Outflow facility was measured by pressure-controlled perfusion in ex vivo eyes from C57BL/6 wild-type (WT) or transgenic mice expressing human endothelial NO synthase (eNOS) fused to green fluorescent protein (GFP) superimposed on the endogenously expressed murine eNOS (eNOS-GFPtg). In WT mice, exogenous NO delivered by 100 μM S-nitroso-N-acetylpenicillamine (SNAP) increased outflow facility by 62 ± 28% (SD) relative to control eyes perfused with the inactive SNAP analog N-acetyl-d-penicillamine (NAP; n = 5, P = 0.016). In contrast, in eyes from eNOS-GFPtg mice, SNAP had no effect on outflow facility relative to NAP (-9 ± 4%, P = 0.40). In WT mice, the nonselective NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, 10 μM) decreased outflow facility by 36 ± 13% (n = 5 each, P = 0.012), but 100 μM l-NAME had no detectable effect on outflow facility (-16 ± 5%, P = 0.22). An eNOS-selective inhibitor (cavtratin, 50 μM) decreased outflow facility by 19 ± 12% in WT (P = 0.011) and 39 ± 25% in eNOS-GFPtg (P = 0.014) mice. In the conventional outflow pathway of eNOS-GFPtg mice, eNOS-GFP expression was localized to endothelial cells lining Schlemm's canal and the downstream vessels, with no apparent expression in the trabecular meshwork. These results suggest that endogenous NO production by eNOS within endothelial cells of Schlemm's canal or downstream vessels contributes to the physiological regulation of aqueous humor outflow facility in mice, representing a viable strategy to more successfully lower IOP in glaucoma.

Endothelial nitric oxide synthase deficient mice are protected from lipopolysaccharide induced acute lung injury

Lipopolysaccharide (LPS) derived from the outer membrane of gram-negative bacteria induces acute lung injury (ALI) in mice. This injury is associated with lung edema, inflammation, diffuse alveolar damage, and severe respiratory insufficiency. We have previously reported that LPS-mediated nitric oxide synthase (NOS) uncoupling, through increases in asymmetric dimethylarginine (ADMA), plays an important role in the development of ALI through the generation of reactive oxygen and nitrogen species. Therefore, the focus of this study was to determine whether mice deficient in endothelial NOS (eNOS^-/-) are protected against ALI. In both wild-type and eNOS^-/- mice, ALI was induced by the intratracheal instillation of LPS (2 mg/kg). After 24 hours, we found that eNOS^-/-mice were protected against the LPS mediated increase in inflammatory cell infiltration, inflammatory cytokine production, and lung injury. In addition, LPS exposed eNOS^-/- mice had increased oxygen saturation and improved lung mechanics. The protection in eNOS^-/- mice was associated with an attenuated production of NO, NOS derived superoxide, and peroxynitrite. Furthermore, we found that eNOS^-/- mice had less RhoA activation that correlated with a reduction in RhoA nitration at Tyr³⁴. Finally, we found that the reduction in NOS uncoupling in eNOS^-/- mice was due to a preservation of dimethylarginine dimethylaminohydrolase (DDAH) activity that prevented the LPS-mediated increase in ADMA. Together our data suggest that eNOS derived reactive species play an important role in the development of LPS-mediated lung injury.

Glucose uptake during contraction in isolated skeletal muscles from neuronal nitric oxide synthase μ knockout mice

Inhibition of nitric oxide synthase (NOS) significantly attenuates the increase in skeletal muscle glucose uptake during contraction/exercise, and a greater attenuation is observed in individuals with Type 2 diabetes compared with healthy individuals. Therefore, NO appears to play an important role in mediating muscle glucose uptake during contraction. In this study, we investigated the involvement of neuronal NOSμ (nNOSμ), the main NOS isoform activated during contraction, on skeletal muscle glucose uptake during ex vivo contraction. Extensor digitorum longus muscles were isolated from nNOSμ(-/-) and nNOSμ(+/+) mice. Muscles were contracted ex vivo in a temperature-controlled (30°C) organ bath with or without the presence of the NOS inhibitor N(G)-monomethyl-l-arginine (L-NMMA) and the NOS substrate L-arginine. Glucose uptake was determined by radioactive tracers. Skeletal muscle glucose uptake increased approximately fourfold during contraction in muscles from both nNOSμ(-/-) and nNOSμ(+/+) mice. L-NMMA significantly attenuated the increase in muscle glucose uptake during contraction in both genotypes. This attenuation was reversed by L-arginine, suggesting that L-NMMA attenuated the increase in muscle glucose uptake during contraction by inhibiting NOS and not via a nonspecific effect of the inhibitor. Low levels of NOS activity (~4%) were detected in muscles from nNOSμ(-/-) mice, and there was no evidence of compensation from other NOS isoform or AMP-activated protein kinase which is also involved in mediating muscle glucose uptake during contraction. These results indicate that NO regulates skeletal muscle glucose uptake during ex vivo contraction independently of nNOSμ.

The effect of a selective neuronal nitric oxide synthase inhibitor 3-bromo 7-nitroindazole on spatial learning and memory in rats

Since the discovery of nitric oxide (NO) as a neuronal messenger, its way to modulate learning and memory functions is subject of intense research. NO is an intercellular messenger in the central nervous system and is formed on demand through the conversion of L-arginine to L-citrulline via the enzyme nitric oxide synthase (NOS). Neuronal form of nitric oxide synthase may play an important role in a wide range of physiological and pathological conditions. Therefore the aim of this study was to investigate the effects of chronic 3-bromo 7-nitroindazole (3-Br 7-NI), specific neuronal nitric oxide synthase (nNOS) inhibitor, administration on spatial learning and memory performance in rats using the Morris water maze (MWM) paradigm. Male rats received either 3-Br 7-NI (20mg/kg/day) or saline via intraperitoneal injection for 5days. Daily administration of the specific neuronal nitric oxide synthase (nNOS) inhibitor, 3-Br 7-NI impaired the acquisition of the MWM task. 3-Br 7-NI also impaired the probe trial. The MWM training was associated with a significant increase in the brain-derived neurotrophic factor (BDNF) mRNA expression in the hippocampus. BDNF mRNA expression in the hippocampus did not change after 3-Br 7-NI treatment. L-arginine significantly reversed behavioural parameters, and the effect of 3-Br 7-NI was found to be NO-dependent. There were no differences in locomotor activity and blood pressure in 3-Br 7-NI treated rats. Our results may suggest that nNOS plays a key role in spatial memory formation in rats.

Significance of nitric oxide synthases: Lessons from triple nitric oxide synthases null mice

Nitric oxide (NO) is synthesized by three distinct NO synthases (neuronal, inducible, and endothelial NOSs), all of which are expressed in almost all tissues and organs in humans. The regulatory roles of NOSs in vivo have been investigated in pharmacological studies with non-selective NOS inhibitors. However, the specificity of the inhibitors continues to be an issue of debate, and the authentic significance of NOSs is still poorly understood. To address this issue, we generated mice in which all three NOS genes are completely disrupted. The triple NOSs null mice exhibited cardiovascular abnormalities, including hypertension, arteriosclerosis, myocardial infarction, cardiac hypertrophy, diastolic heart failure, and reduced EDHF responses, with a shorter survival. The triple NOSs null mice also displayed metabolic abnormalities, including metabolic syndrome and high-fat diet-induced severe dyslipidemia. Furthermore, the triple NOSs null mice showed renal abnormalities (nephrogenic diabetes insipidus and pathological renal remodeling), lung abnormalities (accelerated pulmonary fibrosis), and bone abnormalities (increased bone mineral density and bone turnover). These results provide evidence that NOSs play pivotal roles in the pathogenesis of a wide variety of disorders. This review summarizes the latest knowledge on the significance of NOSs in vivo, based on lessons learned from experiments with our triple mutant model.

Cyclooxygenase inhibition does not alter methacholine-induced sweating

Cholinergic agents (e.g., methacholine) induce cutaneous vasodilation and sweating. Reports indicate that either nitric oxide (NO), cyclooxygenase (COX), or both can contribute to cholinergic cutaneous vasodilation. Also, NO is reportedly involved in cholinergic sweating; however, whether COX contributes to cholinergic sweating is unclear. Forearm sweat rate (ventilated capsule) and cutaneous vascular conductance (CVC, laser-Doppler perfusion units/mean arterial pressure) were evaluated in 10 healthy young (24 ± 4 yr) adults (7 men, 3 women) at four skin sites that were continuously perfused via intradermal microdialysis with 1) lactated Ringer (control), 2) 10 mM ketorolac (a nonselective COX inhibitor), 3) 10 mM N(G)-nitro-l-arginine methyl ester (l-NAME, a nonselective NO synthase inhibitor), or 4) a combination of 10 mM ketorolac + 10 mM l-NAME. At the four skin sites, methacholine was simultaneously infused in a dose-dependent manner (1, 10, 100, 1,000, 2,000 mM). Relative to the control site, forearm CVC was not influenced by ketorolac throughout the protocol (all P > 0.05), whereas l-NAME and ketorolac + l-NAME reduced forearm CVC at and above 10 mM methacholine (all P < 0.05). Conversely, there was no main effect of treatment site (P = 0.488) and no interaction of methacholine dose and treatment site (P = 0.711) on forearm sweating. Thus forearm sweating (in mg·min(-1)·cm(-2)) from baseline up to the maximal dose of methacholine was not different between the four sites (at 2,000 mM, control 0.50 ± 0.23, ketorolac 0.44 ± 0.23, l-NAME 0.51 ± 0.22, and ketorolac + l-NAME 0.51 ± 0.23). We show that both NO synthase and COX inhibition do not influence cholinergic sweating induced by 1-2,000 mM methacholine.

Modulation of resistance artery tone by the trace amine β-phenylethylamine: dual indirect sympathomimetic and α1-adrenoceptor blocking actions

The trace amine β-phenylethylamine (PEA) is normally present in the body at low nanomolar concentrations but can reach micromolar levels after ingestion of drugs that inhibit monoamine oxidase and primary amine oxidase. In vivo, PEA elicits a robust pressor response, but there is no consensus regarding the underlying mechanism, with both vasodilation and constriction reported in isolated blood vessels. Using functional and biochemical approaches, we found that at low micromolar concentrations PEA (1-30 μM) enhanced nerve-evoked vasoconstriction in the perfused rat mesenteric bed but at a higher concentration (100 μM) significantly inhibited these responses. The α2-adrenoceptor antagonist rauwolscine (1 µM) also enhanced nerve-mediated vasoconstriction, but in the presence of both rauwolscine (1 µM) and PEA (30 µM) together, nerve-evoked responses were initially potentiated and then showed time-dependent rundown. PEA (10 and 100 μM) significantly increased noradrenaline outflow from the mesenteric bed as determined by high-pressure liquid chromatography coupled with electrochemical detection. In isolated endothelium-denuded arterial segments, PEA (1 µM to 1 mM) caused concentration-dependent reversal of tone elicited by the α1-adrenoceptor agonists noradrenaline (EC50 51.69 ± 10.8 μM; n = 5), methoxamine (EC50 68.21 ± 1.70 μM; n = 5), and phenylephrine (EC50 67.74 ± 16.72 μM; n = 5) but was ineffective against tone induced by prostaglandin F2 α or U46619 (9,11-dideoxy-9α,11α-methanoepoxyprostaglandin F2 α). In rat brain homogenates, PEA displaced binding of both [(3)H]prazosin (Ki ≈ 25 μM) and [(3)H]rauwolscine (Ki ≈ 1.2 μM), ligands for α1- and α2-adrenoceptors, respectively. These data provide the first demonstration that dual indirect sympathomimetic and α1-adrenoceptor blocking actions underlie the vascular effects of PEA in resistance arteries.

Differential neuromodulatory role of NO in anxiety and seizures: an experimental study

Nitric oxide is a simple, ubiquitous, diatomic molecule with complex neuromodulatory functions. Anxiety and seizures are closely similar neurobehavioral disorders and are regulated by limbic system. The present study evaluated the regulatory roles of NO in these pathophysiological states in experimental models. In test for anxiety, aminophylline induced anxiogenic responses were assessed by the elevated plus maze (EPM) test, and a low dose of the drug (50 mg/kg) reduced both open arm entries and open arm time in rats. Pretreatment with the NO mimetic, L-arginine (500 and 1000 mg/kg) and melatonin (50 mg/kg) attenuated aminophylline induced anxiogenesis whereas the NO synthase inhibitors, L-NAME and 7-NI (30 mg/kg) aggravated the anxiogeneic response. Such aminophylline induced neurobehavioral suppression in the EPM activity was accompanied by increases in MDA levels and reductions in GSH and NOx activity in brain homogenates - changes which were reversed by L-arginine and melatonin pretreatments. In tests for seizures, aminophylline induced seizures and mortality at higher dose levels of the drug (300 mg/kg). Interestingly, such seizures and mortality in rats were antagonized by L-NAME and 7-NI pretreatments. On the other hand, L-arginine tended to potentiate seizures after sub-convulsive dose (100 mg/kg) of this methylxanthine. Aminophylline induced seizures were accompanied by greater elevations in brain MDA levels, whereas, GSH levels were consistently lowered. Unlike that seen during anxiety, NOx levels were increased in brain homogenates of these rats. The changes in oxidative stress markers were neutralized by NO synthase inhibitors. Synergistic anticonvulsant effect on aminophylline seizures was seen when L-NAME was combined with melatonin. These pharmacological and biochemical data indicate that aminophylline induced anxiety and seizures are differentially modulated by NO.

The role of nitric oxide in spatial memory stages, hippocampal ERK and CaMKII phosphorylation

Nitric oxide (NO) is an important intercellular messenger in the control of physiologic functions. It is synthesized by 3 different nitric oxide synthase enzymes (NOS). Uses of non-selective NOS inhibitor (L-NAME) have shown that NO is involved in neuronal plasticity and memory. This study aimed to determine the differential role of NO in spatial memory formation steps. In addition, regarding the roles of ERK and CaMKII in hippocampal plasticity, the hippocampal ERK and CaMKII activities were assessed to identify the effect of L-NAME on those proteins during each phase of memory. Adult male Sprague-Dawely rats weighing 220-280 g were trained in a single session consisting of 8 trials. To evaluate the effect of L-NAME on acquisition, L-NAME (3 or 10 mg/kg/i.p.) was administered 30 min before training. To assess its effect on the consolidation phase, L-NAME (3 or 10 mg/kg/i.p.) was injected immediately after training and a probe test was carried out 24 h later to analyse memory retention. To determine its effect on memory retrieval L-NAME (3 or 10 mg/kg/i.p.) was injected 30 min before probe trial which was conducted 24 h after training. The hippocampi were isolated after behavioural studies and western blotting analysis on hippocampal lysates was performed to illustrate the levels of phosphorylated ERK and CaMKII. The results showed that pre-training administration of L-NAME in 10 mg/kg but not 3mg/kg deteriorates acquisition. Post-training and pre-probe administration of L-NAME in 10 mg/kg but not 3 mg/kg impaired animal's performance in probe test. Additionally L-NAME treatment decreased the amount of phosphorylated (activated) ERK and CaMKII in the hippocampus. This study showed that endogenous nitric oxide is involved not only in all stages of memory, but also in ERK and CaMKII activation in the hippocampus during all 3 stages of memory.

Regulation of nociceptive transduction and transmission by nitric oxide

The potential involvement of nitric oxide (NO), a diffusible gaseous signaling messenger, in nociceptive transduction and transmission has been extensively investigated. However, there is no consistent and convincing evidence supporting the pronociceptive action of NO at the physiological concentration, and the discrepancies are possibly due to the nonspecificity of nitric oxide synthase inhibitors and different concentrations of NO donors used in various studies. At the spinal cord level, NO predominantly reduces synaptic transmission by inhibiting the activity of NMDA receptors and glutamate release from primary afferent terminals through S-nitrosylation of voltage-activated calcium channels. NO also promotes synaptic glycine release from inhibitory interneurons through the cyclic guanosine monophosphate/protein kinase G signaling pathway. Thus, NO probably functions as a negative feedback regulator to reduce nociceptive transmission in the spinal dorsal horn during painful conditions.

Circulating blood endothelial nitric oxide synthase contributes to the regulation of systemic blood pressure and nitrite homeostasis

OBJECTIVE

Mice genetically deficient in endothelial nitric oxide synthase (eNOS(-/-)) are hypertensive with lower circulating nitrite levels, indicating the importance of constitutively produced nitric oxide (NO•) to blood pressure regulation and vascular homeostasis. Although the current paradigm holds that this bioactivity derives specifically from the expression of eNOS in endothelium, circulating blood cells also express eNOS protein. A functional red cell eNOS that modulates vascular NO• signaling has been proposed.

APPROACH AND RESULTS

To test the hypothesis that blood cells contribute to mammalian blood pressure regulation via eNOS-dependent NO• generation, we cross-transplanted wild-type and eNOS(-/-) mice, producing chimeras competent or deficient for eNOS expression in circulating blood cells. Surprisingly, we observed a significant contribution of both endothelial and circulating blood cell eNOS to blood pressure and systemic nitrite levels, the latter being a major component of the circulating NO• reservoir. These effects were abolished by the NOS inhibitor L-NG-nitroarginine methyl ester and repristinated by the NOS substrate L-arginine and were independent of platelet or leukocyte depletion. Mouse erythrocytes were also found to carry an eNOS protein and convert (14)C-arginine into (14)C-citrulline in NOS-dependent fashion.

CONCLUSIONS

These are the first studies to definitively establish a role for a blood-borne eNOS, using cross-transplant chimera models, that contributes to the regulation of blood pressure and nitrite homeostasis. This work provides evidence suggesting that erythrocyte eNOS may mediate this effect.

Effect of nitric oxide on anterior segment physiology in monkeys

PURPOSE

To determine the effect of the nitric oxide donor, sodium nitroprusside (SNP), and the nitric oxide synthase (NOS) inhibitor, L-nitro-arginine-methylester (L-NAME), on IOP, mean arterial pressure (MAP), pupil diameter (PD), refraction (Rfx), aqueous humor formation (AHF), and outflow facility (OF) in monkeys.

METHODS

Monkeys were treated with single or multiple topical treatments of 500 μg SNP or L-NAME to one eye. IOP was determined by Goldmann applanation tonometry, PD with vernier calipers in room light, Rfx by Hartinger coincidence refractometry, AHF by fluorophotometry, and MAP with a blood pressure monitor. OF was determined by two-level constant pressure perfusion following anterior chamber exchange.

RESULTS

Following four topical treatments with 500 μg SNP, 30 minutes apart, IOP was significantly decreased from 2 to 6 hours compared with the contralateral control with the maximum IOP reduction of 20% at 3 hours (P < 0.001). PD, Rfx, and AHF were unchanged. Effects on MAP were variable. OF after SNP exchange was significantly increased by 77% (P < 0.05) at 10(-3) M. Topical L-NAME had no effect on IOP, PD, Rfx, or MAP.

CONCLUSIONS

Enhancement of nitric oxide concentration at targeted tissues in the anterior segment may be a useful approach for IOP reduction for glaucoma therapy. Additional studies are warranted before conclusions can be made regarding the effect of NOS inhibition on ocular physiology in nonhuman primates.

Atorvastatin enhance efficacy of mesenchymal stem cells treatment for swine myocardial infarction via activation of nitric oxide synthase

BACKGROUND

In a swine model of acute myocardial infarction (AMI), Statins can enhance the therapeutic efficacy of mesenchymal stem cell (MSCs) transplantation. However, the mechanisms remain unclear. This study aims at assessing whether atorvastatin (Ator) facilitates the effects of MSCs through activation of nitric oxide synthase (NOS), especially endothelial nitric oxide synthase (eNOS), which is known to protect against ischemic injury.

METHODS AND RESULTS

42 miniswines were randomized into six groups (n = 7/group): Sham operation; AMI control; Ator only; MSC only, Ator+MSCs and Ator+MSCs+NG-nitrol-L-arginine (L-NNA), an inhibitor of NOS. In an open-heart surgery, swine coronary artery ligation and reperfusion model were established, and autologous bone-marrow MSCs were injected intramyocardium. Four weeks after transplantation, compared with the control group, Ator+MSCs animals exhibited decreased defect areas of both "perfusion" defined by Single-Photon Emission Computed Tomography (-6.2±1.8% vs. 2.0±5.1%, P = 0.0001) and "metabolism" defined by Positron Emission Tomography (-3.00±1.41% vs. 4.20±4.09%, P = 0.0004); Ejection fraction by Magnetic Resonance Imaging increased substantially (14.22±12.8% vs. 1.64±2.64%, P = 0.019). In addition, indices of inflammation, fibrosis, and apoptosis were reduced and survivals of MSCs or MSC-derived cells were increased in Ator+MSCs animals. In Ator or MSCs alone group, perfusion, metabolism, inflammation, fibrosis or apoptosis were reduced but there were no benefits in terms of heart function and cell survival. Furthermore, the above benefits of Ator+MSCs treatment could be partially blocked by L-NNA.

CONCLUSIONS

Atorvastatin facilitates survival of implanted MSCs, improves function and morphology of infarcted hearts, mediated by activation of eNOS and alleviated by NOS inhibitor. The data reveal the cellular and molecular mechanism for anti-AMI therapy with a combination of statin and stem cells.

Genetic removal of basal nitric oxide enhances contractile activity in isolated murine collecting lymphatic vessels

The role of nitric oxide (NO) in regulating lymphatic contractile function and, consequently, lymph flow has been the subject of intense study. Despite this, the precise effects of NO on lymphatic contractile activity remain unclear. Recent hypotheses posit that basal levels of endogenous NO increase lymphatic contraction strength as a consequence of lowering frequency (i.e. positive lusitropy), whereas higher agonist-evoked concentrations of NO exert purely inhibitory effects on contractile function. We tested both hypotheses directly by isolating and cannulating collecting lymphatic vessels from genetically modified mice for ex vivo study. The effects of basal NO and agonist-evoked NO were evaluated, respectively, by exposing wild-type (WT), endothelial NO synthase (eNOS)(-/-) and inducible NO synthase (iNOS)(-/-) lymphatic vessels to controlled pressure steps followed by ACh doses. To compare with pharmacological inhibition of eNOS, we repeated both tests in the presence of l-NAME. Surprisingly, genetic removal of basal NO enhanced contraction amplitude significantly without increasing contraction frequency. Higher levels of NO production stimulated by ACh evoked dilation, decreased tone, slowed contraction frequency and reduced fractional pump flow. We conclude that basal NO specifically depresses contraction amplitude, and that greater NO production then inhibits all other aspects of contractile function. Further, this work demonstrates definitively that mouse collecting lymphatic vessels exhibit autonomous, large-amplitude contractions that respond to pressure similarly to collecting lymphatics of other mammalian species. At least in the peripheral lymphatic vasculature, NO production depresses contractile function, which influences lymph flow needed for fluid regulation, humoral immunity and cancer metastasis.

Inhibition of atrial fibrillation by low-level vagus nerve stimulation: the role of the nitric oxide signaling pathway

PURPOSE

We examined the role of the phosphatidylinositol-3 kinase (PI3K)/nitric oxide (NO) signaling pathway in low-level vagus nerve stimulation (LLVNS)-mediated inhibition of atrial fibrillation (AF).

METHODS

In 17 pentobarbital anesthetized dogs, bilateral thoracotomies allowed the attachment of electrode catheters to the superior and inferior pulmonary veins and atrial appendages. Rapid atrial pacing (RAP) was maintained for 6 h. Each hour, programmed stimulation was used to determine the window of vulnerability (WOV), a measure of AF inducibility, at all sites. During the last 3 h, RAP was overlapped with right LLVNS (50 % below that which slows the sinus rate). In group 1 (n = 7), LLVNS was the only intervention, whereas in groups 2 (n = 6) and 3 (n = 4), the NO synthase inhibitor N (G)-nitro-L-arginine methyl ester (L-NAME) and the PI3K inhibitor wortmannin, respectively, were injected in the right-sided ganglionated plexi (GP) during the last 3 h. The duration of acetylcholine-induced AF was determined at baseline and at 6 h. Voltage-sinus rate curves were constructed to assess GP function.

RESULTS

LLVNS significantly decreased the acetylcholine-induced AF duration by 8.2 ± 0.9 min (p < 0.0001). Both L-NAME and wortmannin abrogated this effect. The cumulative WOV (the sum of the individual WOVs) decreased toward baseline with LLVNS (p < 0.0001). L-NAME and wortmannin blunted this effect during the fifth (L-NAME only, p < 0.05) and the sixth hour (L-NAME and wortmannin, p < 0.05). LLVNS suppressed the ability of GP stimulation to slow the sinus rate, whereas L-NAME and wortmannin abolished this effect.

CONCLUSION

The anti-arrhythmic effects of LLVNS involve the PI3K/NO signaling pathway.

Contributions of nitric oxide synthases, dietary nitrite/nitrate, and other sources to the formation of NO signaling products

Mice lacking all three nitric oxide synthase (NOS) genes remain viable even though deletion of the major downstream target of NO, soluble guanylyl cyclase, is associated with a dramatically shortened life expectancy. Moreover, findings of relatively normal flow responses in eNOS knockouts are generally attributed to compensatory mechanisms including upregulation of remaining NOS isoforms, but the alternative possibility that dietary nitrite/nitrate (NOx) may contribute to basal levels of NO signaling has never been investigated.

AIM

The aim of the present study was to examine how NO signaling products (nitrosated and nitrosylated proteins) and NO metabolites (nitrite, nitrate) are affected by single NOS deletions and whether dietary NOx plays a compensatory role in any deficiency. Specifically, we sought to ascertain whether profound alterations of these products arise upon genetic deletion of either NOS isoform, inhibition of all NOS activity, NOx restriction, or all of the above.

RESULTS

Our results indicate that while some significant changes do indeed occur, they are surprisingly moderate and compartmentalized to specific tissues. Unexpectedly, even after pharmacological inhibition of all NOSs and restriction of dietary NOx intake in eNOS knockout mice significant levels of NO-related products remain. Innovation/Conclusion: These findings suggest that a yet unidentified source of NO, unrelated to NOSs or dietary NOx, may be sustaining basal NO signaling in tissues. Given the significance of NO for redox regulation in health and disease, it would seem to be important to identify the nature of this additional source of NO products as it may offer new therapeutic avenues for correcting NO deficiencies.

Effect of nitric oxide compounds on monkey ciliary muscle in vitro

The effects of various nitric oxide compounds and their inhibitors on monkey ciliary muscle contraction in vitro were investigated in both the longitudinal and circular vectors. The responses to nitric oxide compounds in carbachol precontracted ciliary muscle consisted of an initial relaxation often followed by recovery to near carbachol precontracted levels while the compound was still present. Sodium nitroprusside produced the greatest relaxation responses (nearly 100% relaxation in both vectors at 10(-3) M). The highest concentrations of isosorbide dinitrate (10(-4) M) and L-arginine (10(-3) M) produced relaxation responses of approximately 50% in both vectors. 8-Bromo cyclic GMP produced the smallest relaxation responses (25-35%). Nitric oxide synthase inhibition enhanced carbachol contraction up to 20% in the longitudinal but not the circular vector. Phosphodiesterase inhibition did not further enhance the relaxation response to L-arginine. Guanylate cyclase inhibition partially attenuated the relaxation response to sodium nitroprusside. Nitric oxide generating compounds were effective in relaxing precontracted monkey ciliary muscle in vitro. Endogenous production of nitric oxide is likely involved in the regulation of the contractile response in monkey ciliary muscle. Nitric oxide generating compounds may have potential value in therapeutic areas where modulation of ciliary muscle tension is desirable.

Gender differences in the effects of streptozotocin-induced diabetes on parasympathetic vasodilatation in the rat submandibular gland

OBJECTIVES

Submandibular vasodilatory responses are impaired in male streptozotocin-diabetic rats. However, the effects of diabetes on submandibular vascular reactivity in female rats have not been examined. The purpose of this study was to determine whether there are gender differences in the effects of diabetes on parasympathetic vasodilatation in the rat submandibular gland.

METHODS

Diabetes was induced using streptozotocin, and vascular responses (calculated as the % increase in submandibular vascular conductance) to parasympathetic stimulation (1-10 Hz) were measured using laser-Doppler flowmetry. To estimate the relative contributions of nitric oxide (NO), prostacyclin (PGI2) and endothelium-derived hyperpolarizing factor (EDHF), vascular conductance was measured before and after inhibition of cyclooxygenase (COX) and NO synthase (NOS).

RESULTS

Frequency-dependent increases in blood flow were observed in both male and female rats, but the contribution of EDHF was greater in females than in males. Further, PGI2 appeared to play a role only in males. Vasodilatory responses were diminished in all diabetic animals, and when compared with their respective controls the degree of impairment was similar in males and females. However, in diabetic males inhibition of COX and NOS had little or no effect, whereas inhibition of NO, but not COX, resulted in a further significant decrease in vascular responses in diabetic females.

CONCLUSIONS

Parasympathetic vasodilatation in the rat submandibular gland is diminished equally in diabetic males and females. However, in males diabetes predominantly impairs PGI2- and NO-dependent vasodilatation, whereas in females the contribution of EDHF-mediated pathways are affected and NO-dependent vasodilatation is preferentially maintained.

Vascular dilation by paeonol--a mechanism study

The goal of this study was to investigate the mechanism underlaying the vasodilatory effect of paeonol, a major active element from the root bark of Chinese herbs Paeonia suffruticosa Andr. and Cynanchum paniculatum (Bunge) Kitagawa. Paeonol relaxed isolated rat aorta rings by 95.6% while the 10(-6) M forskolin-induced vasodilatation used as 100%. The EC(50) of vasodilatation by paeonol is 2.9x10(-4) M. Although paeonol exerted endothelium-independent relaxation, L-NAME treatment inhibited paeonol-induced vasodilation of endothelium intact rings, while indomethacin did not. Both L-NAME and ODQ did not affect paeonol relaxation in the rings without endothelium. In addition, paeonol markedly elevated NO generation in cultured endothelial cells. Pre-treatment of propranolol, glibenclamide, TEA and BaCl(2) did not affect paeonol relaxation of endothelium removed rings. On the other hand, pre-treated of rings (without endothelium) with paeonol markedly blocked vasoconstriction induced by AngII, PGF(2alpha), 5-HT, dopamine, vasopressin, endothelin-1 and PE. The paeonol incubation also significantly attenuated KCl-induced contraction which mainly depended on Ca(2+) influx. In Ca(2+)-free medium (containing 10(-4) M of EGTA and 60 mM of KCl), paeonol suppressed the contraction curve of CaCl(2). In addition, paeonol also inhibited contraction by PE in Ca(2+) free solution (containing 10(-4) M of EGTA) which mainly relied on intracellular Ca(2+) release. Whole-cell patch-clamp experiment showed that paeonol shifted the I-V curve and the peak value of calcium currents was significantly inhibited. In conclusion, our study suggested that voltage-dependent and receptor-operated Ca(2+) channel, as well as intracellular Ca(2+) release were all inhibited by paeonol. An intracellular Ca(2+) regulatory mechanism may be responsible to potent vasodilatory effect of paeonol.

Severe dyslipidaemia, atherosclerosis, and sudden cardiac death in mice lacking all NO synthases fed a high-fat diet

AIMS

The precise role of the nitric oxide synthase (NOS) system in lipid metabolism remains to be elucidated. We addressed this point in mice that we have recently developed and that lack all three NOS isoforms.

METHODS AND RESULTS

Wild-type (WT), singly, doubly, and triply NOS(-/-) mice were fed either a regular or high-cholesterol diet for 3-5 months. The high-cholesterol diet significantly increased serum low-density lipoprotein (LDL) cholesterol levels in all the genotypes when compared with the regular diet. Importantly, when compared with the WT genotype, the serum LDL cholesterol levels in the high-cholesterol diet were significantly and markedly elevated only in the triply NOS(-/-) genotype, but not in any singly or doubly NOS(-/-) genotypes, and this was associated with remarkable atherosclerosis and sudden cardiac death, which occurred mainly in the 4-5 months after the high-cholesterol diet. Finally, hepatic LDL receptor expression was markedly reduced only in the triply NOS(-/-) genotype, accounting for the diet-induced dyslipidaemia in the genotype.

CONCLUSION

These results provide the first direct evidence that complete disruption of all NOS genes causes severe dyslipidaemia, atherosclerosis, and sudden cardiac death in response to a high-fat diet in mice in vivo through the down-regulation of the hepatic LDL receptor, demonstrating the critical role of the whole endogenous NOS system in maintaining lipid homeostasis.

Role of nitric oxide in hyperpnea-induced bronchoconstriction and airway microvascular permeability in guinea pigs

The present study aimed to evaluate the role of nitric oxide (NO) on hyperpnea-induced bronchoconstriction (HIB) and airway microvascular hyperpermeability (AMP). Sixty-four guinea pigs were anesthetized, tracheotomized, cannulated, and connected to animal ventilator to obtain pulmonary baseline respiratory system resistance (Rrs). Animals were then submitted to 5 minutes hyperpnea and Rrs was evaluated during 15 minutes after hyperpnea. AMP was evaluated by Evans blue dye (25 mg/kg) extravasation in airway tissues. Constitutive and inductible NO was evaluated by pretreating animals with N(G)-nitro-L-arginine methyl ester (L-NAME) (50 mg/kg), aminoguadinine (AG) (50 mg/kg), and L-arginine (100 mg/kg) and exhaled NO (NOex) was evaluated before and after drug administration and hyperpnea. The results show that L-NAME potentiated (57%) HIB and this effect was totally reversed by L-arginine pretreatment, whereas AG did not have effect on HIB. L-NAME decreased basal AMP (48%), but neither L-NAME nor AG had any effect on hyperpnea-induced AMP. NOex levels were decreased by 50% with L-NAME, effect that was reversed by L-arginine treatment. These results suggest that constitutive but not inducible NO could have a bronchoprotective effect on HIB in guinea pigs. The authors also observed that neither constitutive nor inducible NO seems to have any effect on hyperpnea-induced AMP.

Impaired vascular responses to parasympathetic nerve stimulation and muscarinic receptor activation in the submandibular gland in nonobese diabetic mice

Introduction

Decreased vascular responses to salivary gland stimulation are observed in Sjögren's syndrome patients. We investigate whether impaired vascular responses to parasympathetic stimulation and muscarinic receptor activation in salivary glands parallels hyposalivation in an experimental model for Sjögren's syndrome.

Methods

Blood flow responses in the salivary glands were measured by laser Doppler flowmeter. Muscarinic receptor activation was followed by saliva secretion measurements. Nitric oxide synthesis-mediated blood flow responses were studied after administration of a nitric oxide synthase inhibitor. Glandular autonomic nerves and muscarinic 3 receptor distributions were also investigated.

Results

Maximal blood flow responses to parasympathetic stimulation and muscarinic receptor activation were significantly lower in nonobese diabetic (NOD) mice compared with BALB/c mice, coinciding with impaired saliva secretion in nonobese diabetic mice (P < 0.005). Nitric oxide synthase inhibitor had less effect on blood flow responses after parasympathetic nerve stimulation in nonobese diabetic mice compared with BALB/c mice (P < 0.02). In nonobese diabetic mice, salivary gland parasympathetic nerve fibres were absent in areas of focal infiltrates. Muscarinic 3 receptor might be localized in the blood vessel walls of salivary glands.

Conclusions

Impaired vasodilatation in response to parasympathetic nerve stimulation and muscarinic receptor activation may contribute to hyposalivation observed in nonobese diabetic mice. Reduced nitric oxide signalling after parasympathetic nerve stimulation may contribute in part to the impaired blood flow responses. The possibility of muscarinic 3 receptor in the vasculature supports the notion that muscarinic 3 receptor autoantibodies present in nonobese diabetic mice might impair the fluid transport required for salivation. Parasympathetic nerves were absent in areas of focal infiltrates, whereas a normal distribution was found within glandular epithelium.

Trial registration

The trial registration number for the present study is 79-04/BBB, given by the Norwegian State Commission for Laboratory Animals.

Inhibiting the neuronal isoform of nitric oxide synthase has similar effects on the compensatory choroidal and axial responses to myopic defocus in chicks as does the non-specific inhibitor L-NAME

In birds, the choroid plays a role in the visual regulation of eye growth, thickening in response to myopic defocus, and thinning in response to hyperopic defocus, in both cases moving the retina towards the image plane. This response is rapid, occurring within hours of the defocus stimulus. These changes are consistently associated with slower changes in the sclera, that result in the appropriate changes in axial elongation, decreasing growth in response to myopic defocus and increasing it in response to hyperopic defocus. The molecular mechanisms underlying the scleral response involve changes in the synthesis of extracellular matrix molecules, however, those underlying the changes in choroidal thickness are not known. However, evidence suggests that it may involve the gaseous signal molecule nitric oxide, as nitric oxide is a potent smooth muscle relaxant, and injections of the non-specific nitric oxide synthase inhibitor L-NAME transiently inhibits the thickening response. Interestingly, it also dis-inhibits ocular growth, in accordance with a mechanistic link between the two responses. If nitric oxide is part of the signal cascade underlying the visual regulation of eye growth, it would be important to ascertain the source of the molecule. As a first step towards doing so, we used various more specific NOS inhibitors and studied their effects on the choroidal and growth responses. Birds (7-12 days old) were fitted with +10 D lenses on one eye. On that day, single intravitreal injections (30 microl) of the following inhibitors were used: nNOS inhibitor N(omega)-propyl-L-arginine (n=12), iNOS inhibitor L-NIL (n=16), eNOS/iNOS inhibitor L-NIO (n=15), non-specific inhibitor L-NMMA (n=30) or physiological saline (n=18). Ocular dimensions were measured using high-frequency A-scan ultrasonography at the start of the experiment, and at 7, 24 and 48 h after. We found that the nNOS inhibitor N(omega)-propyl-L-arginine had the same inhibitory effects on the choroidal response, and dis-inhibition of the growth response, as did L-NAME; neither of the other inhibitors had any effect except L-NMMA. We conclude that the choroidal compensatory response is influenced by nNOS, possibly from the intrinsic choroidal neurons, or the parasympathetic innervation from the ciliary and/or pterygopalatine ganglia.

Nonselective NOS inhibition blunts the sweat response to exercise in a warm environment

The role of nitric oxide synthase (NOS) inhibition in modulating human thermoregulatory control of sweating and cutaneous dilation was examined in 10 subjects (5 men and 5 women). Three intradermal microdialysis probes were placed in nonglabrous skin of the dorsum of the forearm. The control site was perfused with 0.9% saline, while the two remaining sites were perfused with a nonselective NOS inhibitor: 10 mM N(G)-nitro-L-arginine (L-NAME) or 10 mM N(G)-monomethyl-L-arginine (L-NMMA). Local sweat rate (SR) and skin blood flow (laser-Doppler velocimetry) were monitored directly over the path of the intradermal microdialysis probe while arterial blood pressure was measured in the opposite arm noninvasively. Thermoregulatory responses were induced by cycle ergometer exercise (60% peak oxygen consumption) in a warm environment (30 degrees C). Esophageal temperature increased 1.5 +/- 0.2 degrees C during the 30 min of exercise. The cutaneous dilator response between 5 and 30 min of exercise in the heat was attenuated by both 10 mM L-NAME and 10 mM L-NMMA (P < 0.05). However, 10 mM L-NAME was more effective in blunting the rise in cutaneous vascular conductance during exercise than L-NMMA (P < 0.05). NOS inhibition also reduced the rise in local SR between 10 and 30 min of exercise (P < 0.05). In this case, 10 mM L-NMMA was more effective in limiting the increase in local SR than 10 mM L-NAME (P < 0.05). We conclude that local production of nitric oxide in the skin or around the sweat gland augments local SR and cutaneous dilation during exercise in the heat.

Nitric oxide and prostaglandin inhibition during acetylcholine-mediated cutaneous vasodilation in humans

Acetylcholine-induced endothelium-dependent vasodilation in conduit arteries primarily depends on nitric oxide (NO). However, the biochemical mediators in the microvasculature remain less well defined. We tested whether prostaglandins and NO are responsible for cutaneous acetylcholine-mediated vasodilation and if they interact to modulate vasodilation. We measured skin blood flow (SBF) using laser Doppler flow (LDF) with intradermal microdialysis in the calves of 23 healthy volunteers. We examined the response of SBF to different doses of acetylcholine (0.01-100 mM), the nonisoform-specific NO synthase inhibitor, nitro-L-arginine (NLA, 10 mM), the nonspecific cyclo-oxygenase (COX) inhibitor, ketorolac (Keto, 10 mM), and combined NLA + Keto. NLA had no effect on baseline SBF, while Keto increased baseline SBF by approximately 150%. The increase was blunted with combined NLA + Keto. SBF increased by approximately 700% with the highest acetylcholine concentration and reduced by approximately 60% by NLA. Ketorolac alone also reduced the response to acetylcholine, although the reduction varied between 10 and 20% at differing acetylcholine doses. NLA plus ketorolac reduced the responses to different doses of acetylcholine by some 30%, which was intermediate to NOS or COX inhibition alone. These data suggest that cutaneous acetylcholine-mediated endothelium-dependent vasodilation is highly NO-dependent and is also strongly related to the interactions of NO with prostaglandins.