The effect of methylmercury (CH3HgCl) on the production of endothelium-derived relaxing factor (EDRF) by cultured human umbilical vascular endothelial cells based on its anti-aggregatory effect on human platelets

The effect of methylmercury (CH₃HgCl) on the production of endothelium-derived relaxing factor (EDRF) by cultured human umbilical vascular endothelial cells (HUVECs) based on its antiaggregatory effect on human platelets was examined. HUVECs were harvested from umbilical veins by collagenase treatment. The platelet aggregation test was performed with cuvettes lined with HUVECs. Platelet aggregation induced by 0.05 units thrombin/ml was inhibited in the presence of HUVECs. This HUVEC-dependent anti-platelet aggregatory effect was enhanced by the addition of bradykinin (10 nmol/L), which stimulates the production of EDRF. Indomethacin (IND, 1 mol/L) reduced the HUVEC-dependent anti-platelet aggregatory effect. The effect ofN ^G-monomethyl-L-arginine (L-NMMA, 100 mol/L), an inhibitor of nitric oxide synthase (NOS) in endothelial cells, on HUVECs pretreated with IND showed almost complete platelet aggregation similar to results without HUVECs. The anti-platelet aggregatory effect of HUVECs pretreated with IND seemed to depend mainly on EDRF. Methylmercury (MeHg) (20–50 mol/L) induced dose-dependent platelet aggregation in cuvettes, without HUVECs. Methylmercury (30 mol/L) induced less platelet aggregation in the presence of HUVECs than in their absence. The degree of inhibitory effect by HUVECs on MeHg-induced platelet aggregation was reduced dose-dependently (30–50 mol/L MeHg). Methylmercury-induced platelet aggregation at 50 mol/L MeHg with or without HUVECs was similar. These findings suggest that this simple new experimental system is useful for assessing the production of EDRF by HUVECs, and show that MeHg inhibits the production of EDRF by HUVECs, which may be involved in the etiology of cardiovascular diseases such as hypertension and arteriosclerosis.Abbreviations BK bradykinin - EDRF endothelium-derived relaxing factor - HUVECs human umbilical vascular endothelial cells - IND indomethacin - L-NMMA N ^G-monomethyl-L-arginine - MeHg methylmercury     

Nitric Oxide Participates in the Stimulatory and Neurotoxic Action of Endothelin on Rat Striatal Dopaminergic Neurons

1. Our method of real-time monitoring of dopamine release from rat striatal slices revealed that endothelin (ET)-3-induced dopamine release was inhibited by N ^G-methyl-L-arginine (L-NMMA; 1 mM), an inhibitor of nitric oxide (NO) synthase, while N ^G-methyl-D-arginine (D-NMMA; 1 mM), an inactive isomer of L-NMMA, had no effect.2. The inhibition of L-NMMA (0.1 mM) became apparent when tissues were pretreated with tetrodotoxin (1 M) for 30 min and subsequently exposed to ET-3 (4 M).3. L-NMMA (0.1 and 1 mM) dose dependently protected against ET-3-triggered hypoxic/hypoglycemic impairment of striatal responses to high K⁺.4. Thus, NO may work as a promoter in mediation of the stimulatory and neurotoxic action of ET-3 on the striatal dopaminergic system, presumably by interacting with interneurons in the striatum.     

Development of an Enzyme-Linked Immunosorbent Assay System for the Determination of Asymmetric Dimethylarginine Using a Specific Monoclonal Antibody

We produced a monoclonal antibody (mAb) against N ^G,N ^G-dimethyl-L-arginine (asymmetric dimethylarginine: ADMA), an endogenous competitive inhibitor of nitric oxide synthase (NOS), and developed an enzyme-linked immunosorbent assay (ELISA). The competitive ELISA method using the mAb determined 5 nM–100 nM ADMA, and ADMA levels in human plasma and urine were found to be 0.78 μM and 51.3 μmol/g of creatinine respectively.     

Cocaine kindling in mice

Previous studies proposed the involvement of theN-methyl-D-aspartate (NMDA) type of glutamate receptors in the development of sensitization to the convulsive effect of cocaine (cocaine kindling). The present study was undertaken to determine, first, if cocaine kindling is associated with enhanced sensitivity of the NMDA receptor to the convulsive response ofN-methyl-D,L-aspartate (NMDLA), and second, whether in vivo modulation of nitric oxide synthase (NOS) function regulates the development of cocaine kindling. The following results were observed:

1. Cocaine-kindled animals were significantly more susceptible to the convulsive effect of the NMDA receptor agonist NMDLA than saline controls;
2. Pretreatment with the NOS inhibitor N^G-nitro-L-arginine methyl ester (L-NAME; 100 mg/kg; ip) blocked the development of cocaine kindling;
3. The protective effect of L-NAME was partially reversed with the coadministration of the NOS substrate,L-arginine (300 mg/kg; ip), but notD-arginine; and
4. L-Arginine (300 mg/kg; ip), but notD-arginine, amplified the development of cocaine kindling. Taken together, these findings suggest that supersensitivity of the NMDA receptor and activation of NOS may underlie the development of cocaine kindling.

     

Asymmetric Dimethylarginine,an Endogenous NOS Inhibitor,Is Actively Metabolized in Rat Erythrocytes

N ^G,N ^G-Dimethyl-L-arginine (asymmetric dimethylarginine: ADMA) is an endogenous competitive inhibitor of nitric oxide synthase (NOS). Plasma ADMA concentrations have been reported to increase in connection with diseases associated with an impaired endothelial L-arginine/NO pathway. In this study, we investigated the metabolism of ADMA in circulating blood cell populations to elucidate the regulatory mechanism of elevation of plasma ADMA, a novel risk factor for cardiovascular disease. We found by RT-PCR and Western blot analyses that protein arginine methyltransferase (PRMT)1 and dimethylarginine dimethylaminohydrolase (DDAH)-1, responsible for the biosynthesis and degradation of ADMA respectively, are expressed in erythrocytes (ECs), leukocytes, and platelets. We also identified a major ADMA-containing protein in ECs as catalase, confirmed by GST-pull down assay to bind to PRMT1 in vitro. This is the first report that the ADMA-metabolizing system, including the arginine methylation of proteins and the breakdown of free ADMA, occurs in circulating blood cell-populations, and that catalase in ECs might be a potential protein targeted by PRMT1.     

Prolonged inhibition of brain nitric oxide synthase by short-term systemic administration of nitro-l-arginine methyl ester

We studied the dose-response characteristics and the temporal profile of inhibition of brain nitric oxide (NO) synthase (NOS) elicited by i.v. administration of the NOS inhibitor nitro-l-arginine methyl ester (L-NAME). L-NAME was administered i.v. in awake rats equipped with a venous cannula. L-NAME was injected in cumulative doses of 5, 10, 20 and 40 mg/kg and rats were sacrificed 30 min after the last dose. NOS catalytic activity was assayed in forebrain cytosol as the conversion of [³H]l-arginine into [³H]l-citrulline. L-NAME attenuated brain NOS activity in a dose-dependent manner but enzyme activity could not be inhibited by more than 50%. After a single 20 mg/kg injection of L-NAME the inhibition of brain NOS activity was time dependent and reached a stable level at 2 hrs (52% of vehicle). Inhibition after a single injection was still present at 96 hrs, albeit to a lower magnitude. We conclude that intravenous administration of L-NAME in rats at concentrations commonly used in physiological experiments leads to a dose and time-dependent but partial inhibition of brain NOS catalytic activity. The finding that the inhibition persists for several days after a single administration is consistent with the hypothesis that nitro-L-arginine, the active principle of L-NAME, binds to NOS irreversibly.     

The role of nitric oxide in the spatial heterogeneity of basal microvascular blood flow in the rat diaphragm

The effects of N-nitro-L-arginine (L-NOARG) and N^G-monomethyl-L-arginine (L-NMMA) on the spatialdistribution of diaphragmatic microvascular blood flow were assessed in anesthetized, mechanically ventilated rats. Microvascular blood flow was measured after different periods at either a fixed site (Q_stat) or 25 different sites (Q_scan) using computer-aided laser-Doppler flowmetry (LDF) scanning. The value of Q_stat was unaffected after 15–20 min superfusion with any one of the following agents: L-NOARG (0.1 mM), L-NMMA (0.1 mM), L-arg (10 mM). The cumulative frequency histogram of the Q_scan value in the control group displayed a non-Gaussian distribution that was not significantly affected after 15 min superfusion with the vehicle of L-NOARG. Superfusion with either L-NMMA or L-NOARG at 0.1 mM for 15 min displaced the histogram of cumulative frequency to the left, with the median value of blood flow decreasing by 10 to 20%. However, skewness and kurtosis of the distribution of basal Q_scan were unaffected after superfusion of either of the L-arg analogues. Pretreatment with L-arg (10 mM), followed by co-administration of L-arg (10 mM) with L-NOARG (0.1 mM) only partially prevented L-NOARG from exerting this inhibitory effect on the distribution of basal Q_scan, while pretreatment with L-arg in the same manner could prevent L-NMMA from exerting its inhibitory effect. There was a weak but significant linear relationship between the magnitude of basal Q_scan and normalized changes in basal Q_scan after superfusion of either of the L-arg analogues. In conclusion, a basal NO activity is present in the diaphragmatic microvascular bed of rats. LDF scanning rather may yield more vivid information about the extent of overall tissue perfusion than conventional LDF whenever basal NO activity is involved. Moreover, the parallel flow profiles after NO synthase blockade suggest that the spatial inhomogeneity of basal diaphragmatic microvascular blood flow is not dependent on basal NO formation.     

Central blockade of nitric oxide synthesis induces hyperthermia that is prevented by indomethacin in rats

The effect of blocking brain nitric oxide (NO) synthesis on body temperature regulation was tested in conscious rats. NO synthase was inhibited by administration of equivalent doses of N^G-nitro-L-arginine methyl ester (L-NAME) or N^G-monomethyl L-arginine monoacetate (L-NMMA) into a lateral cerebral ventricle (ICV) and core temperature was monitored. An ICV injection of 300 μg L-NAME increased colonic temperature in rats (n=8) by 1.9±0.1 °C (P<0.001). The increase in temperature in response to blockade of NO synthesis was significant by 1 h after injection and sustained for more than 3 h. The hyperthermic response to central NO blockade (using L-NMMA) was found to be dose-dependent between 2.8 to 282 μg. Intravenous administration of L-NAME at the highest dose used in the study (300 μg) had no effect on temperature, indicating that the mechanism was mediated by the brain. Pre-treatment with indomethacin (300 μg) blocked hyperthermic responses to ICV L-NAME (300 μg) administration. We conclude that, blockade of nitric oxide induces a cyclooxygenase-dependent hyperthermia in conscious rats that is mediated by the brain.     

Effects of nitric oxide synthase inhibitors on systemic hypotension, cytokines and inducible nitric oxide synthase expression and lung injury following endotoxin administration in rats

Endotoxin shock is characterized by systemic hypotension, hyporeactiveness to vasoconstrictors and acute lung edema. A nitric oxide synthase (NOS) inhibitor, N^G-monomethyl-L-arginine (L-NMMA) has been shown to be effective in reversing acute lung injury. In the present study, we evaluated the effects of NOS blockade by different mechanisms on the endotoxin-induced changes. In anesthetized rats, lipopolysaccharide (LPS,Klebsiella pneumoniae) was administered intravenously in a dose of 10 mg/kg. LPS caused sustained systemic hypotension accompanied by an eightfold increase of exhaled NO during an observation period of 4 h. After the experiment, the lung weight was obtained and lung tissues were taken for the determination of mRNA expressions of inducible NOS (iNOS), interleukin-1 (IL-1) and tumor necrosis factor--(TNF-). Histological examination of the lungs was also performed. In the control group injected with saline solution, mRNA expressions of iNOS, IL-1 and TNF- were absent. Four hours after LPS, the mRNA expressions of iNOS and IL-1 were still significantly enhanced, but TNF- was not discernibly expressed. LPS also caused a twofold increase in lung weight. Pathological examination revealed endothelial damage and interstitial edema. Various NOS inhibitors were given 1 h after LPS administration. These agents included N-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), a constitutive NOS and iNOS inhibitor; S,S-1,4-phenylene-bis-(1,2-ethanedinyl) bis-isothiourea dihydrobromide (1,4-PBIT, 10 mg/kg), a relatively specific iNOS inhibitor, and dexamethasone (3 mg/kg), an inhibitor of iNOS expression. These NOS inhibitors all effectively reversed the systemic hypotension, reduced the exhaled NO concentration and prevented acute lung injury. The LPS-induced mRNA expressions of iNOS and IL-1 were also significantly depressed by these NOS inhibitors. Our results suggest that NO production through the iNOS pathway is responsible for endotoxin-induced lung injury. Certain cytokines such as IL-1 are possibly involved. These changes are minimized by NOS inhibitors through different mechanisms.     

Chronic administration of a nitric oxide synthase inhibitor,Nω-nitro-l-arginine,and drug-induced increase in cerebellar cyclic GMP in vivo

N-nitro-l-arginine (N^G-nitro-l-arginine) is a potent nitric oxide synthase inhibitor which crosses the blood brain barrier and does not undergo extensive metabolism in vivo. In this study, effect of chronic pretreatment of N-nitro-l-arginine (75 mg/kg, i.p., twice daily for 7 days) on the harmaline- (100 mg/kg, s.c.), picrotoxin- (4 mg/kg, s.c.), pentylenetetrazole- (50 mg/kg, i.p.), andl-glutamic acid- (400 g/10 l/mouse, i.c.v.) induced increase in cerebellar cGMP was assessed. All the four drugs produced significant increase in cerebellar cGMP in vehicle pretreated control animals. Cerebellar cGMP increase induced by harmaline, picrotoxin, andl-glutamic acid was attentuated in N-nitro-l-arginine pretreated animals. These results indicate that in vivo cerebellar cGMP levels are increased by the prototype excitatory amino acid receptor agonist,l-glutamic acid and also by the drugs which augment the excitatory amino acid transmission. Furthermore, parenteral chronic administration of N-nitro-l-arginine blocks NO synthase in the brain and hence cerebellar cGMP response in chronic N-nitro-l-arginine treated animals could be used as a tool to assess the physiological functions of nitric oxide in vivo.Part of this work was presented at the Experimental Biology 93 FASEB Meeting at New Orleans, March 1993.     

The Nitric Oxide Synthase Inhibitor NG-nitro-L-Arginine Methyl Ester Potentiates Insulin Secretion Stimulated by Glucose and L-Arginine Independently of its Action on ATP-Sensitive K+ Channels

The nature of the action of the nitric oxide synthase (NOS) inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) on hormone release from isolated islets was investigated. We found that glucose-induced insulin release was potentiated by L-NAME in the absence or presence of diazoxide, a potent channel opener, as well as in the presence of diazoxide plus a depolarizing concentration of K⁺. At a low, physiological glucose concentration L-NAME did not influence insulin secretion induced by K⁺ but inhibited glucagon secretion. L-arginine-induced insulin release was potentiated by L-NAME. This potentiation was observed also in the presence of K⁺ plus diazoxide. Further, glucagon release induced by L-arginine as well as by L-arginine plus K⁺ and diazoxide was suppressed by L-NAME. The results strongly suggest that the L-NAME-induced potentiation of insulin secretion in response to glucose or L-arginine as well as the inhibitory effects on glucagon secretion are largely mediated by L-NAME directly suppressing islet NOS activity. Hence NO apparently affects insulin and glucagon secretion independently of membrane depolarization events.     

Effects of tensile stress on the α1 nicotinic acetylcholine receptor expression in maxillofacial skeletal myocytes

The present study was to test the hypothesis that 11,12-epoxyeicosatrienoic acid (11,12-EET), a metabolic product of arachidonic acid by cytochrome P450 epoxygenase, regulates nitric oxide (NO) generation of the l-arginine/NO synthase (NOS) pathway in human platelets. Human platelets were incubated in the presence or absence of different concentrations of 11,12-EET for 2 h at 37°C, followed by measurements of activities of the l-arginine/NOS pathway. Incubation with 11,12-EET increased the platelet NOS activity, nitrite production, cGMP content, and the platelet uptake of l-[³H]arginine in a concentration-dependent manner. In addition, 11,12-EET attenuated intracellular free Ca²⁺ accumulation stimulated by collagen, which was at least partly mediated by EET-activated l-arginine/NOS pathway. It is suggested that 11,12-EET regulates platelet function through up-regulating the activity of the l-arginine/NOS/NO pathway.     

Suppression of Cytokine Production in T Helper Type 2 Cells by Nitric Oxide in Comparison with T Helper Type 1 Cells

We examined the effect of nitric oxide (NO) on cytokine production in T helper (Th) cell subsets, using murine splenic CD4⁺ T cells and two types of Th clones. Interferon-gamma-treated murine peritoneal exudate cells (IFN-PEC) suppressed DNA synthesis to 60% of the control level in CD4⁺ T cells stimulated with the anti-CD3 monoclonal antibody. The production of IL-2 and IL-4 in the CD4⁺ T cells decreased to 63.2% and 9.2%, respectively, of the control value by co-culture with IFN-PEC. The addition of N^G-monomethyl-L -arginine (L-NMMA) partially recovered the suppression of DNA synthesis. In the presence of indomethacin, the suppression of DNA synthesis was partially inhibited and the reduction in the cytokine production caused by IFN-PEC was partially recovered. The simultaneous addition of N^G-monomethyl-L -arginine (L-NMMA) and indomethacin completely inhibited not only the suppression of DNA synthesis but also the reduction in the cytokine production caused by IFN-PEC. Moreover, DNA synthesis in the Th2 clone was suppressed to a greater extent than that in the Th1 clone by co-culture with IFN-PEC. This suppression in the Th1 clone was inhibited by the addition of L-NMMA, whereas the DNA synthesis in the Th2 clone was not recovered by L-NMMA. In addition, sodium nitroprusside (SNP) suppressed IL-4 production in the Th2 clone but had no effect on IL-2 production in the Th1 clone. In the experiment of the co-culture with IFN-PEC, the inhibitory-effect of NO on T cell activation was not clarified by the influence of prostaglandins. However, in conclusion, cytokine production in Th2 cells may be more susceptible to NO than that in Th1 cells.     

Effect of L-arginine on Na+,K+-ATPase activity in rat aorta endothelium

The effect of L-arginine on the Na⁺,K⁺-ATPase activity in rat aorta endothelium was studied at its physiological concentrations in the range of 10^–6-10^–3 M. The enzyme activity was 35.5% increased by low concentrations of L-arginine (10^–5 M) and its activity was 32.3-37.1% decreased at the L-arginine concentrations of 10^–4-10^–3 M. A similar inhibition (by 34.5-42.8%) was also found in the presence of a NO-donor nitroglycerol (10^–4-10^–3 M). An optical isomer of L-arginine, D-arginine, at the concentrations of 10^–5 M also increased the enzyme activity by 37.1%, but its inhibiting effect was much less pronounced and was 15.7% at the D-arginine concentration of 10^–3 M. An inhibitor of NO-synthase, L-NAME (N^G-nitroarginine, methyl ester), failed to inhibit Na⁺,K⁺-ATPase. However, the presence of L-NAME abolished the inhibition of Na⁺,K⁺-ATPase by high concentrations of L-arginine. Thus, the effect of L-arginine on the endothelial Na⁺-pump depended on its concentration, and it is suggested that the enzyme inhibition by high concentrations of L-arginine should be associated with activation of the endogenous synthesis of NO.     

The modulation of NMDA receptors and <Emphasis Type="SmallCaps">l</Emphasis>-arginine/nitric oxide pathway is implicated in the anti-immobility effect of creatine in the tail suspension test

The modulation of N-methyl-D-aspartate receptor (NMDAR) and l-arginine/nitric oxide (NO) pathway is a therapeutic strategy for treating depression and neurologic disorders that involves excitotoxicity. Literature data have reported that creatine exhibits antidepressant and neuroprotective effects, but the implication of NMDAR and l-arginine/nitric oxide (NO) pathway in these effects is not established. This study evaluated the influence of pharmacological agents that modulate NMDAR/l-arginine-NO pathway in the anti-immobility effect of creatine in the tail suspension test (TST) in mice. The NOx levels and cellular viability in hippocampal and cerebrocortical slices of creatine-treated mice were also evaluated. The anti-immobility effect of creatine (10 mg/kg, po) in the TST was abolished by NMDA (0.1 pmol/mouse, icv), d-serine (30 µg/mouse, icv, glycine-site NMDAR agonist), arcaine (1 mg/kg, ip, polyamine site NMDAR antagonist), l-arginine (750 mg/kg, ip, NO precursor), SNAP (25 μg/mouse, icv, NO donor), L-NAME (175 mg/kg, ip, non-selective NOS inhibitor) or 7-nitroindazole (50 mg/kg, ip, neuronal NOS inhibitor), but not by DNQX (2.5 µg/mouse, icv, AMPA receptor antagonist). The combined administration of sub-effective doses of creatine (0.01 mg/kg, po) and NMDAR antagonists MK-801 (0.001 mg/kg, po) or ketamine (0.1 mg/kg, ip) reduced immobility time in the TST. Creatine (10 mg/kg, po) increased cellular viability in hippocampal and cerebrocortical slices and enhanced hippocampal and cerebrocortical NO _x levels, an effect potentiated by l-arginine or SNAP and abolished by 7-nitroindazole or L-NAME. In conclusion, the anti-immobility effect of creatine in the TST involves NMDAR inhibition and enhancement of NO levels accompanied by an increase in neural viability.     

Targeting the superoxide/nitric oxide ratio by L-arginine and SOD mimic in diabetic rat skin

Abstract

Setting the correct ratio of superoxide anion (O₂^?-) and nitric oxide (^?NO) radicals seems to be crucial in restoring disrupted redox signaling in diabetic skin and improvement of ^?NO physiological action for prevention and treatment of skin injuries in diabetes. In this study we examined the effects of L-arginine and manganese(II)-pentaazamacrocyclic superoxide dismutase (SOD) mimic – M40403 in diabetic rat skin. Following induction of diabetes by alloxan (blood glucose level ≥12?mMol l?^?1) non-diabetic and diabetic male Mill Hill hybrid hooded rats were divided into three subgroups: (i) control, and receiving: (ii) L-arginine, (iii) M40403. Treatment of diabetic animals started after diabetes induction and lasted for 7 days. Compared to control, lower cutaneous immuno-expression of endothelial NO synthase (eNOS), heme oxygenase 1 (HO1), manganese SOD (MnSOD) and glutathione peroxidase (GSH-Px), in parallel with increased NFE2-related factor 2 (Nrf2) and nitrotyrosine levels characterized diabetic skin. L-arginine and M40403 treatments normalized alloxan-induced increase in nitrotyrosine. This was accompanied by the improvement/restitution of eNOS and HO1 or MnSOD and GSH-Px protein expression levels in diabetic skin following L-arginine, i.e. SOD mimic treatments, respectively. The results indicate that L-arginine and M40403 stabilize redox balance in diabetic skin and suggest the underlying molecular mechanisms. Restitution of skin redox balance by L-arginine and M40403 may represent an effective strategy to ameliorate therapy of diabetic skin.     

Nitric oxide and superoxide radical are involved in both initiation and development of adjuvant arthritis in rats

Nitric oxide synthase(NOS) inhibitor, N^ω-nitro-L-arginine methyl ester (L-NAME, 10–300 mg/kg) and L-N^G-monomethyl-arginine (L-NMMA, 30–300 mg/kg) suppressed the swellings of adjuvant-injected paw of rats (25–54%) at day 2 and 8 when dosed intraperitoneally and orally for 4 days from day -1 to day 2 after adjuvant. L-NAME (30–300 mg/kg) also suppressed the edema of the non adjuvant-injected paws (15–42%) at day 28. Local injection of this inhibitor (2 and 10 mg/kg) was without effect. L-arginine (1 g/kg, i.p.), impaired the suppression by L-NAME. Bovine blood Cu, Zn-superoxide dismutase (SOD, 3 mg/kg, i.p.: 28% suppression) and L-NAME (30 mg/kg i.p.: 36% suppression) showed additive effect (52%) in adjuvant-injected paws at day 8 when co-injected. As the effect of 30 mg/kg L-NAME corresponded nearly to that of 10 mg/kg Voltaren^R, this NOS inhibitor would be worth considering as an anti-inflammatory agent. Sodium nitroprusside (NO-donor) and methylene blue (guanylate cyclase inhibitor) had no effect. L-NAME was also suppressive when dosed after adjuvant inoculation and NO is involved in the development and maintenance of swelling.     

Inhibition of neuronal nitric oxide synthase (n-cNOS) reverses the corticotrophin-induced behavioral effects in rats

The nitric oxide (NO) synthase inhibitor N^G-monomethyl-L-arginine (N-NMMA) and the competitive substrate for NO synthase L-arginine were used to determine the role of endogenous NO on the behavioral and neuroendocrine responsiveness following systemic corticotrophin in dexamethasone-suppressed rats. Corticotrophin (50-200 mU/kg, s.c.) dose-dependently decreased behavioral activity in the actimeter and produced significant anxiolytic and anti-risk activity in the plus-maze behavior test, without affecting systolic blood pressure. Rats given corticotrophin showed significant increased plasma corticosterone and reduced adrenal ascorbic acid level. These behavioral and adrenal responses of corticotrophin were dose dependently blocked by metyrapone (20 and 50 mg/kg, i.p.), an inhibitor of steroid 11-hydroxylase in adrenal and neural tissues that block steroidogenesis. Intracerebroventricular administration of L-NMMA (20 g/rat in 10 l) significantly prevented the behavioral hypoactivity and anxiolytic-like responses of corticotrophin without influencing the adrenal responsiveness. The effect of L-NMMA was completely reversed by preadministration of L-arginine (300 mg/kg, i.p.). These results suggest that neuronal nitric oxide pathway plays an important modulating role in the behavioral effects of corticotrophin by mechanisms other than those involving cardiovascular effects.     

Effect of lisinopril on rat liver tissues in L-NAME induced hypertension model

N ^G-Nitro-l-arginine methyl ester hydrochloride (L-NAME) is a non-specific nitric oxide (NO) inhibitor and it has been used to eliminate the role of NO in many studies like animal models for hypertension. In this study, we aimed to investigate whether lisinopril treatment has any biochemical and/or histopathological effect on rat liver tissue in a L-NAME-induced hypertension model. Forty-eight 6-weeks-old male Spraque–Dawley rats were used in the study. The animals used in the study were randomly divided into four equal groups. To induce hypertension, L-NAME was added to drinking water at a concentration of 600 mg/l and each rat was given 75 mg/kg/day of L-NAME for 6 weeks. Tail cuff systolic blood pressure (SBP) was measured at first, third, and sixth weeks. There was a significant difference between the experiment groups and controls. In only lisinopril given and L-NAME plus lisinopril administered groups, each rat was given 10 mg/kg of lisinopril for 6 weeks. At the end of the study, the animals were sacrificed. Blood and tissue samples were collected for biochemical and histopathological analysis. It has been observed that mean NO level was significantly decreased in L-NAME given group (p<0.05). Mean ALT levels were significantly increased in lisinopril and L-NAME plus lisinopril given groups, when compared with the control group (p<0.05). AST levels were in normal range in all groups (p>0.05). Hepatocyte degeneration was prominent in lisinopril given group, whereas mononuclear cell infiltration was significant in L-NAME given groups. Although the beneficial effects in L-NAME-induced hypertension treatment, lisinopril can lead to some unexpected results like hepatocyte degeneration, serum enzyme level elevation, and slight mononuclear cell infiltration.     

Nitric oxide synthase inhibition by L-NAME prevents the decrease of Na+,K+-ATPase activity in midbrain of rats subjected to arginine administration

In the present study we investigated the effect of acute administration of L-arginine on Na⁺,K⁺-ATPase and Mg²⁺-ATPase activities and on some parameters of oxidative stress (chemiluminescence and total radical-trapping antioxidant parameter-TRAP) in midbrain of adult rats. We also tested the effect of L-NAME on the effects produced by arginine. Sixty-day-old rats were treated with an acute intraperitoneal injection of saline (group I, control), arginine (0.8 g/kg) (group II), L-NAME (2 mg/kg) (group III) or arginine (0.8 g/kg) plus L-NAME (2 mg/kg) (group IV). Na⁺,K⁺-ATPase activity was significantly reduced in the arginine-treated rats, but was not affected by other treatments. In contrast, Mg²⁺-ATPase activity was not altered by any treatment. Furthermore, chemiluminescence was significantly increased and TRAP was significantly decreased in arginine-treated rats, whereas the simultaneous injection of L-NAME prevented these effects. These results demonstrate that in vivo arginine administration reduces Na⁺,K⁺-ATPase activity possibly through free radical generation induced by NO formation.