Involvement Of Nitric Oxide Pathway Research Articles

Minocycline Attenuates Depressive-Like Behaviour Induced by Rat Model of Testicular Torsion: Involvement of Nitric Oxide Pathway.

Testicular torsion/detorsion (T/D) can induce depression in pre- and post-pubertal patients. This study was conducted to investigate the psychological impact of testicular torsion and mechanism underlying its depressive-like behaviour, as well as antidepressant-like activity of minocycline and possible involvement of nitric oxide (NO)/cyclic GMP pathway in this paradigm in male rats undergoing testicular T/D. Unilateral T/D was performed in 36 male adult Wistar rats, and different doses of minocycline were injected alone or combined with N(ω) -nitro-l-arginine methyl ester (l-NAME), non-specific NO synthase (NOS) inhibitor; aminoguanidine (AG), specific inducible NOS inhibitor; l-arginine, an NO precursor; and selective PDE5I, sildenafil. After assessment of locomotor activity in open-field test, immobility times were recorded in the forced swimming test (FST). Moreover, 30 days after testicular T/D, testicular venous testosterone and serum nitrite concentrations were measured. A correlation was observed between either a decrease in plasma testosterone or an increase in serum nitrite concentrations with prolongation in immobility time in the testicular T/D-operated rats FST. Minocycline (160 mg/kg) exerted the highest significant antidepressant-like effect in the operated rats in the FST (p < 0.001). Furthermore, combination of subeffective doses of minocycline (80 mg/kg) and either l-NAME (10 mg/kg) or AG (50 mg/kg) demonstrated a significant robust antidepressant-like activity in T/D group (p < 0.01). Consequently, NO/cGMP pathway was involved in testicular T/D-induced depressive-like behaviour and antidepressant-like activity of minocycline in the animal model. Moreover, a contribution was observed between either decreased testosterone or elevated serum nitrite levels and depressive-like behaviour following testicular T/D.

&amp;lt;i&amp;gt;α,β&amp;lt;/i&amp;gt;-Methylene-ATP-Induced Inhibition of Acetylcholine Release on the Stellate Ganglion: Contribution of Nitric Oxide

In this study, we investigated the possible involvement of nitric oxide pathways in the presynaptic inhibition of acetylcholine release induced by ATP analogs in dogs. We performed the study using HPLC with electrochemical detection and the nitric oxide detection-HPLC system. The amount of acetylcholine released in response to preganglionic stimulation at 5 Hz for 10 min was reduced in a concentration-dependent manner after exposure to 10-7 - 10-4 M α,β-methylene-ATP (α,β-meATP), but not by the P2Y receptor agonist, 2-methyl-thio-ATP (2MeSATP) or the P2X1 receptor agonist, β,γ-methylene-ATP (β,γ-meATP), at the same concentrations. The inhibition of acetylcholine release induced by α,β-meATP was antagonized by: the nonselective P2 receptor antagonist, pyridoxalphosphate-6-azophenyl-2’,4’-disulphonic acid (PPADS); the P2X1, P2X3 and P2X2/3 receptors antagonist, 2’-(or-3’)-O-trinitrophenyl-ATP (TNP-ATP); the neuronal nitric oxide synthase (nNOS) inhibitor, 3-bromo-7-nitroindazole; the soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ); the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethy-limidazoline-1-oxyl-3-oxide (carboxy-PTIO). Exposure to 10-5 M, but not 10-4 M, α,β-meATP, for 30 min increased the levels of , and this increase was antagonized by TNP-ATP and 3-bromo-7-nitroindazole. These results show that P2X receptor activation inhibits stellate ganglionic transmission by reducing acetylcholine release from presynaptic nerve terminals and that this inhibition seems to involve, at least in part, the activation of endogenous NO production and cGMP pathways.

Chronic administration of modafinil induces hyperalgesia in mice: Reversal by l-NG-nitro-arginine methyl ester and 7-nitroindazole

Modafinil [2-((diphenylmethyl) sulfinyl) acetamide] is a central nervous system stimulant. It has received considerable attention as a potential psychotropic agent in several psychiatric disorders. The current study was carried out to investigate the effect of modafinil after acute administration on animal models of pain in mice. Also, this study evaluated the effect of l-NG-nitroarginine methyl ester (l-NAME), 7-nitroindazole (7-NI) and naloxone following chronic administration of modafinil. Modafinil was administered in the doses of 50, 100 or 200mg/kg once in acute study and it showed significantly increased tail-flick latency (tfl) and paw-licking latency. In formalin test modafinil (100mg/kg) significantly reduced licking/biting time in both early and late phases in comparison to control. In chronic study, modafinil 100mg/kg administered for 10 days, produced a progressive decrease in the reaction time (i.e., tfl/paw-licking latency) in comparison to day 1 values which started building up from day 4 and fully established at day 6, indicating hyperalgesic response. Prior administration of 7-NI (on day 7) and l-NAME (on day 10) prevented the hyperalgesic response while naloxone on day 10 did not have a significant effect on modafinil-induced hyperalgesia. These results demonstrate that modafinil has a potential role in pain as it exhibited antinociceptive effect after acute administration in a dose-dependent manner and on chronic administration it caused hyperalgesia. This hyperalgesia is reversed by nitric oxide synthase inhibitors, suggesting the possibility of involvement of nitric oxide pathway. Further studies are required to evaluate the role of modafinil in clinical pain.

EVALUATION OF NITRIC OXIDE OR OPIOID RECEPTORS INVOLVEMENT IN ANTINOCICEPTIVE PROPERTIES OF SILYMARIN

Objective: It has been shown that Silybum marianum or its extracts have hepatoprotective, antioxidant, anticancer, anti-inflammatory and anti-diabetic effects. Nitric oxide (NO) plays an important role in neurotransmission, neuroprotection, neurotoxicity and pathological pain, as a neurotransmitter or neuromodulator in the central nervous system. Therefore, this experiment was performed in order to assess the analgesic effects of single and multiple-dosed ip administration of silymarin and the probable role of nitric oxide or opioid receptors using tail flick assay. Results: Based on our results, only silymarin 100 mg/kg showed analgesic properties. Since naloxone did not change silymarin’s analgesic effects, it is concluded that opioid receptors are not involved. Although in the presence of L-arginine, analgesic effect of silymarin remained intact, but it is not possible to strongly determine the involvement of nitric oxide pathway here. Based on our results, the difference between anti nociceptive properties of single and multiple-dosed treatment of silymarin 100 mg/kg is not significant. Conclusion: It is concluded that silymarin exert its analgesic effects via other mechanisms. Inhibiting 5-lipooxygenase and neutrophil chemotaxis to inflammation location could be the probable ways of silymarin’s action.

Vaccinium myrtillus Ameliorates Unpredictable Chronic Mild Stress Induced Depression: Possible Involvement of Nitric Oxide Pathway

Chronic unpredictable stressors can produce a situation similar to clinical depression and such animal models can be used for the preclinical evaluation of antidepressants. Nitric oxide, a secondary messenger molecule, has been implicated in neurotransmission, synaptic plasticity, learning, aggression and depression. Vaccinium myrtillus (bilberry) extract is a potent inhibitor of reactive oxygen/nitrogen species and cytokine production. The present study investigated the role of nitric oxide in the antidepressant action of Vaccinium myrtillus in unpredictable chronic mild stress-induced depression in mice. Animals were subjected to different stress paradigms daily for a period of 21 days to induce depressive-like behavior. Pretreatment with L-arginine significantly reversed the protective effect of bilberry (500 mg/kg) on chronic stress-induced behavioral (immobility period, sucrose preference) and biochemical (lipid peroxidation and nitrite levels; endogenous antioxidant activities) in stressed mice. Furthermore, L-NAME (10 mg/kg) pretreatment with a sub-effective dose of bilberry (250 mg/kg) significantly potentiated the protective effect of bilberry extract. The study revealed that modulation of the nitric oxide pathway might be involved in antidepressant-like effects of Vaccinium myrtillus in stressed mice.

Involvement of nitric oxide pathways in neurogenic pulmonary edema induced by vagotomy

OBJECTIVE: The objective of this study was to evaluate the involvement of peripheral nitric oxide (NO) in vagotomy-induced pulmonary edema by verifying whether the nitric oxide synthases (NOS), constitutive (cNOS) and inducible (iNOS), participate in this mechanism.INTRODUCTION:It has been proposed that vagotomy induces neurogenic pulmonary edema or intensifies the edema of other etiologies.METHODS:Control and vagotomized rats were pretreated with 0.3 mg/kg, 3.0 mg/kg or 39.0 mg/kg of L-NAME, or with 5.0 mg/kg, 10.0 mg/kg or 20.0 mg/kg of aminoguanidine. All animals were observed for 120 minutes. After the animals' death, the trachea was catheterized in order to observe tracheal fluid and to classify the severity of pulmonary edema. The lungs were removed and weighed to evaluate pulmonary weight gain and edema index.RESULTS:Vagotomy promoted pulmonary edema as edema was significantly higher than in the control. This effect was modified by treatment with L-NAME. The highest dose, 39.0 mg/kg, reduced the edema and prolonged the survival of the animals, while at the lowest dose, 0.3 mg/kg, the edema and reduced survival rates were maintained. Aminoguanidine, regardless of the dose inhibited the development of the edema. Its effect was similar to that observed when the highest dose of L-NAME was administered. It may be that the non-selective blockade of cNOS by the highest dose of L-NAME also inhibited the iNOS pathway.CONCLUSION:Our data suggest that iNOS could be directly involved in pulmonary edema induced by vagotomy and cNOS appears to participate as a protector mechanism.

Effect of pentobarbital on pH and electrolyte levels after induced seizure in rats

We studied the effects of high doses of pentobarbital (PB) and carbamazepine (CBZ) on electrolyte levels and pH in an epileptic animal model. Pentobarbital decreased Ca2+ and Na+ levels without pentylenetetrazole (PTZ). After this, Ca2+ and Na+ levels continued to decrease except when CBZ was used, which preserved the Ca2+ levels PTZ may have opposed effects on PB. Our results suggest that PB causes changes in electrolyte levels and pH, but these changes are diminished by CBZ.

Nitric oxide involvement in estrous cycle-dependent changes of the behavioral responses of female rats in the elevated plus-maze test

Nitric oxide (NO)/cGMP pathway is known as a mediator in anxiety modulation. In this study, we assessed the involvement of NO pathway in the estrous cycle-related changes of anxiety level in rat. By using elevated plus-maze test, we studied the changes of serum nitrate and nitrite (NO x) levels in comparison to the estrous cycle-dependent changes of anxiety state. Then, we tested the effects of nitric oxide synthase (NOS) inhibitor, L-NAME (10, 60 mg/kg, i.p.), and the NO precursor, l-arginine (100 mg/kg, i.p.) on anxiety modulatory properties of exogenous ovarian hormones in ovariectomized (OVX) rats. Compared with other cycle phases and with OVX rats, cycling rats spent more time in open arms and had lower levels of serum NO x levels during metestrous while they spent less time in open arms and had lower levels of serum NO x levels during proestrous. In OVX rats, L-NAME (60 mg/kg, i.p.) exerted anxiolytic effect while l-arginine showed no effect. In comparison with corn oil-treated controls, estradiol benzoate (10 μg/kg, subcutaneously (s.c.)) significantly increased the serum NO x level and exerted anxiogenic effect, which was dose-dependently inhibited by L-NAME but was not changed by l-arginine. In contrast, progesterone (25 mg/kg, s.c.) significantly decreased the serum NO x level and exerted anxiolytic effect, which was abolished by l-arginine but was not affected by L-NAME. These findings suggest that NO system might be involved in the estrous cycle-related changes of anxiety level, probably by mediating the effect of ovarian sex hormones.

Involvement of nitric oxide pathway in the acute anticonvulsant effect of melatonin in mice

Melatonin, the major hormone produced by the pineal gland, is shown to have anticonvulsant effects. Nitric oxide (NO) is a known mediator in seizure susceptibility modulation. In the present study, the involvement of NO pathway in the anticonvulsant effect of melatonin in pentylenetetrazole (PTZ)-induced clonic seizures was investigated in mice. Acute intraperitoneal administration of melatonin (40 and 80 mg/kg) significantly increased the clonic seizure threshold induced by intravenous administration of PTZ. This effect was observed as soon as 1 min after injection and lasted for 30 min with a peak effect at 3 min after melatonin administration. Combination of per se non-effective doses of melatonin (10 and 20 mg/kg) and nitric oxide synthase (NOS) substrate l-arginine (30, 60 mg/kg) showed a significant anticonvulsant activity. This effect was reversed by NOS inhibitor N(G)-nitro- l-arginine methyl ester ( l-NAME, 30 mg/kg), implying an NO-dependent mechanism for melatonin effect. Pretreatment with l-NAME (30 mg/kg) and N(G)-nitro- l-arginine ( l-NNA, 10 mg/kg) inhibited the anticonvulsant property of melatonin (40 and 80 mg/kg) and melatonin 40 mg/kg, respectively. Specific inducible NOS (iNOS) inhibitor aminoguanidine (100 and 300 mg/kg) did not affect the anticonvulsant effect of melatonin, excluding the role of iNOS in this phenomenon, while pretreatment of with 7-NI (50 mg/kg), a preferential neuronal NOS inhibitor, reversed this effect. The present data show an anticonvulsant effect for melatonin in i.v. PTZ seizure paradigm, which may be mediated via NO/ l-arginine pathway by constitutively expressed NOS.

Involvement of nitric oxide pathways in short term modulation of tyrosine hydroxylase activity by endothelins 1 and 3 in the rat anterior hypothalamus

The ability of endothelins 1 and 3 (ET-1 and ET-3) to reduce neuronal norepinephrine release through ETB receptor activation involving nitric oxide (NO) pathways in the rat anterior hypothalamus region (AHR) was previously reported. In the present work, we studied the effects of ET-1 and -3 on tyrosine hydroxylase (TH) activity and the possible involvement of NO pathways. Results showed that ET-1 and -3 (10 nM) diminished TH activity in AHR and this effect was blocked by a selective ETB receptor antagonist (100 nM BQ-788), but not by a ET A receptor antagonist (BQ-610). To confirm these results, 1 μM IRL-1620 (ET B agonist) reduced TH activity whereas 300 nM sarafotoxin S6b falled to modify it. N ω-Nitro- l-arginine methyl ester (10 μM), 7-nitroindazole (10 μM), 1 H-[1,2,4]oxadiazolo[4,3- a]quinoxalin-1-ona (10 μM), KT5823 (2 μM), inhibitors of nitric oxide synthase, neuronal nitric oxide synthase, NO-sensitive-guanylyl cyclase, and protein kinase G, respectively, did not modify the reduction of TH activity produced by ETs. In addition, both 100 μM sodium nitroprusside and 50 μM 8-bromoguanosine-3′,5′-cyclic monophosphate (NO donor and guanosine-3′,5′-cyclic monophosphate analog, respectively) diminished TH activity. Present results showed that ET-1 and ET-3 diminished TH activity through the activation of ET B receptors involving the NO/guanosine-3′,5′-cyclic monophosphate/protein kinase G pathway. Taken jointly present and previous results it can be concluded that both ETs play an important role as modulators of norepinephrine neurotransmission in the rat AHR.

Lithium inhibits the modulatory effects of morphine on susceptibility to pentylenetetrazole-induced clonic seizure in mice: involvement of a nitric oxide pathway

Lithium has been reported to inhibit opioid-induced properties. The present study examined the effect of acute and chronic administration of lithium chloride (LiCl) on morphine's biphasic modulation of susceptibility to pentylenetetrazole (PTZ)-induced clonic seizure in mice. We also examined the possible involvement of nitric oxide (NO) pathway in lithium effect. Both acute (0.1 and 1 mg/kg) and chronic (same doses, 21 consecutive days) administration of LiCl completely inhibited the anticonvulsant and proconvulsant effects of morphine (at doses 1 and 30 mg/kg, respectively). A very low and per se noneffective dose of LiCl (0.05 mg/kg) significantly inhibited both phases of morphine effect when administered concomitant with a noneffective low dose of naloxone (0.1 mg/kg). The NO synthase inhibitor N G-nitro- l-arginine methyl ester (L-NAME) at a per se noneffective dose of 0.3 mg/kg potentiated the inhibitory effects of low doses of LiCl (0.01 and 0.05 mg/kg) on both phases of morphine effect. l-arginine, a NO synthase substrate, at a per se noneffective dose of 30 mg/kg reversed the inhibitory effects of lithium (1 mg/kg). Lithium is capable of antagonizing both modulatory effects of morphine on seizure susceptibility even at relatively low doses. These inhibitory effects of lithium may also involve NO synthesis.

Fibronectin fragments elevate nitric oxide (NO) and inducible NO synthetase (iNOS) levels in bovine cartilage and iNOS inhibitors block fibronectin fragment mediated damage and promote repair.

To determine whether fibronectin fragments (Fn-f) upregulate nitric oxide (NO) and inducible NO synthetase (iNOS) levels in explants and whether iNOS inhibitors block Fn-f mediated cartilage damage or promote repair. Bovine cartilage explants were studied. Explants were cultured with Fn-f and involvement of NO pathway investigated. Induction of iNOS was tested by RT-PCR. Upregulation of iNOS protein was visualized by Western blotting. Proteoglycan (PG) content of cartilage treated with iNOS inhibitors was tested by dye binding assays of cartilage digests. Fn-fs elevated NO release in explants and upregulated iNOS protein and mRNA while native Fn had only weak activity. Three different iNOS inhibitors blocked Fn-f mediated PG depletion from explants and facilitated restoration of PG in pre-damaged cartilage. The Fn-f cartilage damaging pathway involves upregulation of iNOS. Interestingly, iNOS inhibitors not only blocked damage but repaired damaged cartilage. This may be the first report of reparative activities of iNOS inhibitors.

Nitric oxide/guanylate cyclase pathways and flow in anterior segment perfusion.

The nitric oxide/guanylate cyclase pathway has been suggested to participate in the regulation of intraocular pressure. In the present study, the involvement of nitric oxide pathways on the outflow through the trabecular meshwork was assessed using pharmacological manipulation of the nitric oxide pathway. Anterior segments of human donor eyes were maintained in an organ culture perfusion system, and the effects of L-NAME, an inhibitor of nitric oxide synthase, on the flow rate was determined. In a second series, the effects of consecutive application of L-arginine as substrate for nitric oxide synthase, L-NAME, and sodium nitroprusside, a nitric oxide-donor, were studied. The cyclic GMP levels in the perfusate were assessed with an ELISA immunoassay kit. In the first series of experiments, L-NAME caused a statistically significant decrease in flow rate of 10%, accompanied by a decrease in cGMP levels. In the second series, L-arginine did not alter flow, and the effect of L-NAME seen in the first series was prevented by the high preload of L-arginine. Nitroprusside caused a significant 10% increase of flow rate. In the perfusate, cGMP levels were not altered by L-arginine and L-NAME, but were increased after nitroprusside. Under organ culture perfusion conditions, modulation of the nitric oxide/guanylate cyclase system alters the flow rate through the trabecular meshwork within a total range of 20%; i.e. the difference between inhibition of NO synthesis and the presence of a NO-donor. These results indicate that the nitric oxide/guanylate cyclase system plays a role in aqueous humour dynamics and, therefore, in the regulation of intraocular pressure.

Involvement of nitric oxide pathway in prostaglandin F 2 α–induced preterm labor in rats

OBJECTIVE: Our purpose was to investigate the roles of nitric oxide and prostaglandins in controlling parturition. STUDY DESIGN: Pregnant rats on day 18 of gestation were injected intraperitoneally with prostaglandin F 2α, prostaglandin F 2α plus diethylenetriamine–nitric oxide (a donor of nitric oxide), prostaglandin F 2α plus diethylenetriamine without nitric oxide, or vehicle. Uterine nitrite production, nitric oxide synthase messenger ribonucleic acid and contractile response in vitro, and serum progesterone levels were measured. The labor and delivery of the rats also were monitored. RESULTS: Exogenously administered prostaglandin F 2α significantly inhibited nitric oxide production by the uterus in a time-dependent manner with maximal effects observed 48 hours after prostaglandin F 2α treatment. Messenger ribonucleic acid for inducible nitric oxide synthase but not endothelial nitric oxide synthase messenger ribonucleic acid in the uterus was significantly inhibited by prostaglandin F 2α with maximal inhibition at 48 hours after prostaglandin F 2α injection. The serum progesterone concentration was substantially reduced by prostaglandin F 2α, and this reduction was partially reversed by administration of diethylenetriamine–nitric oxide but not diethylenetriamine without nitric oxide. Prostaglandin F 2α caused increases in contractile activity of the uterus in a dose-dependent manner. Diethylenetriamine–nitric oxide (10 –4 mol/L) blocked prostaglandin F 2α–induced contractions. Premature parturition was induced within 48 hours after prostaglandin F 2α injection in 100% of the animals. Coadministration of diethylenetriamine–nitric oxide completely prevented the preterm labor induced by prostaglandin F 2α. CONCLUSION: Prostaglandin F 2α inhibited inducible nitric oxide synthase messenger ribonucleic acid and subsequent nitric oxide generation in the rat uterus. Nitric oxide can prevent prostaglandin F 2α–induced preterm labor, possibly by attenuating the fall in serum progesterone and blocking uterine contractions induced by prostaglandin F 2α administration. (Am J Obstet Gynecol 1997;177:907-17)

Mechanisms of coronary microvascular dilation induced by the activation of pertussis toxin-sensitive G proteins are vessel-size dependent. Heterogeneous involvement of nitric oxide pathway and ATP-sensitive K+ channels.

G proteins are critically important mediators of many signal transduction systems. In the present study, we investigated the effect of direct activation of pertussis toxin (PTX)-sensitive G protein (GPTX) on coronary arterial microvascular tone in 37 open-chest anesthetized dogs in vivo. Coronary arterial microvessels on the surface of the beating left ventricle were visualized by performing fluorescence coronary microangiography using an intravital microscope with a floating objective system. Microvessels were divided into two groups, small microvessels (inner diameter, < or = 130 microns) and large microvessels (inner diameter, > 130 microns). Topically applied mastoparan (G protein activator, 10, 30, and 100 mumol/L) produced homogeneous microvascular dilation in a concentration-dependent manner (10 mumol/L, 7.9 +/- 2.0%; 30 mumol/L, 10.3 +/- 2.4%; and 100 mumol/L, 16.7 +/- 4.5% in small microvessels; 10 mumol/L, 5.3 +/- 1.2%; 30 mumol/L, 9.8 +/- 2.5%; and 100 mumol/L, 15.5 +/- 3.9% in large microvessels). These dilations were reversed to constriction by pretreatment with PTX (300 ng/mL, 2 hours) in both microvessel groups. Blockade of nitric oxide production by NG-nitro-L-arginine (LNNA, 300 mumol/L) offset the mastoparan-induced dilation in large microvessels but not in small microvessels. Cosuperfusion of glibenclamide (10 mumol/L) with LNNA produced constriction of all sizes of microvessels in response to mastoparan, whereas charybdotoxin (10 nmol/L) did not affect the mastoparan effect. Pretreatment with glibenclamide alone reversed mastoparan dilation to constriction in small microvessels, whereas it only offset the dilation without producing constriction in large microvessels. We conclude that the activation of GPTX produces homogeneous coronary arterial microvascular dilation and that the underlining mechanisms of the dilation are vessel size dependent. The L-arginine-nitric oxide pathway mediates the dilation only in large microvessels, whereas ATP-sensitive K+ channel activation plays a central role in the dilation of small microvessels when GPTX is directly activated. ATP-sensitive K+ channels are also involved in the dilation of large microvessels in a synergistic fashion with nitric oxide production.

Nitric Oxide in Retina: Relation to Excitatory Amino Acids and Excitotoxicity

This study was undertaken to determine whether nitric oxide pathways exist in the retina and are linked to excitatory amino acid (EAA)-induced increases in cyclic guanosine monophosphate (cGMP). Exposure of embryonic day 15 chick retina for 5 min to either 1 mM glutamate, 100 μM NMDA or 100 μM kainate (KA) increased cGMP content 2-3-fold. The putative environmental neurotoxins, domoic acid (DO, 20 μM), and β-oxalyl-amino-l-alanine (BOAA, 200 μM), but not β-methyl-amino-l-alanine (BMAA, 3 mM), also increased cGMP. The nitric oxide synthase inhibitor N-nitro-l-arginine (NNA) and nitric oxide scavenger, hemoglobin, completely blocked the increases in cGMP induced by the above glutamate-agonists. These glutamate agonist induced increases in cGMP were receptor mediated. MK-801, a NMDA receptor antagonist, blocked NMDA, and partially blocked glutamate-stimulated, cGMP formation. CNQX, a KA/AMPA receptor antagonist blocked cGMP increases produced by KA, BOAA and partially blocked those evoked by DO and glutamate. In order to examine the involvement of nitric oxide pathways in NMDA-mediated toxicity, the ability of NNA to protect against delayed excitotoxic damage caused by a 60 min exposure to NMDA was assessed. Delayed cell death, determined by LDH release and histology, following a 24 hr recovery period after NMDA treatment, was unchanged by the presence of NNA. NNA did not interfere with acute NMDA-stimulated GABA release indicating that NNA did not effect NMDA receptor interactions. These studies demonstrate that nitric oxide pathways exist in embryonic retina and link EAA receptor activation to cGMP formation; however, this pathway may not play a role in NMDA-mediated excitotoxicity.

Involvement of nitric oxide pathway in Non-Adrenergic Non-Cholinergic (NANC) relaxation in the rat stomach: Differential innervation of nanc nerves in the longitudinal and circular muscle of the fundus

1. 1. The effects of N G-nitro- l-arginine ( l-NNA) on non-adrenergic, non-cholinergic (NANC) relaxation elicited by transmural nerve stimulation (TNS) or high K + were studied in the rat stomach fundus in order to investigate the mode of innervation of NANC nerves in the longitudinal and the circular muscle of the fundus. 2. 2. Relaxation responses of the fundus to TNS were larger in circular than in longitudinal muscle strips. 3. 3. Treatment with l-NNA (10 −5M) reduced slightly but significantly the relaxation induced by TNS in both circular and longitudinal muscle strips of the fundus. The inhibitions of the TNS-induced relaxation by l-NNA were reversed partly by l-arginine (10 −3M). 4. 4. Although K + produced concentration-dependent contraction in longitudinal muscle strips of the fundus, low concentration of K + (20 mM) produced rapid and long-lasting relaxation in circular muscle strips of the fundus. 5. 5. The 20 mM of K +-induced relaxation in circular muscle strips was significantly inhibited by l-NNA (10 −5M) or oxyhemoglobin (2 × 10 −5M). The inhibition of the K + (20 mM)-induced relaxation by l-NNA was reversed by l-arginine (10 −3M). 6. 6. These results suggest that NO is one of mediators or transmitters in the NANC relaxation of the rat fundus, and that the density of NO-containing NANC nerves in the stomach fundus is richer in circular than in longitudinal muscle.

Involvement of nitric oxide pathway in the PAF-induced relaxation of rat thoracic aorta.

1. The mechanism of the vasorelaxant effect of platelet activating factor (PAF) on rat thoracic aorta and the effect of aging on the PAF-induced relaxation were investigated. 2. PAF at concentrations causing relaxation induced marked increases in guanosine 3':5'-cyclic monophosphate (cyclic GMP) production, but did not induce an increase in adenosine 3':5'-cyclic monophosphate (cyclic AMP). 3. Removal of the endothelium by mechanical rubbing, and treatment with the PAF antagonists CV-3988, CV-6209 and FR-900452, the nitric oxide biosynthesis inhibitor, NG-nitro L-arginine, the radical scavenger, haemoglobin, and the soluble guanylate cyclase inhibitor, methylene blue, inhibited PAF-induced relaxation and abolished or attenuated PAF-stimulated cyclic GMP production. 4. The relaxation was greatest in arteries from rats aged 4 weeks. With an increase in age, the response of the arteries to PAF was attenuated. 5. Endothelium-dependent cyclic GMP production also decreased with increase in age of the rats. 6. These results suggest that PAF stimulates production of nitric oxide from L-arginine by acting on the PAF receptors in the endothelium, which in turn stimulates soluble guanylate cyclase in the smooth muscle cells, and so increases production of cyclic GMP, thus relaxing the arteries. Age-associated decrease in PAF-induced relaxation may result from a reduction of cyclic GMP formation.