Distal Esophageal Spasm: An Updated Review

Distal esophageal spasm is characterized by premature contractions of the distal esophageal smooth muscle leading to non-obstructive dysphagia and non-cardiac chest pain. Diagnosis requires the presence of symptoms along with evidence of at least 20% premature contractions in the setting of a normal lower esophageal sphincter relaxation on high-resolution manometry. New updates to the Chicago Classification have improved the diagnostic accuracy of this method. Functional lumen imaging probe is a growing diagnostic modality that gives a more complete picture of esophageal motility. Pharmacologic treatment remains inadequate. Endoscopic myotomy might be of benefit for non-achalasia esophageal motility disorders. More research is required to better understand the pathophysiology and develop safe and long-lasting management for this disease.

Nitric Oxide in the Management of Respiratory Consequences in COVID-19: A Scoping Review of a Different Treatment Approach

The severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) virus causing COVID-19 significantly affects the respiratory functions of infected individuals by massively disrupting the pulmonary oxygenation and activating the synthesis of proinflammatory cytokines, inducing severe oxidative stress, enhanced vascular permeability, and endothelial dysfunction which have rendered researchers and clinicians to depend on prophylactic treatment due to the unavailability of proper disease management approaches. Previous studies have indicated that nitric oxide (NO) application appears to be significant concerning the antiviral activities, antioxidant, and anti-inflammatory properties in relieving disease-related symptoms. To identify, explore, and map the literature on the role of nitric oxide in the management of respiratory consequences in COVID-19 through this scoping review, Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed during the search to answer the focal question: "What are the potential uses of nitric oxide in the management of respiratory failure in COVID-19?" Administering exogenous NO in the form of inhaled gas or stimulating the system to produce NO appears to be a suitable option to manage COVID-19-induced pneumonia and respiratory illness. This treatment modality seems to attenuate respiratory distress among patients suffering from severe infections or patients with comorbidities. Exogenous NO at different doses effectively reduces systemic hyperinflammation and oxidative stress, improves arterial oxygenation, and restores pulmonary alveolar cellular integrity to prevent the lungs and other organs from further damage. This therapy could pave the way for better management of COVID-19 before the onset of disease-related complications.

Nitric oxide alleviates cell death through protein S-nitrosylation and transcriptional regulation during the ageing of elm seeds

Seed ageing is a major problem in the conservation of germplasm resources. The involvement of possible signalling molecules during seed deterioration needs to be identified. In this study, we confirmed that nitric oxide (NO), a key signalling molecule in plants, plays a positive role in the resistance of elm seeds to deterioration. To explore which metabolic pathways were affected by NO, an untargeted metabolomic analysis was conducted, and 163 metabolites could respond to both NO and the ageing treatment. The primary altered pathways include glutathione, methionine, and carbohydrate metabolism. The genes involved in glutathione and methionine metabolism were up-regulated by NO at the transcriptional level. Using a biotin switch method, proteins with an NO-dependent post-translational modification were screened during seed deterioration, and 82 putative S-nitrosylated proteins were identified. Eleven of these proteins were involved in carbohydrate metabolism, and the activities of the three enzymes were regulated by NO. In combination, the results of the metabolomic and S-nitrosoproteomic studies demonstrated that NO could activate glycolysis and inhibit the pentose phosphate pathway. In summary, the combination of these results demonstrated that NO could modulate carbohydrate metabolism at the post-translational level and regulate glutathione and methionine metabolism at the transcriptional level. It provides initial insights into the regulatory mechanisms of NO in seed deterioration.

Nitric oxide sensor proteins with revolutionary potential

This article comments on: Calvo-Begueria L, Rubio MC, Martínez JI, Pérez-Rontomé C, Delgado MJ, Bedmar EJ, Becana M. 2018. Redefining nitric oxide production in legume nodules through complementary insights from electron paramagnetic resonance spectroscopy and specific fluorescent probes. Journal of Experimental Botany 69, 3703–3714.

Constitutive expression of mammalian nitric oxide synthase in tobacco plants triggers disease resistance to pathogens

Nitric oxide (NO) is known for its role in the activation of plant defense responses. To examine the involvement and mode of action of NO in plant defense responses, we introduced calmodulin-dependent mammalian neuronal nitric oxide synthase (nNOS), which controls the CaMV35S promoter, into wild-type and NahG tobacco plants. Constitutive expression of nNOS led to NO production and triggered spontaneous induction of leaf lesions. Transgenic plants accumulated high amounts of H(2)O(2), with catalase activity lower than that in the wild type. nNOS transgenic plants contained high levels of salicylic acid (SA), and they induced an array of SA-, jasmonic acid (JA)-, and/or ethylene (ET)-related genes. Consequently, NahG co-expression blocked the induction of systemic acquired resistance (SAR)-associated genes in transgenic plants, implying SA is involved in NO-mediated induction of SAR genes. The transgenic plants exhibited enhanced resistance to a spectrum of pathogens, including bacteria, fungi, and viruses. Our results suggest a highly ranked regulatory role for NO in SA-, JA-, and/or ET-dependent pathways that lead to disease resistance.

Haemoglobin modulates NO emission and hyponasty under hypoxia-related stress in Arabidopsis thaliana

Nitric oxide (NO) and ethylene are signalling molecules that are synthesized in response to oxygen depletion. Non-symbiotic plant haemoglobins (Hbs) have been demonstrated to act in roots under oxygen depletion to scavenge NO. Using Arabidopsis thaliana plants, the online emission of NO or ethylene was directly quantified under normoxia, hypoxia (0.1-1.0% O(2)), or full anoxia. The production of both gases was increased with reduced expression of either of the Hb genes GLB1 or GLB2, whereas NO emission decreased in plants overexpressing these genes. NO emission in plants with reduced Hb gene expression represented a major loss of nitrogen equivalent to 0.2mM nitrate per 24h under hypoxic conditions. Hb gene expression was greatly enhanced in flooded roots, suggesting induction by reduced oxygen diffusion. The function could be to limit loss of nitrogen under NO emission. NO reacts with thiols to form S-nitrosylated compounds, and it is demonstrated that hypoxia substantially increased the content of S-nitrosylated compounds. A parallel up-regulation of Hb gene expression in the normoxic shoots of the flooded plants may reflect signal transmission from root to shoot via ethylene and a role for Hb in the shoots. Hb gene expression was correlated with ethylene-induced upward leaf movement (hyponastic growth) but not with hypocotyl growth, which was Hb independent. Taken together the data suggest that Hb can influence flood-induced hyponasty via ethylene-dependent and, possibly, ethylene-independent pathways.

The hemibiotrophic cacao pathogen Moniliophthora perniciosa depends on a mitochondrial alternative oxidase for biotrophic development

The tropical pathogen Moniliophthora perniciosa causes witches' broom disease in cacao. As a hemibiotrophic fungus, it initially colonizes the living host tissues (biotrophic phase), and later grows over the dead plant (necrotrophic phase). Little is known about the mechanisms that promote these distinct fungal phases or mediate the transition between them. An alternative oxidase gene (Mp-aox) was identified in the M. perniciosa genome and its expression was analyzed througout the fungal life cycle. In addition, the effects of inhibitors of the cytochrome-dependent respiratory chain (CRC) and alternative oxidase (AOX) were evaluated on the in vitro development of M. perniciosa. Larger numbers of Mp-aox transcripts were observed in the biotrophic hyphae, which accordingly showed elevated sensitivity to AOX inhibitors. More importantly, the inhibition of CRC prevented the transition from the biotrophic to the necrotrophic phase, and the combined use of a CRC and AOX inhibitor completely halted fungal growth. On the basis of these results, a novel mechanism is presented in which AOX plays a role in the biotrophic development of M. perniciosa and regulates the transition to its necrotrophic stage. Strikingly, this model correlates well with the infection strategy of animal pathogens, particularly Trypanosoma brucei, which uses AOX as a strategy for pathogenicity.

Nitric oxide production is not required for dihydrosphingosine-induced cell death in tobacco BY-2 cells

Sphinganine or dihydrosphingosine (d18:0, DHS), one of the most abundant free sphingoid Long Chain Base (LCB) in plants, is known to induce a calcium dependent programmed cell death (PCD) in tobacco BY-2 cells. In addition, we have recently shown that DHS triggers a production of H2O2, via the activation of NADPH oxidase(s). However, this production of H2O2 is not correlated with the DHS-induced cell death but would rather be associated with basal cell defense mechanisms. In the present study, we extend our current knowledge of the DHS signaling pathway, by demonstrating that DHS also promotes a production of nitric oxide (NO) in tobacco BY-2 cells. As for H2O2, this NO production is not necessary for cell death induction. 

Involvement of nitric oxide in learning & memory processes

Nitric oxide (NO), synthesized from the amino acid, L-arginine by nitric oxide synthase (NOS) has received attention as a neurotransmitter in the brain. NO has been found to induce cognitive behaviour in experimental animals. In order to show evidence for the involvement of NO in learning and memory processes, the reports indicating the effects of its precursor, donors, and inhibitors of its synthesis in mammals, birds, fishes and invertebrates have been reviewed. Further, learning and memory impairment occurring in man and animals due to defective NO activity in the brain due to pathological conditions such as epilepsy, stress, diabetes and side effects of therapeutic agents and reversal of this condition by L-arginine and NO donors have been included. In addition, the reports that indicate ageing-induced impairment of cognition that is known to occur in Alzheimer's disease due to deposition of the toxic protein, beta amyloid and the effect of L-arginine and NO donors in preventing dementia in these patients have been reviewed.

Verifying of participation of nitric oxide in morphine place conditioning in the rat medial septum using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)

BACKGROUND

Role of nitric oxide (NO) in morphine-induced conditioned place preference (CPP) has already been proposed in the rat medial septum (MS), but no molecular evidence has been provided to clear this fact.

METHODS

Effects of intraseptal injections of L-arginine and/or NG-nitro-L-arginine methyl ester (L-NAME) on morphine place conditioning in Wistar rats were examined. Morphine (2.5-7.5 mg/kg) was injected s.c. using a three-day schedule of an unbiased place preference. All of the brain samples were examined histochemically by nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), the main marker for NO activation.

RESULTS

Morphine induced a significant CPP in the rats. Single injections of L-arginine or L-NAME (0.3, 1.0 and 3.0 µg/rat) did not induce CPP. In addition, co-administration of morphine (5.0 mg/kg) with L-arginine or L-NAME (0.3, 1.0 and 3.0 µg/rat) did not affect morphine response. However, administration of L-arginine (0.3, 1.0 and 3.0 µg/rat) prior to morphine conditioning testing enhanced the expression of morphine response. Moreover, pre-injection of L-NAME (0.3, 1.0 and 3.0 µg/rat) to L-arginine (0.3 µg/rat) did not reverse the response to the agent. The expression of NADPH-d was observed in the rat brain samples treated by L-arginine. A decreased expression of NADPH-d was also observed in rats pre-injected by L-NAME.

CONCLUSION

This finding strongly suggests that NO system in the rat MS has an impact on the expression of morphine rewarding, and that the NO participates in place conditioning induced of morphine.

H2O2 mediates the regulation of ABA catabolism and GA biosynthesis in Arabidopsis seed dormancy and germination

H(2)O(2) is known as a signal molecule in plant cells, but its role in the regulation of aqbscisic acid (ABA) and gibberellic acid (GA) metabolism and hormonal balance is not yet clear. In this study it was found that H(2)O(2) affected the regulation of ABA catabolism and GA biosynthesis during seed imbibition and thus exerted control over seed dormancy and germination. As seen by quantitative RT-PCR (QRT-PCR), H(2)O(2) up-regulated ABA catabolism genes (e.g. CYP707A genes), resulting in a decreased ABA content during imbibition. This action required the participation of nitric oxide (NO), another signal molecule. At the same time, H(2)O(2) also up-regulated GA biosynthesis, as shown by QRT-PCR. When an ABA catabolism mutant, cyp707a2, and an overexpressing plant, CYP707A2-OE, were tested, ABA content was negatively correlated with GA biosynthesis. Exogenously applied GA was able to over-ride the inhibition of germination at low concentrations of ABA, but had no obvious effect when ABA concentrations were high. It is concluded that H(2)O(2) mediates the up-regulation of ABA catabolism, probably through an NO signal, and also promotes GA biosynthesis. High concentrations of ABA inhibit GA biosynthesis but a balance of these two hormones can jointly control the dormancy and germination of Arabidopsis seeds.

Osteoinductive LIM mineralization protein-1 suppresses activation of NF-kappaB and selectively regulates MAPK pathways in pre-osteoclasts

LIM mineralization protein-1 (LMP-1) is an intracellular regulator of bone formation and has been shown to be osteoinductive in vitro and in vivo. The effect of LMP-1 on other aspects of bone homeostasis has not been previously studied. In a pilot study we observed that LMP-1 decreased nitric oxide (NO) production in pre-osteoclasts. Here we report a new anti-inflammatory effect of LMP-1 and define its mechanism of action in lipopolysaccharide (LPS)-stimulated RAW 264.7 pre-osteoclasts. We found that LMP-1 significantly inhibited LPS-induced NO production. LMP-1 also effectively inhibited the expression of inducible nitric oxide synthase (iNOS), potently suppressed the transcriptional activity and nuclear translocation of nuclear factor kappa B (NF-kappaB), and prevented the phosphorylation of inhibitor of kappa B (IkappaB). Interestingly, LMP-1 had no effect on Receptor-Activator of Nuclear Factor B Ligand (RANKL)-induced activation of NF-kappaB. Furthermore, LMP-1 had no effect on the LPS-induced phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), whereas it did attenuate the phosphorylation of c-Jun NH2-terminal kinase (JNK) while enhancing phosphorylation of p38 mitogen-activated protein kinases (p38 MAPK). These results suggest that LMP-1 has an anti-inflammatory effect, and this effect is, at least in part, due to the inhibition of NO production by the suppression of NF-kappaB activation and selective regulation of mitogen-activated protein kinase (MAPK) pathways.

Rapid accumulation of NO regulates ABA catabolism and seed dormancy during imbibition in Arabidopsis

Nitric oxide's (NO) involvement in breaking seed dormancy has been demonstrated in previous research but its action mechanism remains to be clarified. We observed that a rapid accumulation of NO induces an equally rapid decrease of abscisic acid (ABA) that is required for the NO's action in Arabidopsis. In addition, the NO-induced ABA decrease correlates with the regulation of CYP707A2 transcription and the (+)-abscisic acid 8'-hydroxylase (encoded by CYP707A2) protein expression. By analyzing cyp707a1, cyp707a2 and cyp707a3 mutants, we found that CYP707A2 plays a major role in ABA catabolism during the first stage of imbibition. Fluorescent images demonstrate that NO is released rapidly in the early hours at the endosperm layer during imbibition. Evidently such response precedes the enhancement of ABA catabolism which is required for subsequent seed germination.

Effects of the vasodilating beta-blocker nebivolol on smoking-induced endothelial dysfunction in young healthy volunteers

OBJECTIVE

To assess the effect of nebivolol, a highly selective third generation beta1-adrenoceptor antagonist with an endothelium-dependent vasodilatory action, on smoking-induced endothelial dysfunction.

RESEARCH DESIGN AND METHODS

This open-label study examined the effect of 14 daily doses of 5 mg nebivolol on forearm blood flow in 21 healthy, young, male, light smokers (< or =5 cigarettes/day), measured by plethysmography on Days 1, 7, and 14. The primary endpoint was the difference in forearm blood flow after smoking one standard cigarette from baseline (Day 1) until treatment end on Day 14. Secondary outcomes included the difference in forearm blood flow between Day 1 and Day 7 compared with Day 14 before and after smoking, the effect of nebivolol on blood coagulation parameters, high-sensitive-C-reactive protein (hs-CRP), and the safety and tolerability of nebivolol.

RESULTS

Nebivolol for 14 days did not significantly affect forearm blood flow after smoking. On Day 7 of nebivolol treatment, forearm blood flow after smoking was significantly greater than blood flow before smoking (increase of 0.44 mL/min; p = 0.00656). Serum level ofhs-CRP showed a marked decrease from Day 1 to Day 14. No changes in coagulation parameters were observed over the course of nebivolol treatment. Nebivolol was well tolerated throughout the study.

CONCLUSIONS

The increase in forearm blood flow and the marked decrease in hs-CRP over 14 days of treatment suggest that nebivolol has a positive effect on endothelial function in light smokers, but larger studies are required to confirm these observations.

Nitric oxide is involved in nitrate-induced inhibition of root elongation in Zea mays

BACKGROUND AND AIMS

Root growth and development are closely dependent upon nitrate supply in the growth medium. To unravel the mechanism underlying dependence of root growth on nitrate, an examination was made of whether endogenous nitric oxide (NO) is involved in nitrate-dependent growth of primary roots in maize.

METHODS

Maize seedlings grown in varying concentrations of nitrate for 7 d were used to evaluate the effects on root elongation of a nitric oxide (NO) donor (sodium nitroprusside, SNP), a NO scavenger (methylene blue, MB), a nitric oxide synthase inhibitor (N(omega)-nitro-L-arginine, L-NNA), H(2)O(2), indole-3-acetic acid (IAA) and a nitric reducatse inhibitor (tungstate). The effects of these treatments on endogenous NO levels in maize root apical cells were investigated using a NO-specific fluorescent probe, 4, 5-diaminofluorescein diacetate (DAF-2DA) in association with a confocal microscopy.

KEY RESULTS

Elongation of primary roots was negatively dependent on external concentrations of nitrate, and inhibition by high external nitrate was diminished when roots were treated with SNP and IAA. MB and L-NNA inhibited root elongation of plants grown in low-nitrate solution, but they had no effect on elongation of roots grown in high-nitrate solution. Tungstate inhibited root elongation grown in both low- and high-nitrate solutions. Endogenous NO levels in root apices grown in high-nitrate solution were lower than those grown in low-nitrate solution. IAA and SNP markedly enhanced endogenous NO levels in root apices grown in high nitrate, but they had no effect on endogenous NO levels in root apical cells grown in low-nitrate solution. Tungstate induced a greater increase in the endogenous NO levels in root apical cells grown in low-nitrate solution than those grown in high-nitrate solution.

CONCLUSIONS

Inhibition of root elongation in maize by high external nitrate is likely to result from a reduction of nitric oxide synthase-dependent endogenous NO levels in maize root apical cells.

Endothelial cell dysfunction and the vascular complications associated with type 2 diabetes: assessing the health of the endothelium

Diabetes-associated vascular complications are collectively the major clinical problems facing patients with diabetes and lead to the considerably higher mortality rate than that of the general population. People with diabetes have a much higher incidence of coronary artery disease as well as peripheral vascular diseases in part because of accelerated atherogenesis. Despite the introduction of new therapies, it has not been possible to effectively reduce the high cardiovascular morbidity and mortality associated with diabetes. Of additional concern is the recognition by the World Health Organization that we are facing a global epidemic of type 2 diabetes. Endothelial dysfunction is an early indicator of cardiovascular disease, including that seen in type 2 diabetes. A healthy endothelium, as defined in terms of the vasodilator/blood flow response to an endothelium-dependent vasodilator, is an important indicator of cardiovascular health and, therefore, a goal for corrective interventions. In this review we explore the cellular basis for endothelial dysfunction in an attempt to identify appropriate new targets and strategies for the treatment of diabetes. In addition, we consider the question of biomarkers for vascular disease and evaluate their usefulness for the early detection of and their role as contributors to vascular dysfunction.

Induction of cyclo-oxygenase-2 in human endothelial cells by SIN-1 in the absence of prostaglandin production

Nitric oxide (NO) regulates cyclo-oxygenase (COX) activity in various cell systems and reports conflict in regard to its stimulatory versus inhibitory role. Incubation of human umbilical vein endothelial cells (HUVEC) with SIN-1 (3-morpholinosydnonimine), a donor of NO, resulted in a rapid and dose-dependent increase in the expression of COX-2 as analysed by Western and Northern blotting. Incubation of HUVEC with SIN-1 and interleukine (IL)-1alpha resulted in increased induction of COX-2 compared with IL-1alpha alone and corresponded to an additive effect. The COX-2 induction was dependent on a de novo synthesis since cycloheximide, an inhibitor of protein synthesis, blocked the enzyme expression. The increase in COX-2 expression was not accompanied by a corresponding change in prostaglandin (PG) production. However, the COX activity was partially recovered when immunoprecipitated COX-2 was incubated with arachidonic acid and haematin. Peroxynitrite, a highly reactive nitrogen molecule derived from the interaction of NO and superoxide anion, significantly increased COX-2 expression. Under these conditions and within the limit of detection of the antibody, selective antibody for nitrotyrosine failed to detect nitrated COX-2 in immunoprecipitated COX-2 when cells where incubated with SIN-1 or SIN-1+IL-1alpha. Ro 31-8220, a specific inhibitor of protein kinase (PK) C, blocked the induction of COX-2. Also, SB203580, the selective inhibitor of p38 MAP kinase, strongly blocked the induction of COX-2 by SIN-1 in the presence or absence of IL-1alpha, whereas the MEK-1 inhibitor, PD 98059, affected it to a lesser extent. These data demonstrate that SIN-1 induces COX-2 in HUVEC in the absence of PG formation and suggest a complex regulation of COX-2 expression and PG formation by NO in endothelial cells.

Role of free radicals in the pathogenesis of acute chest syndrome in sickle cell disease

Acute chest syndrome (ACS) of sickle cell disease (SCD) is characterized pathologically by vaso-occlusive processes that result from abnormal interactions between sickle red blood cells (RBCs), white blood cells (WBCs) and/or platelets, and the vascular endothelium. One potential mechanism of vascular damage in ACS is by generation of oxygen-related molecules, such as superoxide (O2-), hydrogen peroxide (H2O2), peroxynitrite (ONOO-), and the hydroxyl (*OH) radical. The present review summarizes the evidence for alterations in oxidant stress during ACS of SCD, and the potential contributions of RBCs, WBCs and the vascular endothelium to this process.

Effects of aging and alterations in dietary sodium intake on total nitric oxide production

Animal studies suggest that nitric oxide (NO) deficiency is linked to salt-sensitive hypertension and that NO activity decreases during normal aging. This study investigates the impact of increasing age and manipulations in dietary salt intake on biochemical indices of the NO system in healthy humans. We measured NO(2) + NO(3) (NO(X); stable oxidation products of NO) and cyclic guanosine monophosphate (cGMP; major second messenger) in plasma and urine of 30 healthy subjects aged 22 to 77 years. Subjects were maintained on controlled low NO(X) and low-, normal-, or high-salt diets for 3 days. Salt sensitivity of blood pressure was seen only in the oldest subjects. Plasma renin activity was suppressed by a high salt intake in all age groups, and baseline values declined with advancing age. Neither age nor salt intake correlated with indices of NO activity over the third 24-hour period of controlled salt intake. In a subgroup of subjects aged 33 +/- 4 years challenged with ultrahigh sodium intake (400 mEq/24 h), again there was no increase in NO(2) + NO(3) or cGMP measures. In contrast to animal studies, there is no correlation in humans between either salt intake or age and total NO production and activity, indicated by NO(2) + NO(3) and cGMP measures. This does not preclude undetected alterations occurring in NO production and/or activity in strategic locations in the kidney and cardiovascular system. Limitations of blood and urine measurements of NO(2) + NO(3) and cGMP as indices of NO activity are discussed.

Upregulation of nitric oxide synthase in mice with severe hypoxia-induced pulmonary hypertension

BACKGROUND

The importance of nitric oxide (NO) in hypoxic pulmonary hypertension has been demonstrated using nitric oxide synthase (NOS) knockout mice. In that model NO from endothelial NOS (eNOS) plays a central role in modulating pulmonary vascular tone and attenuating hypoxic pulmonary hypertension. However, the normal regulation of NOS expression in mice following hypoxia is uncertain. Because genetically engineered mice are often utilized in studies of NO, we conducted the present study to determine how hypoxia alters NOS expression in wild-type mice.

METHOD

Mice were exposed to sea level, ambient conditions (5280 feet) or severe altitude (17,000 feet) for 6 weeks from birth, and hemodynamics and lung NOS expression were assessed.

RESULTS

Hypoxic mice developed severe pulmonary hypertension (right ventricular systolic pressure [RVsP] 60 mmHg) as compared with normoxic mice (27 mmHg). Using quantitative reverse-transcription PCR, it was found that expressions of eNOS and inducible NOS (iNOS) increased 1.5-fold and 3.5-fold, respectively, in the lung. In addition, the level of lung eNOS protein was increased, neuronal NOS (nNOS) protein was unchanged, and iNOS was below the limit of detection. Immunohistochemistry demonstrated no change in lung iNOS or nNOS staining in either central or peripheral areas, but suggested increased eNOS in the periphery following hypoxia.

CONCLUSION

In mice, hypoxia is associated with increases in lung eNOS, possibly in iNOS, but not in nNOS; this suggests that the pattern of lung NOS expression following hypoxia must be considered in studies using genetically engineered mice.

Nerve injury induces a rapid efflux of nitric oxide (NO) detected with a novel NO microsensor

An early step in repair of the leech CNS is the appearance of endothelial nitric oxide synthase (eNOS) immunoreactivity and NOS activity, but coincident generation of NO at the lesion after injury has not been shown. This is important because NO can regulate microglial cell motility and axon growth. Indirect measurement of NO with the standard citrulline assay demonstrated that NO was generated within 30 min after nerve cord injury. A polarographic NO-selective self-referencing microelectrode that measures NO flux noninvasively was developed to obtain higher spatial and temporal resolution. With this probe, it was possible to demonstrate that immediately after the leech CNS was injured, NO left the lesion with a mean peak efflux of 803 +/- 99 fmol NO cm(-2) sec(-1). NO efflux exponentially declined to a constant value, as described through the equation f(t) = y(o) + ae(-t/tau), with tau = 117 +/- 30 sec. The constant y(o) = 15.8 +/- 4.5 fmol cm(-2) represents a sustained efflux of NO. Approximately 200 pmol NO cm(-2) is produced at the lesion (n = 8). Thus, injury activates eNOS already present in the CNS and precedes the accumulation of microglia at the lesion, consistent with the hypothesis that NO acts to stop the migrating microglia at the lesion site.

Possible involvement of endothelium-derived hyperpolarizing factor (EDHF) in the depressor responses to platelet activating factor (PAF) in rats

1. In anaesthetized rats, platelet activating factor (PAF; 1 microg kg(-1)) decreased mean arterial blood pressure by around 60 mmHg (n=18). This depressor response was completely blocked by the PAF antagonist, CV-6209 (1 mg kg(-1)), indicating the role of PAF-specific receptor in the response. 2. N(G)-nitro-L-arginine methyl ester (L-NAME; 50 mg kg(-1)), an NO synthase inhibitor, profoundly elevated systemic blood pressure (n=19), indicating an important role of NO in the basal blood pressure regulation. The depressor response to PAF (1 microg kg(-1)) normalized against that to sodium nitroprusside (SNP) (10 microg kg(-1)) was not substantially different between rats treated without and with L-NAME (n=4). In contrast, the depressor effect of acetylcholine (0.03 - 1.0 microg kg(-1)) normalized against that of SNP (10 microg kg(-1)) was significantly attenuated by L-NAME (n=5). 3. Charybdotoxin (0.4 mg kg(-1)) plus apamin (0.2 mg kg(-1)) significantly attenuated the depressor response to PAF (1 microg kg(-1)) (n=5) without affecting the blood pressure change due to SNP (1 mg kg(-1)) (n=3). Charybdotoxin (0.4 mg kg(-1)) (n=4) or apamin (0.2 mg kg(-1)) (n=4) alone did not affect the PAF-induced depressor response. 4. These findings suggest that EDHF may make a significant contribution to the depressor response to PAF in rats. Although NO plays the determinant role in the basal blood pressure regulation, its contribution to PAF-produced depressor response seems to be less as compared with that to the depressor response to acetylcholine.

Endothelium-derived hyperpolarizing factor but not NO reduces smooth muscle Ca2+ during acetylcholine-induced dilation of microvessels

1. We hypothesized that nitric oxide (NO) and the endothelium-dependent hyperpolarizing factor (EDHF) may dilate microvessels by different cellular mechanisms, namely Ca2+-desensitization versus decrease in intracellular free calcium. 2. Effects of acetylcholine (ACh) and the NO donors sodium nitroprusside (SNP, 0.1 - 10 micromol l(-1)) and S-Nitroso-N-acetyl-D, L-penicillamine (SNAP, 0.01 - 10 micromol l-1) on intracellular calcium ([Ca2+]i, fura 2) and vascular diameter (videomicroscopy) were studied in isolated resistance arteries from hamster gracilis muscle (194+/-12 microm) pretreated with indomethacin and norepinephrine. Membrane potential changes were determined using 1, 3-dibutylbarbituric acid trimethineoxonol (DiBAC4(3)). 3. ACh (0.1 and 1 micromol l-1)-induced dilations were associated with a [Ca2+]i decrease (by 13+/-3 and 32+/-4%) and hyperpolarization of vascular smooth muscle (VSM, by 12+/-1% at 1 micromol l-1 ACh). Nomega-nitro-L-arginine (L-NA, 30 micromol l(-1)) partially inhibited the dilation but did not affect VSM [Ca2+]i decreases or hyperpolarization. In contrast, the KCa channel inhibitors tetrabutylammonium (TBA, 1 mmol l(-1)) and charybdotoxin (ChTX, 1 micromol l(-1)) abolished the ACh-induced [Ca2+]i decrease and the hyperpolarization in VSM while a significant dilation remained (25 and 40%). This remaining dilation was abolished by L-NA. ChTX did not affect [Ca2+]i increase and hyperpolarization in endothelial cells. SNP- or SNAP-induced dilations were not associated with decreases in VSM [Ca2+]i or hyperpolarization although minor transient decreases in VSM [Ca2+]i were observed at high concentrations. 4. These data suggest that ACh-induced dilations in microvessels are predominantly mediated by a factor different from NO and PGI2, presumably EDHF. EDHF exerts dilation by activation of KCa channels and a subsequent decrease in VSM [Ca2+]i, NO dilates the microvessels in a calcium-independent manner.

Chronic administration of adenosine A3 receptor agonist and cerebral ischemia: neuronal and glial effects

We have previously shown that chronic administration of the selective A3 receptor agonist N6-(3-iodobenzyl)-5'-N-methylcarboxoamidoadenosine (IB-MECA) leads to a significant improvement of postocclusive cerebral blood flow, and protects against neuronal damage and mortality induced by severe forebrain ischemia in gerbils. Using immunocytochemical methods we now show that chronic with IB-MECA results in a significant preservation of ischemia-sensitive microtubule associated protein 2 (MAP-2), enhancement of the expression of glial fibrillary acidic protein (GFAP), and a very intense depression of nitric oxide synthase in the brain of postischemic gerbils. These changes demonstrate that the cerebroprotective actions of chronically administered IB-MECA involve both neurons and glial cells, and indicate the possibility of distinct mechanisms that are affected in the course of chronic administration of the drug.

Inhibition of the production of endothelium-derived hyperpolarizing factor by cannabinoid receptor agonists

1. The endogenous cannabinoid, anandamide, has been reported to induce an 'endothelium-derived hyperpolarizing factor (EDHF)-like' relaxation in vitro. We therefore investigated the effects of cannabinoid CB1 receptor agonists; HU 210, delta9-tetrahydrocannabinol (delta9-THC) and anandamide, and a CB1 antagonist/inverse agonist, SR 141716A, on nitric oxide (NO) and EDHF-mediated relaxation in precontracted rings of porcine coronary, rabbit carotid and mesenteric arteries. 2. In rings of mesenteric artery HU 210 and delta9-THC induced endothelium- and cyclo-oxygenase-independent relaxations which were sensitive to SR 141716A. Anandamide (0.03-30 microM) induced a slowly developing, endothelium-independent relaxation which was abolished by diclofenac and was therefore mediated by cyclo-oxygenase product(s). None of the CB1 agonists tested affected the tone of precontracted rings of rabbit carotid or porcine coronary artery. 3. In endothelium-intact segments, HU 210, delta9-THC and anandamide did not affect NO-mediated responses but under conditions of continuous NO synthase/cyclo-oxygenase blockade, significantly inhibited acetylcholine and bradykinin-induced relaxations which are attributed to the production of EDHF. The effects of HU 210 and delta9-THC were not observed when experiments were performed in the presence of SR 141716A suggesting the involvement of the CB1 receptor. 4. In a patch clamp bioassay of EDHF production, HU 210 decreased the EDHF-mediated hyperpolarization of detector smooth muscle cells when applied to the donor segment but was without effect on the membrane potential of detector cells. The inhibition of EDHF production was unrelated to alterations in Ca2+ -signalling or cytochrome P450 activity. 5. These results suggest that the activation of endothelial CB1 receptors appears to be negatively coupled to the production of EDHF.

Altered renal expression of nitric oxide synthase isozymes in spontaneously hypertensive rats

OBJECTIVES

The present study was aimed at exploring whether the pathogenesis of hypertension is related with an altered expression of nitric oxide synthase (NOS) isozymes, i.e., bNOS, iNOS and ecNOS.

METHOD

By Western blot analysis, the expression of NOS isozymes were determined in the kidney isolated from spontaneously hypertensive rats (SHR) and their normotensive control, Wistar-Kyoto rats (WKY). The NOx (nitrite/nitrate) contents were also determined in the kidney and plasma.

RESULTS

The plasma NOx was significantly increased in SHR compared with that in WKY. The basal level of NOx was higher in the medulla and cortex of the kidney in SHR compared with that in WKY rat. bNOS proteins were expressed higher in the outer medulla and cortex, and iNOS proteins were higher in the inner medulla, outer medulla and cortex in SHR. ecNOS expression did not significantly differ between the SHR and WKY.

CONCLUSIONS

These results indicate that the NO generation may not be impaired, but rather increased. It is likely that the increased expression of NOS isozymes is a counter-reactive phenomenon secondary to the increased blood pressure in this model of hypertension.

Inhibition by nitric oxide-releasing compounds of prostacyclin production in human endothelial cells

1. The effects of two chemically unrelated nitric oxide (NO)-releasing compounds were studied on prostacyclin production in lipopolysaccharide (LPS)-stimulated human umbilical vein endothelial cells (HUVECs). The cells expressed cyclooxygenase-2 (COX-2) protein and produced prostacyclin by NS-398-sensitive manner suggesting that prostacyclin production derives principally by COX-2 pathway. 2. A novel NO-releasing oxatriazole derivative GEA 3175 (1-30 microm) inhibited LPS-induced production of prostacyclin in HUVECs in a dose-dependent manner being more potent than the earlier known NO-donor S-nitroso-N-acetylpenicillamine (SNAP). 3. The effects of the two NO-donors on prostacyclin synthesis were reversed when red blood cells were added into the culture indicating that the effects are due to NO released from the compounds. 4. Addition of exogenous arachidonic acid into the culture did not alter the inhibitory action of NO-donors suggesting that phospholipases are not the target of action of NO. 5. The NO-donors did not inhibit prostacyclin production in the presence of a selective COX-2 inhibitor NS-398. These data suggest that NO affects COX-2 pathway rather than has an overall effect on cyclooxygenases. 6. NO-releasing compounds did not alter the level of COX-2 protein expression in LPS-treated HUVECs as measured by Western blot analysis. 7. The results suggest that NO-donors inhibit the activity of COX-2 in human endothelial cells. A link between NO and the regulation of eicosanoid synthesis could represent an important mechanism in controlling vascular and inflammatory responses in pathophysiological states and during treatment with nitrovasodilators.

Structural requirements for roxatidine in the stimulant effect of rat gastric mucin synthesis and the participation of nitric oxide in this mechanism

1. The structural requirements of the histamine H2-receptor antagonist, roxatidine (2-acetoxy-N-(3-[m-(1-piperidinylmethyl)phenoxy]-propyl)acetamide hydrochloride), for the stimulant effect on mucin biosynthesis and their relation to histamine H2-receptor antagonism were identified by considering the structural analogues of this drug using an organ culture system of the rat stomach and competition studies with [125I]iodoaminopotentidine ([125I]-APT) binding to membranes of the guinea pig striatum. 2. [3H]Glucosamine incorporation into mucin during 5 h incubation period was stimulated by roxatidine and its structural analogues A (2-hydroxy-N-(3-[m-(1-piperidinylmethyl)phenoxy]-propyl)acetamide) and B (N-(3-[m-(1-piperidinylmethyl)phenoxy]-propyl)acetamide). This effect was seen in mucosal cultures of the corpus, but not antrum, region. 3. Structural analogues, in which the length of the flexible chain between the benzene ring and the amide structure differs from that of roxatidine, failed to activate mucin synthesis. No significant change in mucus synthesis occurred with the addition of analogues in which the piperidine ring attached to the benzene ring via a methylene bridge was changed. 4. Specific [125I]-APT binding to the histamine H2 receptor of guinea pig brain membranes was inhibited by roxatidine and all structural analogues used in this study, except F (N-(3-[m-(N, N-dimethyl-aminomethyl)phenoxy]-propyl)acetamide). 5. Ranitidine at 10(-4) M did not suppress the roxatidine-induced increase in [3H]glucosamine incorporation into mucin. 6. Roxatidine-induced stimulation of [3H]glucosamine incorporation into mucin was completely blocked by the addition of either NG-nitro-L-arginine (10(-5) M) or 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide sodium salt (10(-5) M). The inhibitory action of NG-nitro-L-arginine was totally reversed by L-arginine (5 x 10(-3) M). 7. These results suggest that the cardinal chemical features of roxatidine for the activation of mucin biosynthesis in the corpus region of the rat stomach are the appropriate length of the flexible chain between the amide structure and the aromatic ring system bearing the methylpiperidinyl group at the meta position. The activity of roxatidine and its analogues to stimulate mucin synthesis is not related to their histamine H2 receptor antagonistic activity. Roxatidine-induced activation of mucin biosynthesis in the corpus tissue is mediated by nitric oxide.

Involvement of nitric oxide in the inhibition of angiogenesis by interleukin-2

Interleukin-2 (IL-2), an immunoregulatory cytokine possessing antitumour activity, is an inducer of nitric oxide (NO) synthesis in mice and man. In this study, the possibility that IL-2 possesses antiangiogenic properties that account for its antitumour effects in vivo was examined. IL-2 caused a dose-dependent inhibition of angiogenesis in the chick embryo chorioallantoic membrane (CAM). This inhibition was completely reversed by the NO synthase inhibitor N(G)-nitro-L-arginine methylester (L-NAME). Furthermore, IL-2 was capable of stimulating NO synthase activity in the CAM in vitro and this effect was suppressed by L-NAME. Addition of IL-2 to human umbilical vein endothelial cells (HUVECs) in culture, had no effect on their growth characteristics. These results suggest that IL-2 may be an important antiangiogenic molecule causing its effect via nitric oxide synthesis. The antiangiogenic activity of IL-2 may be, at least in part, responsible for its antitumour properties.

Evidence for a role for nitric oxide in relation of the frog oesophageal body to electrical field stimulation

1. Electrical field stimulation (EFS) (1-10 Hz, 30 V, 2 ms) of frog oesophageal body strips resulted in frequency-dependent non-adrenergic, non-cholinergic (NANC) relaxations. 2. Tetrodotoxin (TTX) (10(-6)-10(-5) M) had no effect on EFS evoked relaxations with a 2 ms pulse width. At a pulse width of 0.5 ms only the responses to the highest frequency (10 Hz) were significantly inhibited by TTX at 10(-5) M. Relaxation at 2 ms pulse width were unaffected by omega-conotoxin (10(-6) M), nifedipine (10(-6) M) or cobalt (5 x 10(-4) M). 3. NG-nitro-L-arginine (L-NOARG) (10(-6)-10(-4) M), a nitric oxide synthase (NOS) inhibitor, caused a concentration-dependent inhibition of the EFS-induced NANC relaxant responses. The inhibitory effect of L-NOARG was both prevented and reversed by L-arginine but not D-arginine (5 x 10(-3) M). 4. The phosphodiester type V inhibitor (PDE V), SK&F 96231 (10(-7)-10(-4) M), caused a concentration-dependent potentiation of both the percentage relaxation and the duration of the relaxant responses to EFS. 5. ODQ (10(-7)-10(-5) M), a guanylate cyclase inhibitor, produced a concentration-dependent inhibition of EFS-evoked NANC relaxations. 6. Oxyhaemoglobin (10(-6) M), which binds nitric oxide (NO), inhibited NANC relaxations to EFS. 7. The NO donor sodium nitroprusside (SNP) (10(-8)-10(-4) M) produced a concentration-dependent inhibition of evoked tone. L-NOARG (10(-4) M) had no effect on the SNP evoked relaxations. Preincubation with oxyhaemoglobin (10(-6) M) caused a reduction in the SNP (10(-6)-10(-5) M) induced relaxations. 8. These results suggest NO is the relaxant transmitter of the frog oesophageal body and the source of NO may be non-neuronal.

Central role of intracellular calcium stores in acute flow- and agonist-evoked endothelial nitric oxide release

1. We have used a cascade bioassay system and isolated arterial ring preparations to investigate the contribution of Ca2+ release from endothelial intracellular stores to nitric oxide (NO) production evoked by increases in shear stress and by acetylcholine in rabbit aorta. 2. Experiments were performed before and following incubation with either the endoplasmic reticulum Ca(2+)-ATPase inhibitors cyclopiazonic acid (CPA, 10 microM) and thapsigargin (TSG, 1 microM) or ryanodine (30, 100 microM) which binds to a specific endoplasmic reticulum Ca(2+)-release channel. 3. In cascade bioassay all three agents induced relaxations of the recipient ring (CPA, 24.4 +/- 3.8%; TSG, 51.5 +/- 10.6%; ryanodine, 17.4 +/- 1.6%) which were significantly attenuated by preincubation of the donor with 100 microM NG-nitro-L-arginine methyl ester (L-NAME). However, in isolated rings, only CPA and TSG induced L-NAME-sensitive relaxations (CPA 52.7 +/- 6.5%; TSG 61.3 +/- 7%). 4. Addition of superoxide dismutase (SOD) to the donor perfusate evoked relaxations of the recipient ring in cascade bioassay (13.3 +/- 1.4%, n = 22). Prior administration of SOD attenuated relaxations to TSG (23.2 +/- 3.8% n = 4) and ryanodine (1.7 +/- 0.8%, n = 4), and pre-incubation with TSG and ryanodine blunted SOD-induced responses (4 +/- 1.5%, n = 4 and 8.9 +/- 1.1%, n = 4, respectively). By contrast, no interaction was observed between the relaxations evoked by SOD and CPA. In isolated rings, SOD exerted no direct relaxant and did not modulate relaxations to CPA, TSG or ryanodine. 5. In cascade bioassay studies time-averaged shear stress was manipulated with dextran (1-4% w/v, 800000 MW) to increase perfusate viscosity. NO-dependent relaxation of the recipient ring induced by increased perfusate viscosity was significantly attenuated by CPA (P < 0.01; n = 6) and TSG (P < 0.05; n = 7), but not by ryanodine (n = 6). 6. Endothelium-dependent relaxations to acetylcholine (0.1-30 microM) in cascade bioassay and in isolated aortic ring preparations were markedly attenuated by pretreatment with CPA and TSG, but were unaffected by ryanodine. Ryanodine and CPA caused only a small attenuation of endothelium-independent relaxations to sodium nitroprusside (0.001-10 microM), whereas TSG had no effect. 7. We conclude that release of Ca2+ from CPA- and TSG-sensitive endothelial stores is necessary for NO release evoked by acute flow changes and agonists in rabbit abdominal aorta. Ca(2+)-induced Ca2+ release via the ryanodine-sensitive release channel plays no direct role in these responses. Free radical interactions may complicate the interpretation of findings in cascade bioassay compared with isolated ring preparations.

NG-nitro-L-arginine methyl ester inhibits bone metastasis after modified intracardiac injection of human breast cancer cells in a nude mouse model

We investigated the effects of NG-nitro-L-arginine-methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, on bone metastasis of human breast cancer, MDA-231 cells. Tumor cells (2 x 10(5) cells in 0.2 ml of phosphate-buffered saline; PBS) were injected through the diaphragm into the left ventricle of the heart of laparotomized nude mice (male 5-week-old ICR-nu/nu). L-NAME (2 mg/mouse/injection in 0.1 ml of PBS) was given intraperitoneally to mice 6 h and 3 h before and immediately, 3 h, 6 h, 18 h and 21 h after the intracardiac injection of tumor cells. As a control, 0.1 ml of PBS was injected instead of L-NAME. The effect of NG-nitro-D-arginine-methyl ester (D-NAME; 2 mg/mouse/injection), an inactive analogue of L-NAME, was also investigated to evaluate the specificity of L-NAME action. Radiographical examination 31 days after the tumor-cell injection showed that the incidence and number of osteolytic bone metastases and the number of bones with metastasis in L-NAME-treated mice were significantly reduced compared with those in PBS-treated mice (P < 0.05). The differences between PBS-treated and D-NAME-treated mice were not significant. Our findings suggest that specific and appropriate NOS inhibitors may represent a new pharmacological approach to therapy for cancer patients at risk of developing osteolytic bone metastases.

Inhibitory effect of a new steroidal saponin, OSW-1, on ovarian functions in rats

1. This study was undertaken to determine the effects of OSW-1 (3 beta, 16 beta, 17 alpha-trihydroxycholest-5-en-22-one 16-O-(2-O-4-methoxybenzoyl-beta-D-xylopyranosyl)- (1-->3)-(2-O-acetyl-alpha-L-arabinopyranoside)) on the pituitary-ovarian system and the functions of aortic smooth muscle. 2. A single s.c. injection of OSW-1 (9 micrograms kg-1) on the morning of pro-oestrus inhibited the occurrence of the expected next pro-oestrus, whereas administration of OSW-1 at a dose of 4.5 micrograms kg-1 did not affect the oestrous cycle. OSW-1 treatment on the day of dioestrus-1 did not affect the oestrous cycle. 3. At doses of 4.5 and 9 micrograms kg-1 OSW-1, the serum oestradiol (E2) levels at the expected next pro-oestrus were significantly lower than in control (pro-oestrus). The serum luteinizing hormone (LH) levels 4 days after 9 micrograms kg-1 OSW-1 treatment were also markedly lower than those of control. OSW-1 (4.5 micrograms kg-1) did not affect the levels of inhibin, progesterone and gonadotrophins on the same day. 4. OSW-1 did not inhibit the preovulatory LH surge which occurs on the afternoon of pro-oestrus day. 5. The expression of mRNA coding for the cholesterol side chain cleavage cytochrome P-450 (p450scc), an ovarian steroidal limiting enzyme, was suppressed at 24 and 96 h after OSW-1 treatment. 6. Administration of OSW-1 (9 micrograms kg-1) tended to reduce the relaxation of isolated thoracic aorta ring preparations induced by acetylcholine, while there was no difference in the relaxation induced by sodium nitroprusside. 7. Our results show that OSW-1 inhibits ovarian E2 secretion and that the decrease in E2 secretion may contribute to its effects on the oestrous cycle and the sensitivity of the thoracic aorta to relaxation. The decrease in the levels of ovarian steroids induced by OSW-1 may be due to its direct inhibitory action on the gene expression of the steroidal enzyme and on the proliferation of granulosa cells in the ovary.

The induction of nitric oxide-mediated relaxation of human isolated pulmonary arteries by PACAP

1. The effects of pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) were analysed in human isolated circular segments of pulmonary arteries. Guinea-pig pulmonary arteries were used for comparison. The responses obtained were analysed in relation to the vascular endothelium and the nitric oxide (NO) synthase inhibitor NG-monomethyl L-arginine (L-NMMA). 2. PACAP and VIP induced concentration-dependent relaxations of precontracted pulmonary arteries. The maximal dilator response (Imax, %) and the potency (pEC50 value) were the same for both peptides, and there were no differences in the effects obtained on human and guinea-pig segments. PACAP and VIP were both more potent that acetylcholine (ACh). 3. Removal of the vascular endothelium abolished the PACAP induced dilator response in pulmonary arteries from both species. The VIP induced dilatation was unaffected, whereas the response to ACh was abolished. L-NMMA given before PACAP inhibited the dilatation. Furthermore, L-NMMA also reversed the dilatation already induced by PACAP and excess concentrations of L-arginine restored the dilator response of the L-NMMA treated arteries. 4. PACAP is a potent dilator of human pulmonary arteries. Although the dilator effect seems to be similar in amplitude to the one induced by VIP, the present results suggest differences in the underlying mechanisms of action (endothelium-dependency) between the two peptides.

Mechanism of nitric oxide-induced contraction in the rat isolated small intestine

1. The contractile response to nitric oxide (NO) in ral ileal myenteric plexus-longitudinal muscle strips was pharmacologically analysed. 2. NO (10(-7) M) induced only contraction while 10(-6) M NO induced contraction followed by relaxation. Methylene blue (up to 10(-4) M) did not affect the NO-induced contractions but significantly reduced the relaxation evoked by 10(-6) M NO. Administration of 8-bromo-cyclic GMP (10(-6)-10(-4) M) only induced relaxation. 3. Sodium nitroprusside (SNP; 10(-7)-10(-5) M) induced concentration-dependent contractions per se; the contractile response to NO, administered within 10 min after SNP, was concentration-dependently reduced. The guanosine 3':5'-cyclic monophosphate (cyclic GMP) content of the tissues was not increased during contractions with 10(-8) M NO and 10(-6) M SNP; it was increased by a factor of 2 during contraction with 10(-7) M NO, and by a factor of 12 during relaxation with 3 x 10(-6) M NO. 4. The NO-induced contractions were not affected by ryanodine (3 x 10(-5) M) but were concentration-dependently reduced by nifedipine (10(-8)-10(-7) M) and apamin (3 x 10(-9)-3 x 10(-8) M). 5. These results suggest that cyclic GMP is not involved in the NO-induced contraction in the rat small intestine. The NO-induced contraction is related to extracellular Ca2+ influx through L-type Ca2+ channels, that might be activated in response to the closure of Ca(2+)-dependent K+ channels.

Effect of N omega-nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor, on stress- and morphine-induced prolactin release in male rats

1. The effect of the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) was investigated on stress- and morphine-induced prolactin (PRL) secretion in vivo in male rats, by use of a stress-free blood sampling and drug administration method by means of a permanent indwelling catheter in the right jugular vein. 2. Three doses of L-NAME were tested (1, 10 and 30 mg kg-1) and were given intraperitoneally one hour before blood sampling; control rats received saline. After the first blood sample, rats received an initial intravenous injection of morphine (3, 6 or 12 mg kg-1) or were subjected to immobilization stress. In the case of a morphine administration, rats received a second dose of morphine (3, 6 or 6 mg kg-1, respectively) 90 min later, when tolerance had developed, while rats subjected to immobilization stress received 6 mg kg-1 morphine 90 min after onset of stress. 3. L-NAME had no effect on basal plasma PRL concentration. However, it potentiated acute morphine-induced PRL secretion and attenuated the subsequent tolerance in a dose-dependent way. Immobilization stress-induced PRL secretion was inhibited dose-dependently by L-NAME, as was its subsequent tolerance to morphine; however, in this case, in a reversed dose-dependent way. 4. When the highest dose of morphine (12 mg kg-1) was combined with the highest dose of L-NAME pretreatment (30 mg kg-1), all rats showed a dramatic potentiation of the morphine-induced PRL rise compared to controls. Moreover, all of these rats died within 90 min after the administration of morphine. 5. These results show that NO plays a role in the acute opioid action on PRL release during stress as well as in the development of tolerance to the opioid effect, and some possible mechanisms are discussed.