Efficiency of two nitrification inhibitors (dicyandiamide and 3, 4-dimethypyrazole phosphate) on soil nitrogen transformations and plant productivity: a meta-analysis.

Dicyandiamide (DCD) and 3, 4-dimethypyrazole phosphate (DMPP) are often claimed to be efficient in regulating soil N transformations and influencing plant productivity, but the difference of their performances across field sites is less clear. Here we applied a meta-analysis approach to compare effectiveness of DCD and DMPP across field trials. Our results showed that DCD and DMPP were equally effective in altering soil inorganic N content, dissolve inorganic N (DIN) leaching and nitrous oxide (N2O) emissions. DCD was more effective than DMPP on increasing plant productivity. An increase of crop yield by DMPP was generally only observed in alkaline soil. The cost and benefit analysis (CBA) showed that applying fertilizer N with DCD produced additional revenues of $109.49 ha(-1) yr(-1) for maize farms, equivalent to 6.02% increase in grain revenues. In comparisons, DMPP application produced less monetary benefit of $15.67 ha(-1) yr(-1). Our findings showed that DCD had an advantage of bringing more net monetary benefit over DMPP. But this may be weakened by the higher toxicity of DCD than DMPP especially after continuous DCD application. Alternatively, an option related to net monetary benefit may be achieved through applying DMPP in alkaline soil and reducing the cost of purchasing DMPP products.

Minimizing nitrous oxide in biological nutrient removal from municipal wastewater by controlling copper ion concentrations.

In this study, nitrous oxide (N(2)O) production during biological nutrient removal (BNR) from municipal wastewater was reported to be remarkably reduced by controlling copper ion (Cu(2+)) concentration. Firstly, it was observed that the addition of Cu(2+) (10-100 µg/L) reduced N(2)O generation by 54.5-73.2 % and improved total nitrogen removal when synthetic wastewater was treated in an anaerobic-aerobic (with low dissolved oxygen) BNR process. Then, the roles of Cu(2+) were investigated. The activities of nitrite and nitrous oxide reductases were increased by Cu(2+) addition, which accelerated the bio-reductions of both nitrite to nitric oxide (NO (2) (-) → NO) and nitrous oxide to nitrogen gas (N(2)O → N(2)). The quantitative real-time polymerase chain reaction assay indicated that Cu(2+) addition increased the number of N(2)O reducing denitrifiers. Further investigation showed that more polyhydoxyalkanoates were utilized in the Cu(2+)-added system for denitrification. Finally, the feasibility of reducing N(2)O generation by controlling Cu(2+) was examined in two other BNR processes treating real municipal wastewater. As the Cu(2+) in municipal wastewater is usually below 10 µg/L, according to this study, the supplement of influent Cu(2+) to a concentration of 10-100 µg/L is beneficial to reduce N(2)O emission and improve nitrogen removal when sludge concentration in the BNR system is around 3,200 mg/L.

Anti-inflammatory effects of Cynanchum taiwanianum rhizome aqueous extract in IL-1ß-induced NRK-52E cells.

CONTEXT: Cynanchum taiwanianum T. Yamaza (Asclepiadaceae) is a medicinal herb used in folk medicine for the treatment of several inflammation-related diseases such as hepatitis and dermatitis in Taiwan. OBJECTIVE: In the present study, we investigated the anti-inflammatory effect of C. taiwanianum T. Yamaza rhizome aqueous extract (CTAE). MATERIALS AND METHODS: The present study investigated the anti-inflammatory effect of CTAE using IL-1ß-induced NRK-52E cells. Production of NO and PGE(2) by ELISA, the mRNA and protein expression of iNOS and COX-2, phosphorylation of IκBα, and activation of NF-κB by RT-PCR and western blotting were determined. RESULTS: The CTAE significantly (P < 0.05) inhibited NO and PGE(2) production (decreased by 46.1% and 51%, respectively), and also significantly (P < 0.05) attenuated protein and mRNA expression of iNOS and COX-2 (decreased by 90% and 55% for iNOS and by 72% and 74%% for COX-2, respectively) in IL-1ß-induced NRK-52E cells, in a dose-dependent manner, without obvious cytotoxic effects. Furthermore, the CTAE suppressed the NF-κB nuclear translocation, in terms of inhibition of IκBα phosphorylation. DISCUSSION AND CONCLUSION: Our results provided evidence for its folkloric uses and suggest that the anti-inflammatory activities of CTAE may result from the inhibition of inflammatory mediators, such as NO and PGE(2), and an upstream suppression of a NF-κB-dependent mechanism, might be involved.

Amlodipine ameliorates endothelial dysfunction in mesenteric arteries from spontaneously hypertensive rats.

1. Endothelial dysfunction plays a critical role in the development and progression or pathogenesis of hypertension. Amlodipine, a calcium channel blocker, is an effective antihypertensive agent. We investigated the effects of amlodipine on endothelial dysfunction in mesenteric arteries from spontaneously hypertensive rats (SHR). 2. Eight-week-old SHR were treated with amlodipine (10 mg/kg per day) for 8 weeks. Control SHR and Wistar-Kyoto (WKY) rats were treated with saline. Systolic blood pressure (SBP) was measured by the tail-cuff method. Isometric tension changes of isolated mesenteric arterial rings were recorded continuously by a myograph system. Serum contents of malondialdehyde (MDA) and total nitrate/nitrite (NO(x) ) were determined. Vascular superoxide anion production was analysed with dihydroethidium (DHE) fluorescence. 3. The contractile responses to KCl and phenylephrine were greater in untreated SHR than in WKY. Acetylcholine (ACh)-induced relaxation was significantly impaired in untreated SHR. Amlodipine treatment reduced the contractions and improved relaxation to ACh. In WKY, relaxation to ACh was inhibited by N(G) -nitro-l-arginine methyl ester (l-NAME) and not changed by ascorbic acid. In untreated SHR, the response to ACh was unaffected by l-NAME, whereas it was improved by ascorbic acid. Amlodipine restored the inhibitory effect of l-NAME on ACh-induced relaxation, but ascorbic acid no longer exerted its facilitating effect. Amlodipine prevented the rise in SBP and ameliorated abnormalities in serum MDA and NO in untreated SHR. DHE assay showed an increased intravascular superoxide generation in untreated SHR, which was abrogated by amlodipine. 4. Treatment of SHR with amlodipine resulted in amelioration of endothelial dysfunction by anti-oxidant activity and improvement in NO availability.

Antagonism of the antinociceptive effect of nitrous oxide by inhibition of enzyme activity or expression of neuronal nitric oxide synthase in the mouse brain and spinal cord.

Previous studies have implicated nitric oxide (NO) in the antinociceptive response to the anesthetic gas nitrous oxide (N(2)O). The present study was conducted to confirm this NO involvement using pharmacological and gene knockdown and knockout strategies to inhibit the supraspinal and spinal production of NO. Antinociceptive responsiveness to 70% N(2)O was assessed using the acetic acid (0.6%) abdominal constriction test in NIH Swiss mice following intracerebroventricular (i.c.v.) or intrathecal (i.t.) pretreatment with the NOS-inhibitor l-N(G)-nitro arginine methyl ester (L-NAME) or an antisense oligodeoxynucleotide (AS-ODN) directed against neuronal NOS (nNOS). Experiments were also conducted in mice homozygous for a defective nNOS gene (nNOS(-/-)). Mice that were pretreated i.c.v. or i.t. with L-NAME (1.0 microg) both exhibited 80-90% reduction in the magnitude of the N(2)O-induced antinociceptive response. Mice that were pretreated i.c.v. or i.t. with nNOS AS-ODN (3 x 25microg) exhibited a 60-80% antagonism of the antinociceptive response. Compared to wild-type mice, nNOS knockout mice showed a 60% reduction in N(2)O-induced antinociception. These findings consistently demonstrate that transient or developmental suppression of nNOS expression significantly reduces antinociceptive responsiveness to N(2)O. NO of both supraspinal and spinal origin, therefore, plays an important role in the antinociceptive response to N(2)O.

Nociceptin receptor antagonist JTC-801 inhibits nitrous oxide-induced analgesia in mice.

The mechanism of the analgesic effect of nitrous oxide (N(2)O) has not been completely clarified. Although we have reported that the analgesic effect of N(2)O was significantly decreased in nociceptin-orphanin FQ (N/OFQ) receptor (NOP)-deficient mice, the effect of nociceptin receptor antagonists on N(2)O-induced analgesia has not been reported. In this investigation, we examined the effect of the NOP antagonist JTC-801 on N(2)O-induced analgesia in 129Sv mice by the writhing test and tail flick test, and demonstrated that the analgesic effect of N(2)O was suppressed by the intraperitoneal administration of JTC-801.

In vitro effects of nitric oxide synthase inhibitor L-NAME on oral squamous cell carcinoma: a preliminary study.

It has been reported that increased nitric oxide synthase (NOS) expression and nitric oxide (NO) production may play an important role in cancer biology. The aim of this study was to determine the roles of NO in tumour cellular proliferation and DNA or RNA synthesis, and to investigate the therapeutic potential of NOS inhibitors in oral cancer. After exposure to different concentrations of the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), the growth of TSCCa cells, established from a patient with squamous cell carcinoma of the tongue, was evaluated using MTT and crystal violet assay. DNA or RNA synthesis, inducible/endothelial NOS (iNOS/eNOS) mRNA expression and NO production were then examined to determine the possible mechanisms of inhibitory effects of L-NAME on TSCCa cells. L-NAME had an inhibitory effect on TSCCa cell growth in both a concentration- and time-dependent manner. Acridine orange staining revealed that DNA and/or RNA synthesis of TSCCa cells was reduced after treatment with L-NAME. An in situ hybridisation (ISH) study showed clearly that L-NAME down-regulated eNOS and iNOS mRNA expression and this was followed by a decrease in NO production. It is postulated that the NOS/NO pathway may be implicated in cellular proliferation and DNA or RNA synthesis of cancer cells, apart from promoting tumour angiogenesis. Further studies have provided with new insight into the mechanisms by which NOS/NO takes part in oral carcinogenesis, and possible therapeutic interventions based on the NOS/NO pathway for tumour progression control.

General anesthetics inhibit the nitrous-oxide-induced activation of corticotropin releasing factor containing neurons in rats.

The activation of intracerebral corticotropin releasing factor (CRF) system is involved in nitrous oxide analgesia. We evaluated the effect of general anesthetics on nitrous-oxide-induced CRF activation and antinociception. Male Sprague-Dawley rats inhaled isoflurane (0%, 0.6%, 1.0% and 1.5%) or were administered with intravenous propofol (0, 0.1 and 0.2 mg/kg/min), with or without 75% nitrous oxide inhalation, for 90 min. The brain was fixed with fixative, and brain sections, including the paraventricular nucleus of the hypothalamus, were double immunostained with c-Fos and CRF antibodies to assess the activation of CRF-containing neurons. In other groups of rats, the effect of propofol on nitrous oxide antinociception was evaluated with tail flick latency tests. Both inhaled isoflurane and intravenous propofol inhibited nitrous-oxide-induced activation of CRF neurons, suggesting that these general anesthetics may inhibit one of the analgesic mechanisms of nitrous oxide. Indeed, propofol inhibited the antinociceptive action of nitrous oxide, as evaluated with tail flick latencies (TFL).

Antagonism of nitrous oxide-induced anxiolytic-like behavior in the mouse light/dark exploration procedure by pharmacologic disruption of endogenous nitric oxide function.

RATIONALE: Previous studies have shown the anxiolytic-like effects of nitrous oxide (N(2)O) to be sensitive to antagonism by non-specific inhibitors of nitric oxide synthase (NOS). OBJECTIVES: The present study was conducted to demonstrate further the involvement of nitric oxide (NO) and ascertain whether a specific isoform of NOS is involved in N(2)O-induced behavior in mice. METHODS: Male NIH Swiss mice were tested in the light/dark exploration test to determine how N(2)O-induced behavior was affected by the following pretreatments: the NO scavenger hemoglobin (Hb); the selective nNOS-inhibitor S-methyl- l-thiocitrulline (SMTC); the selective eNOS-inhibitor N(5)-(1-iminoethyl)- l-ornithine ( l-NIO); and the selective iNOS-inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT). Furthermore, NOS activity was assessed in the whole brain as well as five brain areas of N(2)O- versus room air-exposed mice to determine the effects of N(2)O on NOS activity. RESULTS: The behavioral effects of N(2)O in the light/dark exploration test were significantly attenuated following pretreatment with Hb (2.0 nmol, i.c.v.), SMTC (0.3 micro g and 1.0 micro g per mouse, i.c.v.) and the higher dose of l-NIO (30 mg/kg, s.c.). However, the N(2)O-induced behavioral effect was unaltered by pretreatment with either the lower dose of l-NIO (10 mg/kg, s.c.) or AMT (1.0 mg/kg and 3.0 mg/kg, s.c.). Finally exposure to 50% N(2)O for 15 min significantly increased NOS activity in the cerebellum and corpus striatum but not in other brain regions or whole brain. CONCLUSION: These findings provide further support for the hypothesis that NO is involved in N(2)O-induced anxiolytic-like behavior and that this NO is the product of nNOS enzyme activity.

Dicyandiamide and 3,4-dimethyl pyrazole phosphate decrease N2O emissions from grassland but dicyandiamide produces deleterious effects in clover.

The application of nitrogen fertilisers leads to different ecological problems such as nitrate leaching and the release of nitrogenous gases. N2O is a gas involved in global warming, therefore, agricultural soils can be regarded as a source of global warming. Soil N2O production comes from both the nitrification and denitrification processes. From an ecological viewpoint, using nitrification inhibitors with ammonium based fertilisers may be a potential management strategy to lower the fluxes of N2O, thus decreasing its undesirable effect. In this study, the nitrification inhibitors (NIs) dicyandiamide (DCD) and 3,4-dimethyl pyrazole phosphate (DMPP) have been evaluated as management tools to mitigate N2O emissions from mineral fertilisation and slurry application in grassland systems (experiments 1 and 2), and to assess the phytotoxic effect of these inhibitors per se on clover (experiment 3). Both nitrification inhibitors acted in maintaining soil nitrogen (N) in ammonium form, decreasing cumulative N2O emissions. DCD, but not DMPP, produced phytotoxic effects and yield reduction in white clover. A nutrient imbalance, which led to a senescence process visually observed as chlorosis and necrosis at the border of the leaves, was noted.

Suppressive effect of nitrous oxide on motor evoked potentials can be reversed by train stimulation in rabbits under ketamine/fentanyl anaesthesia, but not with additional propofol.

The effect of nitrous oxide on myogenic motor evoked potentials (MEPs) after multipulse stimulation is controversial. We investigated the effects of propofol in this paradigm. MEPs were elicited electrically by a single pulse and by trains of three and five pulses in rabbits anaesthetized with ketamine and fentanyl. Nitrous oxide 30-70% was given and MEPs were recorded. After washout of nitrous oxide, propofol was given as a bolus of 10 mg kg(-1) followed by 0.8 (n=9) or 1.6 mg kg(-1) min(-1) (n=8) as a continuous infusion. Nitrous oxide was then re-administered and MEPs were recorded. Without propofol, nitrous oxide significantly reduced the amplitude of MEPs dose-dependently, but this effect was reversed by multipulse stimulation. Administration of low-dose propofol enhanced nitrous oxide-induced suppression, and this effect was reversed by five-pulse stimulation. However, high-dose propofol produced a greater increase in suppression, such that even five-pulse stimulation did not overcome the suppression. The results suggest that the degree of reversal of nitrous oxide-induced MEP suppression produced by multipulse stimulation is affected by the administration of propofol.

Antagonism of nitrous oxide antinociception in mice by intrathecally administered antisera to endogenous opioid peptides.

Previously it was demonstrated that nitrous oxide antinociception in the mouse abdominal constriction test is mediated by kappa-opioid receptors. Since nitrous oxide is thought to cause the neuronal release of endogenous opioid peptide to stimulate opioid receptors, this study was designed to identify the opioid peptides involved, especially in the spinal cord, by determining whether nitrous oxide antinociception can be differentially inhibited by intrathecally (i. t.) administered antisera to different opioid peptides. Male NIH Swiss mice were pretreated i.t. with rabbit antisera to opioid peptides then exposed 24 h later to one of three different concentrations of nitrous oxide in oxygen. Dose-response curves constructed from the data indicated that the antinociceptive effect of nitrous oxide was significantly antagonized by antisera to various dynorphins (DYNs) and methionine-enkephalin (ME), but not by antiserum to beta-endorphin (beta-EP). The AD(50) values for nitrous oxide antinociception were significantly elevated by antisera to DYNs and ME but not beta-EP. These findings of this study support the hypothesis that nitrous oxide antinociception in the mouse abdominal constriction test involves the neuronal release of DYN and ME in the spinal cord.

The analgesic action of nitrous oxide is dependent on the release of norepinephrine in the dorsal horn of the spinal cord.

BACKGROUND: The authors and others have demonstrated that supraspinal opiate receptors and spinal alpha2 adrenoceptors are involved in the analgesic mechanism for nitrous oxide (N2O). The authors hypothesize that activation of opiate receptors in the periaqueductal gray results in the activation of a descending noradrenergic pathway that releases norepinephrine onto alpha2 adrenoceptors in the dorsal horn of the spinal cord. METHODS: The spinal cord was transected at the level of T3-T4 in rats and the analgesic response to 70% N2O in oxygen was determined by the tail flick latency test. In a separate experiment in rats a dialysis fiber was positioned transversely in the dorsal horn of the spinal cord at the T12 level. The following day, the dialysis fiber was infused with artificial cerebrospinal fluid at a rate of 1.3 microl/min, and the effluent was sampled at 30-min intervals. After a 60-min equilibration period, the animals were exposed to 70% N2O in oxygen. The dialysis experiment was repeated in animals that were pretreated with naltrexone (10 mg/kg, intraperitoneally) before N2O. In a third series, spinal norepinephrine was depleted with n-(2-chloroethyl)-n-ethyl-2-bromobenzylamine (DSP-4), and the analgesic response to 70% N2O in oxygen was determined. RESULTS: The analgesic effect of N2O was prevented by spinal cord transection. After exposure to N2O, there was a fourfold increase in norepinephrine released in the first 30-min period, and norepinephrine was still significantly elevated after 1 h of exposure. The increased norepinephrine release was prevented by previous administration of naltrexone. Depletion of norepinephrine in the spinal cord blocked the analgesic response to N2O. CONCLUSIONS: A descending noradrenergic pathway in the spinal cord links N2O-induced activation of opiate receptors in the periaqueductal gray, with activation of alpha2 adrenoceptors in the spinal cord. N2O-induced release of norepinephrine in the dorsal horn of the spinal cord is blocked by naltrexone, as is the analgesic response. Spinal norepinephrine is necessary for the analgesic response to the N2O.

Effects of naloxone on nitrous oxide actions in healthy volunteers.

A number of studies have examined the effects of naloxone on nitrous oxide-induced analgesia with conflicting results. In the present study the effects of a relatively high dose of naloxone was examined to determine its effects on nitrous oxide-induced analgesia, as well as on the subjective and psychomotor effects of nitrous oxide. Fourteen subjects participated in a four-session crossover trial in which they received intravenous injections of either saline or 30mg/70kg naloxone 10min into a 35min period in which they were inhaling either 100% oxygen or 30% nitrous oxide in oxygen. Ten minutes after the naloxone administration, subjects were tested on the cold pressor test. Mood and psychomotor performance were also assessed before, during and after the inhalation period. Subjects reported higher pain ratings after the naloxone injection than the saline injection, but there was no evidence of naloxone reversing the analgesic effects of nitrous oxide. Similarly while naloxone also affected mood and impaired psychomotor performance, there was no evidence of naloxone reversing the effect of nitrous oxide on these measures. The results of this study call into question the role of the opioidergic system in mediating various effects of nitrous oxide in humans.

[Effects of anesthetics on somatosensory evoked potentials by median nerve stimulation in human--analyses after single administration in volunteers].

In the present study, effects of midazolam, thiopental sodium, propofol, and nitrous oxide upon SEP in a clinically used dose were investigated on 24 male volunteers. In addition, antagonistic actions of flumazenil and naloxone against effects of midazolam and nitrous oxide, respectively, on SEP were studied. Midazolam had no effect on latencies of N 20 and P 25, but increased latency of P 45 and attenuated P 100 amplitude. Flumazenil reversed these effects of midazolam of P 45 latency and P 100 amplitude to their control values. While thiopental sodium and propofol suppressed P 100 amplitude, they had no effect on N 20, P 25, P 45 latencies. Nitrous oxide elongated latencies of N 20, P 25, P 45 and decreased P 100 amplitude. Naloxone reversed the effects of nitrous oxide on N 20 and P 25 latencies without affecting increased P 45 latency and attenuated P 100 amplitude. These results suggest that midazolam might have an analgesic action of suppressing cortical sensory neurons, whereas thiopental sodium and propofol have no effect on neurons in the primary sensory cortex. The finding that naloxone antagonized the increased latencies of N 20 and P 25 by nitrous oxide could be explained by the analgesic action of nitrous oxide that could be mediated by opioid receptors. The results also indicate that electrical activities of the cortical neurons in the associated area are more susceptible to psychotropic agents than those in the primary sensory cortex. The effects of anesthetics on SEP appear to reflect their characteristics of functioning mechanisms on cortical neurons. Analysis of SEP is, therefore, useful for the assessment of the mechanism and the acting site of anesthetics in the sensory cortex.

Opiate receptors in the periaqueductal gray mediate analgesic effect of nitrous oxide in rats.

The site of action and the pathways which are activated by nitrous oxide (N2O) to produce an analgesic effect are not well defined. Experiments were designed to determine whether N2O produces analgesia by activating opiate receptors or alpha2-adrenoceptors in periaqueductal gray. The analgesic effect of N2O was determined using the tail flick response to noxious radiant heat in lightly anesthetized rats. Different antagonists were bilaterally microinjected into ventrolateral periaqueductal gray to determine whether the analgesic effect produced by N2O was reversed. The increase in the tail flick latencies produced by N2O was reversed by bilateral microinjection into the ventrolateral part of periaqueductal gray with the opiate receptor antagonist naloxone 2.5 microg/0.5 microl, but not with the alpha2-adrenoceptors antagonist yohimbine 1.5 microg/0.5 microl. These results indicate that the N2O analgesic effect is mediated by activation of opiate receptors, but not alpha2-adrenoceptors, in the periaqueductal gray. Combined with the previous experiments that the N2O analgesic effect is reversed by intrathecal injection of an alpha2-adrenoceptor antagonist but not by an opiate receptor antagonist, it seems likely that N2O causes activation of the opiate receptors in the periaqueductal gray, which in turn activate the noradrenergic descending pathways to the spinal cord to produce the analgesic effect.

Visual evoked potentials and nitrous oxide-induced neuronal depression: role for benzodiazepine receptors.

We have examined the role of benzodiazepine receptors in nitrous oxide-induced neuronal depression in rats. The changes in neuronal excitability induced by nitrous oxide and the benzodiazepine inverse agonist, Ro15-4513, were monitored by measurement of visual evoked potentials (VEP). Administration of Ro15-4513 10 mg kg-1 i.p., in rats breathing air, did not affect the amplitude or latency of VEP. However, the same concentrations of Ro15-4513 antagonized nitrous oxide-induced depression of VEP amplitudes. We conclude that antagonism of nitrous oxide-induced depression by Ro15-4513 indicates that at least part of the decreased neuronal excitability caused by nitrous oxide could be ascribed to interactions with the GABAA receptor complex.

Volatile anaesthetics antagonize nitrous oxide and morphine-induced analgesia in the rat.

We reported previously that nitrous oxide induces pre-emptive analgesia that is partially antagonized by naloxone and totally antagonized by halothane. The aims of this study were to determine if halothane and isoflurane are similar in this respect and to examine if volatile anaesthetics antagonize the analgesic effect of exogenous opioids. We found that 75% nitrous oxide prolonged tail-flick latency by 37% and this analgesia was dose-dependently inhibited by halothane and, less effectively, by isoflurane. In contrast, morphine 1.25 mg kg-1 i.v. also prolonged tail-flick latency by 35% but, unlike nitrous oxide-induced analgesia, this effect was attenuated only by high doses of halothane and was unaffected by isoflurane. Neither halothane nor isoflurane alone altered the tail-flick response. We conclude that both halothane and isoflurane dose-dependently antagonized nitrous oxide analgesia but antagonized morphine-induced analgesia to a lesser extent.