Asymmetric Dimethylarginine (ADMA) in cardiovascular and renal disease.

BACKGROUND: Asymmetric Dimethylarginine (ADMA) is a modified amino acid formed when intracellular arginine is methylated by methyltransferases that are widely distributed throughout the body. Nitric oxide (NO) is produced from l-arginine in a reaction catalyzed by three distinct isoforms of NO synthase (NOS). NO has emerged as a mediator involved in maintenance of vascular tonus, blood pressure regulation, inhibition of platelet aggregation, leukocyte and endothelial cell interaction and vascular permeability. ADMA is an important inhibitor that competes with NOS and compromises NO synthesis. OBJECTIVE: This review aims to compile articles involving renal and cardiovascular diseases in which plasma ADMA was assessed in order to clarify its role in these diseases. CONCLUSION: Although current knowledge suggests that ADMA has a role in the onset of cardiovascular and renal diseases, its actions are poorly understood. Clarifying its biochemical mechanisms is essential for improving disease management and promoting better quality of life for these patients.

Óxido nítrico e arginina di-metil assimétrica: possível via de explicação para o trabalho de parto pré-termo / Nitric oxide and asymmetric dimethyl arginine: a novel pathway to explain preterm labor

O trabalho de parto pré-termo (TPPT) assim como as outras causas de prematuridade respondem pela maior parcela da mortalidade e morbidade neonatal no mundo. Várias vias metabólicas já foram estudadas e diversas alterações já foram encontradas em pacientes que desenvolve TPPT. A via metabólica do óxido nítrico (NO) é reconhecida como um dos possíveis mecanismos de desencadeamento fisiopatológico do TPPT. Níveis elevados de dimetil-arginina assimétrica (ADMA), substância endógena inibidora da NO sintetase, estão relacionados com o desencadeamento de TPPT e com maiores taxas de complicações neonatais. O presente estudo aborda as evidências sobre a relação do TPPT e ADMA e as possíveis aplicações clínicas dessa associação.(AU)

Pre-term labor (PTL), as well as the other causes of prematurity, account for the largest portion of neonatal mortality and morbidity in the world. Several metabolic pathways were studied and a significative number of impairments have already been found in patients who develop PTL. The metabolic pathway of nitric oxide (NO) is recognized as one of the possible mechanisms of pathophysiological PTL?s trigger. High levels of asymmetric dimethyl arginine (ADMA), endogenous inhibitory substance of NO synthetase, are related to the triggering of PTL and with higher rates of neonatal complications. The present study addresses the evidence on the relationship of PTL and ADMA and possible clinical applications of this association.(AU)

Evaluation of mechanisms involved in the antinociception of the ethanol extract from the inner bark of Caesalpinia pyramidalis in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Caesalpinia pyramidalis Tul. (Fabaceae) is an endemic tree of the Northeast region of Brazil, mainly in the Caatinga region. More commonly, inner bark or flowers are traditionally used to treat many painful and inflammatory processes. A common use of this plant is made by macerating a handful of its stem bark in a liter of wine or sugarcane brandy. It is drunk against stomachache, dysenteries, and diarrheas. MATERIALS AND METHODS: The ethanol extract of Caesalpinia pyramidalis inner bark was used in mice via oral route, at the doses of 10, 30, and 100mg/kg, in behavioral models of nociception and investigates some of the mechanisms underlying this effect. RESULTS: The ethanol extract (30 and 100mg/kg, P<0.001), given orally, produced dose dependent inhibition of acetic acid-induced visceral pain. The ethanol extract also caused significant and dose-dependent inhibition of capsaicin-(100mg/kg, P<0.001) and glutamate-(10, 30, and 100mg/kg, P<0.01) induced pain. The antinociception caused by the ethanol extract (30mg/kg) in the abdominal constriction test was significantly attenuated (P<0.001) by intraperitoneal treatment of mice with l-arginine (600mg/kg). CONCLUSIONS: Collectively, the present results suggest that the ethanol extract of Caesalpinia pyramidalis produced dose-related antinociception in several models of pain through mechanisms that involved both glutamatergic system and/or the l-arginine-nitric oxide pathway, supporting the folkloric usage of the plant to treat various painful processes.

Involvement of the L-arginine/nitric oxide/cyclic guanosine monophosphate pathway in peripheral antinociception induced by N-palmitoyl-ethanolamine in rats.

N-palmitoyl-ethanolamine (PEA) is an endogenous substance that was first identified in lipid tissue extracts. It has been classified as a CB(2) receptor agonist. Exogenous PEA has the potential to become a valid treatment for neuropathic and inflammatory pain. In spite of the well-demonstrated antiinflammatory properties of PEA, its involvement in controlling pain pathways remains poorly characterized. The participation of the L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway in peripheral antinociception has been established by our group to the µ-, κ- or δ-opioid receptor agonists, nonsteroidal analgesics, α(2C) -adrenoceptor agonists, and even nonpharmacological electroacupuncture. The aim of this study was to verify whether the peripheral antinociception effects of PEA involve the activation of this pathway. All drugs were locally administered to the right hind paw of male Wistar rats. The paw pressure test was used, with hyperalgesia induced by intraplantar injection of prostaglandin E(2) . PEA elicited a local peripheral antinociceptive effect that was antagonized by the nonselective NO synthase (NOS) inhibitor L-NOARG and the selective neuronal NOS (nNOS) inhibitor L-NPA. Selective inhibition of endothelial (eNOS) and inducible (iNOS) NOS via L-NIO and L-NIL, respectively, was ineffective at blocking the effects of a local PEA injection. In addition, the dosage of nitrite in the homogenized paw, as determined by colorimetric assay, indicated that exogenous PEA is able to induce NO release. The soluble guanylyl cyclase inhibitor ODQ antagonized the PEA effect, whereas the cGMP-phosphodiesterase inhibitor zaprinast potentiated the antinociceptive effect of low-dose PEA. This study provides evidence that PEA activates nNOS, thus initiating the NO/cGMP pathway and inducing peripheral antinociceptive effects.

The peripheral L-arginine-nitric oxide-cyclic GMP pathway and ATP-sensitive K⁺ channels are involved in the antinociceptive effect of crotalphine on neuropathic pain in rats.

Crotalphine, a 14 amino acid peptide first isolated from the venom of the South American rattlesnake Crotalus durissus terrificus, induces a peripheral long-lasting and opioid receptor-mediated antinociceptive effect in a rat model of neuropathic pain induced by chronic constriction of the sciatic nerve. In the present study, we further characterized the molecular mechanisms involved in this effect, determining the type of opioid receptor responsible for this effect and the involvement of the nitric oxide-cyclic GMP pathway and of K⁺ channels. Crotalphine (0.2 or 5 µg/kg, orally; 0.0006 µg/paw), administered on day 14 after nerve constriction, inhibited mechanical hyperalgesia and low-threshold mechanical allodynia. The effect of the peptide was antagonized by intraplantar administration of naltrindole, an antagonist of δ-opioid receptors, and partially reversed by norbinaltorphimine, an antagonist of κ-opioid receptors. The effect of crotalphine was also blocked by 7-nitroindazole, an inhibitor of the neuronal nitric oxide synthase; by 1H-(1,2,4) oxadiazolo[4,3-a]quinoxaline-1-one, an inhibitor of guanylate cyclase activation; and by glibenclamide, an ATP-sensitive K⁺ channel blocker. The results suggest that peripheral δ-opioid and κ-opioid receptors, the nitric oxide-cyclic GMP pathway, and ATP-sensitive K⁺ channels are involved in the antinociceptive effect of crotalphine. The present data point to the therapeutic potential of this peptide for the treatment of chronic neuropathic pain.

Ketamine activates the L-arginine/Nitric oxide/cyclic guanosine monophosphate pathway to induce peripheral antinociception in rats.

BACKGROUND: The involvement of the L-arginine/nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway in antinociception has been implicated as a molecular mechanism of antinociception produced by several antinociceptive agents, including µ-, κ-, or δ-opioid receptor agonists, nonsteroidal analgesics, cholinergic agonist, and α2C adrenoceptor agonist. In this study, we investigated whether ketamine, a dissociative anesthetic N-methyl-D-aspartate receptor antagonist, was also capable of activating the L-arginine/NO/cGMP pathway and eliciting peripheral antinociception. METHODS: The rat paw pressure test was used, with hyperalgesia induced by intraplantar injection of prostaglandin E2. All drugs were locally administered into the right hindpaw of male Wistar rats. RESULTS: Ketamine (10, 20, 40, 80 µg/paw) elicited a local antinociceptive effect that was antagonized by the nonselective NOS inhibitor L-NOARG (12, 18, and 24 µg/paw) and by the selective neuronal NOS inhibitor L-NPA (12, 18, and 24 µg/paw). In another experiment, we used the inhibitors L-NIO and L-NIL (24 µg/paw) to selectively inhibit endothelial and inducible NOS, respectively. These 2 drugs were ineffective at blocking the effects of the peripheral ketamine injection. In addition, the level of nitrite in the homogenized paw indicated that exogenous ketamine is able to induce NO release. The soluble guanylyl cyclase inhibitor ODQ (25, 50, and 100 µg/paw) blocked the action of ketamine, and the cGMP-phosphodiesterase inhibitor zaprinast (50 µg/paw) enhanced the antinociceptive effects of low-dose ketamine (10 µg/paw). CONCLUSIONS: Our results suggest that ketamine stimulates the L-arginine/NO/cyclic GMP pathway via neuronal NO synthase to induce peripheral antinociceptive effects.

Inmunonutrición: segunda parte / Immunonutrition: second part

El concepto de inmunonutrición se refiere a la adición de nutrimentos específicos a los regímenes de nutrición enteral o parenteral, en concentraciones mayores a las habitualmente contenidas en las dietas normales, para lograr un efecto farmacológico determinado que mejore la función inmunitaria. Todos los conceptos mencionados indican que el eje intestinoneuroendocrino tiene un papel significativo al influir en la vulnerabilidad del hospedero a infecciones. Entre los inmunonutrimentos se encuentran: arginina, glutamina, ácidos grasos ù-3, prebióticos, zinc, y vitamina A.

The concept of immunonutrition concerns the addition of specific nutrients to the regimes of enteral or parenteral nutrition, at concentrations greater than those usually contained in normal diets to achieve a given pharmacological effect to improve immune function. All the concepts above indicate that gutneuroendocrine axis plays a significant role in influencing host vulnerability to infection. Among inmunonutriments are: arginine, glutamine, ù-3 fatty acids, prebiotics, zinc, and vitamin A.

Involvement of NMDA receptors and L-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effects of escitalopram in the forced swimming test.

Escitalopram is a serotonin reuptake inhibitor used in the treatment of depression and anxiety disorders. This study investigated the effect of escitalopram in forced swimming test (FST) and in the tail suspension test (TST) in mice, and tested the hypothesis that the inhibition of NMDA receptors and NO-cGMP synthesis is implicated in its mechanism of action in the FST. Escitalopram administered by i.p. route reduced the immobility time both in the FST (0.3-10 mg/kg) and in the TST (0.1-10 mg/kg). Administration of escitalopram by p.o route (0.3-10 mg/kg) also reduced the immobility time in the FST. The antidepressant-like effect of escitalopram (3mg/kg, p.o.) in the FST was prevented by the pretreatment of mice with NMDA (0.1 pmol/site, i.c.v.), l-arginine (750 mg/kg, i.p., a substrate for nitric oxide synthase) or sildenafil (5mg/kg, i.p., a phosphodiesterase 5 inhibitor). The administration of 7-nitroindazole (50 mg/kg, i.p., a neuronal nitric oxide synthase inhibitor), methylene blue (20 mg/kg, i.p., an inhibitor of both nitric oxide synthase and soluble guanylate cyclase) or ODQ (30 pmol/site i.c.v., a soluble guanylate cyclase inhibitor) in combination with a subeffective dose of escitalopram (0.1 mg/kg, p.o.) reduced the immobility time in the FST as compared with either drug alone. None of the drugs produced significant effects on the locomotor activity in the open-field test. Altogether, our data suggest that the antidepressant-like effect of escitalopram is dependent on inhibition of either NMDA receptors or NO-cGMP synthesis. The results contribute to the understanding of the mechanisms underlying the antidepressant-like effect of escitalopram and reinforce the role of NMDA receptors and l-arginine-NO-GMP pathway in the mechanism of action of antidepressant agents.

Characterization of the L-arginine-NO-cGMP pathway in spontaneously hypertensive rat platelets: the effects of pregnancy.

Nitric oxide (NO) is a short-lived intercellular messenger that provides an efficient vascular regulatory mechanism to support homeostasis and prevent thrombosis. Endothelial dysfunction and reduced NO bioavailability have a central role in hypertension associated with pregnancy. The purpose of this study was to investigate the impact of pregnancy on the L-arginine-NO-cGMP pathway in platelets and its correlation to platelet function and blood pressure in normotensive rats and spontaneously hypertensive rats (SHRs). Platelets were obtained from blood on the 20th day of pregnancy from female SHRs (SHR-P) and normotensive controls (P) or age-matched nonpregnant rats (SHR-NP and NP). Intraplatelet NO synthase (NOS) activity was reduced in P compared to NP, despite unchanged L-arginine influx. The expression levels of endothelial NOS (eNOS) and inducible NOS (iNOS) were diminished during pregnancy in normotensive rats. Paradoxically, cyclic guanosine monophosphate (cGMP) levels were similar between NP and P, as were phosphodiesterase type 5 (PDE5) expression and platelet aggregation induced by adenosine diphosphate. In SHRs, L-arginine influx was reduced in SHR-P compared to SHR-NP. SHR-P exhibited impaired NOS activity and reduced iNOS expression compared with SHR-NP. Soluble guanylyl cyclase and PDE5 expression in platelets were lower in SHR-P than in SHR-NP, whereas no differences were noted between groups with respect to cGMP levels. However, increased levels of cGMP were observed in SHR-P compared to normotensive groups and platelet aggregability remained unaltered. In conclusion, these observations prompted the hypothesis that normal platelet aggregation in pregnant SHRs may be related to a reduction in PDE5 expression and consequently the maintenance of cGMP levels, independently of reduced platelet NO bioavailability.

The arginylation-dependent association of calreticulin with stress granules is regulated by calcium.

Post-translational modifications of proteins are important for the regulation of cell functions; one of these modifications is post-translational arginylation. In the present study, we show that cytoplasmic CRT (calreticulin) is arginylated by ATE1 (arginyl-tRNA protein transferase). We also show that a pool of CRT undergoes retrotranslocation from the ER (endoplasmic reticulum) to the cytosol, because in CRT-knockout cells transfected with full-length CRT (that has the signal peptide), cytoplasmic CRT appears as a consequence of its expression and processing in the ER. After the cleavage of the signal peptide, an N-terminal arginylatable residue is revealed prior to retrotranslocation to the cytoplasm where arginylation takes place. SGs (stress granules) from ATE1-knockout cells do not contain CRT, indicating that CRT arginylation is required for its association to SGs. Furthermore, R-CRT (arginylated CRT) in the cytoplasm associates with SGs in cells treated with several stressors that lead to a reduction of intracellular Ca2+ levels. However, in the presence of stressors that do not affect Ca2+ levels, R-CRT is not recruited to these loci despite the fact that SGs are formed, demonstrating Ca2+-dependent R-CRT association to SGs. We conclude that post-translational arginylation of retrotranslocated CRT, together with the decrease in intracellular Ca2+, promotes the association of CRT to SGs.

Asymmetric dimethylarginine (ADMA) and endothelial dysfunction: implications for atherogenesis.

Atherosclerotic coronary heart disease is the leading cause of morbidity and mortality in industrialized countries, and endothelial dysfunction is considered a precursor phenomenon. The nitric oxide produced by the endothelium under the action of endothelial nitric oxide synthase has important antiatherogenic functions. Its reduced bioavailabilty is the beginning of the atherosclerotic process. The addition of two methyl radicals to arginine, through the action of methyltransferase nuclear proteins, produces asymmetric dimethylarginine, which competes with L-arginine and promotes a reduction in nitric oxide formation in the vascular wall. The asymmetric dimethylarginine, which is itself considered a mediator of the vascular effects of the several risk factors for atherosclerosis, can be eliminated by renal excretion or by the enzymatic action of the dimethylarginine dimethylaminohydrolases. Several basic science and clinical research studies suggest that the increase in asymmetric dimethylarginine occurs in the context of chronic renal insufficiency, dyslipidemia, high blood pressure, diabetes mellitus, and hyperhomocysteinemy, as well as with other conditions. Therapeutic measures to combat atherosclerosis may reverse these asymmetric dimethylarginine effects or at least reduce the concentration of this chemical in the blood. Such an effect can be achieved with competitor molecules or by increasing the expression or activity of its degradation enzyme. Studies are in development to establish the true role of asymmetric dimethylarginine as a marker and mediator of atherosclerosis, with possible therapeutic applications. The main aspects of the formation and degradation of asymmetric dimethylarginine and its implication in the atherogenic process will be addressed in this article.

Asymmetric dimethylarginine (ADMA) and endothelial dysfunction: implications for atherogenesis: [review]

Atherosclerotic coronary heart disease is the leading cause of morbidity and mortality in industrialized countries, and endothelial dysfunction is considered a precursor phenomenon. The nitric oxide produced by the endothelium under the action of endothelial nitric oxide synthase has important antiatherogenic functions. Its reduced bioavailabilty is the beginning of the atherosclerotic process. The addition of two methyl radicals to arginine, through the action of methyltransferase nuclear proteins, produces asymmetric dimethylarginine, which competes with L-arginine and promotes a reduction in nitric oxide formation in the vascular wall. The asymmetric dimethylarginine, which is itself considered a mediator of the vascular effects of the several risk factors for atherosclerosis, can be eliminated by renal excretion or by the enzymatic action of the dimethylarginine dimethylaminohydrolases. Several basic science and clinical research studies suggest that the increase in asymmetric dimethylarginine occurs in the context of chronic renal insufficiency, dyslipidemia, high blood pressure, diabetes mellitus, and hyperhomocysteinemy, as well as with other conditions. Therapeutic measures to combat atherosclerosis may reverse these asymmetric dimethylarginine effects or at least reduce the concentration of this chemical in the blood. Such an effect can be achieved with competitor molecules or by increasing the expression or activity of its degradation enzyme. Studies are in development to establish the true role of asymmetric dimethylarginine as a marker and mediator of atherosclerosis, with possible therapeutic applications. The main aspects of the formation and degradation of asymmetric dimethylarginine and its implication in the atherogenic process will be addressed in this article.

Antidepressant-like effect of folic acid: Involvement of NMDA receptors and L-arginine-nitric oxide-cyclic guanosine monophosphate pathway.

Antidepressant-like activity of folic acid in forced swimming test and in the tail suspension test was demonstrated previously by our group. In this study we investigated the involvement of N-methyl-d-aspartate (NMDA) receptors and l-arginine-nitric oxide (NO)-cyclic guanosine monophosphate pathway in its antidepressant-like effect in the forced swimming test in mice. The antidepressant-like effect of folic acid (10 nmol/site, i.c.v.) was prevented by the pretreatment of mice with NMDA (0.1 pmol/site, i.c.v.), l-arginine (750 mg/kg, i.p., substrate for nitric oxide synthase), S-nitroso-N-acetyl-penicillamine (SNAP, 25 microg/site, i.c.v, a NO donor) or sildenafil (5 mg/kg, i.p., phosphodiesterase 5 inhibitor). The administration of 7-nitroindazole (25 and 50 mg/kg, i.p., a specific neuronal nitric oxide synthase (nNOS) inhibitor) or methylene blue (20 mg/kg, i.p., direct inhibitor of both nitric oxide synthase and soluble guanylate cyclase) in combination with a sub-effective dose of folic acid (1 nmol/site, i.c.v.) reduced the immobility time in the FST as compared with either drug alone. Together the results suggest that the antidepressant-like effect of folic acid in the forced swimming test is dependent on an inhibition of either NMDA receptors or NO and cGMP synthesis.

[Role of nitric oxide in the control of the pulmonary circulation: physiological, pathophysiological, and therapeutic implications]. / Papel do óxido nítrico na regulação da circulação pulmonar: implicações fisiológicas, fisiopatológicas e terapêuticas.

Nitric oxide (NO) is an endogenous vasoactive compound that contributes to pulmonary vascular homeostasis and is produced by three nitric oxide synthase (NOS) isoforms-neuronal NOS (nNOS); inducible NOS (iNOS); and endothelial NOS (eNOS)-all three of which are present in the lung. Studies using pharmacological inhibitors or knockout mice have shown that eNOS-derived NO plays an important role in modulating pulmonary vascular tone and attenuating pulmonary hypertension. However, studies focusing on the role of iNOS have shown that this isoform contributes to the pathophysiology of acute lung injury and acute respiratory distress syndrome. This review aimed at outlining the role played by NO in the control of pulmonary circulation, both under physiological and pathophysiological conditions. In addition, we review the evidence that the L-arginine-NO-cyclic guanosine monophosphate pathway is a major pharmacological target in the treatment of pulmonary vascular diseases.

Papel do óxido nítrico na regulação da circulação pulmonar: implicações fisiológicas, fisiopatológicas e terapêuticas / Role of nitric oxide in the control of the pulmonary circulation: physiological, pathophysiological, and therapeutic implications

O nitric oxide (NO, óxido nítrico) é um mediador endógeno vasoativo que contribui para a homeostase vascular pulmonar. O NO é produzido por três isoformas das nitric oxide synthases (NOS, óxido nítrico sintases)-NOS neuronial (nNOS); NOS induzida (iNOS); e NOS endotelial (eNOS)-estando as três presentes no pulmão. Estudos que utilizaram inibidores farmacológicos ou camundongos knockout têm demonstrado que o NO derivado da eNOS desempenha importantes papéis ao modular o tônus vascular pulmonar e atenuar a hipertensão pulmonar. Por outro lado, estudos focados no papel da iNOS têm mostrado que essa isoforma contribui para a fisiopatologia da lesão pulmonar aguda e da síndrome do desconforto respiratório agudo. Esta revisão objetivou delinear o papel desempenhado pelo NO no controle da circulação pulmonar, tanto em condições fisiológicas como fisiopatológicas. Além disso, revisamos as evidências de que a via L-arginina-NO-guanosina monofosfato cíclico seja um importante alvo farmacológico para a terapia de doenças vasculares pulmonares.

Nitric oxide (NO) is an endogenous vasoactive compound that contributes to pulmonary vascular homeostasis and is produced by three nitric oxide synthase (NOS) isoforms-neuronal NOS (nNOS); inducible NOS (iNOS); and endothelial NOS (eNOS)-all three of which are present in the lung. Studies using pharmacological inhibitors or knockout mice have shown that eNOS-derived NO plays an important role in modulating pulmonary vascular tone and attenuating pulmonary hypertension. However, studies focusing on the role of iNOS have shown that this isoform contributes to the pathophysiology of acute lung injury and acute respiratory distress syndrome. This review aimed at outlining the role played by NO in the control of pulmonary circulation, both under physiological and pathophysiological conditions. In addition, we review the evidence that the L-arginine-NO-cyclic guanosine monophosphate pathway is a major pharmacological target in the treatment of pulmonary vascular diseases.

Dengue fever activates the L-arginine-nitric oxide pathway: an explanation for reduced aggregation of human platelets.

In patients with Dengue fever, a viral inflammatory syndrome, haemorrhage is a significant pathological feature, yet the underlying mechanisms remain unclear. Nitric oxide (NO) is an important regulator of platelet function, inhibiting aggregation, recruitment and adhesion to the vascular endothelium. We have investigated whether changes in the activity of the L-arginine-NO pathway in human platelets may account for increased bleeding in patients with Dengue fever. A total of 16 patients with Dengue fever and 18 age-matched healthy volunteers participated in the study. Collagen induced platelet aggregation in a dose-dependent manner in both Dengue patients and controls, but the degree of platelet aggregation was significantly reduced in the patient group. Elevated rates of L-arginine transport in Dengue fever patients were associated with enhanced NO synthase activity and elevated plasma fibrinogen levels. The present study provides the first evidence that Dengue fever is associated with increased L-arginine transport and NO generation and reduced platelet aggregation.

Diphenyl diselenide exerts antidepressant-like and anxiolytic-like effects in mice: involvement of L-arginine-nitric oxide-soluble guanylate cyclase pathway in its antidepressant-like action.

This study investigated the possible antidepressant-like and anxiolytic-like effects of diphenyl diselenide, (PhSe)(2) in mice. The involvement of L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the antidepressant-like effect was also evaluated. The immobility times in the tail suspension test (TST) and forced swimming test (FST) were reduced by (PhSe)(2) (5-100 mg/kg; oral route, p.o.). The antiimmobility effect of (PhSe)(2) (5 mg/kg, p.o.) in the TST was prevented by pretreatment of mice with L-arginine [a substrate for nitric oxide synthase (NOS)], methylene blue [an inhibitor of NO synthase and sGC] and sildenafil [a phosphodiesterase 5 inhibitor]. Furthermore, a sub-effective dose of (PhSe)(2) (0.1 mg/kg, p.o.) produced a synergistic antidepressant-like effect with N(G)-nitro-L-arginine [L-NNA; 0.3mg/kg, i.p. inhibitor of NOS], (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one [ODQ; 30 pmol/site i.c.v., a specific inhibitor of soluble guanylate cyclase (sGC)], fluoxetine and imipramine in the TST. (PhSe)(2) (50-100 mg/kg, p.o.) induced anxiolytic-like effect in the elevated plus-maze test and light/dark box. Together the results indicate that (PhSe)(2) elicited significant antidepressant-like and anxiolytic-like effects. The antidepressant-like action caused by (PhSe)(2) seems to involve an interaction with L-arginine-NO-cGMP pathway.

Antinociceptive properties of the ethanolic extract and of the triterpene 3beta,6beta,16beta-trihidroxilup-20(29)-ene obtained from the flowers of Combretum leprosum in mice.

The present study examined the antinociceptive effects of the ethanolic extract (EE) and of the triterpene 3beta,6beta,16beta-trihidroxilup-20(29)-ene obtained from the flowers of Combretum leprosum in chemical and thermal behavioural models of pain in mice. The EE (10-1000 mg/kg) given orally (p.o.), 1 h prior to testing, produced dose-dependent inhibition of acetic acid-induced visceral pain, with mean ID50 value of 131.9 mg/kg. In the formalin test, the EE (10-300 mg/kg, p.o.) also caused significant inhibition of both the early (neurogenic pain) and the late (inflammatory pain) phases of formalin-induced licking, however, it was more potent and efficacious in relation to the late phase of the formalin test, with mean ID50 values for the neurogenic and the inflammatory phases of approximately 300 and 88.8 mg/kg, respectively. The EE (10-1000 mg/kg, p.o.) also caused significant and dose-dependent inhibition of capsaicin- and glutamate-induced pain, with mean ID50 values of 160.5 and 38.3 mg/kg, respectively. Furthermore, the triterpene 3beta,6beta,16beta-trihidroxilup-20(29)-ene (1-30 mg/kg), given p.o., 1 h prior to testing, also produced dose-related inhibition of glutamate-induced pain, with a mean ID50 value of 5.6 mg/kg. When assessed in a thermal model of pain, the EE (10-300 mg/kg, p.o.) and fentanyl (100 microg/kg, s.c.) caused a significant and marked increase in the latency response on the hot-plate test (50 degrees C). The antinociception caused by EE (100 mg/kg, p.o.) in the glutamate test was significantly attenuated by intraperitoneal (i.p.) treatment of mice with naloxone (opioid receptor antagonist, 1 mg/kg), pindolol (a 5-HT 1A/1B receptor/beta adrenoceptor antagonist, 1 mg/kg), WAY100635 (a 5-HT 1A receptor antagonist, 0.7 mg/kg) or ketanserin (a 5-HT 2A receptor antagonist, 0.3 mg/kg). In contrast, EE (100 mg/kg, p.o.) antinociception was affected neither by L-arginine (precursor of nitric oxide, 600 mg/kg) nor by ondansetron (a 5-HT3 receptor antagonist, 0.5 mg/kg) i.p. treatment. It was not associated with non-specific effects such as muscle relaxation or sedation. Together, these results indicate that EE produces dose-related antinociception in several models of chemical and thermal pain through mechanisms that involve an interaction with opioid and serotonergic (i.e., through 5-HT 1A/1B and 5-HT 2A receptors) systems.

Evidence for the involvement of L-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effect of memantine in mice.

This study investigated the involvement of the L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the antidepressant-like effect of an acute administration of memantine in the forced swimming test (FST) in mice, since this signaling pathway is supposed to play a significant role in depression. The antidepressant-like effect of memantine (3 mg/kg, i.p.) was prevented by pretreatment with L-arginine (750 mg/kg, i.p.) or S-nitroso-N-acetyl-penicillamine (SNAP, 25 microg/site, i.c.v.), but not with d-arginine (750 mg/kg, i.p.).The treatment of mice with NG-nitro-L-arginine (L-NNA, 0.03 and 0.3 mg/kg, i.p.) potentiated the effect of a subeffective dose of memantine (0.3 mg/kg, i.p.) in the FST. Moreover, the pretreatment of mice with (1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one) (ODQ, 30 pmol/site, i.c.v.) produced a synergistic antidepressant-like effect with subeffective doses of memantine (0.3 and 1 mg/kg, i.p.) in the FST. Furthermore, the reduction in the immobility time elicited by memantine (3 mg/kg, i.p.) in the FST was prevented by pretreatment with sildenafil (5 mg/kg, i.p.). Taken together, the results demonstrate that memantine produced an antidepressant-like effect in the FST that seems to be mediated through an interaction with the L-arginine-NO-cGMP pathway.

delta-Opioid receptor agonist SNC80 elicits peripheral antinociception via delta(1) and delta(2) receptors and activation of the l-arginine/nitric oxide/cyclic GMP pathway.

In this study, we characterized the role of delta(1) and delta(2) opioids receptors, as well the involvement of the l-arginine/NO/cGMP pathway in the peripheral antinociception induced by delta-opioid receptor agonist (+)-4-[(alphaR)-alpha-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80). The paw pressure test was utilized, in which pain sensitivity is increased by intraplantar injection of prostaglandin E(2) (2 microg). Administration of SNC80 (20, 40 and 80 microg/paw) decreased the hyperalgesia induced by prostaglandin E(2) in a dose-dependent manner. The possibility that the higher dose of SNC80 (80 microg) has a central or systemic effect was excluded, since administration of the drug into the contralateral paw did not elicit antinociception in the right paw. 7-Benzylidenenaltrexone (BNTX), 5, 10 and 20 microg/paw, and 17-(Cyclopropylmethyl)-6,7-didehydro-3,14beta-dihydroxy-4,5alpha-epoxy-6,7-2',3'-benzo[b]furanomorphinan (naltriben), 2.5, 5 and 10 microg/paw, delta(1) and delta(2) opioid receptor antagonist respectively, elicited partial antagonism of the peripheral antinociceptive effect of the SNC80 (80 microg). The BNTX (10 microg/paw)-naltriben (5 microg/paw) combination completely antagonized the peripheral antinociception induced by SNC80 (80 microg). Further, blockers of the l-arginine/NO/cGMP pathway, N(G)-nitro-l-arginine (12, 18 and 24 microg/paw) and methylene blue (125, 250 and 500 microg/paw) were observed reverting the peripheral antinociceptive effect of SNC80. This study provides evidence that the peripheral antinociception induced by SNC80 occurs via delta(1) and delta(2) receptors and may result from l-arginine/NO/cGMP pathway activation.