7-Nitroindazole reduces nitric oxide concentration in rat hippocampus after transient forebrain ischemia

We investigated the effects of 7-nitroindazole, a specific inhibitor of neuronal nitric oxide (NO) synthase, on NO concentration and on blood flow in rat hippocampus after transient forebrain ischemia which was induced by 4-vessel occlusion for 10 min. NO concentration was measured directly by an NO-selective electrode method. Hippocampal blood flow was also estimated by laser Doppler flowmetry. 7-Nitroindazole [0 (vehicle), 12.5, 25, 50 or 100 mg/kg] was administered intraperitoneally 20 min before ischemia. 7-Nitroindazole at any dose used did not affect basal NO levels before ischemia. 7-Nitroindazole (25, 50 and 100 mg/kg) reduced the NO concentration significantly during post-ischemic early reperfusion. Before 10 min of ischemia and during post-ischemic early reperfusion, there were no significant differences in hippocampal basal blood flow and reactive hyperemia between vehicle- and 7-nitroindazole-treated groups. These results demonstrate that the neuronal NO synthase inhibitor, 7-nitroindazole, can effectively inhibit NO synthesis in rat hippocampus during post-ischemic early reperfusion.     

7-Nitroindazole, a neuronal nitric oxide synthase inhibitor, impairs passive-avoidance and elevated plus-maze memory performance in rats

The role of nitric oxide (NO) on cognitive performance in a modified elevated plus-maze (mEPM) and passive-avoidance (PA) task was investigated by using the NO synthase (NOS) inhibitor 7-nitroindazole (7-NI) and an NO precursor l-arginine. The interaction between the activation of N-methyl-d-aspartate (NMDA) receptors and NO synthesis on memory retention was also studied. 7-NI, l-arginine or MK-801, a non-competitive NMDA receptor antagonist were injected intraperitoneally (i.p) to male Wistar rats 30 min before the first training session of the PA test or 30 min before on the first day testing (acquisition session) of mEPM task. Transfer latency, the time rat took to move from the open arm to the enclosed arm, was used as an index of learning and memory in a mEPM test. The retention session was performed 24 h after the acquisition one. In the PA task, the retention test was carried out 24 h after training and reduction of retention latency was used to evaluate the acquisition of learning and memory. Blood glucose level and locomotor activity of the rats was also evaluated. 7-NI (10, 20, 25, 50 mg/kg) and MK-801 (0.15 mg/kg) significantly prolonged the transfer latency on retention session in a mEPM test and shortened step-through latency in PA test. 7-NI-induced impairment in memory and learning was partly reversed by l-arginine (200 mg/kg), a competitive substrate for NOS. However subeffective doses of 7-NI (5 mg/kg) and MK-801 (0.075 mg/kg) given in combination significantly impaired plus-maze and PA performances in rats. Thus NMDA receptor mediated NO pathways may be implicated in the PA and mEPM behaviours in rats. Since 7-NI does not affect blood pressure and did not alter blood glucose level and locomotor activity in conscious rats, 7-NI-induced impairment of memory is not due to either hypertension, changes in blood glucose level or effects on locomotor activity.     

Acute inhibition of glutathione biosynthesis alters endothelial function and blood pressure in rats

The present study investigated the role of nitric oxide (NO) in the rewarding effects of D-methamphetamine using 7-nitroindazole, a potent inhibitor of neuronal nitric oxide synthase (nNOS), as determined by the conditioned place preference paradigm. Male Sprague-Dawley rats treated with D-methamphetamine (1 mg/kg) or saline every other day for 8 days (four drug and four saline sessions) developed marked place preference for the drug-paired side. The administration of 7-nitroindazole (12.5-50 mg/kg) 30 min prior to the exposure to D-methamphetamine dose-dependently attenuated the acquisition of D-methamphetamine-induced conditioned place preference. In addition, when it was acutely administered 30 min prior to the testing session of an already established D-methamphetamine-induced conditioned place preference, 7-nitroindazole (12.5-50 mg/kg) attenuated the expression of this conditioned response in a dose-dependent manner, while 7-nitroindazole (25 and 50 mg/kg) alone showed no place preference effects. These findings indicate that nitric oxide (NO) is involved in the rewarding properties of methamphetamine and suggest that selective nNOS inhibitors maybe useful in the management of methamphetamine abuse.     

7-Nitroindazole,a neuronal nitric oxide synthase inhibitor,impairs passive-avoidance and elevated plus-maze memory performance in rats

The role of nitric oxide (NO) on cognitive performance in a modified elevated plus-maze (mEPM) and passive-avoidance (PA) task was investigated by using the NO synthase (NOS) inhibitor 7-nitroindazole (7-NI) and an NO precursor l-arginine. The interaction between the activation of N-methyl-d-aspartate (NMDA) receptors and NO synthesis on memory retention was also studied. 7-NI, l-arginine or MK-801, a non-competitive NMDA receptor antagonist were injected intraperitoneally (i.p) to male Wistar rats 30 min before the first training session of the PA test or 30 min before on the first day testing (acquisition session) of mEPM task. Transfer latency, the time rat took to move from the open arm to the enclosed arm, was used as an index of learning and memory in a mEPM test. The retention session was performed 24 h after the acquisition one. In the PA task, the retention test was carried out 24 h after training and reduction of retention latency was used to evaluate the acquisition of learning and memory. Blood glucose level and locomotor activity of the rats was also evaluated.7-NI (10, 20, 25, 50 mg/kg) and MK-801 (0.15 mg/kg) significantly prolonged the transfer latency on retention session in a mEPM test and shortened step-through latency in PA test. 7-NI-induced impairment in memory and learning was partly reversed by l-arginine (200 mg/kg), a competitive substrate for NOS. However subeffective doses of 7-NI (5 mg/kg) and MK-801 (0.075 mg/kg) given in combination significantly impaired plus-maze and PA performances in rats. Thus NMDA receptor mediated NO pathways may be implicated in the PA and mEPM behaviours in rats. Since 7-NI does not affect blood pressure and did not alter blood glucose level and locomotor activity in conscious rats, 7-NI-induced impairment of memory is not due to either hypertension, changes in blood glucose level or effects on locomotor activity.     

Repeated treatment with the traditional medicine Unsei-in inhibits substance P-induced itch-associated responses through downregulation of the expression of nitric oxide synthase 1 in mice

Unsei-in inhibits substance P (SP)-induced scratching of mice after repeated administration. The involvement of cutaneous nitric oxide (NO) in the SP-induced scratching led us to investigate the effects of Unsei-in on the cutaneous NO system in mice. Seven-day oral administration of Unsei-in (300, but not 100, mg/kg daily) significantly inhibited scratching and the increase of cutaneous NO after intradermal SP injection. The NO synthase 1 (NOS1) inhibitor 7-nitroindazole (1 nmol/site) decreased SP-induced scratching and NO production. Repeated administration of Unsei-in (300 mg/kg) reduced the cutaneous NOS1 level. The results suggest that the inhibition of cutaneous NOS1 expression and NO production participates in the antipruritic action of Unsei-in.     

Nitric oxide synthase mediates delta opioid receptor-induced hypothermia in rats

The role of nitric oxide (NO) production in delta opioid receptor-induced hypothermia has not been reported. The present study investigated the effect of nitric oxide synthase (NOS) inhibitors on the hypothermic effect of (+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC-80), a nonpeptide delta opioid agonist. SNC-80 (35 mg/kg, i.p.) administered to rats caused a significant hypothermia. N-nitro-L-arginine methyl ester (L-NAME) (10, 25 and 50 mg/kg, i.p.), a NOS inhibitor, and 7-nitroindazole (7-NI) (5 and 10 mg/kg, i.p.), a neuronal NOS inhibitor, were ineffective. For combined administration, L-NAME (50 mg/kg, i.p.) or 7-NI (10 mg/kg, i.p.) attenuated SNC-80-evoked hypothermia. To determine the involvement of central NOS, L-NAME (0.25, 0.5 and 1 mg/rat) was administered i.c.v. 30 min prior to SNC-80 (35 mg/kg, i.p.). Experiments revealed that L-NAME (1 mg/rat, i.c.v.) attenuated SNC-80-induced hypothermia. The present data demonstrate that central NO production is necessary for delta opioid receptor-induced hypothermia.     

Effect of 7-nitroindazole alone and in combination with phenobarbitone and diazepam on picrotoxin-induced convulsions in rats

There are no reports on the effect of 7-nitroindazole (7-NI) on chemically-induced convulsions. Hence, in the present study, its (100 and 200 mg/kg) action was tested alone and in combination with phenobarbitone (20 mg/kg) and diazepam (0.25 mg/kg) on picrotoxin (PCT)-induced convulsions in rats. The changes produced by 7-NI on nitric oxide synthase (NOS) activity and nitric oxide (NO) concentration were determined in the brain. The effect of 7-NI was tested in L-arginine (1000 mg/kg) pretreated (30 min) animals. The smaller dose (100 mg/kg) of 7-NI did not alter NOS activity and NO concentration, but inhibited PCT-induced convulsions indicating that its anticonvulsant action was devoid of an involvement of NO. But, an inhibition of NOS activity, by a larger (200 mg/kg) dose of it, resulted in a promotion of the convulsant action of PCT and in an impairment of the anticonvulsant effect of both phenobarbitone and diazepam. The proconvulsant action of 7-NI was reverted by L-arginine. These results suggest that 100 and 200 mg/kg of 7-NI produce distinguishable action on PCT-induced convulsions because NOS activity is inhibited by 200 mg/kg and not by 100 mg/kg of it. The results further suggest that NO acts as anticonvulsant and that the NOS inhibitors, like 7-NI, cannot be used as an anticonvulsant either alone or in combination with other anticonvulsants.     

Different effects of nitric oxide synthase inhibitors on convulsions induced by nicotine in mice

Acute intraperitoneal (i.p.) administration of N(G)-nitro-L-arginine (NNA, 10, 20 and 40 mg/kg), a non-selective nitric oxide synthase (NOS) inhibitor, significantly and dose-dependently decreased the incidence of convulsions induced by i.p. nicotine (NIC) in mice, whereas 7-nitroindazole (7NI, 50 and 100 mg/kg i.p.), a selective neuronal NOS inhibitor, had a proconvulsant effect. Aminoguanidine (100 mg/kg ip), a specific inducible NOS inhibitor, remained without an effect on convulsive behavior. L-arginine, a nitric oxide (NO) precursor, which independently has no effect on convulsions, markedly reversed the anticonvulsant effect of NNA; yet only partially reversed the proconvulsant effect of 7NI when injected at 500 mg/kg i.p.. Convulsions evoked by intracerebroventricular injection of NIC were significantly suppressed by ip NNA(40 mg/kg i.p.) and enhanced by i.p. 7NI (100 mg/kg i.p.); however, these effects of NNA and 7NI were less potent than those seen when NIC was administered i.p.. The present study revealed essential differences in the action of NOS inhibitors in NIC-induced convulsions. It appears that only NO produced by constitutive NOS is involved in the mechanism of NIC-induced convulsions. The proconvulsant effect of 7NI may result from the mechanisms unrelated to NOS inhibition.     

Stress–restress evokes sustained iNOS activity and altered GABA levels and NMDA receptors in rat hippocampus

Rationale Stress-related glucocorticoid and glutamate release have been implicated in hippocampal atrophy evident in patients with post-traumatic stress disorder (PTSD). Glutamatergic mechanisms activate nitric oxide synthase (NOS), while gamma-amino-butyric acid (GABA) may inhibit both glutamatergic and nitrergic transmission. Animal studies support a role for NOS in stress.Objectives We have studied the role of NOS and glucocorticoids, as well as inhibitory and excitatory transmitters, in a putative animal model of PTSD that emphasizes repeated trauma.Methods Hippocampal NOS activity, N-methyl-d-aspartate (NMDA) receptor binding characteristics and GABA levels were studied in Sprague-Dawley rats 21 days after exposure to a stress–restress paradigm, using radiometric analysis, radioligand studies and high-performance liquid chromatography (HPLC) analysis with electrochemical detection, respectively. The NOS isoform involved, and the role of stress-mediated corticosterone release in NOS activation, was verified with the administration of selective iNOS and nNOS inhibitors, aminoguanidine (50 mg/kg/day i.p.) and 7-nitroindazole (12.5 mg/kg/day i.p.), and the steroid synthesis inhibitor, ketoconazole (24 mg/kg/day i.p.), administered for 21 days prior to and during the stress procedure.Results Stress evoked a sustained increase in NOS activity, but reduced NMDA receptor density and total GABA levels. Aminoguanidine or ketoconazole, but not 7-nitroindazole or saline, blocked stress-induced NOS activation.Conclusions Stress–restress-mediated glucocorticoid release activates iNOS, followed by a reactive downregulation of hippocampal NMDA receptors and dysregulation of inhibitory GABA pathways. The role of NO in neuronal toxicity, and its regulation by glutamate and GABA has important implications in stress-related hippocampal degeneration.     

Biphasic modulation by nitric oxide of caspase activation due to malonate injection in rat striatum

The present study examined caspase activation and its modulation by nitric oxide (NO) in a model of oxidative stress induced by injection of malonate (3 micromol), a mitochondrial toxin, into rat striatum. Caspase-3-like enzymatic activity was maximal 6 h after malonate while NO production evaluated by its metabolites nitrites and nitrates was increased at 3 h. The neuronal NO-synthase inhibitor 7-nitroindazole reduced malonate induced-NO production by 50% at 25 mg/kg and enhanced by 32% caspase activation. This result suggests that a moderate production of NO potentiates caspase activation, an effect counterbalanced by NO itself at higher concentrations. Accordingly, complete inhibition of NO production by 7-nitroindazole at 50 mg/kg did not modify malonate-induced caspase activity. Thus NO production by the neuronal isoform of NO-synthase is not the major event leading to caspase activation due to malonate. However, NO seems to have pro- and anti-caspase effects that neutralize each other.     

Demonstrating the dose- and time-related effects of 7-nitroindazole on picrotoxin-induced convulsions, memory formation, brain nitric oxide synthase activity, and nitric oxide concentration in rats

In this study, the dose (50, 100, 150, and 200 mg/kg)- and time (30 and 60 min)- related effects of 7-nitroindazole (7-NI), a neuronal specific inhibitor of nitric oxide synthase (NOS) were tested on picrotoxin (5 mg/kg)-induced convulsions and memory formation in rats. The changes produced by these doses of 7-NI were determined on NOS activity and nitric oxide (NO) concentration in the brain. The effects of 7-NI were tested in animals pretreated (30 min) with L-arginine (500 and 1000 mg/kg). 7-NI, at 50 and 100 mg/kg, did not produce significant changes in NOS activity and NO concentration in the brain and memory formation. However, the convulsant action of picrotoxin was inhibited in a dose-dependent manner in these animals. A time-dependent decrease in the activity of NOS and the concentration of NO, a promotion of picrotoxin-induced convulsions, and an impairment of memory were found in animals treated with 150 and 200 mg/kg of 7-NI. The larger and not the smaller dose of L-arginine raised the concentration of NO, inhibited picrotoxin-induced convulsions and promoted memory process. Either dose of L-arginine failed to prevent 50 and 100 mg/kg of 7-NI from inhibiting convulsions. The effects of the larger doses of 7-NI (150 and 200 mg/kg) were effectively prevented by the increase of NO and not the ineffective dose of L-arginine. These results suggest that 7-NI (50 and 100 mg/kg) decreases convulsions by a nonspecific mechanism and that an inhibition of NOS by the larger doses of it (150 and 200 mg/kg) results in proconvulsant action and memory impairment. The data further show that the margin between the protective and proconvulsant doses of 7-NI is relatively narrow. These results have been taken together with the earlier reports that 7-NI produces learning impairment and fails to increase the anticonvulsant effect of traditional antiepileptic agents on experimentally induced convulsions to conclude that 7-NI can never emerge as an anticonvulsant agent for clinical use.     

Involvement of the NMDA receptor, NO-cyclic GMP and nuclear factor K-beta in an animal model of repeated trauma

Post-traumatic stress disorder (PTSD) may be associated with shrinkage of the hippocampus, with glutamate release causally related to these events. Recent animal studies strongly implicate activation of the nitric oxide (NO)-cascade in anxiety and stress. Using an animal model of repeated trauma, the effect of stress was investigated on the hippocampal NO-cGMP signalling pathway, specifically the release of nitrogen oxides (NOx) and its modulation by NMDA receptor-, NO-, cGMP- and nuclear factor K-beta (NFK-beta)-selective drugs. Immediately after stress, rats received the glutamate NMDA receptor antagonist, memantine (MEM; 5 mg/kg i.p./d), the NO synthase inhibitor, 7-nitroindazole sodium salt (7-NINA; 20 mg/kg i.p./d), the cGMP-specific PDE inhibitor, sildenafil (SIL; 10 mg/kg i.p./d) or the NFkappa-beta antagonist, pyrollidine dithiocarbamate (PDTC; 70 mg/kg i.p./d), for 7 days. Stress significantly increased hippocampal NOx on day 7 post-stress, which was blocked by either 7-NINA or PDTC, while MEM was without effect. SIL, however, significantly augmented stress-induced NOx accumulation. Increased cGMP therefore acts as a protagonist in driving stress-related events, while both nNOS (neuronal NOS) and iNOS (inducible/immunological NOS) may represent a therapeutic target in preventing the effects of severe stress. The value of NMDA receptor antagonism, however, appears limited in this model.     

利多卡因对家兔心肌缺血／再灌注损伤Na^＋-K^＋-ATPase、Ca^2＋ -Mg^2＋ -ATPase及NO的作用

目的:研究利多卡因对心肌缺血/再灌注损伤家兔心肌Na -K -ATPase、Ca2 -Mg2 -ATPase及血清NO的影响。方法:24只家兔随机分为3组:假手术组(A组)、缺血/再灌注组(B组)、利多卡因组(C组),每组8只。B组、C组阻断左冠状动脉前降支40 min,再灌注90 min,A组仅穿线不结扎。C组于开放冠状动脉再灌注前经颈静脉注射利多卡因5 mg/kg,A、B组注射等量生理盐水。于再灌注90min取颈静脉血测定NO。再灌注90 min后取心肌组织测定NOS、Na -K -ATPase、Ca2 -Mg2 -ATPase。结果:心肌组织Ca2 -Mg2 -ATPaseB组较A、C组降低(P<0.01);Na -K -ATPase B组较A、C组降低(P<0.01);血清NO、心肌组织NOS:B组较A、C组降低(P<0.01)。结论:利多卡因对心肌缺血/再灌注损伤具有保护作用。     

Use of an electrochemical nitric oxide sensor to detect neuronal nitric oxide production in conscious, unrestrained rats

INTRODUCTION: Amperometric sensors that directly measure nitric oxide (NO) are readily employed in pharmacologic research. While several of these sensors have been developed, none has been investigated for use in conscious, freely moving animals. An approach was developed and validated for real-time quantitation of neuronal NO production in rats without restricting locomotor activity or other potentially useful behavioral endpoints. METHODS: Male Sprague-Dawley rats were equipped with a femoral vein or intraperitoneal cannula. A guide cannula and an amperometric NO sensor were placed in the left and right hippocampus, respectively. Following recovery, rats received a 6-h intravenous infusion of saline, L-arginine (an NO precursor; 250 or 500 mg/kg/h), or incremental intraperitoneal 7-nitroindazole (an NO synthase inhibitor; 200-mg/kg loading dose and 100 mg/kg every 2 h). The sensor recorded NO production continuously and microdialysis samples were collected incrementally throughout the experiment. Griess assay analysis of microdialysate samples was compared to sensor readings in vivo. In vitro degradation of an NO donor also was used to validate sensor performance. RESULTS: Exogenous administration of L-arginine resulted in incremental increases in the neuronal NO signal. A reduction in NO production was observed during administration of 7-nitroindazole, a selective neuronal NO synthase inhibitor. A significant correlation was observed in vitro between the Griess assay analysis, an indirect analytical approach, and the NO sensor readings. The lack of a strong correlation between these measures in vivo is consistent with the indirect nature of the Griess assay. DISCUSSION: The current approach allows real-time determination of neuronal NO production in unrestrained rats. This model will be invaluable in evaluating pharmacologic issues regarding brain tissue NO synthesis, assessing brain NO synthase as a molecular target, and establishing the effects of pharmacologic agents on neuronal NO production.     

Pharmacokinetics and Pharmacodynamics of 7-Nitroindazole,a Selective Nitric Oxide Synthase Inhibitor,in the Rat Hippocampus

Purpose. This study was conducted to assess the pharmacokinetics and pharmacodynamics of 7-nitroindazole (7-NI), a selective inhibitor of neuronal nitric oxide synthase (NOS). Methods. Male Sprague-Dawley rats were equipped with peritoneal/venous cannulae and a microdialysis probe in the hippocampal cortex. Rats received 7-NI in peanut oil (25 mg/kg) ip every 2 h for 14 h or peanut oil alone. Blood samples were obtained at timed intervals for serum 7-NI; brain tissue microdialysate for determination of extracellular 7-NI and NO was obtained every 20 min. A pharmacokinetic-pharmacodynamic model was constructed to evaluate the effects of 7-NI on NOS activity. Results. Consistent with previous reports, NOS activity in controls evidenced circadian variation. These cyclic changes in NO production were incorporated into the model of 7-NI effects on NOS. 7-NI produced a rapid (within 2 h) decrease in hippocampal NO. Under the conditions of this experiment, 7-NI produced an 50% decrease in hippocampal NO, which was sustained during 7-NI administration. The decrease in NOS activity by 7-NI was concentration-dependent with an apparent IC₅₀ of 17 g/ml. Conclusions. Multiple ip injections of 7-NI result in a predictable, sustained decrease in NO production in the hippocampus. The pharmacokinetic-pharmacodynamic model developed allows design of dosing regimens that can produce designated changes in brain NO content, facilitating use of 7-NI to probe the pharmacological implications of NO in the central nervous system.     

Sensory nitrergic meningeal vasodilatation and non-nitrergic plasma extravasation in anaesthesized rats

The aim of the present study was to evaluate the role of nitric oxide (NO) of sensory neural origin in neurogenic inflammatory response in the trigeminovascular system. Antidromic vasodilatation and plasma extravasation in response to electrical stimulation (15 V, 5 Hz, 0.5 ms, 100 impulses) of the trigeminal ganglion were investigated in the dura mater and nasal mucosa/upper eyelid by laser Doppler flowmetry and [(125)I]-labelled bovine serum albumin, respectively. Electrical stimulation of the trigeminal ganglion of rats elicited a reproducible ipsilateral enhancement of both meningeal and nasal mucosal blood flow. N(omega)-nitro-L-arginine (L-NNA; 4, 8, and 16 mg/kg, i.v.), a nonselective inhibitor of nitric oxide synthase (NOS), inhibited antidromic vasodilatation both in the dura mater (15.86+/-2.05%, 22.82+/-2.51%, and 36.28+/-4.37%) and nasal mucosa (35.46+/-8.57%, 58.72+/-9.2%, and 89.99+/-8.94%) in a dose-dependent manner. Specific inhibitors of neuronal NOS, 7-nitroindazole (7-NI; 20 mg/kg, i.v.) and 3-bromo-7-nitroindazole (3Br-7NI; 10 mg/kg, i.v.) were administered to assess the possible role of NO released from the trigeminal sensory fibres. The meningeal vasodilatation was inhibited by both 3Br-7NI and 7-NI (63.36+/-7.7% and 49+/-6.5%, respectively). The nasal hyperaemic response was also reduced by 3Br-7NI (78.26+/-8.7%). Plasma extravasation in the dura mater and upper eyelid evoked by electrical stimulation of the trigeminal ganglion (25 V, 5 Hz, 0,5 ms, 5 min), expressed as extravasation ratios (ERs) of the stimulated vs. nonstimulated sides, was 1.80+/-0.8 and 4.63+/-1.24, respectively. This neurogenic oedema formation was not inhibited by neither L-NNA nor 3Br-7NI. It is concluded that neural nitrergic mechanisms are involved in the meningeal vasodilatation evoked by electrical stimulation of the trigeminal ganglion.     

Endothelium-independent constriction of isolated, pressurized arterioles by Nomega-nitro-L-arginine methyl ester (L-NAME)

BACKGROUND AND PURPOSE: Nitric oxide synthase (NOS) inhibitors cause vasoconstriction in pressurized arterioles with myogenic tone. This suggests either tonic production of NO modulates myogenic tone or a direct, NOS-independent effect of the NOS inhibitors. The nature of the contractile effect of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM) on pressurised arterioles was investigated. EXPERIMENTAL APPROACH: Segments of rat cremaster muscle first-order arteriole were cannulated on glass micropipettes and maintained at an intraluminal pressure of 50, 70 or 120 mmHg. KEY RESULTS: L-NAME and the related compound L-NA (100 microM) constricted pressurized vessels with myogenic tone. Removal of the endothelium did not cause constriction or alter myogenic tone, however the constrictor effect of L-NAME persisted. The constrictor effect of L-NAME was abolished by L-arginine (1 mM). Other NO and cGMP pathway inhibitors, including the nNOS inhibitor 7-nitroindazole (100 muM), the NO scavenger carboxy-PTIO (100 microM), the guanylate cyclase inhibitor ODQ (10 microM) and the cGMP inhibitor Rp-8CPT-cGMPS (10 microM) did not cause constriction of the arterioles. L-NAME caused a small (3-4 mV) but not statistically significant depolarization of the arteriolar smooth muscle at both pressures. The constrictor effect was not prevented by the K(+)-channel antagonist tetraethyl ammonium (TEA, 1 mM) or the K(ATP) channel antagonist glibenclamide (1 microM). CONCLUSIONS AND IMPLICATIONS: These observations demonstrate that L-NAME causes an endothelium- and NOS-independent contraction of vascular smooth muscle in isolated skeletal muscle arterioles. It is suggested that the underlying mechanism relates to an arginine binding interaction.     

Effect of inhibition of neuronal nitric oxide synthase and L-arginine supplementation on renal ischaemia-reperfusion injury and the renal nitric oxide system

The role of nitric oxide synthases (NOS) and the nitric oxide (NO) substrate l-arginine in renal ischaemia-reperfusion (I/R) has been studied extensively. However, the results reported are often controversial. In the present study, we examined the effects of the neuronal (n) NOS inhibitor 7-nitroindazole (7-NI) and L-arginine administration on renal I/R injury and the renal NO system in rats. Following 7 days pretreatment with 7-NI (50 mg/kg per day), L-arginine (2 g/kg per day) or vehicle (dimethylsulphoxide : sesame oil, 1 : 9), the left renal vascular pedicles were clamped for 50 min in male Sprague-Dawley rats and kidneys were removed 24 h after reperfusion (n = 7/group). Neither 7-NI nor L-arginine had any effect on parameters of renal function, the grade of tissue injury or the number of terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL)-positive tubular cells compared with vehicle-treated rats. 7-Nitroindazole decreased nNOS mRNA expression and inducible (i) NOS protein levels, but had no effect on endothelial NOS expression. L-arginine supplementation increased mRNA expression of all NOS isoforms, but only increased protein expression of iNOS. The results of the present study demonstrate that selective inhibition of nNOS has no effect on renal injury, indicating that nNOS does not play a central role in the pathophysiology of renal I/R. In addition, although L-arginine has no effect on renal I/R injury in the model used in the present study, its administration increases the mRNA expression of NOS isoforms.     

Synergistic neuroprotective effects by combining an NMDA or AMPA receptor antagonist with nitric oxide synthase inhibitors in global cerebral ischaemia.

We have investigated the neuroprotective effects of combining an NMDA or AMPA receptor antagonist with a nitric oxide synthase (NOS) inhibitor in the gerbil model of global cerebral ischaemia. Ischaemia was induced by occlusion of the common carotid arteries for 5 min. (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,1 0-imine (MK-801, 2.5 mg/kg i.p.) or (3S,4aR,6R,8aR)-6-[2-(1(2)H-tetrazole-5-yl)]decahydroisoq uinoline-3-carboxylic acid (LY293558, 20 mg/kg i.p.) and 7-nitroindazole (25 mg/kg i.p.) or N-[4-(2-[[(3-chlorophenyl)methyl]amino]ethyl) phenyl]-2-thiophenecarboximidamide dihydrochloride (ARL17477, 25 mg/kg i.p.) were administered alone or in combination (i.e., MK-801 with 7-nitroindazole or ARL17477 or LY293558 with 7-nitroindazole or ARL17477). In the present studies, both MK-801 and LY293558 provided significant degree of neuroprotection, while 7-nitroindazole and ARL17477 also provided some neuroprotection, which failed to reach significance in every case. However, the combination of MK-801 with 7-nitroindazole or ARL17477 provided 21% or 44% greater protection than the total protection or either alone. Likewise, the combination of LY293558 with 7-nitroindazole or ARL17477 provided 14.5% and 35% greater protection than total protection of either compound alone. These results indicate that several pathways contribute to ischaemic cell death and combining excitatory amino antagonists and NOS inhibitors provides greater protection than either alone. Therefore, combination therapy should be considered as an approach for treating ischaemic conditions.     

Role of nitric oxide in maintenance of basal oral tissue blood flow in anesthetized cats.

Experiments were undertaken to determine if nitric oxide (NO) plays a role in regulation of basal blood flow in the oral cavity of pentobarbital anesthetized cats and, if so, to quantify this effect using dose-response relationships. Blood flow was continuously measured from the surface of the tongue and mandibular gingiva (laser-Doppler flowmetry) and from the lingual artery (ultrasonic flowmetry). Cardiovascular parameters also were recorded. Administration of the nonselective inhibitor of nitric oxide synthase (NOS), L-NAME (0.08-20 mg/kg i.v.), produced a dose-related increase of blood pressure associated with decreases of blood flow at all three measurement sites. Maximal blood flow depression of 50-60% was seen 30-60 min after administration of 1.25 mg/kg of L-NAME. D-NAME (1.25 mg/kg i.v.) was inactive at all sites. Subsequent administration of L-arginine partially reversed effects of L-NAME in the lingual artery and tongue, but not in the gingival circulation. The neuronally selective NOS inhibitor, 7-nitroindazole (7-NI, 30 mg/kg i.p.), was devoid of effect on any of the measured parameters. These results suggest that endothelial (but not neuronally derived) NO plays an important role in control of basal blood flow in oral tissues of the cat.