Role of nitric oxide, bradykinin B2 receptor, and TRPV1 in the airway alterations caused by simvastatin in rats

Dry cough has been reported in patients receiving statin therapy. However, the underlying mechanism or other possible alterations in the airways induced by statins remain unknown. Thus, the aim of this study was to evaluate whether simvastatin promotes alterations in airways, such as bronchoconstriction and plasma extravasation, as well as the mechanism involved in these events. Using methods to detect alterations in airway resistance and plasma extravasation, we demonstrated that simvastatin [20 mg/kg, intravenous (i.v.)] caused plasma extravasation in the trachea (79.8 + 14.8 μg/g/tissue) and bronchi (73.3 + 8.8 μg/g/tissue) of rats, compared to the vehicle (34.2 + 3.6 μg/g/tissue and 29.3 + 5.3 μg/g/tissue, respectively). NG-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg, intraperitoneal), a nitric oxide (NO) synthase inhibitor, Icatibant [HOE 140, 10 nmol/50 μl, intratracheal (i.t.)], a bradykinin B2 antagonist, and capsazepine (100 nmol/50 μl, i.t.), a TRPV1 antagonist, attenuated simvastatin-induced plasma extravasation. Simvastatin (5, 10 and 20 mg/kg) did not cause bronchoconstriction per se, but exacerbated the bronchoconstrictive response to bradykinin (30 nmol/kg, i.v.), a B2 agonist (0.7 + 0.1 ml/H2O), or capsaicin (30 nmol/kg, i.v.), a TRPV1 agonist (0.8 + 0.1 ml/H2O), compared to the vehicle (0.1 + 0.04 ml/H2O and 0.04 + 0.01 ml/H2O, respectively). The bronchoconstriction elicited by bradykinin (100 nmol/kg, i.v.) in simvastatin non-treated rats was inhibited by L-NAME. The exacerbation of bronchoconstriction induced by bradykinin or capsaicin in simvastatin-treated rats was inhibited by L-NAME, HOE 140 or capsazepine. These results suggest that treatment with simvastatin promotes the release of bradykinin, which, via B2 receptors, releases NO that can then activate the TRPV1 to promote plasma extravasation and bronchoconstriction.

Ethyl Rosmarinate Prevents the Impairment of Vascular Function and Morphological Changes in L-NAME-Induced Hypertensive Rats

Background and Objectives: The potent, endothelium-independent, vasorelaxant effect of ethyl rosmarinate, an ester derivative of rosmarinic acid, makes it of interest as an alternative therapeutic agent for use in hypertension. This study was designed to investigate the effect of ethyl rosmarinate on Nω-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. Materials and Methods: L-NAME was given orally to male Wistar rats for 6 weeks to induce hypertension concurrently with treatment of ethyl rosmarinate at 5, 15, or 30 mg/kgor enalapril at 10 mg/kg Systolic blood pressure (SBP), heart rate, and body weight of all experimental groups were recorded weekly, while the vascular sensitivity and histological changes of the aorta were evaluated at the end of the experiment. Results: For all treatment groups, the data indicated that ethyl rosmarinate significantly attenuated the SBP in hypertensive rats induced by L-NAME, with no significant differences in heart rate and body weight. In addition, the response of vascular sensitivity to acetylcholine (ACh) was improved but there was no significant difference in the response to sodium nitroprusside (SNP). Furthermore, the sensitivity of the aorta to phenylephrine (PE) was significantly decreased. The thickness of the aortic wall did not differ between groups but the expression of endothelial nitric oxide synthase (eNOS) was increased in ethyl rosmarinate- and enalapril-treated groups compared with the hypertensive group. Conclusions: Ethyl rosmarinate is an interesting candidate as an alternative treatment for hypertension due to its ability to improve vascular function and to increase the expression of eNOS similar to enalapril which is a drug commonly used in hypertension.

Effects of N-nitro L-arginine methyl ester and α-tocopherol on testicular oxidative stress caused by exposure to cigarette smoke

Testis is a rich organ with blood vessels. For this reason, it is possible that the toxic substances of the cigarette carried in the blood change the balance between the oxidant and the antioxidant system in this organ. In this study, it was aimed to investigate the effects of N-nitro L-arginine methyl ester and α-tocopherol on testicular oxidative stress caused by exposure to cigarette smoke. 45 wistar male rats were used in the study. Five groups were formed: control, cigarette smoke, cigarette smoke + α-tocopherol, cigarette smoke + N-nitro L-arginine methyl ester and cigarette smoke + α-tocopherol + N-nitro L-arginine methyl ester. Biochemical and histological evaluations were performed to determine the damage caused by cigarette smoke. It was observed that there were structural and functional disturbances at the cellular and hormonal level in the smoking group. Biochemical evaluations showed that cellular damage was reduced in treatment groups. Histological examinations were revealed that the damage caused by cigarette smoke exposure was eliminated in treatment groups. As a result of our study, we think that oxidative damage and hormonal irregularity in the testes tissue caused by cigarette smoke exposure can be improved with α-tocopherol and N-nitro L-arginine methyl ester application.

Interactive effects of apelin, renin-angiotensin system and nitric oxide in treatment of obesity-induced type 2 diabetes mellitus in male albino rats

Apelin and its receptor (APJ) are involved in the regulation of a variety of pathophysiological processes. We studied the effect of apelin treatment on obesity-induced type 2 diabetes mellitus (T2DM) and possible interaction between apelin/APJ system and renin-angiotensin system (RAS). Forty eight male albino rats were divided into two groups: control group and diabetic group. Diabetic group was subdivided into: control diabetic, apelin-treated, apelin + losartan-treated, apelin + l-NAME-treated and losartan-treated diabetic subgroup. Administration of apelin-13 yielded an improvement of IR, dyslipidaemia, inflammation, oxidative stress with significant decrease in AT1R gene expression and significant increase in ACE2 gene expression in adipose tissues. Losartan + apelin yielded a further significant decrease in ATR1 gene expression, glycaemic indices, serum TGs and TPA versus Apelin only. Adding l-NAME in subgroup (2D) reversed the effect of apelin. We suggested that the beneficial effect of Apelin is mainly mediated by NO-activated pathway and/or ACE2/Ang (1-7) dependent pathway.

Gastroprotection of Calein D against Ethanol-Induced Gastric Lesions in Mice: Role of Prostaglandins, Nitric Oxide and Sulfhydryls

Peptic ulcers are currently treated with various drugs, all having serious side effects. The aim of this study was to evaluate the gastroprotective activity of calein D (from Calea urticifolia), a sesquiterpene lactone with a germacrane skeleton. Gastric lesions were induced in mice by administering ethanol (0.2 mL) after oral treatment with calein D at 3, 10 and 30 mg/kg, resulting in 13.15 ± 3.44%, 77.65 ± 7.38% and 95.76 ± 2.18% gastroprotection, respectively, to be compared with that of the control group. The effect found for 30 mg/kg of calein D was not reversed by pretreatment with N^G-nitro-l-arginine methyl ester (l-NAME, 70 mg/kg, ip), indomethacin (10 mg/kg, sc) or N-ethylmaleimide (NEM, 10 mg/kg, sc). Hence, the mechanism of action of calein D does not involve NO, prostaglandins or sulfhydryl compounds. Calein D was more potent than carbenoxolone, the reference drug. The findings for the latter are in agreement with previous reports.

Pressure-dependent NOS activation contributes to endothelial hyperpermeability in a model of acute heart failure

Aims: Acute increases in left ventricular end diastolic pressure (LVEDP) can induce pulmonary edema (PE). The mechanism(s) for this rapid onset edema may involve more than just increased fluid filtration. Lung endothelial cell permeability is regulated by pressure-dependent activation of nitric oxide synthase (NOS). Herein, we demonstrate that pressure-dependent NOS activation contributes to vascular failure and PE in a model of acute heart failure (AHF) caused by hypertension.Methods and results: Male Sprague-Dawley rats were anesthetized and mechanically ventilated. Acute hypertension was induced by norepinephrine (NE) infusion and resulted in an increase in LVEDP and pulmonary artery pressure (Ppa) that were associated with a rapid fall in PaO2, and increases in lung wet/dry ratio and injury scores. Heart failure (HF) lungs showed increased nitrotyrosine content and ROS levels. L-NAME pretreatment mitigated the development of PE and reduced lung ROS concentrations to sham levels. Apocynin (Apo) pretreatment inhibited PE. Addition of tetrahydrobiopterin (BH4) to AHF rats lung lysates and pretreatment of AHF rats with folic acid (FA) prevented ROS production indicating endothelial NOS (eNOS) uncoupling.Conclusion: Pressure-dependent NOS activation leads to acute endothelial hyperpermeability and rapid PE by an increase in NO and ROS in a model of AHF. Acute increases in pulmonary vascular pressure, without NOS activation, was insufficient to cause significant PE. These results suggest a clinically relevant role of endothelial mechanotransduction in the pathogenesis of AHF and further highlights the concept of active barrier failure in AHF. Therapies targetting the prevention or reversal of endothelial hyperpermeability may be a novel therapeutic strategy in AHF.

L-NAME decreases the amount of nitric oxide and enhances the toxicity of cadmium via superoxide generation in barley root tip

Exposure of barley roots to mM concentrations of L-NAME for 30 min caused a considerable root growth inhibition in a dose-dependent manner. The inhibition of root growth was higher in seedlings co-treated with Cd and L-NAME, compared with roots treated with Cd alone, despite the fact that L-NAME markedly reduced the uptake of Cd by roots. Treatment of roots with L-NAME evoked a decrease in NO level in both control and Cd-treated root tips only after a relatively long lag period, which overlaps with an increase in superoxide and H₂O₂ levels and peroxynitrite generation. L-NAME-induced root growth inhibition is alleviated not only by the application of the NO donor SNP but also by the ROS and peroxynitrite scavengers. Our results indicate that L-NAME, a NOS inhibitor in the animal kingdom, indeed evokes NO depletion also in the plant tissues; however, it does not occur due to the action of L-NAME as an inhibitor of NOS or NOS-like activity, but as a consequence of L-NAME-induced enhanced superoxide generation, leading to increased peroxynitrite level in the root tips due to the reaction between superoxide and NO.

Effect of Nitric Oxide Synthase Inhibition in Experimental Pseudomonas keratitis in Rabbits

Purpose

The aim of this study was to assess the efficacy of the nitric oxide synthase inhibitor L-NG-nitro-arginine-methyleser (L-NAME) in the treatment of experimental Pseudomonas keratitis.

Methods

Twelve young New Zealand white rabbits were given intrastromal injections of Pseudomonas aeruginosa strains. Twenty-four hours later, the rabbits were randomly divided into four groups: group 1 was treated with topical 0.3% ciprofloxacin drops and a single subconjunctival injection of L-NAME (150 mg/kg); group 2 received topical 0.3% ciprofloxacin drops alone; group 3 received a single subconjunctival injection of L-NAME alone; group 4, the control group, was treated with topical balanced salt solution (BSS) drops. One drop of either ciprofloxacin of BSS was applied at each treatment interval. Twenty-six hours after the start of treatment, the eyes were examined by slit lamp to assess inflammation. Aqueous humor specimens were collected from each eye to measure the nitric oxide concentration. Corneas were removed to count bacteria results.

Results

Slit lamp examination cell scores were significantly lower for groups 1 and 3 than groups 2 and 4 eyes (p = 0.002 to p = 0.004). No viable bacteria were detected in the corneas of groups 1 and 2. Group 3 corneas had significantly fewer bacteria (6.33 ± 0.42 × 103) than group 4 (5.94 ± 0.16 × 104) (p < 0.05). Nitric oxide levels in the aqueous humor were significantly lower for group 1 eyes than for groups 2, 3, or 4 (p = 0.02, p = 0.01, and p = 0.003, respectively).

Conclusions

We conclude that nitric oxide synthase inhibitors may be a useful adjunct but are not a replacement for traditional antibiotic drop therapy.

Ghrelin enhances food intake and carbohydrate oxidation in a nitric oxide dependent manner

In the present study we sought to investigate interactions between hypothalamic nitric oxide (NO) and ghrelin signaling on food intake and energy substrate utilization as measured by the respiratory exchange ratio (RER). Guide cannulae were unilaterally implanted in either the arcuate (ArcN) or paraventricular (PVN) nuclei of male Sprague-Dawley rats. Animals were pretreated with subcutaneous (2.5-10mg/kg/ml) or central (0-100pmol) N-nitro-l-Arginine methyl ester (l-NAME) followed by 50pmol of ghrelin administered into either the ArcN or PVN. Both l-NAME and ghrelin were microinjected at the onset of the active cycle and food intake and RER were assessed 2h postinjection. RER was measured as the ratio of the volume of carbon dioxide expelled relative to the volume of oxygen consumed (VCO₂/VO₂) using an open-circuit indirect calorimeter. Our results demonstrated that peripheral and central l-NAME pretreatment dose-dependently attenuated ghrelin induced increases in food intake and RER in either the ArcN or PVN. In fact the 100pmol dose largely reversed the metabolic effects of ghrelin in both anatomical regions. These findings suggest that ghrelin enhancement of food intake and carbohydrate oxidation in the rat ArcN and PVN is NO-dependent.

Angiotensin-(1-7)-dependent vasorelaxation of the renal artery exhibits unique angiotensin and bradykinin receptor selectivity

Angiotensin-(1-7) [Ang-(1-7)] exhibits blood pressure lowering actions, inhibits cell growth, and reduces tissue inflammation and fibrosis which may functionally antagonize an activated Ang II-AT₁ receptor axis. Since the vascular actions of Ang-(1-7) and the associated receptor/signaling pathways vary in different vascular beds, the current study established the vasorelaxant properties of the heptapeptide in the renal artery of male Wistar male rats. Ang-(1-7) produced an endothelium-dependent vasodilator relaxation of isolated renal artery segments pre-contracted by a sub-maximal concentration of phenylephrine (PE) (3×10^-7M). Ang-(1-7) induced vasodilation of the rat renal artery with an ED₅₀ of 3±1nM and a maximal response of 42±5% (N=10). The two antagonists (10^-5M each) for the AT₇/Mas receptor (MasR) [D-Pro⁷]-Ang-(1-7) and [D-Ala⁷]-Ang-(1-7) significantly reduced the maximal response to 12±1% and 18±3%, respectively. Surprisingly, the AT₂R receptor antagonist PD123319, the AT₁R antagonist losartan and B₂R antagonist HOE140 (10^-6M each) also significantly reduced Ang-(1-7)-induced relaxation to 12±2%, 22±3% and 14±7%, respectively. Removal of the endothelium or addition of the soluble guanylate cyclase (sGC) inhibitor ODQ (10^-5M) essentially abolished the vasorelaxant response to Ang-(1-7) (10±4% and 10±2%, P <0.05). Finally, the NOS inhibitor LNAME (10^-4M) reduced the response to 13±2% (p<0.05), but the cyclooxygenase inhibitor indomethacin failed to block the Ang-(1-7) response. We conclude that Ang-(1-7) exhibits potent vasorelaxant actions in the isolated renal artery that are dependent on an intact endothelium and the apparent stimulation of a NO-sGC pathway. Moreover, Ang-(1-7)-dependent vasorelaxation was sensitive to antagonists against the AT₇/Mas, AT₁, AT₂ and B₂ receptor subtypes.

Prostanoids counterbalance the synergism between endothelin-1 and angiotensin II in mesenteric veins of trained rats

Exercise-induced adaptations of the modulating mechanisms that influence the angiotensin (Ang II) responses assume different features depending on the venous bed. In femoral veins, exercise mobilizes vasodilator prostanoids to cooperate with NO in order to maintain reduced Ang II responses. On the other hand, exercise's influence on the Ang II responses in veins that drain blood from the mesenteric region has been poorly described. Therefore, the present study aimed to identify the effects of a single bout of exercise, as well as exercise training, on the Ang II responses in mesenteric veins. The present study also aimed to investigate the involvement of prostanoids, NO and ET-1 in eventual exercise-induced modifications in these veins. To this end, mesenteric veins taken from resting-sedentary, exercised-sedentary, resting-trained and exercised-trained animals were studied in organ baths. In addition, the mRNA expression of prepro-endothelin-1 (ppET-1), as well as that of the ET_A and ET_B receptors, were quantified by real-time PCR in these veins. The results show that, either in absence or in presence of L-NAME, the Ang II responses were not different between groups. In the presence of indomethacin, higher Ang II responses were observed in the resting-trained animals than in the resting-sedentary animals. This difference, however, disappeared when L-NAME, BQ-123 or BQ-788 were added during incubation. In addition, no differences in ppET-1, ET_A or ET_B mRNA expression were observed between groups. Furthermore, in the presence of PD123,319, the Ang II responses in the exercised-sedentary animals were higher than those in the resting-sedentary animals. In conclusion, exercise training mobilizes endothelin-1 (ET-1) to reinforce the Ang II-induced responses mainly through ET_A activation. On the other hand, vasodilator prostanoids are mobilized to act in parallel with NO in order to counterbalance the Ang II responses that have been potentiated by ET-1 in these trained animals.

Centrally administered TNF increases arterial blood pressure independently of nitric oxide synthase

INTRODUCTION

Emerging evidence indicates that increased levels of TNF in the brain are associated with hypertension. Nitric oxide synthase (NOS) is involved in the central control of the cardiovascular system, exerting both pro- and antihypertensive effects. TNF induces hypothalamic synthesis of nitric oxide.

AIM

We checked if acutely administered TNF into the cerebral ventricles affects arterial blood pressure, heart rate and baroreflex sensitivity, and whether TNF actions are dependent on NOS in normotensive rats.

METHODS

We carried out hemodynamic measurements in 6 groups of freely moving, adult Sprague-Dawley male rats, intracerebroventricularly (ICV) infused with either: 1) saline (5μl/h); 2) TNF (200ng/5μl/h); 3) non-selective NO synthase inhibitor - l-NG-Nitroarginine Methyl Ester (l-NAME) (1mg/5μl/h); 4) TNF together with l-NAME (200ng and 1mg/5μl/h, respectively); 5) neuronal NO synthase inhibitor - 7-nitroindazole sodium salt (7-NI) (20μg/10μl/h); 6) or TNF together with 7-NI (200ng and 20μg/10μl/h, respectively). Mean arterial blood pressure (MABP), heart rate (HR) and spontaneous baroreflex sensitivity (sBRS) evaluated by the sequence method were analysed.

RESULTS

ICV infusion of TNF caused a significant increase in MABP accompanied by a transient increase in HR, and a decrease in sBRS. ICV infusion of l-NAME increased MABP, but it did not change HR, nor sBRS. ICV infusion of 7-NI did not affect MABP, nor HR, nor sBRS. TNF administered together with l-NAME increased MABP with a transient increase in HR without changes of sBRS. Similarly, ICV infusion of TNF with 7-NI increased MABP without changes in HR and sBRS.

CONCLUSIONS

Centrally administered TNF increases MABP and HR and blunts sBRS. The pressor effect of TNF appears to be independent of NOS activity in the brain. Inhibition of nNOS restores sBRS in TNF treated rats.

Ethanol withdrawal induces anxiety-like effects: Role of nitric oxide synthase in the dorsal raphe nucleus of rats

Nitric oxide (NO) mediated transmission in the dorsal raphe nucleus (DRN) has been shown to be involved in the modulation of anxiety-like behaviors. We investigated whether inhibition of nitric oxide synthase (NOS) in the DRN would prevent anxiety-like behavior induced by ethanol withdrawal. Male Wistar rats were treated with ethanol 2-6% (v/v) for a period of 21 days. Ethanol withdrawal was induced by abrupt discontinuation of the treatment. Experiments were performed 48 h after ethanol discontinuation. Rats with a guide cannula aimed at the DRN received intra-DRN injections of the non-selective NOS inhibitor NG-nitro-l-arginine methyl ester (l-NAME), selective neuronal NOS (nNOS) inhibitor N(ω)-propyl-l-arginine (NPLA), or selective inhibitor of inducible NOS (iNOS) N-([3-(aminomethyl)phenyl] methyl) ethanimidamidedihydrochloride (1400W). Five minutes later, the animals were tested in the elevated plus maze (EPM). Plasma ethanol levels were determined by gas chromatography. There was a reduction in plasma ethanol levels 48 h after ethanol withdrawal. Rats from the ethanol withdrawal group showed decreased exploration of the open arms of the EPM with no change in the exploration of enclosed arms. Intra-DRN treatment with l-NAME (100 nmoles/0.2 μL) and 1400W (1 nmol/0.2 μL), but not NPLA (10 nmoles/0.2 μL) in the DRN attenuated the decrease in the exploration of the open arms of the EPM induced by ethanol withdrawal. The major new finding of the present study is that iNOS in the DRN plays a role in the anxiety-like behavior induced by ethanol withdrawal.

Influence of Electroacupuncture Stimulation on Nitric Monoxide Production in Vascular Endothelial Cells in Rats

BACKGROUND/AIM

In Chinese medicine, blood stasis termed as 'Oketsu' means 'preceding state' or 'symptomatic of sickness'. Traditional Chinese medicine may improve blood flow by vasodilation or blood clotting inhibition. Although acupuncture influences the blood circulatory system, its underlying mechanisms remain unclear. Herein we evaluated changes in NO, as reflected by changes in NO2 (-), platelet aggregation, oxidative stress and endocrine responses after acupuncture stimulation in rats.

MATERIALS AND METHODS

Acupuncture stimulation was administered to rats randomly divided into five groups: control, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) injection, restraint stress (RS), restraint plus acupuncture stimulation (RA), and restraint plus acupuncture with L-NAME (RLA).

RESULTS

Compared to those in the RS group, levels of NO2 (-), endothelial nitric oxide synthase (NOS) protein and its mRNA significantly increased and those of hydroperoxide and soluble P-selectin significantly decreased in the RA group.

CONCLUSION

Acupuncture stimulation regulates vascular endothelium NOS function and affects vascular resistance and blood characteristics through NO. Additionally, NO produced may modulate excessive reactive oxygen development and blood platelet activation.

[The changes in the biochemical indices of blood in cobalt intoxication on the background of the regulators of the expression of endothelial NO-synthase]

On the background of chronic cobalt intoxication in rats develops oxidative stress. This is accompanied by a decrease in the content of total metabolites of nitric oxide in the blood serum. The reasons for lower levels of the vasodilatation factor are the following: a deficiency of L-arginine and the increase in the content of the inhibitor of NOS-3. We found a decrease in the bioavailability of nitric oxide due to the increase in the content of oxidized low density lipids, total cholesterol and cholesterol-lowering lipids high density.

Endothelial nitric oxide synthase and superoxide mediate hemodynamic initiation of intracranial aneurysms

Background

Hemodynamic insults at arterial bifurcations are believed to play a critical role in initiating intracranial aneurysms. Recent studies in a rabbit model indicate that aneurysmal damage initiates under specific wall shear stress conditions when smooth muscle cells (SMCs) become pro-inflammatory and produce matrix metalloproteinases (MMPs). The mechanisms leading to SMC activation and MMP production during hemodynamic aneurysm initiation are unknown. The goal is to determine if nitric oxide and/or superoxide induce SMC changes, MMP production and aneurysmal remodeling following hemodynamic insult.

Methods

Bilateral common carotid artery ligation was performed on rabbits (n = 19, plus 5 sham operations) to induce aneurysmal damage at the basilar terminus. Ligated animals were treated with the nitric oxide synthase (NOS) inhibitor LNAME (n = 7) or the superoxide scavenger TEMPOL (n = 5) and compared to untreated animals (n = 7). Aneurysm development was assessed histologically 5 days after ligation. Changes in NOS isoforms, peroxynitrite, reactive oxygen species (ROS), MMP-2, MMP-9, and smooth muscle α-actin were analyzed by immunohistochemistry.

Results

LNAME attenuated ligation-induced IEL loss, media thinning and bulge formation. In untreated animals, immunofluorescence showed increased endothelial NOS (eNOS) after ligation, but no change in inducible or neuronal NOS. Furthermore, during aneurysm initiation ROS increased in the media, but not the intima, and there was no change in peroxynitrite. In LNAME-treated animals, ROS production did not change. Together, this suggests that eNOS is important for aneurysm initiation but not by producing superoxide. TEMPOL treatment reduced aneurysm development, indicating that the increased medial superoxide is also necessary for aneurysm initiation. LNAME and TEMPOL treatment in ligated animals restored α-actin and decreased MMPs, suggesting that eNOS and superoxide both lead to SMC de-differentiation and MMP production.

Conclusion

Aneurysm-inducing hemodynamics lead to increased eNOS and superoxide, which both affect SMC phenotype, increasing MMP production and aneurysmal damage.

Late-life enalapril administration induces nitric oxide-dependent and independent metabolic adaptations in the rat skeletal muscle

Recently, we showed that administration of the angiotensin-converting enzyme inhibitor enalapril to aged rats attenuated muscle strength decline and mitigated apoptosis in the gastrocnemius muscle. The aim of the present study was to investigate possible mechanisms underlying the muscle-protective effects of enalapril. We also sought to discern the effects of enalapril mediated by nitric oxide (NO) from those independent of this signaling molecule. Eighty-seven male Fischer 344 × Brown Norway rats were randomly assigned to receive enalapril (n = 23), the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; n = 22), enalapril + L-NAME (n = 19), or placebo (n = 23) from 24 to 27 months of age. Experiments were performed on the tibialis anterior muscle. Total NOS activity and the expression of neuronal, endothelial, and inducible NOS isoforms (nNOS, eNOS, and iNOS) were determined to investigate the effects of enalapril on NO signaling. Transcript levels of tumor necrosis factor-alpha (TNF-α) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) were assessed to explore actions of enalapril on inflammation and mitochondrial biogenesis, respectively. Protein expression of energy-sensing and insulin signaling mediators, including protein kinase B (Akt-1), phosphorylated Akt-1 (pAkt-1), mammalian target of rapamycin (mTOR), AMP-activated protein kinase subunit alpha (AMPKα), phosphorylated AMPKα (pAMPKα), and the glucose transporter GLUT-4, was also determined. Finally, the generation of hydrogen peroxide (H2O2) was quantified in subsarcolemmal (SSM) and intermyofibrillar (IFM) mitochondria. Enalapril increased total NOS activity, which was prevented by L-NAME co-administration. eNOS protein content was enhanced by enalapril, but not by enalapril + L-NAME. Gene expression of iNOS was down-regulated by enalapril either alone or in combination with L-NAME. In contrast, protein levels of nNOS were unaltered by treatments. The mRNA abundance of TNF-α was reduced by enalapril relative to placebo, with no differences among any other group. PCG-1α gene expression was unaffected by enalapril and lowered by enalapril + L-NAME. No differences in protein expression of Akt-1, pAkt-1, AMPKα, pAMPKα, or GLUT-4 were detected among groups. However, mTOR protein levels were increased by enalapril compared with placebo. Finally, all treatment groups displayed reduced SSM, but not IFM H2O2 production relative to placebo. Our data indicate that enalapril induces a number of metabolic adaptations in aged skeletal muscle. These effects result from the concerted modulation of NO and angiotensin II signaling, rather than from a dichotomous action of enalapril on the two pathways. Muscle protection by enalapril administered late in life appears to be primarily mediated by mitigation of oxidative stress and pro-inflammatory signaling.

Effects of VEGF and nitric oxide synthase inhibition on blood–brain barrier disruption in the ischemic and non-ischemic cerebral cortex

OBJECTIVES

This study was performed to compare the effects of exogenous vascular endothelial growth factor (VEGF) and nitric oxide synthase (NOS) inhibition on blood-brain barrier (BBB) disruption in the ischemic cortex (IC) and non-ischemic contralateral cortex (CC) during the early stage of focal cerebral ischemia in rats.

METHODS

A middle cerebral artery (MCA) was occluded after a craniotomy in each rat under isoflurane anesthesia. Two more craniotomies were performed over the contralateral non-ischemic hemisphere to expose cerebral cortex. For the control rats, the normal saline patches were applied to all three craniotomy holes (control group). To inhibit NOS, NG-nitro-L-arginine-methyl ester (L-NAME) (10 mg/kg) was administered i.v. 20 minutes after MCA occlusion (L-NAME group). In another group, VEGF (10(-10) M) was topically applied 30 minutes after MCA occlusion on the IC as well as one of the holes of the contralateral cortex (VEGF group). To investigate the effects of the combination of VEGF and L-NAME, both L-NAME and VEGF were administered as described above (L-NAME+ VEGF group). The transfer coefficient (Ki) of 14C-alpha-aminoisobutyric acid and the volume of 3H-dextran (70 000 Da) distribution were determined to measure the degree of BBB disruption at 1 hour after MCA occlusion.

RESULTS

In the control group, Ki of the IC was significantly higher than the contralateral cortex (CC) (p<0.005). VEGF application increased the Ki of the IC further when compared with the control group (+51%, p<0.05%). L-NAME administration produced no significant decrease in the Ki of the IC when compared with the control group. With L-NAME+ VEGF administration, the Ki of the IC became significantly lower than that of the VEGF alone (-38%, p<0.005). Thus, L-NAME produced a much greater decrease in the Ki of the IC in the VEGF treated than the control animals (p<0.05). In the non-IC, VEGF, L-NAME, or their combination did not affect BBB disruption. The volume of dextran distribution followed a similar pattern to Ki.

DISCUSSION

Our data suggest that even in the early stage of focal cerebral ischemia, the degree of BBB disruption in response to the exogenous VEGF is much greater in the ischemic than in the non-IC and that the mechanism of the increase of BBB disruption by VEGF in the IC involves the NOS pathway.

Systemic inhibition of nitric oxide synthesis in non-diabetic individuals produces a significant deterioration in glucose tolerance by increasing insulin clearance and inhibiting insulin secretion

AIMS/HYPOTHESIS

Endogenous NO inhibits insulin release in isolated beta cells and insulin-degrading enzyme activity in hepatocytes, while NO release from endothelial cells has been suggested to enhance insulin action. We assessed the overall effect of systemic inhibition of endogenous NO synthesis on glucose homeostasis in humans.

METHODS

Twenty-four non-diabetic volunteers underwent two hyperglycaemic (+7 mmol/l) clamps with either saline or L-NG-nitroarginine methyl ester (L-NAME, at rates of 2.5, 5, 10 and 20 μg min⁻¹ kg⁻¹) infusion. Another five volunteers underwent an OGTT with either saline or L-NAME (20 μg min⁻¹ kg⁻¹) infusion. Blood pressure and heart rate were measured to monitor NO blockade; during the OGTT, endothelial function was assessed by peripheral arterial tonometry and insulin secretion by C-peptide deconvolution and insulin secretion modelling.

RESULTS

Compared with saline, L-NAME at the highest dose raised mean blood pressure (+20 ± 2 mmHg), depressed heart rate (-12 ± 2 bpm) and increased insulin clearance (+50%). First-phase insulin secretion was impaired, but insulin sensitivity (M/I index) was unchanged. During the OGTT, L-NAME raised 2 h plasma glucose by 1.8 mmol/l (p < 0.01), doubled insulin clearance and impaired beta cell glucose sensitivity while depressing endothelial function.

CONCLUSIONS/INTERPRETATION

In humans, systemic NO blockade titrated to increase blood pressure and induce endothelial dysfunction does not affect insulin action but significantly impairs glucose tolerance by increasing plasma insulin clearance and depressing insulin secretion, namely first-phase and beta cell glucose sensitivity.

[Electron paramagnetic resonance study of nitric oxide production in rat heart during hypokinesia]

By the method of EPR spectroscopy we studied the intensity of nitric oxide (NO) production after modeling of hypokinesia in rats (limitation of moving activity) through analyses of the amount of NO-containing paramagnetic complexes in tissues of heart and liver. Experimental animals were kept during 60 day protracted hypokinesia. NO amount was assessed by the intensity of EPR spectra of complex (DEDTC)2-Fe(2+)-NO. It was established that after 60 day hypokinesia the 2-3 fold increase of NO quantity occured in heart and liver tissues. The application of a nonspecific inhibitor of NO-synthases, L-NAME, in suspended rats led to a decreased NO quantity up to the value more lower than in control. The obtained results show that the main contribution to the increase in the intensity of NO production during hypokinesia belongs to the fermentative pathway of NO production and the formation of NO by nitrite-reductase activity is not enhanced during hypokinesia.

Maternal hypertension induced by NO blockade does not program adult metabolic diseases in growth-restricted rat fetuses

OBJECTIVE

Preeclampsia is a frequent and potentially lethal placental insufficiency pathology causing maternal hypertension and proteinuria, as well as a high rate of intrauterine growth retardation (IUGR) in offspring. Reduced nitric oxide (NO) production may play a role in the mechanisms of this disease. As exposure to adverse early life environment and IUGR has been proposed to increase cardiometabolic diseases risk, we investigated in rats the effects of maternal NO blockade on growth and metabolic phenotype of offspring.

MATERIAL AND METHODS

Osmotic pumps were implanted in pregnant rats at E17 and diffused saline or L-NAME (50mg/day), a nitric oxide synthesis inhibitor. At birth, IUGR male newborns without limb defects were selected. Body growth, feeding behavior and glucose tolerance were evaluated in offspring. Organs weights, plasma level of several metabolic hormones and genes expressions were determined in fasted 9month-old rats.

RESULTS

L-NAME mothers had elevated blood pressure at E20. Male offspring from L-NAME mothers had a markedly reduced birth weight and developed postnatal catch-up growth during lactation. Some L-NAME newborns presented some limb defects but were not selected in this study (1/3 of all pups). Improved glucose tolerance and hyperphagia after fasting were found in 3-month-old L-NAME rat but not thereafter. In 9-month-old L-NAME rats, a moderate increase of food intake during the light phase and, after fasting, an augmentation of plasma insulin and a reduction of brown adipose tissue (BAT) deposit were found associated with an increased expression of UCP-1 mRNA in this tissue.

CONCLUSIONS

Despite IUGR and postnatal catch up growth, male rats exposed to L-NAME did not develop metabolic diseases when limb defects were not induced by L-NAME. We postulate that maternal hypertension during late gestation is not a major 'programming' metabolic factor for offspring.

Essential role of nitric oxide in acute ischemic preconditioning: S-nitros(yl)ation versus sGC/cGMP/PKG signaling?

Nitric oxide (NO) plays an important role in acute ischemic preconditioning (IPC). In addition to activating soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) signaling pathways, NO-mediated protein S-nitros(yl)ation (SNO) has been recently shown to play an essential role in cardioprotection against ischemia-reperfusion (I/R) injury. In our previous studies, we have shown that IPC-induced cardioprotection could be blocked by treatment with either N-nitro-L-arginine methyl ester (L-NAME, a constitutive NO synthase inhibitor) or ascorbate (a reducing agent to decompose SNO). To clarify NO-mediated sGC/cGMP/PKG-dependent or -independent (i.e., SNO) signaling involved in IPC-induced cardioprotection, mouse hearts were Langendorff-perfused in the dark to prevent SNO decomposition by light exposure. Treatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, a highly selective inhibitor of sGC) or KT5823 (a potent and selective inhibitor of PKG) did not abolish IPC-induced acute protection, suggesting that the sGC/cGMP/PKG signaling pathway does not play an important role in NO-mediated cardioprotective signaling during acute IPC. In addition, treatment with ODQ in IPC hearts provided an additional protective effect on functional recovery, in parallel with a higher SNO level in these ODQ+IPC hearts. In conclusion, these results suggest that the protective effect of NO is not related primarily to activation of the sGC/cGMP/PKG signaling pathway, but rather through SNO signaling in IPC-induced acute cardioprotection.

A role for nitric oxide within the nucleus tractus solitarii in the development of muscle mechanoreflex dysfunction in hypertension

Evidence suggests that the muscle mechanoreflex, a circulatory reflex that raises blood pressure and heart rate (HR) upon activation of mechanically sensitive afferent fibres in skeletal muscle, is overactive in hypertension. However, the mechanisms underlying this abnormal reflex function have yet to be identified. Sensory input from the mechanoreflex is processed within the nucleus tractus solitarii (NTS) in the medulla oblongata. Within the NTS, the enzymatic activity of nitric oxide synthase produces nitric oxide (NO). This centrally derived NO has been shown to modulate muscle reflex activity and serves as a viable candidate for mediating the mechanoreflex dysfunction that develops in hypertension. We hypothesized that mechanoreflex dysfunction in hypertension is mediated by abnormal alterations in NO production in the NTS. Mechanically sensitive afferent fibres were stimulated by passively stretching hindlimb muscle before and after blocking the endogenous production of NO within the NTS via microdialysis of the NO synthase inhibitor L-NAME (1 and 5 mM) in normotensive Wistar-Kyoto rats and spontaneously hypertensive rats (SHRs). Changes in HR and mean arterial pressure in response to stretch were significantly larger in SHRs compared with Wistar-Kyoto rats prior to L-NAME dialysis. Attenuating NO production via L-NAME in normotensive rats recapitulated the exaggerated cardiovascular response to stretch observed in SHRs. Dialysing L-NAME in SHRs further accentuated the increases in HR and mean arterial pressure elicited by stretch. These findings support the contention that reductions in NO production within the NTS contribute to the generation of abnormal cardiovascular control by the skeletal muscle mechanoreflex in hypertension.

Role of nitric oxide in the control of the gastric motility within the nucleus ambiguus of rats

This study aims to investigate whether exogenous nitric oxide (NO) plays a role in controlling gastric motility within the nucleus ambiguus (NA). Experiments were performed on male Wistar rats anaesthetized with chloral hydrate. A latex balloon, connected to a pressure transducer, was inserted into the pylorus through the fundus for continuous recording of the change of gastric smooth muscle contractile curves. Microinjection of the NO-donor sodium nitroprusside (SNP; 5 nmol) or L-arginine (L-Arg; 5 nmol) into the NA significantly inhibited gastric motility, whereas the treatment of NO-synthase inhibitor N-nitro-L-arginine methylester (L-NAME) increased gastric motility remarkably. The negative effect of SNP or L-Arg on gastric motility was abolished by bilateral subdiaphragmatic vagotomy as well as by intravenous injection of ganglionic blocker, hexamethonium bromide (Hb). These results demonstrated that NO inhibited gastric motility by activating the cholinergic preganglionic neurons in the NA and through the mediation of vagus nerves.

L-Arginine ameliorates cardiac left ventricular oxidative stress by upregulating eNOS and Nrf2 target genes in alloxan-induced hyperglycemic rats

Hyperglycemia is independently related with excessive morbidity and mortality in cardiovascular disorders. L-Arginine-nitric oxide (NO) pathway and the involvement of NO in modulating nuclear factor-E2-related factor-2 (Nrf2) signaling were well established. In the present study we investigated, whether L-arginine supplementation would improve the myocardial antioxidant defense under hyperglycemia through activation of Nrf2 signaling. Diabetes was induced by alloxan monohydrate (90 mg kg(-1) body weight) in rats. Both non-diabetic and diabetic group of rats were divided into three subgroups and they were administered either with L-arginine (2.25%) or L-NAME (0.01%) in drinking water for 12 days. Results showed that L-arginine treatment reduced the metabolic disturbances in diabetic rats. Antioxidant enzymes and glutathione levels were found to be increased in heart left ventricles, thereby reduction of lipid peroxidation by L-arginine treatment. Heart histopathological analysis further validates the reversal of typical diabetic characteristics consisting of alterations in myofibers and myofibrillary degeneration. qRT-PCR studies revealed that L-arginine treatment upregulated the transcription of Akt and downregulated NF-κB. Notably, transcription of eNOS and Nrf2 target genes was also upregulated, which were accompanied by enhanced expression of Nrf2 in left ventricular tissue from diabetic and control rats. Under these findings, we suggest that targeting of eNOS and Nrf2 signaling by L-arginine supplementation could be used as a potential treatment method to alleviate the late diabetic complications.

Cardiac H11 kinase/Hsp22 stimulates oxidative phosphorylation and modulates mitochondrial reactive oxygen species production: Involvement of a nitric oxide-dependent mechanism

H11 kinase/Hsp22 (Hsp22), a small heat shock protein upregulated by ischemia/reperfusion, provides cardioprotection equal to ischemic preconditioning (IPC) through a nitric oxide (NO)-dependent mechanism. A main target of NO-mediated preconditioning is the mitochondria, where NO reduces O₂ consumption and reactive oxygen species (ROS) production during ischemia. Therefore, we tested the hypothesis that Hsp22 overexpression modulates mitochondrial function through an NO-sensitive mechanism. In cardiac mitochondria isolated from transgenic (TG) mice with cardiac-specific overexpression of Hsp22, mitochondrial basal, ADP-dependent, and uncoupled O₂ consumption was increased in the presence of either glucidic or lipidic substrates. This was associated with a decrease in the maximal capabilities of complexes I and III to generate superoxide anion in combination with an inhibition of superoxide anion production by the reverse electron flow. NO synthase expression and NO production were increased in mitochondria from TG mice. Hsp22-induced increase in O₂ consumption was abolished either by pretreatment of TG mice with the NO synthase inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) or in isolated mitochondria by the NO scavenger phenyltetramethylimidazoline-1-oxyl-3-oxide. L-NAME pretreatment also restored the reverse electron flow. After anoxia, mitochondria from TG mice showed a reduction in both oxidative phosphorylation and H₂O₂ production, an effect partially reversed by L-NAME. Taken together, these results demonstrate that Hsp22 overexpression increases the capacity of mitochondria to produce NO, which stimulates oxidative phosphorylation in normoxia and decreases oxidative phosphorylation and reactive oxygen species production after anoxia. Such characteristics replicate those conferred by IPC, thereby placing Hsp22 as a potential tool for prophylactic protection of mitochondrial function during ischemia.

Nicorandil attenuates monocrotaline-induced vascular endothelial damage and pulmonary arterial hypertension

Background

An antianginal K_ATP channel opener nicorandil has various beneficial effects on cardiovascular systems; however, its effects on pulmonary vasculature under pulmonary arterial hypertension (PAH) have not yet been elucidated. Therefore, we attempted to determine whether nicorandil can attenuate monocrotaline (MCT)-induced PAH in rats.

Materials and Methods

Sprague-Dawley rats injected intraperitoneally with 60 mg/kg MCT were randomized to receive either vehicle; nicorandil (5.0 mg·kg⁻¹·day⁻¹) alone; or nicorandil as well as either a K_ATP channel blocker glibenclamide or a nitric oxide synthase (NOS) inhibitor N^ω-nitro-l-arginine methyl ester (l-NAME), from immediately or 21 days after MCT injection. Four or five weeks later, right ventricular systolic pressure (RVSP) was measured, and lung tissue was harvested. Also, we evaluated the nicorandil-induced anti-apoptotic effects and activation status of several molecules in cell survival signaling pathway in vitro using human umbilical vein endothelial cells (HUVECs).

Results

Four weeks after MCT injection, RVSP was significantly increased in the vehicle-treated group (51.0±4.7 mm Hg), whereas it was attenuated by nicorandil treatment (33.2±3.9 mm Hg; P<0.01). Nicorandil protected pulmonary endothelium from the MCT-induced thromboemboli formation and induction of apoptosis, accompanied with both upregulation of endothelial NOS (eNOS) expression and downregulation of cleaved caspase-3 expression. Late treatment with nicorandil for the established PAH was also effective in suppressing the additional progression of PAH. These beneficial effects of nicorandil were blocked similarly by glibenclamide and l-NAME. Next, HUVECs were incubated in serum-free medium and then exhibited apoptotic morphology, while these changes were significantly attenuated by nicorandil administration. Nicorandil activated the phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) pathways in HUVECs, accompanied with the upregulation of both eNOS and Bcl-2 expression.

Conclusions

Nicorandil attenuated MCT-induced vascular endothelial damage and PAH through production of eNOS and anti-apoptotic factors, suggesting that nicorandil might have a promising therapeutic potential for PAH.

[Effect of nitric oxide on 1 ml: peritoneal macrophages activity in normal pregnancy in white rats]

The activity of peritoneal macrophages, nitrotyrosine concentration and condition of free radical processes in normal pregnancy in white rats against the background of the introduction of donator (sodium nitrite) and inhibitor (Nw-nitro-L-arginine methyl ester) of nitric oxide was studied. During normal pregnancy in animals, nitrotyrosine concentration, the activity of free radical processes, and phagocytosis increase. With the introduction of nitric oxide donator, NO level increases and after the injection of antagonist of nitric oxide it is reduced. These changes are accompanied by increased lipid peroxidation and activation of phagocytic activity of macrophages.

Repeated PTZ treatment at 25-day intervals leads to a highly efficient accumulation of doublecortin in the dorsal hippocampus of rats

BACKGROUND

Neurogenesis persists throughout life in the adult mammalian brain. Because neurogenesis can only be assessed in postmortem tissue, its functional significance remains undetermined, and identifying an in vivo correlate of neurogenesis has become an important goal. By studying pentylenetetrazole-induced brain stimulation in a rat model of kindling we accidentally discovered that 25±1 days periodic stimulation of Sprague-Dawley rats led to a highly efficient increase in seizure susceptibility.

METHODOLOGY/PRINCIPAL FINDINGS

By EEG, RT-PCR, western blotting and immunohistochemistry, we show that repeated convulsive seizures with a periodicity of 25±1 days led to an enrichment of newly generated neurons, that were BrdU-positive in the dentate gyrus at day 25±1 post-seizure. At the same time, there was a massive increase in the number of neurons expressing the migratory marker, doublecortin, at the boundary between the granule cell layer and the polymorphic layer in the dorsal hippocampus. Some of these migrating neurons were also positive for NeuN, a marker for adult neurons.

CONCLUSION/SIGNIFICANCE

Our results suggest that the increased susceptibility to seizure at day 25±1 post-treatment is coincident with a critical time required for newborn neurons to differentiate and integrate into the existing hippocampal network, and outlines the importance of the dorsal hippocampus for seizure-related neurogenesis. This model can be used as an in vivo correlate of neurogenesis to study basic questions related to neurogenesis and to the neurogenic mechanisms that contribute to the development of epilepsy.

[Correction of endothelial dysfunction by L-arginine under experimental pre-eclampsia conditions]

The ADMA-like pre-eclampsia in pregnant rats was modeled by daily introduction of L-NAME in a dose of 25 mg/kg for 7 days. L-arginine (200 mg/kg) prevented the development of arterial hypertension and a decrease in placentary microcirculation and microalbuminuria. The possibility of using L-arginine for the prevention of competitive eNOS inhibition by ADMA is discussed.

[Involvement of NO-dependent mechanisms of apelin action in myocardial protection against ischemia/reperfusion damage]

Apelin 12 (A-12) was synthesized by the automatic solid phase method with the use of Fmoc technology. The synthesized peptide was purified by preparative HPLC and identified by 1H-NMR spectroscopy and mass spectrometry. Acute myocardial infarction was induced by 40-min LAD occlusion followed by 60-min reperfusion in narcotized Wistar rats. A-12 was administrated at the onset of the reperfusion at doses of 0.07, 0.35 and 0.70 micromole/kg; N(G)-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, was applied at a dose of 10 mg/kg 10 min prior to reperfusion alone or before A-12 administration (0.35 micromole/kg); saline was used in control. The indicated A-12 doses induced a transient reduction of the arterial systolic blood pressure (ASBP) to 85, 58, and 56% of the initial level, respectively, which was accompanied by its recovery by the end of reperfusion. All A-12 doses significantly limited myocardial infarct size by 26, 40 and 33%, respectively, compared to the value in control. After administration of A-12 at dose of 0.35 micromol/kg, this effect was combined with reduction of MB-creatine kinase (MB-CK) and lactate dehydrogenase (LDH) activities in plasma at the end of reperfusion by 56 and 47%, respectively, compared to the values in control. Inhibition of NO formation by L-NAME increased SABP but did not affect myocardial infarct size compared with that in control. Coadministration of L-NAME and A-12 resulted in lesser reduction of ASBP during reperfusion than injection of A-12 alone. This intervention led to an increase in infarct size by 26% with concomitant 1.8- and 1.5-times elevation of MB-CK and LDH activities, respectively, compared to the values in the A-12 group. The results indicate that NO is involved as a mediator of the effects of A-12 on the overall protection consisting in a limitation of infarct size and reduction of postischemic cardiomyocyte membrane damage. Cardioprotective mechanisms of apelin action are discussed.

Modification by L-NAME of Codeine Induced Analgesia: Possible Role of Nitric Oxide

Objectives were to investigate the effect of nonselective nitric oxide synthase (NOS) inhibitor, L-NAME on codeine-induced analgesia and to see the role of NO in its antinociceptive effect. Also, to see if L-NAME can potentiate the antinociceptive response of sub-effective dose of codeine and to explore if opioid receptors have some role to play in L-NAME effects. Mice were injected with selected doses of codeine or other selected agents intraperitoneally and the latency to hot plate was recorded at zero, 15, 30, and 60 min of the treatments. The antinociceptive response of codeine (10 mg/kg, i.p.) was studied in comparison to those of the NOS inhibitor, L-NAME, and of nitric oxide donor, sodium nitroprusside (SNP). Assessment of nitrates and nitrites (NOx) in the sera of treated mice were also made. Codeine (20 mg/kg dose), induced analgesia significantly and dose dependently only after 15 min. L-NAME at 20, 40, and 80 mg/kg dose levels significantly changed the nonanalgesic effect of codeine (10 mg/kg) to highly significant analgesia. The effect of L-NAME 40 mg/kg was significantly higher than the other two doses and was almost equal to that of the higher dose of codeine. Naloxone itself did not show any intrinsic effect but almost abolished the L-NAME-codeine induced analgesia. Similarly, SNP (1 mg/kg) reversed the decrease in reaction time by L-NAME-codeine to its control values, significantly. Pretreatment with L-NAME rendered the nonanalgesic dose of codeine significantly analgesic almost in an equal potency to the high dose of codeine alone and indicate that the NO modulatory effect on the opioid analgesic codeine is probably, at least in part, through opioid receptors.

Spinal neuronal NOS activation mediates sigma-1 receptor-induced mechanical and thermal hypersensitivity in mice: involvement of PKC-dependent GluN1 phosphorylation

BACKGROUND AND PURPOSE We recently demonstrated that activation of the spinal sigma-1 receptor induces mechanical and thermal hypersensitivity via calcium-dependent second messenger cascades and phosphorylation of the spinal NMDA receptor GluN1 subunit (pGluN1). Here we examined the role of NO in this process, as it plays a critical role in PKC-mediated calcium signalling and the potentiation of NMDA receptor function. EXPERIMENTAL APPROACH The effects of intrathecal (i.t.) pretreatment with nNOS inhibitors on PRE084 (sigma-1 receptor agonist)-induced pain were assessed in mice by use of mechanical allodynia and thermal hyperalgesia tests. Western blot analysis, immunoprecipitation and immunohistochemical techniques were used to determine effects of these treatments on spinal pGluN1-immunoreactive (ir) cells, whether PRE084 induces a time-dependent modification of nNOS activity in the dorsal horn, and if any changes in nNOS activity can be blocked by sigma-1 receptor, calcineurin or soluble guanylyl cyclase (sGC) inhibitors. KEY RESULTS PRE084, injected i.t., induced mechanical and thermal hypersensitivity, and increased the number of PKC- and PKA-dependent pGluN1-ir cells in spinal cord. This PRE084-induced hypersensitivity and increase in PKC-dependent pGluN1 expression were blocked by pretreatment with N(G) -nitro-L-arginine methyl ester (L-NAME) or 7-nitroindazole (7-NI). PRE084 also time-dependently decreased the ratio of phosphorylated nNOS (pnNOS) to nNOS expression and the number of spinal pnNOS-ir cells. This decrease in pnNOS was prevented by BD1047, a sigma-1 receptor antagonist and cyclosporin A, a calcineurin inhibitor, but not by a sGC inhibitor. CONCLUSIONS AND IMPLICATIONS Spinal sigma-1 receptor-induced sensitization is mediated by an increase in nNOS activity, which is associated with an NO-induced increase in PKC-dependent pGluN1 expression.

The impact of L-NAME and L-arginine chronic toxicity induced lesions on ascites--pulmonary hypertension syndrome development in broiler chickens

The impact of L-arginine (LA), a precursor for synthesis of nitric oxide (NO), and N-omega-nitro-L-arginine methyl ester (L-NAME, LN), a non-selective inhibitor of the enzyme producing nitric oxide (nitric oxide synthase; NOS) chronic toxicity induced lesions on Ascites - Pulmonary hypertension syndrome (PHS) development was investigated in 140 one-day-old male broiler chickens (ROSS) during the first 5 weeks of life. Every second day the animals were treated intraperitoneally (ip) with L-NAME (10 mg/kg of body weight; BW), L-arginine (100 mg/kg BW), L-arginine and L-NAME in combination (100 mg/kg BW and 10 mg/kg BW respectively), and with physiological saline (0.90% w/v of NaCl; 0.5 mL/kg BW). Seven birds from each group were euthanized every week. The histopathological examination of the heart, the liver, the lungs, the blood vessels and the lymphoid organs, was performed. Also the organ index values were determined. At the end of the experiment the pre-ascitic condition or ascites - PHS was confirmed in five dead animals in the L-NAME-treated group. In the same group the edema was the most prominent histopathological change confirmed in the heart and in the lungs of the sacrificed chickens. In L-arginine-treated group the congestion and the haemorrhages were the striking changes in the same organs with the highest degree in the last two weeks of trial. While the focal disruption of myocardiofibriole and hepatocytes were predominant lesions in L-NAME-treated chickens (5th and 4th weeks, respectively), in L-NAME/L-arginine-treated group only the mild focal myocardial degeneration was seen. According to the most of the results of present investigation, it was concluded that the consecutive treatment with L-NAME provoked ascites - PHS, while L-arginine has protective effect in this animal model of disease.

Involvement of nitric oxide in corticosterone release and glucose metabolism in food deprived rats

This study was performed to investigate the involvement of nitric oxide (NO) in corticosterone, endpoint product of hypothalamo-pituitary-adrenal (HPA) axis activation, and metabolic responses to 3 days of food deprivation. To investigate this aim, we used a nonspecific inhibitor of nitric oxide synthases, N-nitro- L-arginine methyl ester (L-NAME). In food deprived group we have noted a significant increase in plasma corticosterone concentration accompanied by a significant depletion in hepatic glycogen content with concomitant increase in glycogen phosphorylase (GP) activity by 63.72%, key enzyme of glycogenolysis and decrease in hexokinase (HK) activity by 25.16%, leading to significant decrease in glucose concentration. However, L-NAME administration in food deprived rats decreased slightly corticosterone level and GP activity (16.39%) and increased HK activity (11.26%) as compared to food deprived group. Considering these results, we can deduce that in food deprivation nitric oxide is involved in the regulation of corticosterone release and in glucose metabolic responses via glycogenolysis activation by the stimulation of GP activity and the inhibition of HK activity. However, more studies are necessary to further clarify the mechanisms by which NO induces these responses.

Contribution of nitric oxide synthase (NOS) activity in blood-brain barrier disruption and edema after acute ischemia/reperfusion in aortic coarctation-induced hypertensive rats

BACKGROUND

Nitric oxide synthase (NOS) activity is increased during hypertension and cerebral ischemia. NOS inactivation reduces stroke-induced cerebral injuries, but little is known about its role in blood-brain barrier (BBB) disruption and cerebral edema formation during stroke in acute hypertension. Here, we investigated the role of NOS inhibition in progression of edema formation and BBB disruptions provoked by ischemia/reperfusion injuries in acute hypertensive rats.

METHODS

Rats were made acutely hypertensive by aortic coarctation. After 7 days, the rats were randomly selected for the recording of carotid artery pressure, or regional cerebral blood flow (rCBF) using laser Doppler. Ishcemia induced by 60-min middle cerebral artery occlusion (MCAO), followed by 12-h reperfusion. A single i.p. dose of L-NAME (1 mg/kg) was injected before MCAO. After evaluation of neurological disabilities, rats were slaughtered under deep anesthesia to assess cerebral infarction volume, edema, or BBB disruption.

RESULTS

A 75-85% reduction in rCBF was occurred during MCAO which returned to pre-occluded levels during reperfusion. Profound neurological disabilities were evidenced after MCAO alongside with severe cerebral infarctions (628 ± 98 mm3), considerable edema (4.05 ± 0.52%) and extensive BBB disruptions (Evans blue extravasation, 8.46 ± 2.03 mug/g). L-NAME drastically improved neurological disabilities, diminished cerebral infarction (264 ± 46 mm3), reduced edema (1.49 ± 0.47%) and BBB disruption (2.93 ± 0.66 mug/g).

CONCLUSION

The harmful actions of NOS activity on cerebral microvascular integrity are intensified by ischemia/reperfusion injuries during acute hypertension. NOS inactivation by L-NAME preserved this integrity and diminished cerebral edema.

Lack of heterologous receptor desensitization induced by angiotensin II type 1 receptor activation in isolated normal rat thoracic aorta

We tested whether heterologous receptor desensitization induced by activation of AT1 receptors may explain the purported relaxation produced by angiotensin II in normal rat aorta. Also, the role for AT2 receptors in the promotion of vasodilation was studied. In endothelium-intact and endothelium-denuded aortic rings, angiotensin II elicited biphasic contractions, which were significantly depressed when repeated in each tissue. Angiotensin II produced biphasic responses on phenylephrine preconstricted endothelium-intact and endothelium-denuded tissues, without reducing precontractile tone. These responses were abolished in the presence of the AT1 receptor antagonist losartan, but no relaxing responses to angiotensin II were uncovered. PD123319 did not influence angiotensin II responses in endothelium-intact tissues precontracted with phenylephrine; thus, under AT2 receptors blockade the contractile effects of angiotensin II were not overexposed. In conclusion, angiotensin II-induced biphasic responses can be attributed to AT1 receptors activation and rapid desensitization with time. Desensitization proved to be homologous in nature, since precontractile tone induced by phenylephrine was not depressed by angiotensin II (i.e., angiotensin II did not induce heterologous α1-adrenergic receptors desensitization). We found no functional evidence of the participation of AT2 receptors in angiotensin II elicited biphasic contractions. Angiotensin II does not exert relaxant effects in normal rat aorta.

Expression of type I GNRH receptor and in vivo and in vitro GNRH-I effects in corpora lutea of pseudopregnant rabbits

The expression of type I GNRH receptor (GNRHR-I) and the direct role of GNRH-I on corpora lutea (CL) function were studied in the pseudopregnant rabbit model. Immunohistochemistry evidenced GNRHR-I and GNRH-I in luteal cells at early (day 4 pseudopregnancy)-, mid (day 9)-, and late (day 13)-luteal stages. Real-time RT-PCR and western blotting revealed GNRHR-I mRNA and protein at the three luteal stages. Buserelin in vivo treatment at days 9 and 13 decreased plasma progesterone levels for 48 and 24  h respectively. In in vitro cultured CL, buserelin reduced progesterone secretion, increased prostaglandin F(2α) (PGF(2α)) secretion and cyclo-oxygenase-2 (COX-2) and nitric oxide synthase (NOS) activities at days 9 and 13, and decreased PGE₂ at day 13. Co-incubation with antagonists for GNRH-I (antide), inositol 1,4,5-trisphosphate (IP₃, 2-amino-ethoxydiphenylborate), and diacylglycerol (DAG, 1-hexadecyl-2-acetyl glycerol) or inhibitors for phospholipase C (PLC, compound 48/80), and protein kinase C (PKC, staurosporine) counteracted the buserelin effects. Buserelin co-incubated with COX inhibitor (acetylsalicylic acid) increased progesterone and decreased PGF(2α) and NOS activity at days 9 and 13, whereas co-incubation with NOS inhibitor (N-nitro-l-arginine methyl ester) increased progesterone at the same luteal stages. These results suggest that GNRHR-I is constitutively expressed in rabbit CL independently of luteal stage, whereas GNRH-I down-regulates directly CL progesterone production via PGF(2α) at mid- and late-luteal stages of pseudopregnancy, utilizing its cognate type I receptor with a post-receptorial mechanism that involves PLC, IP₃, DAG, PKC, COX-2, and NOS.

Verifying of participation of nitric oxide in morphine place conditioning in the rat medial septum using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)

BACKGROUND

Role of nitric oxide (NO) in morphine-induced conditioned place preference (CPP) has already been proposed in the rat medial septum (MS), but no molecular evidence has been provided to clear this fact.

METHODS

Effects of intraseptal injections of L-arginine and/or NG-nitro-L-arginine methyl ester (L-NAME) on morphine place conditioning in Wistar rats were examined. Morphine (2.5-7.5 mg/kg) was injected s.c. using a three-day schedule of an unbiased place preference. All of the brain samples were examined histochemically by nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), the main marker for NO activation.

RESULTS

Morphine induced a significant CPP in the rats. Single injections of L-arginine or L-NAME (0.3, 1.0 and 3.0 µg/rat) did not induce CPP. In addition, co-administration of morphine (5.0 mg/kg) with L-arginine or L-NAME (0.3, 1.0 and 3.0 µg/rat) did not affect morphine response. However, administration of L-arginine (0.3, 1.0 and 3.0 µg/rat) prior to morphine conditioning testing enhanced the expression of morphine response. Moreover, pre-injection of L-NAME (0.3, 1.0 and 3.0 µg/rat) to L-arginine (0.3 µg/rat) did not reverse the response to the agent. The expression of NADPH-d was observed in the rat brain samples treated by L-arginine. A decreased expression of NADPH-d was also observed in rats pre-injected by L-NAME.

CONCLUSION

This finding strongly suggests that NO system in the rat MS has an impact on the expression of morphine rewarding, and that the NO participates in place conditioning induced of morphine.

A combination antioxidant therapy prevents age-related hearing loss in C57BL/6 mice

OBJECTIVE

Age-related hearing loss (ARHL) is characterized by gradual, progressive sensorineural hearing loss, which impairs communication, lending to clinical depression and social withdrawal. There are currently no effective treatments for ARHL. The purpose of this study is to evaluate the potential of a combination antioxidant therapy in preventing ARHL.

STUDY DESIGN

Randomized controlled trial.

SETTING

Animal study.

SUBJECTS AND METHODS

C57BL/6 mice, a recognized animal model of ARHL, were assigned to one of three groups: early treatment (n = 12), late treatment (n = 9), or control group (n = 9). Treatment groups of mice were fed with a combination agent comprising six antioxidant agents that target four sites within the oxidative pathway: L-cysteine-glutathione mixed disulfide, ribose-cysteine, NW-nitro-L-arginine methyl ester, vitamin B12, folate, and ascorbic acid. Auditory brainstem response (ABR) thresholds were recorded at baseline and every three months following initiation of treatment.

RESULTS

Threshold shifts from baseline were decreased in the treatment groups when compared to the control group at all tested frequencies (P < 0.001). The ABR threshold shift at 12 months of age for the control group was 34.7 dB with a 95% confidence interval (CI) of +/-1.6. The mean threshold shifts for the early and late treatment groups were 7.5 dB (+/-0.87, 95% CI) and 9.2 dB (+/-1.6, 95% CI).

CONCLUSION

Combination antioxidant therapy effectively decreased threshold shifts on ABR within an animal model of ARHL. Combination antioxidant therapy, with further research and investigation, may provide a safe and cost-effective method of preventing presbycusis in the growing elderly population.

Nitric oxide and renal protection in morphine-dependent rats

Morphine treatment for 5 days protects heart against ischemia-reperfusion (IR) injury. This study evaluated the involvement of nitric oxide (NO) in morphine-induced renal protection. Three weeks after right nephrectomy, increasing doses of morphine were administered (20-30 mg kg(-1)day(-1), 5 days) to develop dependence in rats. The left kidney underwent 45-min ischemia and 24-h reperfusion. Some rats were pretreated with naloxone (5 mg kg(-1)) or L-NAME (20 mg kg(-1)). In one group, IR was induced 24h after the last dose of morphine during the withdrawal period. Plasma nitrite/nitrate levels and serum creatinine and BUN were measured. Creatinine clearance and fractional excretion of sodium (FE(Na)) were calculated. Myeloperoxidase (MPO) activity, malondialdehyde (MDA) level, and inducible NO synthase (iNOS) expression were determined and histopathology was studied in the left kidney. IR increased serum creatinine and BUN, plasma NO (p<0.01), FE(Na), iNOS expression (p<0.001), MPO activity, MDA level, and tissue damage and decreased creatinine clearance. Morphine decreased plasma NO (p<0.05 vs IR), serum creatinine and BUN (p<0.01), FE(Na), MPO activity, MDA level, iNOS expression, and tissue damage (p<0.05), but increased creatinine clearance (p<0.05). Pretreatment with naloxone significantly increased NO production and iNOS expression in morphine-treated rats after IR (p<0.01 vs morphine dependence+IR). Pretreatment with L-NAME in morphine-treated rats decreased NO production (10.7+/-1.9, p<0.01 vs morphine dependence+IR) but could not change iNOS expression after IR. Both naloxone and L-NAME significantly abolished the protective effects of morphine dependence on functional and histological factors. The protective effect of morphine dependence on serum creatinine, BUN, FE(Na), and creatinine clearance persisted during the withdrawal period, whereas iNOS expression decreased. NO production was not decreased during the withdrawal period (p>0.1 vs morphine dependence+IR group). Morphine dependence provided renal protection in the acute phase and during withdrawal. Excessive increase or decrease in NO production abolished the effects of morphine, which suggested a role for balanced NO production and iNOS expression.

Hyperbaric oxygen preconditioning reduces the incidence of decompression sickness in rats via nitric oxide

Divers are at risk of decompression sickness (DCS) when the ambient pressure decrease exceeds a critical threshold. Hyperbaric oxygen (HBO2) preconditioning has been used to prevent various injuries, but the protective effect on DCS has not been well explored. To investigate the prophylactic effect of HBO2 on DCS, rats were pretreated with HBO2 (250 kPa-60 minutes) (all the pressures described here are absolute pressure) for 18 hours before a simulated air dive (700 kPa-100 minutes) with fast decompression to the surface at the rate of 200 kPa/min (n=33). During the following 30 minutes, the rats walked in a 3 m/minute rotating cage and were monitored for signs of DCS. The control rats were pretreated with normobaric air (n=30), normoxic hyperbaric nitrox (250 kPa, 8.4% O2) (n=13), or N(G)-nitro-L-arginine methyl ester (L-NAME) 30 minutes before HBO2 exposure (n=13). Nitric oxide (NO) levels were recorded immediately and 18 hours after HBO2 exposure in the brain and spinal cord. The incidence of DCS in rats pretreated with HBO2 was 30.3%, which was significantly lower than those treated with normobaric air (63.3%) (p<0.05) or hyperbaric nitrox (61.5%) (p<0.05). The onset time of DCS of the rats pretreated with HBO2 was significantly delayed compared with those treated with air (p<0.05). L-NAME nullified the HBO2 preconditioning effect. HBO2 increased NO level in the rat brain and spinal cord right after exposure; this effect was inhibited by L-NAME. Taken together, HBO2 preconditioning reduced the incidence of DCS in rats, and NO was involved in the prophylactic effect.

Hyperbaric oxygen treatment induces a 2-phase antinociceptive response of unusually long duration in mice

Hyperbaric oxygen (HBO(2)) therapy is approved by the FDA for limited clinical indications but is reported to produce pain relief in several chronic pain conditions. However, there have been no studies to explain this apparent analgesic effect of HBO(2). Research conducted in our laboratory demonstrates that 4 daily 60-minute HBO(2) treatments at 3.5 absolute atmospheres induced an unparalleled antinociceptive response that consists of 1) an early phase that lasted at least 6 hours after the HBO(2) treatment before dissipating; and 2) a late phase that emerged about 18 hours after the early phase and lasted for up to 3 weeks. The early phase was sensitive to antagonism by acutely intracerebroventricular (i.c.v.)-administered opioid antagonist naltrexone and the nitric oxide synthase (NOS)-inhibitor L-NAME. The late phase was inhibited by treatment with i.c.v. naltrexone or L-NAME during the 4 daily HBO(2) treatments but was not antagonized by either naltrexone or L-NAME following acute pretreatment 2 weeks after HBO(2) treatment. These experimental results implicate a novel mechanism that is activated by HBO(2), resulting in an antinociceptive response of unusually long duration that is of potential interest in the clinical management of pain.

PERSPECTIVE

Hyperbaric oxygen treatment of mice can induce a 2-phase antinociceptive response of unusually long duration. Nitric oxide and opioid receptors appear to initiate or mediate both phases of the antinociceptive response. Further elucidation of the underlying mechanism may potentially identify molecular targets that cause long-lasting activation of endogenous analgesic systems.

Involvement of nitric oxide-cGMP pathway in the anticonvulsant effects of lithium chloride on PTZ-induced seizure in mice

Lithium is still the mainstay in the treatment of affective disorders as a mood stabilizer. Lithium also shows some anticonvulsant properties. While the underlying mechanisms of action of lithium are not yet exactly understood, we used a model of clonic seizure induced by pentylenetetrazole (PTZ) in male NMRI mice to investigate whether the anticonvulsant effect of lithium is mediated via NO-cGMP pathway. Injection of a single effective dose of lithium chloride (25 mg/kg) intraperitoneally (i.p.) increased significantly the seizure threshold (P<0.01). The anticonvulsant properties of the effective dose of lithium were prevented by pre-treatment with the per se non-effective doses of L-ARG [the substrate for nitric oxide synthase; NOS] (30 and 50 mg/kg) or sildenafil [a phosphodiesterase 5 inhibitor] (10 and 20 mg/kg). L-NAME [a non-specific NOS inhibitor] (5, 15 and 30 mg/kg), 7-NI [a specific neural NOS inhibitor] (30 and 60 mg/kg) or MB [a guanylyl cyclase inhibitor] (0.5 and 1 mg/kg) augmented the anticonvulsant effect of a sub-effective dose of lithium (10 mg/kg, i.p.). Whereas several doses of aminoguanidine [an inducible NOS inhibitor] (20, 50 and 100 mg/kg) failed to alter the anticonvulsant effect of lithium. Our findings demonstrated that nitric oxide-cyclic GMP pathway could be involved in the anticonvulsant properties of the lithium chloride. In addition, the role of constitutive NOS versus inducible NOS is prominent in this phenomenon.

Intra-arterial AICA-riboside administration induces NO-dependent vasodilation in vivo in human skeletal muscle

In animal models, administration of the adenosine analog AICA-riboside has shown beneficial effects on ischemia-reperfusion injury and glucose homeostasis. The vascular and/or metabolic effects of AICA-riboside administration in humans remain to be established. AICA-riboside was infused intra-arterially in four different dosages up to 8 mg x min(-1) x dl(-1) in 24 healthy subjects. Forearm blood flow (FBF) and glucose uptake and plasma glucose, free fatty acid, and AICA-riboside concentrations were assessed. We also combined AICA-riboside infusion (2 mg x min(-1) x dl(-1)) with the intra-arterial administration of the adenosine receptor antagonist caffeine (90 microg x min(-1) x dl(-1); n = 6) and with the endothelial NO synthase inhibitor l-NMMA (0.4 mg x min(-1) x dl(-1); n = 6). Additional in vitro experiments were performed to explain our in vivo effects of AICA-riboside in humans. AICA-riboside increased FBF dose dependently from 2.0 +/- 0.2 to 13.2 +/- 1.9 ml x min(-1) x dl(-1) maximally (P < 0.05 for all dosages). The latter was not reduced by caffeine administration but was significantly attenuated by l-NMMA infusion. Despite high plasma AICA-riboside concentrations, forearm glucose uptake did not change. In vitro experiments showed rapid uptake of AICA-riboside by the equilibrative nucleoside transporter in erythrocytes and subsequent phosphorylation to AICA-ribotide. We conclude that AICA-riboside induces a potent vasodilator response in humans that is mediated by NO. Despite high local plasma concentrations, AICA-riboside does not increase skeletal muscle glucose uptake.

Different role of isoproterenol and NOS inhibitors on salivary ducts of rats

OBJECTIVES

Nitric oxide (NO) is a diffusible intracellular messenger that is present in saliva. Chronic treatment with isoproterenol, a beta receptor agonist, stimulates the release of NO from acinar cells and induces salivary gland hypertrophy. The aim of this study was to investigate the effect of NO synthesis inhibitors and isoproterenol on rat salivary glands. We analyzed salivary gland weight and the number of ducts per unit area (0.5mm(2)) by NADPH-diaphorase histochemistry (to identify the presence of the enzyme NO synthase-NOS) and haematoxylin-and-eosin (HE).

METHODS

For 8 days male Wistar rats received daily single intraperitoneal injections of saline or a NOS inhibitor (40mg/kg N(omega)-nitro-L-arginine L-NOARG or N(omega)-nitro-l-arginine methyl ester L-NAME). This was followed, 30min later, by subcutaneous injection of isoproterenol (2 or 5mg/kg) or saline.

RESULTS

Isoproterenol increased parotid and submandibular gland weights. Isoproterenol (2mg/kg) induced a decrease of ducts per unit area inversely correlated to the weight of the parotid gland. This effect was augmented by L-NAME. In the submandibular gland L-NAME attenuated isoproterenol (2mg/kg) weight increase. In the submandibular gland isoproterenol and NOS inhibitors induced an increase in ducts per unit area (HE and NADPH-diaphorase). No effect was observed in the sublingual gland.

CONCLUSION

To our knowledge this is the first description of isoproterenol and NOS inhibitors increasing duct density in the submandibular gland. Our results corroborate the hypothesis that NO plays different roles in parotid and submandibular glands.

[Model of gastroesophageal reflux concomitant with functional constipation in conditions of nitric oxide synthase inhibition]

Gastroesophageal reflux combined with functional constipation prevented bythe introduction of nitric oxide synthase blocker. Gastroesophageal reflux simulated by the administration of nitric oxide donor - methylene blue at fundal department of the stomach and constipation - by free ligation overlaid on the terminal division sigmoid colon of rats. The protective effect of nitric oxide synthase blocker on the gastroesophageal reflux development was demonstrated.

Nitric oxide protects against ischemic acute renal failure through the suppression of renal endothelin-1 overproduction

To elucidate the role of nitric oxide in the pathogenesis of ischemic acute renal failure, we investigated the effects of FK409, a spontaneous nitric oxide donor, and N(G)-nitro-L-arginine methyl ester, a non-selective nitric oxide synthase inhibitor, on ischemia/reperfusion-induced renal injury and endothelin-1 overproduction in post-ischemic kidneys. Ischemic acute renal failure was induced by occlusion of the left renal artery and vein for 45 minutes followed by reperfusion, 2 weeks after contralateral nephrectomy. At 24 hours after reperfusion, renal function in untreated acute renal failure rats markedly decreased and histological examination revealed severe renal damage of the kidney. Increases in renal endothelin-1 contents were evident in the acute renal failure rats at 2 and 24 hours after reperfusion, respectively. Pretreatment with FK409 (1 or 3 mg/kg, intravenously) dose-dependently ameliorated renal injuries and suppressed the elevation of endothelin-1 content induced by ischemia/reperfusion. In contrast, N(G)-nitro-L-arginine methyl ester (1 or 10 mg/kg, intravenously) pretreatment dose-dependently aggravated renal injuries of acute renal failure rats, and the effect is accompanied by further increase in the renal endothelin-1 contents. These results suggest that both exogenous and endogenous nitric oxide have protective effects against ischemia/reperfusion-induced renal dysfunction and tissue damage, probably through the suppression of endothelin-1 overproduction in post-ischemic kidneys.

Effects of tetrahydrobiopterin on nitric oxide bioavailability and renal hemodynamics in healthy volunteers

BACKGROUND

The endothelial nitric oxide (NO) system plays a central role in regulating vascular tone. Endothelial dysfunction has been closely linked to reduced activity in the NO system. Tetrahydrobiopterin (BH4) is an essential cofactor of all NO synthase isoforms.

METHODS

We examined the effects of BH4 on the NO system assessed by measurement of serum cGMP levels and NO breakdown products (NOx) in 12 healthy volunteers.

RESULTS

Application of a total of 19 mg/kg BH4 intravenously (i.v.) over 3 hours led to a dose-dependent increase in serum cGMP concentrations from a median 3.3 nM (interquartile range [IQR] 1.1-5.6) to 5.7 nM (IQR 2.4-13.3, p=0.008) and NOx from a median 49.3 microM (IQR 39.8-56.6) to 59.7 microM (39.6-85.5) (p=0.058). Systemic and renal hemodynamics measured by inulin and p-aminohippuric acid (PAH) clearance remained unchanged. Plasma renin activity was significantly increased (2.0 [IQR 1.0-2.8] to 2.3 ng AngI/mL per hour [IQR 1.7-4.0], p=0.045), whereas aldosterone, erythropoietin and B-type natriuretic peptide levels did not change. In a second study, oral BH4 given over 3 days (800 mg/day) similarly increased serum cGMP and ameliorated the depressive effects of the NO synthase inhibitor L-NAME (1.5 mg/kg i.v.) on the glomerular filtration rate.

CONCLUSIONS

Application of BH4 in high doses is safe and enhances formation of cGMP, pointing to increased bioavailability of NO.

Effect of motilin on the discharge of rat hippocampal neurons responding to gastric distension and its potential mechanism

The study aims to find the effect of motilin on neuronal activity of gastric distension-responsive neurons in rat hippocampus and its possible mechanism. Single unit discharges in the hippocampal CA1 region were recorded extracellularly by means of four-barrel glass micropipettes in anesthetized rats and the expression of nNOS in hippocampus was observed by fluo-immunohistochemistry staining. Of the 171 recorded neurons, 76.0% were GD-excitatory (GD-E) neurons and 24.0% were GD-inhibited (GD-I) neurons. The 57.6% of GD-E neurons showed an excitatory response to motilin and the same effect was observed in 51.7% GD-I neurons. However, when NOS inhibitor nitro-l-arginine methyl ester (l-NAME) was administrated previously, the followed motilin-induced excitatory responsiveness of GD-responsive neurons was reduced. In contrast, discharge activity of GD-responsive neurons with motilin was enhanced by pretreatment of NO precursor l-arginine. The expression of nNOS-IR positive neurons was significantly increased in CA1 after administration of motilin. Our findings suggested that motilin excited the GD-responsive neurons in the hippocampal CA1 region and the excitatory effect of motilin may be mediated by the endogenous NO.