Effects of nitric oxide on morphine self-administration in rat

Previous studies have reported that morphine exerts its effects in part through the release of nitric oxide (NO). In the present study, the effects of acute and chronic administration of the NO precursor, L-arginine and NO synthase (NOS) inhibitor, L-nitro-amino-methyl-ester (L-NAME) on morphine self-administration in rats were investigated. The animals were initially trained to press a lever using food as reinforcer. Rats were surgically prepared with a chronic Silastic catheter implanted in the external jugular vein. Five days after surgery, they were trained to press a lever for drug self-administration. The present data indicate that L-arginine (0.05, 0.1, and 0.15 mg/kg/injection) but not L-NAME (0.05, 0.1, and 0.15 mg/kg/injection) induced self-administration behavior and increased locomotion. The response induced by L-arginine (0.1 mg/kg/injection) was reduced by pretreatment with L-NAME (5, 10, and 15 mg/kg ip). Both the acute (5, 10, and 15 mg/kg ip) and the chronic (200 mg/kg ip; twice daily for 4 days) administration of L-arginine reduced morphine self-administration. However, acute (5, 10, and 20 mg/kg ip) and chronic (50 mg/kg ip; twice daily for 4 days) administration of L-NAME increased morphine self-administration significantly. It can be concluded that NO may have a role in morphine self-administration.     

Modulation of stress-induced neurobehavioral changes by nitric oxide in rats

The involvement of nitric oxide (NO) in stress-induced neurobehavioral changes in rats was evaluated using the elevated plus maze and open field tests. Restraint stress (1 h) reduced both the number of entries and time spent in open arms, with both expressed as percent of controls (no restraint stress), and these changes were reversed with diazepam (1 mg/kg) and the NO precursor, L-arginine (500 and 1000 mg/kg) pretreatment. The nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME) (50 mg/kg), aggravated restraint stress effects in the elevated plus maze test, whereas the lower dose (10 mg/kg) of the drug attenuated the same. In the open field test, the restraint stress-induced (a) increased entry latency and (b) decreased ambulation and rearing were reversed by diazepam and L-arginine and L-NAME (10 mg/kg), whereas L-NAME (50 mg/kg) aggravated restraint stress effects. The neuronal nitric oxide synthase inhibitor, 7-nitroindazole (10 and 50 mg/kg), did not influence these restraint stress-induced behavioral changes to any significant extent. Biochemical data showed that L-NAME (10 and 50 mg/kg.) induced opposite effects on the total brain nitrate/nitrite content during restraint stress. The results indicate a possible involvement of NO in stress-induced neurobehavioral effects.     

L-arginine protects against stress-induced gastric mucosal lesions by preserving gastric mucus

1. We have shown that exogenously administered L-arginine protects against water immersion restraint (WIR) stress-induced gastric mucosal lesions in rats through preservation of nitric oxide (NO) generation via constitutive nitric oxide synthase (cNOS), but not inducible nitric oxide synthase (iNOS), in the gastric mucosa. We have also indicated that impaired gastric mucus synthesis and secretion occur through a decrease in gastric cNOS activity in WIR-stressed rats. Therefore, in the presesnt study, we examined whether exogenously administered L-arginine exerts a protective effect against WIR stress-induced gastric mucosal lesions in rats through preservation of gastric mucus synthesis and secretion by NO generated from the administered amino acid via cNOS in the gastric mucosa. 2. Rats were subjected to WIR stress for 3 and 6 h. Either L-arginine (150-600 mg/kg) or D-arginine (600 mg/kg) was injected intraperitoneally 0.5 h prior to WIR stress. Either N(G)-monomethyl L-arginine (L-NMMA; 100 mg/kg) or N(G)-monomethyl D-arginine (D-NMMA; 100 mg/kg) was injected subcutaneously 0.5 h prior to WIR stress. Total NOS, cNOS, iNOS, nitrite and nitrate (breakdown products of NO), hexosamine (an index of gastric mucin) and adherent mucus were assayed in the gastric mucosa. 3. Pretreatment with L-arginine, but not D-arginine, protected against gastric mucosal lesions in rats subjected to WIR stress for 3 and 6 h in a dose-dependent manner. Pretreatment with L-arginine, but not D-arginine, attenuated decreases in hexosamine and adherent mucus concentrations and cNOS activity and increases in total NOS and iNOS activities and nitrite/nitrate concentration in the gastric mucosal tissue of rats subjected to WIR stress for 3 and 6 h in a dose-dependent manner. Both the protective effect of L-arginine against gastric mucosal lesions and the attenuating effect of the amino acid on the decreases in gastric mucosal hexosamine and adherent mucus concentrations and cNOS activity in rats subjected to WIR stress for 6 h were counteracted by cotreatment with L-NMMA, a nitric oxide synthase inhibitor, but not D-NMMA. 4. These results suggest that exogenously administered L-arginine exerts a protective effect against stress-induced gastric mucosal lesions in rats at least partly through preservation of gastric mucus synthesis and secretion by NO produced from the administered amino acid via cNOS in gastric mucosal tissue.     

Mediation of nitric oxide in inhibitory effect of morphine against electroshock-induced convulsions in mice

Nitric oxide (NO) and morphine have been coupled in many physiological as well as pathological processes. The present study examined the involvement of the L-arginine/NO pathway in the anticonvulsant properties of systemic morphine (2-30 mg/kg) against electroshock seizures (ECS) in mice. Morphine decreased the intensity of maximal electroshock seizures (MES) and increased the threshold for ECS. Neither the NOS substrate L-arginine (30, 60, and 100 mg/kg), the reversible nonspecific NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 3, 10, and 30 mg/kg), the irreversible specific inducible NOS inhibitor aminoguanidine (20, 50, and 100 mg/kg), nor the opioid receptor antagonist naloxone (0.1, 0.3, and 1 mg/kg) did alter per se the ECS threshold or the intensity of MES at doses used. However, both naloxone and L-NAME, but not aminoguanidine, inhibited the anticonvulsant effects of morphine (30 mg/kg) against ECS, while L-arginine potentiated the anticonvulsant effects of lower doses of morphine (2 or 10 mg/kg). Low doses of naloxone (0.1 or 0.3 mg/kg) or L-NAME (3 mg/kg), which did not alter morphine effect per se, showed additive anticonvulsant effects against MES. Thus, the L-arginine/NO pathway seems to play a role in the anticonvulsant properties of morphine against ECS and this mediation involves the constitutive, but not the inducible, form of nitric oxide synthase.     

Nitric oxide involvement in the antidepressant-like effects of acute lithium administration in the mouse forced swimming test.

In the present study we evaluated the involvement of l-arginine/nitric oxide (NO)/cGMP pathway in the antidepressant-like effects of acute lithium administration in the mouse forced swimming test (FST). Lithium, at 30 and 100 mg/kg, significantly reduced the immobility times of mice in the FST, whereas at lower doses (0.5, 5 and 10 mg/kg) had no effect on the immobility time. The NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), at 10 and 30 mg/kg, and the selective neuronal NOS inhibitor N(omega)-propyl-L-arginine (L-NPA), at 5 and 15 mg/kg, had no significant effects on the FST, whereas they significantly decreased the immobility time at 100 and 30 mg/kg, respectively. Combination of non-effective dose of lithium (10 mg/kg) with low doses of L-NAME (30 mg/kg) or L-NPA (15 mg/kg) significantly reduced the immobility times in the FST. Moreover, the guanylyl cyclase inhibitor ODQ at 50 mg/kg significantly decreased the immobility time of mice, whereas it had not significant effects on the FST at 2, 10 and 20 mg/kg. Combination of lithium (10 mg/kg) with 20 mg/kg ODQ significantly decreased the immobility times in the FST. Non-effective doses of L-arginine (750 mg/kg) or sildenafil (5 mg/kg) significantly reversed the antidepressant-like effect of 30 mg/kg lithium in the FST. Neither of the drugs had effect on the locomotor activity. These data indicate the involvement of L-arginine/NO/cGMP pathway in the antidepressant-like effect of lithium in the mouse FST and also might suggest the concurrent administration of NOS inhibitors and lithium as an appropriate strategy for treatment of depression.     

Fenamate-induced enhancement of heterologously expressed HERG currents in Xenopus oocytes

In the present study, the effects of intra-nucleus accumbens injection of L-arginine, a nitric oxide (NO) precursor, and N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, on morphine-induced conditioned place preference in male Wistar rats were investigated. Our data showed that subcutaneous (s.c.) injection of morphine sulphate (0.5-10 mg/kg) significantly increased the time spent in the drug-paired compartment in a dose-dependent manner. Intra-accumbens administration of L-arginine (0.03 and 0.05 microg/rat) with an ineffective dose of morphine (0.5 mg/kg) elicited significant conditioned place preference, while intra-accumbens administration of L-NAME (0.3, 0.1 and 1 microg/rat) decreased the acquisition of conditioned place preference induced by morphine (7.5 mg/kg). The response to different doses of L-arginine was decreased by L-NAME (0.03 microg/rat). L-Arginine and L-NAME by themselves did not elicit any effect on place conditioning. Intra-accumbens administration of L-arginine but not L-NAME significantly decreased the expression of morphine (7.5 mg/kg)-induced place preference. The attenuation of already established morphine-induced place preference on the test day by L-arginine was inhibited by L-NAME. The results indicate that NO may be involved in the acquisition and expression of morphine-induced place preference.     

Low endotoxemia prevents the reduction of gastric blood flow induced by NSAIDs: role of nitric oxide

1 The role of nitric oxide (NO) in the effects of low endotoxemia on gastric damage and blood flow has been evaluated in indomethacin-treated rats. 2 Pretreatment (-1 h) with endotoxin (40 micro g kg(-1)) reduced gastric damage induced by indomethacin (20 mg kg(-1)) in conscious rats. 3 Endotoxin prevented the reduction in gastric blood flow (laser Doppler flowmetry) induced by indomethacin in pentobarbital-anaesthetised rats. 4 Pretreatment with an NO-synthase (NOS) inhibitor (L-NAME, 1 mg kg(-1)) reversed the protective effect of endotoxin on gastric blood perfusion. 5 Endotoxin did not modify the expression of mRNA for endothelial NOS or inducible NOS in the gastric corpus when evaluated 1 h postinjection. However, a 3.8-fold increase in inducible NOS mRNA and a 61% reduction in endothelial NOS mRNA were observed in the gastric corpus 4 h after endotoxin administration. 6 Evaluation of both total and Ca(2+)-dependent NOS activity by analysing the rate of conversion of L-arginine to L-citrulline in gastric corpus homogenates showed no differences between animals treated with endotoxin and those treated with saline 1 or 4 h beforehand. Ca(2+)-independent NOS activity was almost non-apparent in control as well as in endotoxin-treated rats at all the time points analysed. 7 Low endotoxemia preserves blood perfusion and protects the gastric mucosa against the deleterious effects of indomethacin through the endogenous NO release. NO synthesis in response to endotoxin does not involve the inducible NOS, but probably depends on the post-translational/biochemical regulation in vivo of a Ca(2+)-dependent NOS, most probably endothelial NOS.     

Modulation of adjuvant arthritis by endogenous nitric oxide.

1. The role of endogenous nitric oxide (NO) in adjuvant arthritis in Lewis rats has been studied by use of L-arginine, the amino acid from which NO is synthesized, and NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase. Prolonged modulation (35 days) of the L-arginine: NO pathway in rats was achieved by dissolving test compounds in the drinking water (L-arginine: 3, 10 and 30 mg ml-1; L-NAME: 0.1, 1 and 10 mg ml-1). 2. Arthritis was exacerbated by L-arginine and suppressed by L-NAME in a dose-related fashion. Combined treatment with L-NAME (1 mg ml-1) and L-arginine (30 mg ml-1) did not modify the arthritis. 3. Reduced weight gain, which is a feature of adjuvant arthritis, was modified by these compounds so that L-arginine reduced weight gain whereas L-NAME increased weight gain compared with that in control animals. 4. D-Arginine (30 mg ml-1), NG-nitro-D-arginine methyl ester (D-NAME: 1 mg ml-1) and L-lysine (30 mg ml-1), an amino acid not involved in the generation of NO, were without effect on either arthritis or body weight gain. 5. Antigen-stimulated proliferation of T-lymphocytes as well as generation of nitrite (NO2-) and release of acid phosphatase from macrophages were all enhanced in L-arginine-treated arthritic rats and reduced in L-NAME-treated animals. 6. These results suggest that endogenous NO modulates adjuvant arthritis, possibly by interfering with the activation of T-lymphocytes and/or macrophages.     

Influence of nitric oxide on morphine-induced conditioned place preference in the rat central amygdala

Effects of intra-central amygdala injections of L-arginine, a nitric oxide (NO) precursor, and N(G)-nitro-L-arginine methyl ester (L-NAME), a NO synthase (NOS) inhibitor, on morphine-induced conditioned place preference in rats were investigated by using an unbiased 3-day schedule of place conditioning design. Animals receiving once daily injections of morphine (0.5-7.5 mg/kg, subcutaneously, s.c.) or saline (1.0 ml/kg, s.c.) showed a significant place preference in a dose-dependent manner. The maximum response was observed with 5.0 mg/kg of the opioid. Co-administration of morphine (5.0 mg/kg) with L-arginine (0.3, 1.0 and 3.0 microg/rat), but not with L-NAME (0.3, 1.0 and 3.0 microg/rat), during the acquisition of morphine-induced conditioned place preference increased morphine-induced conditioned place preference. The response to L-arginine was blocked by L-NAME preadministration. L-arginine and L-NAME by themselves did not induce conditioned place preference. When L-arginine or L-NAME at 0.3-3.0 microg/rat was administered 1 min before conditioned place preference testing, L-arginine but not L-NAME caused an increase in the expression of morphine-induced conditioned place preference, the effect that was blocked by L-NAME preadministration. A dose of L-arginine (0.3 microg/rat), but not L-NAME, during expression of morphine-induced conditioned place preference produced an increase in locomotion compared with that in the control group. It may be concluded that an increase in the NO levels in the central amygdala may have an effect on the acquisition and expression of morphine-induced conditioned place preference.     

Pentadecapeptide BPC 157, in clinical trials as a therapy for inflammatory bowel disease (PL14736), is effective in the healing of colocutaneous fistulas in rats: role of the nitric oxide-system

We focused on the therapeutic effect of the stable gastric pentadecapeptide BPC 157 and how its action is related to nitric oxide (NO) in persistent colocutaneous fistula in rats (at 5 cm from anus, colon defect of 5 mm, skin defect of 5 mm); this peptide has been shown to be safe in clinical trials for inflammatory bowel disease (PL14736) and safe for intestinal anstomosis therapy. BPC 157 (10 microg/kg, 10 ng/kg) was applied i) in drinking water until the animals were sacrificed at post-operative day 1, 3, 5, 7, 14, 21, and 28; or ii) once daily intraperitoneally (first application 30 min following surgery, last 24 h before sacrifice) alone or with N(G)-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg), L-arginine (200 mg/kg), and their combinations. Sulphasalazine (50 mg/kg) and 6-alpha-methylprednisolone (1 mg/kg) were given once daily intraperitoneally. BPC 157 accelerated parenterally or perorally the healing of colonic and skin defect, leading to the suitable closure of the fistula, macro/microscopically, biomechanically, and functionally (larger water volume sustained without fistula leaking). L-NAME aggravated the healing failure of colocutaneous fistulas, skin, and colon wounds (L-NAME groups). L-Arginine was effective only with blunted NO generation (L-NAME + L-arginine groups) but not without (L-arginine groups). All of the BPC 157 beneficial effects remained unchanged with blunted NO-generation (L-NAME + BPC 157 groups) and with NO substrate (L-arginine + BPC 157 groups) as well as L-NAME and L-arginine co-administration (L-NAME + L-arginine + BPC 157 groups). Sulphasalazine was only moderately effective, and corticosteroid even had an aggravating effect.     

Evidence for an involvement of nitric oxide and gamma aminobutyric acid in the anticonvulsant action of L-arginine on picrotoxin-induced convulsions in rats

Five, 30, and 60 min pretreatment of 1000 mg/kg and not 500 mg/kg of L-arginine inhibited convulsions induced by picrotoxin. The concentrations of nitric oxide (NO) and gamma aminobutyric acid (GABA) were increased in the brain 5, 30, and 60 min after administration of 1000 mg/kg and not 500 mg/kg of L-arginine. A much higher dose of L-arginine (2000 mg/kg), 30 min after administration, produced a lesser anticonvulsant and NO and GABA increasing actions as compared to that produced by 1000 mg/kg of L-arginine. The same dose of L-arginine, 60 min after administration, decreased the concentrations of both NO and GABA and increased the convulsion frequency of picrotoxin. An NO decreasing dose of nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME) decreased brain GABA concentration and increased the convulsant action of picrotoxin. Further, L-NAME pretreatment prevented L-arginine (1000 mg/kg) from producing anticonvulsant and NO and GABA increasing effects. An interpretation of these results suggests that NO synthesized from systemically administered L-arginine inhibits convulsions by increasing the concentration of GABA in the brain. However, the effects of L-arginine are reversible, if it is administered at a higher dose (2000 mg/kg) 60 min prior to the test. It is concluded that L-arginine produces anticonvulsant or proconvulsant action depending upon the dose and time of its administration-related changes in the concentrations of NO and GABA in the brain.     

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.     

Nitric oxide within the ventral tegmental area is involved in mediating morphine reward

In the present study, the effects of intra-ventral tegmental area injection of L-arginine, a nitric oxide (NO) precursor, and N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, on morphine-induced conditioned place preference in male Wistar rats were investigated. Our data showed that subcutaneous (s.c.) injection of morphine sulphate (0.5-10 mg/kg) significantly increased the time spent in the drug-paired compartment in a dose-dependent manner. Intra-ventral tegmental area administration of a low dose of L-arginine (0.05 microg/rat) with an ineffective dose of morphine (0.5 mg/kg) elicited significant conditioned place preference; however, a higher dose of L-arginine (0.1 microg/rat) reduced the morphine response. Intra-ventral tegmental area administration of L-NAME (0.03 and 0.1 microg/rat) decreased the acquisition of morphine (7.5 mg/kg)-induced place preference. The response to different doses of L-arginine was decreased by L-NAME (0.03 microg/rat). L-Arginine and L-NAME by themselves did not elicit any effect on place conditioning; however, intra-ventral tegmental area administration of L-arginine (0.01-0.1 microg/rat) and a higher dose of L-NAME (0.1 microg/rat) significantly decreased the expression of morphine (7.5 mg/kg)-induced place preference. The attenuation of already established morphine-induced place preference on the test day by L-arginine was inhibited by L-NAME (0.03 microg/rat). The results indicate that NO may be involved in the acquisition and expression of morphine-induced place preference.     

Differential role of nitric oxide (NO) in acute and chronic stress induced neurobehavioral modulation and oxidative injury in rats

The present study evaluated the effects of acute and chronic restraint stress (RS 1 h or 6 h), and their modulation by nitrergic agents on neurobehavioral and oxidative stress markers in rats. Acute RS (1 h or 6 h) reduced open arm entries (OAE) and open arm time (OAT) in the elevated plus maze test — which were attenuated by the NO precursor, L-arginine but not influenced appreciably by the NO synthase inhibitor, L-NAME. These behavioral changes were associated with differential changes in brain NO metabolites (NOx) but consistently reduced GSH and raised MDA levels in comparison to the control group. Following RS 1 h × 10 the neurobehavioral suppression and changes in brain oxidative stress markers were less pronounced as compared to the acute RS (1 h) group indicating adaptation. L-arginine pretreatment facilitated this adaptation to chronic RS (1 h). Interestingly RS 6 h × 10, induced severe behavioral suppression and aggravation of MDA and NOx levels and L-NAME pretreatment tended to protect against these chronic RS induced aggravations. These results suggest that acute and chronic RS induces duration/intensity dependent neurobehavioral and oxidative injury which are under the differential regulatory control of NO.     

Role of nitric oxide and mucus in ischemia/reperfusion-induced gastric mucosal injury in rats

The present study aims at investigating the role of nitric oxide (NO) on the oxidative damage in gastric mucosa of rats which received ischemia/reperfusion (I/R) and its relation to mucus. NO synthesis modulators such as L-arginine and N(G)-nitro-L-arginine methyl ester (L-NAME) were injected intraperitoneally to the rats 30 min prior to I/R which was induced by clamping the celiac artery and the superior mesenteric artery for 30 min and reperfusion for 1 h. As a result, I/R increased lipid peroxide production and decreased the contents of glutathione (GSH), cGMP and mucus as well as GSH peroxidase activities of gastric mucosa. I/R decreased the activity and protein of NO synthase (NOS) in gastric mucosa. Pretreatment of L-arginine, a substrate for NOS, prevented I/R-induced alterations of gastric mucosa. However, L-NAME, an NOS inhibitor, deteriorated oxidative damage induced by I/R. In conclusion, NO has an antioxidant defensive role on gastric mucosa by maintaining mucus, GSH and GSH peroxidase, which were related to preservation of cGMP and NOS in gastric mucosa.     

Potentiation of anandamide effects in mesenteric beds isolated from bile duct-ligated rats: role of nitric oxide

Changes in vascular responsiveness are proposed as the basis for some of the cardiovascular complications in cholestasis. Cholestasis is also associated with accumulation of endogenous opioid peptides and evidence of nitric oxide (NO) overproduction. On the other hand, it is well known that anandamide, an endogenous cannabinoid ligand, causes hypotension and a decrease in systemic vascular resistance. In the present study, the possible role of the cannabinoid system in cholestasis-induced mesenteric vascular bed responsiveness was investigated. Mesenteric arteries of bile duct-ligated and sham-operated rats receiving daily administrations of saline were used for evaluating phenylephrine or anandamide dose-response, acute effects of N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM), a non-selective inhibitor of NO synthase (NOS), or naltrexone, an opioid receptors antagonist (1 microM). The other groups of bile duct-ligated and sham-operated rats received daily intraperitoneal administration of L-NAME (20 mg/kg/day), aminoguanidine, a selective inducible NOS (iNOS) inhibitor (150 mg/kg/day) or naltrexone (10 mg/kg/day). After 7 days, the superior mesenteric artery was cannulated and the mesenteric vascular bed was perfused according to the McGregor method. Anandamide-induced relaxation was significantly potentiated in mesenteric vascular beds of bile duct-ligated rats. Chronic treatment of bile duct-ligated animals with L-NAME and aminoguanidine blocked this hyperresponsiveness while the hyperresponsiveness was potentiated at large doses of anandamide on chronic treatment of these animals with naltrexone. Although acute L-NAME treatment of mesenteric beds completely blocked the anandamide-induced vasorelaxation in sham-operated rats, this vasorelaxation still was present in bile duct-ligated animals. Anandamide-induced vasorelaxation remained unaffected after acute naltrexone treatment of mesenteric beds in both bile duct-ligated and sham-operated rats. Our results indicate that (1) there is enhanced anandamide-induced vasorelaxation in cholestatic rats, probably due to a defect in cannabinoid or vanilloid receptors and (2) NO overproduction may be involved in cholestasis-induced vascular hyperresponsiveness.     

N(G)-nitro-L-arginine methylester is protective against ethanol-induced gastric damage in cholestatic rats.

In this study the effect of nitric oxide (NO) synthesis inhibition on ethanol-induced gastric damage was evaluated in bile duct-ligated, sham-operated and unoperated rats. The animals were injected intraperitoneally with saline, L-arginine (200 mg/kg) or N(G)-nitro-L-arginine methylester (L-NAME) in doses of 5, 15 and 30 mg/kg, 30 min before ethanol administration. The animals were killed 1 h after ethanol administration and their stomachs were removed for measurement of gastric mucosal damage. The results showed that L-NAME significantly enhanced the development of gastric mucosal lesions in sham-operated and unoperated rats, while in bile duct-ligated animals, L-NAME decreased and L-arginine enhanced the potentiation of ethanol-induced gastric mucosal damage. The plasma level of nitrite and nitrate was also measured and was significantly higher in bile duct-ligated rats than in control groups. The results suggest that inhibition of NO synthase with L-NAME has different effects on ethanol-induced gastric damage in cholestatic groups and in normal rats and that these effects can be explained by overproduction of NO in bile duct-ligated animals.     

The role of nitric oxide in aloe-induced diarrhoea in the rat

The role of nitric oxide (NO) on aloe-induced diarrhoea was studied in the rat. Nine hours after oral administration, aloe produced diarrhoea at doses of 5 g kg(-1)(20% rats with diarrhoea) and 20 g kg(-1) (100% of rats with diarrhoea). Lower doses of aloe (0.1 and 1 g kg(-1) did not produce a diarrhoeal response. Pre-treatment (i.p.) of rats with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME 2.5-25 mg kg(-1) reduced the diarrhoea induced by aloe (20 g kg(-1) 9 h after its oral administration. L-NAME (25 mg kg(-1)) also reduced the increase in faecal water excretion produced by aloe (20 g kg(-1). L-arginine (1500 mg kg(-1), i.p.), administered to rats pre-treated with L-NAME (25 mg kg(-1), drastically reduced the effect of L-NAME on diarrhoea and increase in faecal water excretion induced by aloe (20 g kg(-1). Given alone, L-arginine did not modify aloe-induced diarrhoea. Basal Ca2+ -dependent NO synthase activity in the rat colon was dose-dependently inhibited by aloe (0.1-20 g kg(-1)) and by aloin (0.1-1 g kg(-1)), the active ingredient of aloe. These results suggest that endogenous NO modulates the diarrhoeal effect of aloe.     

Effect of molsidomine and L-arginine in cyclosporine nephrotoxicity: role of nitric oxide

Cyclosporine A (CsA) is a potent and effective immunosuppressive agent, but its action is frequently accompanied by severe renal toxicity. To determine if the renal alterations are mediated directly by cyclosporine or by secondary homodynamic alterations induced by cyclosporine, we evaluated if L-arginine and a nitric oxide donor, molsidomine could prevent these alterations. Eight groups of rats were employed in this study, group 1 served as control, group 2 rats were treated with CsA (20 mg/kg, s.c. for 21 days), group 3 received CsA along with L-arginine (125 mg/kg in drinking water concurrently with CsA), groups 4 and 5 received CsA along with molsidomine (5 and 10 mg/kg, p.o. 24 h before and 21 days concurrently with CsA), group 6 received CsA along with L-arginine (125 mg/l in drinking water concurrently with CsA) and L-NAME (10 mg/kg), groups 7 and 8 received L-NAME (10 mg/kg) along with CsA and molsidomine (5 and 10 mg/kg), respectively. Renal function was assessed by measuring serum creatinine, blood urea nitrogen, creatinine and urea clearance. Tissue and urine nitrite and nitrate levels were measured to estimate the total nitric oxide levels. The renal oxidative stress was measured by renal malondialdehyde levels, reduced glutathione levels and by enzymatic activity of catalase and superoxide dismutase. Renal morphological alterations were assessed by histopathological examination. CsA administration for 21 days resulted in a marked renal oxidative stress, significantly deranged the renal functions as well as renal morphology. Treatment with L-arginine as well as with molsidomine significantly improved the renal dysfunction; tissue and urine total nitric oxide levels, renal oxidative stress and prevented the alterations in renal morphology. This protection against CsA nephrotoxicity was attenuated by treatment with L-NAME, clearly indicating that NO plays a pivotal role in renoprotective effect of L-arginine and molsidomine against cyclosporine nephrotoxicity.     

Prevention of picrotoxin convulsions-induced learning and memory impairment by nitric oxide increasing dose of L-arginine in rats

Learning and memory processes were tested in adult male rats using a traditional pole-climbing apparatus 30 min after the administration of L-arginine (500 and 1000 mg/kg), the precursor of nitric oxide (NO), and N-nitro-L-arginine methyl ester (L-NAME) (50 and 100 mg/kg), the inhibitor of NO synthesis. The effects of the convulsant (5.0 mg/kg) and a smaller nonconvulsant (2.5 mg/kg) dose of picrotoxin were tested on learning and memory 120 min and 24 h after their administration. The tests were carried out 30 min after L-arginine in animals treated 120 min previously with the convulsant dose of picrotoxin. A dose-dependent enhancement and an inhibition of learning and memory were observed in animals treated with L-arginine and L-NAME, respectively. The convulsant dose of picrotoxin impaired both learning and memory processes. The effect of picrotoxin was reverted following the administration of L-arginine (1000 mg/kg). An interpretation of these results indicates that convulsions induced by picrotoxin produces learning and memory impairment, and that this defect is reversible if NO synthesis is increased in the brain by the systemic administration of L-arginine.