nitroarginine and 1-3-dihydroxy-4-4-5-5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole

Shear stress or vasocontriction causes endothelial nitric oxide (NO) release resulting in the regulation of vascular smooth muscle tone in small resistance arteries. Generation of NO is inhibited by nitric oxide synthase (NOS) inhibitors. In this study, we investigated the effect of residual NO, released even in the presence of NOS inhibitors, on the membrane depolarization and phenylephrine-induced contractions of smooth muscle. For this purpose, we used hydroxocobalamin (HC), an NO scavenger, in the presence of NOS inhibitiors, Nω-nitro- L-arginine (L-NA) or Nω-nitro-L-arginine methyl ester (L-NAME) in mesenteric arteries isolated from rats. Phenylephrine (0,01-10 μM), an α

Topics: Adrenergic alpha-1 Receptor Agonists; Animals; Benzoates; Free Radical Scavengers; Hydroxocobalamin; Imidazoles; Male; Membrane Potentials; Mesenteric Arteries; Muscle Contraction; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Phenylephrine; Protein Kinase Inhibitors; Rats, Wistar

Stress induced by ultraviolet-B (UV-B) irradiation stimulates the accumulation of various secondary metabolites in plants. Nitric oxide (NO) serves as an important secondary messenger in UV-B stress-induced signal transduction pathways. NO can be synthesized in plants by either enzymatic catalysis or an inorganic nitrogen pathway. The effects of UV-B irradiation on the production of baicalin and the associated molecular pathways in plant cells are poorly understood. In this study, nitric oxide synthase (NOS) activity, NO release and the generation of baicalin were investigated in cell suspension cultures of Scutellaria baicalensis exposed to UV-B irradiation. UV-B irradiation significantly increased NOS activity, NO release and baicalin biosynthesis in S. baicalensis cells. Additionally, exogenous NO supplied by the NO donor, sodium nitroprusside (SNP), led to a similar increase in the baicalin content as the UV-B treatment. The NOS inhibitor, Nω-nitro-l-arginine (LNNA), and NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) partially inhibited UV-B-induced NO release and baicalin accumulation. These results suggest that NO is generated by NOS or NOS-like enzymes and plays an important role in baicalin biosynthesis as part of the defense response of S. baicalensis cells to UV-B irradiation.

Topics: Benzoates; Cells, Cultured; Enzyme Inhibitors; Flavonoids; Imidazoles; Molecular Structure; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Plant Cells; Scutellaria baicalensis; Signal Transduction; Time Factors; Ultraviolet Rays

Nitric oxide (NO) is known to be involved in associative memory formation. We investigated the influence of blocking NO function on the reconsolidation of context memory in terrestrial snails (Helix lucorum L.). After a 10 day session of electric shocks in one context only, context memory in snails was observed in test sessions as the significant difference of amplitudes of withdrawal responses to tactile stimuli in two different contexts. After a 1 day rest, a session of 'reminding' was performed, preceded by injection in different groups of the snails with either vehicle or combination of the protein synthesis blocker anisomycin (ANI) with one of the following drugs: the NO scavenger carboxy-PTIO, the NO-synthase inhibitors N-omega-nitro-L-arginin, nitroindazole and NG-nitro-L-arginine methyl ester hydrochloride, or the NO donor S-nitroso-N-acetyl-DL-penicillamine. Testing the context memory at different time intervals after the reminder under ANI injection showed that the context memory was impaired at 24 h and later, whereas the reminder under combined injection of ANI and each of the NO-synthase inhibitors used or the NO scavenger showed no impairment of long-term context memory. Injection of the NO donor S-nitroso-N-acetyl-DL-penicillamine with or without reminder had no effect on context memory. The results obtained demonstrated that NO is necessary for labilization of a consolidated context memory.

Topics: Animals; Anisomycin; Benzoates; Electroshock; Enzyme Inhibitors; Free Radical Scavengers; Helix, Snails; Imidazoles; Indazoles; Memory; Motor Activity; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroarginine; Protein Synthesis Inhibitors; S-Nitroso-N-Acetylpenicillamine; Time Factors

Nitric oxide (NO) is a signaling molecule that mediates many plant responses to biotic and abiotic stresses, including salt stress. Interestingly, salinity increases NO production selectively in mesophyll cells of sorghum leaves, where photosynthetic C₄ phosphoenolpyruvate carboxylase (C₄ PEPCase) is located. PEPCase is regulated by a phosphoenolpyruvate carboxylase-kinase (PEPCase-k), which levels are greatly enhanced by salinity in sorghum. This work investigated whether NO is involved in this effect. NO donors (SNP, SNAP), the inhibitor of NO synthesis NNA, and the NO scavenger cPTIO were used for long- and short-term treatments. Long-term treatments had multifaceted consequences on both PPCK gene expression and PEPCase-k activity, and they also decreased photosynthetic gas-exchange parameters and plant growth. Nonetheless, it could be observed that SNP increased PEPCase-k activity, resembling salinity effect. Short-term treatments with NO donors, which did not change photosynthetic gas-exchange parameters and PPCK gene expression, increased PEPCase-k activity both in illuminated leaves and in leaves kept at dark. At least in part, these effects were independent on protein synthesis. PEPCase-k activity was not decreased by short-term treatment with cycloheximide in NaCl-treated plants; on the contrary, it was decreased by cPTIO. In summary, NO donors mimicked salt effect on PEPCase-k activity, and scavenging of NO abolished it. Collectively, these results indicate that NO is involved in the complex control of PEPCase-k activity, and it may mediate some of the plant responses to salinity.

Topics: Benzoates; Cycloheximide; Imidazoles; Iron; Models, Biological; Nitric Oxide; Nitroarginine; Nitroprusside; Plant Leaves; Plant Stomata; Protein Serine-Threonine Kinases; Salinity; Sodium Chloride; Sorghum; Stress, Physiological

Nitric oxide (NO) plays a key role in many physiological processes in plants, including pollen tube growth. Here, effects of NO on extracellular Ca(2+) flux and microfilaments during cell wall construction in Pinus bungeana pollen tubes were investigated. Extracellular Ca(2+) influx, the intracellular Ca(2+) gradient, patterns of actin organization, vesicle trafficking and cell wall deposition upon treatment with the NO donor S-nitroso-N-acetylpenicillamine (SNAP), the NO synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NNA) or the NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) were analyzed. SNAP enhanced pollen tube growth in a dose-dependent manner, while L-NNA and cPTIO inhibited NO production and arrested pollen tube growth. Noninvasive detection and microinjection of a Ca(2+) indicator revealed that SNAP promoted extracellular Ca(2+) influx and increased the steepness of the tip-focused Ca(2+) gradient, while cPTIO and L-NNA had the opposite effect. Fluorescence labeling indicated that SNAP, cPTIO and L-NNA altered actin organization, which subsequently affected vesicle trafficking. Finally, the configuration and/or distribution of cell wall components such as pectins and callose were significantly altered in response to L-NNA. Fourier transform infrared (FTIR) microspectroscopy confirmed the changes in the chemical composition of walls. Our results indicate that NO affects the configuration and distribution of cell wall components in pollen tubes by altering extracellular Ca(2+) influx and F-actin organization.

Topics: Actin Cytoskeleton; Benzoates; Calcium; Cell Wall; Extracellular Space; Germination; Glucans; Imidazoles; Intracellular Space; Models, Biological; Nitric Oxide; Nitroarginine; Pectins; Pinus; Pollen Tube; Polymerization; Pyridinium Compounds; Quaternary Ammonium Compounds; S-Nitroso-N-Acetylpenicillamine; Spectroscopy, Fourier Transform Infrared; Staining and Labeling; Time Factors

Long-term depression (LTD) of the parallel fiber-Purkinje cell synapse in the cerebellum is a cellular model system that has been suggested to underlie certain forms of motor learning. Induction of cerebellar LTD requires a postsynaptic kinase limb involving activation of mGluR1, protein kinase Calpha (PKCalpha), and phosphorylation of ser-880 on the AMPA receptor subunit GluR2. Several lines of evidence have also implicated a complementary phosphatase limb in which N-methyl-d-aspartate (NMDA) receptor-mediated Ca(2+) influx activates neuronal nitric oxide synthase (nNOS), the ultimate consequences of which are mediated by nitric oxide (NO), cGMP, and inhibition of postsynaptic protein phosphatases. However, the cellular localization of an NMDA/NO cascade has been complicated by the fact that neither functional NMDA receptors nor nNOS are expressed in Purkinje cells. This has lead to a proposal in which NMDA receptors activate nNOS in parallel fibers. Here, we confirm that pharmacological blockade of NMDA receptor or NO signaling blocks induction of LTD. However, no evidence was found for functional NMDA receptors in parallel fiber terminals: blockade of NMDA receptors did not alter either presynaptic Ca(2+) transients or the frequency of miniature excitatory postsynaptic currents. NMDA receptor blockade did abolish a slow depolarization evoked by burst stimulation of parallel fiber-stellate cell synapses. The application of NMDA evoked a Ca(2+) transient in stellate cell terminals but not in parallel fiber terminals. These results are consistent with the hypothesis that an NMDA receptor/NO cascade involved in cerebellar LTD is localized to interneurons rather than parallel fibers.

Topics: 2-Amino-5-phosphonovalerate; Animals; Animals, Newborn; Baclofen; Benzoates; Cadmium Chloride; Cerebellum; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; GABA Agonists; GABA Antagonists; Imidazoles; In Vitro Techniques; Long-Term Potentiation; Magnesium; Models, Neurological; N-Methylaspartate; Nerve Fibers; Nerve Tissue Proteins; Nitric Oxide; Nitroarginine; Phosphinic Acids; Propanolamines; Purkinje Cells; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Synapses; Time Factors

We examined modulation by nitric oxide (NO) of sympathetic neurotransmitter release and vasoconstriction in the isolated pump-perfused rat kidney. Electrical renal nerve stimulation (RNS; 1 and 2 Hz) increased renal perfusion pressure and renal norepinephrine (NE) efflux. Nonselective NO synthase (NOS) inhibitors [N(omega)-nitro-L-arginine methyl ester (L-NAME) or N(omega)-nitro-L-arginine], but not a selective neuronal NO synthase inhibitor (7-nitroindazole sodium salt), suppressed the NE efflux response and enhanced the perfusion pressure response. Pretreatment with L-arginine prevented the effects of L-NAME on the RNS-induced responses. 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), which eliminates NO by oxidizing it to NO(2), suppressed the NE efflux response, whereas the perfusion pressure response was less susceptible to carboxy-PTIO. 8-Bromoguanosine cGMP suppressed and a guanylate cyclase inhibitor [4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one] enhanced the RNS-induced perfusion pressure response, but neither of these drugs affected the NE efflux response. These results suggest that endogenous NO facilitates the NE release through cGMP-independent mechanisms, NO metabolites formed after NO(2) rather than NO itself counteract the vasoconstriction, and neuronal NOS does not contribute to these modulatory mechanisms in the sympathetic nervous system of the rat kidney.

Topics: Animals; Benzoates; Cyclic GMP; Electric Stimulation; Enzyme Inhibitors; Imidazoles; In Vitro Techniques; Indazoles; Kidney; Male; Nervous System; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitroarginine; Norepinephrine; Oxadiazoles; Oxazines; Perfusion; Pressure; Rats; Rats, Wistar

Beta amyloid (Abeta) is implicated in Alzheimer's disease (AD). Abeta(1 - 42) (5, 10, or 20 microM) was able to increase NO release and decrease cellular viability in primary rat cortical mixed cultures. L-NOARG and SMTC (both at 10 or 100 microM) - type I NOS inhibitors - reduced cellular NO release in the absence of Abeta(1 - 42). At 100 microM, both drugs decreased cell viability. L-NIL (10 or 100 microM), and 1400W (1 or 5 microM) - type II NOS inhibitors - reduced NO release and improved viability when either drug was administered up to 4 h post Abeta(1 - 42) (10 microM) treatment. L-NOARG and SMTC (both at 10 or 100 microM) were only able to decrease NO release. Carboxy-PTIO or Trolox (both at 10 or 100 microM) - a NO scavenger and an antioxidant, respectively - increased viability when administered up to 1 h post Abeta(1 - 42) treatment. Either L-NIL (50 microM) or 1400W (3 microM) and Trolox (50 microM) showed synergistic actions. Peroxynitrite (100 or 200 microM) reduced cell viability. Viabilities were improved by L-NIL (100 microM), 1400W (5 microM), carboxy-PTIO (10 or 100 microM), and Trolox (10 or 100 microM). Hence, the data show that Abeta(1 - 42) induced NO release in neurons and glial cells, and that Abeta neurotoxicity is, at least in part, mediated by NO. NO concentration modulating compounds and antioxidant may have therapeutic importance in neurological disorders where oxidative stress is likely involved such as in AD.

Topics: Amyloid beta-Peptides; Animals; Antioxidants; Benzoates; Cell Survival; Cells, Cultured; Cerebral Cortex; Chromans; Citrulline; Dose-Response Relationship, Drug; Enzyme Inhibitors; Imidazoles; Isoenzymes; Lysine; Neuroprotective Agents; Nitrates; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Oxidants; Peptide Fragments; Rats; Rats, Sprague-Dawley; Thiourea; Time Factors

The effects on the nicotinic activation of the coeliac plexus neurons of nitric oxide (NO) released within the coeliac plexus by gastric mechanoreceptors, in particular during gastroduodenal inhibitory reflex, were assessed. This study was performed in the rabbit on an in vitro preparation of the coeliac plexus connected to the stomach and the duodenum. The electrical activity of ganglionic neurons was recorded with intracellular recording techniques. Water-filled balloons were used for gastric distensions and recording of duodenal motility. When a 10-s train of pulses (20-40Hz) of supramaximal intensity was applied to the splanchnic nerves, gradual depression of nicotinic activation occurred. Gastric distension (50 mL, 7.5 min) modulated this depression phenomenon by inhibiting or facilitating the nicotinic activation. In the neurons impaled during the recording of duodenal motility, gastric distension triggered an inhibition of nicotinic activation concomitantly with a gastroduodenal inhibitory reflex organized by the coeliac plexus. If the gastric distensions were performed while the coeliac plexus was superfused by a NO scavenger, the nicotinic activation was unaffected and the gastroduodenal inhibitory reflex was abolished. Moreover, when the coeliac plexus was superfused with an inhibitor of nitric oxide synthase, gastric distensions were without effect on the nicotinic activation. These results demonstrate that NO released within the coeliac plexus by gastric mechanoreceptors, in particular during the gastroduodenal inhibitory reflex, modulates the central nicotinic activation of coeliac plexus neurons, so NO released within a prevertebral ganglion by gastric afferent fibres, in particular during the organization by this ganglion of a reflex regulating the gastrointestinal tract motility, also exerts a gating of the central inputs to the ganglionic neurons.

Topics: Animals; Benzoates; Celiac Plexus; Duodenum; Electric Stimulation; Enzyme Inhibitors; Female; Ganglia, Sympathetic; Gastric Emptying; Gastrointestinal Motility; Imidazoles; Male; Mechanoreceptors; Neural Inhibition; Neurons; Nicotine; Nicotinic Agonists; Nitric Oxide; Nitroarginine; Rabbits; Splanchnic Nerves; Stomach; Synaptic Transmission

We examined the effects of the calcitonin gene-related peptide (CGRP), including the possible participation of nitric oxide (NO), on mucin biosynthesis in the surface epithelium and remaining deep mucosa as well as the entire mucosa and compared the distribution of CGRP and NO synthase (NOS) using a combination of double immunofluorescence labeling and multiple dye filter. Pieces of tissue obtained from the corpus and antrum were incubated in a medium containing [(3)H]glucosamine and CGRP, with or without the NOS inhibitor. CGRP dose-dependently enhanced [(3)H]glucosamine incorporation into the corpus mucin but had no effect on antral mucin biosynthesis. The CGRP receptor antagonist, CGRP-(8-37), prevented the increase in (3)H-labeled corpus mucin. This stimulation of corpus mucin synthesis disappeared after removal of the surface mucus cell layer. CGRP activated the mucin biosynthesis in the surface mucus cells. In the full-thickness corpus mucosa, CGRP-induced activation was completely blocked by the NOS inhibitor. CGRP-immunoreactive fibers were intertwined within the surface mucus cell layer with type I NOS immunoreactivity. These results show that CGRP-stimulated mucin biosynthesis mediated by NO is limited to surface mucus cells of the rat gastric oxyntic mucosa.

Topics: Animals; Antibodies; Benzoates; Calcitonin Gene-Related Peptide; Enzyme Inhibitors; Fluorescent Antibody Technique, Indirect; Glucosamine; Imidazoles; Male; Mucins; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Parietal Cells, Gastric; Peptide Fragments; Pyloric Antrum; Rats; Rats, Wistar; Tritium

Although epidermal growth factor (EGF) accelerates gastric mucin biosynthesis, information on whether its activation is limited to the specific mucus-producing cells is lacking. In this paper, we investigated the effects of EGF on mucin biosynthesis and the expression of its receptor in distinct layers of rat gastric mucosa, including the possible participation of nitric oxide (NO). EGF enhanced the incorporation of [3H]glucosamine and [14C]threonine into the mucin in the full-thickness tissues of the gastric mucosa. This stimulation disappeared on the removal treatment of the surface mucosal layer chiefly consisting of surface mucus cells. The EGF-induced increase in [3H]-labeled mucin in the full-thickness mucosa was not suppressed by either NG-nitro-L-arginine (10(-5) M) or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (10(-5) M). The EGF-receptor-mRNA expression was high in the surface mucosal layer but low in the deep and muscle layers of the stomach. These results suggest that EGF-induced stimulation of mucin biosynthesis is limited to the surface mucus cells of the rat gastric mucosa and is independent of the NO pathway.

Topics: Animals; Benzoates; Culture Techniques; Enzyme Inhibitors; Epidermal Growth Factor; ErbB Receptors; Gastric Mucosa; Humans; Imidazoles; Male; Mucins; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Wistar; Recombinant Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Stimulation, Chemical

1. The coeliac plexus can organize a gastroduodenal inhibitory reflex without action potentials. The involvement of the nitric oxide-cGMP pathway in this reflex was investigated in the rabbit on an in vitro preparation of the coeliac plexus connected to the stomach and duodenum. Intraluminal duodenal pressures were measured with water-filled balloons. Gastric distension inhibited duodenal motility, thus characterizing a gastroduodenal inhibitory reflex organized by the coeliac plexus. 2. L-Arginine, superfused at the coeliac plexus level, enhanced this reflex, whereas Nomega-nitro-L-arginine (L-NOARG) or 2-(4-carboxyphenyl)-4,4,5,5 tetramethylimidazoline-1-oxyl-3-oxide (carboxy PTIO) reduced or abolished it. Moreover, diethylamine/nitric oxide complex superfused at the coeliac plexus level inhibited duodenal motility in the absence of gastric distension. 3. The effects of nitric oxide were mediated through the activation of guanylyl cyclase, as 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) reduced or abolished the gastroduodenal inhibitory reflex, whereas zaprinast enhanced it. Moreover, 8-bromo-cGMP and cGMP, superfused at the coeliac plexus level, inhibited duodenal motility in the absence of gastric distension. 4. On the other hand, when perfused at the visceral level, L-NOARG, propranolol plus phentolamine, and guanethidine did not affect the reflex. Thus, neither nitric oxide nor noradrenaline could be the transmitters released at the muscular level to induce this reflex. 5. Our study demonstrates that the gastroduodenal inhibitory reflex, which is organized by the coeliac plexus without action potentials, is induced by the release within the plexus of nitric oxide acting on the cGMP pathway. These results provide new insights into the control of digestive motility by the prevertebral ganglia.

Topics: Action Potentials; Animals; Arginine; Benzoates; Celiac Plexus; Cyclic GMP; Duodenum; Enzyme Inhibitors; Female; Gastrointestinal Motility; Imidazoles; Male; Muscle, Smooth; Nitric Oxide; Nitroarginine; Oxadiazoles; Quinoxalines; Rabbits; Reflex; Stomach

Relaxation induced by NANC-nerve stimulation is reduced by nitric oxide synthase (NOS) inhibitors but not by superoxide generators or NO scavengers, casting doubts on the precise nature of the neurotransmitter being released by these nerves. The lack of effect of superoxide anion generators to inhibit nitrergic nerve-mediated relaxations has been attributed to the protective action of high tissue levels of superoxide dismutase (SOD). The effects of hydroquinone, hydroxocobalamin and carboxy-PTIO, three NO inactivators which do not depend on superoxide anion generation, upon nitrergic nerve-mediated relaxations of the rat proximal duodenum were determined in order to elucidate whether they are mediated by free NO. GABA and nicotine caused relaxations of isolated segments of the rat proximal duodenum in a concentration-dependent manner that were abolished by tetrodotoxin (TTX). Similarly, transmural electrical stimulation (TES) caused frequency-dependent relaxations that were also abolished by TTX. The NOS inhibitors L-NAME and L-NOARG reduced in a concentration-dependent manner nerve-mediated relaxations elicited by TES, nicotine and GABA. The effect of NOS inhibitors was prevented by L-arginine but not D-arginine. NO caused concentration-dependent relaxations that were not affected by TTX or L-NOARG but were abolished by hydroquinone, hydroxocobalamin and carboxy-PTIO. In contrast, these compounds failed to affect TES-, nicotine- and GABA-induced relaxations. The lack of effect of hydroquinone, hydroxocobalamin and carboxy-PTIO upon nerve-mediated relaxations was unaltered by pretreatment with the SOD irreversible inhibitor DETCA. The present findings show that nitrergic nerve-mediated relaxations of the rat duodenum are unaffected by NO inactivators that do not generate superoxide anion. It is suggested that either a NO-containing molecule that is unreactive with the inactivators tested is the inhibitory neurotransmitter released by nitrergic nerves or that NOS activity fulfills another role in nitrergic nerves which could be related to the release of an still unidentified transmitter.

Topics: Animals; Autonomic Nervous System; Benzoates; Duodenum; Electric Stimulation; gamma-Aminobutyric Acid; Hematinics; Hydroquinones; Hydroxocobalamin; Imidazoles; Male; Muscle Relaxation; Muscle, Smooth; NG-Nitroarginine Methyl Ester; Nitroarginine; Rats; Rats, Wistar

The present study was designed to examine the role of basally released nitric oxide in relaxations to an ATP-sensitive K+ channel opener. Whether relaxations to levcromakalim are modulated by endothelial removal or the inhibitors of vasodilator effects of endothelium-derived nitric oxide, were investigated in the rat aorta. During contractions to phenylephrine (3 x 10(-7) to 10(-6) M), levcromakalim (10(-8) to 10(-5) M) or a nitric oxide donor, 1-hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC-7, 10(-9) to 10(-5) M), was added in a cumulative fashion. Relaxations to levcromakalim (10(-8) to 10(-5) M) were significantly reduced by the endothelium-removal. In aortas with endothelium, relaxations in response to levcromakalim were decreased by selective inhibitors of nitric oxide synthase (N(G)-nitro-L-arginine methyl ester, 10(-4) M) and soluble guanylate cyclase (1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one; ODQ, 10(-5) M) and a scavenger of nitric oxide (carboxy-PTIO, 10(-3) M). Relaxations to levcromakalim in aortas treated with these inhibitors are comparable to those seen in aortas without endothelium. KCl (30 mM) and an ATP-sensitive K+ channel inhibitor, glibenclamide (10(-5) M), abolished relaxations to levcromakalim in aortas with or without endothelium, whereas glibenclamide did not alter relaxations to NOC-7 (10(-9) to 10(-5) M) in aortas without endothelium. These results suggest that in rat aortas, inhibition of vasodilator effects of basally released nitric oxide can reduce relaxations via ATP-sensitive K+ channels, although these channels do not mediate relaxations to exogenously applied nitric oxide.

Topics: Animals; Aorta, Thoracic; ATP-Binding Cassette Transporters; Benzoates; Cromakalim; Endothelium, Vascular; Enzyme Inhibitors; Glyburide; Guanylate Cyclase; Hydrazines; Imidazoles; KATP Channels; Male; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroarginine; Potassium Channels; Potassium Channels, Inwardly Rectifying; Rats; Rats, Inbred WKY; Vasodilator Agents

The effects of agents which affect the action of nitric oxide (NO) were studied intracellularly on the ischemia-induced changes in membrane potential of single CA1 pyramidal neurons of the rat hippocampal slice preparations. The N-methyl-D-aspartate (NMDA) receptor antagonists, (+/-)-2-amino-5-phosphonopentanoic acid (AP5, 250 microM) or Co2 (2 mM) restored the membrane potential in more than 80% of the neurons. In about 60% of the neurons, the membrane potential was partially recovered as a result of exposure to the NO synthase inhibitor, NG-nitro-L-arginine (100 microM). The NO scavengers, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO, 300 microM) and hemoglobin (10 microM) restored the membrane potential in all neurons examined. Superoxide dismutase (50 U/ml) protected about 75% of the neurons from irreversible membrane dysfunction. It is concluded that the release of NO induced by experimental ischemia may result in the irreversible membrane dysfunction, and that a NO scavenger, carboxy-PTIO, prevents the ischemic changes in membrane potential. With respect to ischemic brain damage, the neuroprotection provided by carboxy-PTIO may have clinical relevance in the management of a variety of neurological conditions.

Topics: 2-Amino-5-phosphonovalerate; Animals; Benzoates; Cell Membrane; Cobalt; Glucose; Hemoglobins; Hippocampus; Hypoxia; Imidazoles; In Vitro Techniques; Ischemic Attack, Transient; Male; Membrane Potentials; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Pyramidal Cells; Rats; Rats, Wistar; Reaction Time; Receptors, N-Methyl-D-Aspartate; Superoxide Dismutase

The present study was designed to determine the influence of endogenous acetylcholine and nitric oxide (NO) on spontaneous luminal serotonin (5-hydroxytryptamine, 5-HT) release in the luminally perfused isolated guinea-pig proximal colon in vitro. 5-HT was determined by high-performance liquid chromatography with electro-chemical detection. The luminal outflow of 5-HT was significantly reduced by atropine (0.2 microM), hexamethonium (100 microM), the NO synthase inhibitor NG-nitro-L-arginine (L-NNA, 10 microM) and the NO-trapping agent 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (carboxy-PTIO, 30 microM). Addition of excess L-arginine (300 microM) reversed the inhibitory effect of L-NNA on the 5-HT outflow. Physostigmine (1 microM) caused a great increase (atropine-sensitive) in 5-HT outflow. The enhancing action of physostigmine on 5-HT outflow was partially inhibited by L-NNA (100 microM) or carboxy-PTIO (30 microM), but was unaffected by the muscarinic M1 receptor antagonist pirenzepine (0.2 microM) or a muscarinic M3 receptor antagonist 4-diphenyl-acetoxy-N-methyl-piperidine methiodide (0.2 microM). These results suggest that 5-HT release from luminally perfused proximal colon of the guinea pig is stimulated via a NO pathway and cholinergic pathways which utilize muscarinic synapses and nicotinic synapses. Further, an intrinsic cholinergic-NO link appears to play a role in the stimulation of luminal 5-HT release, which may reflect the release of 5-HT from entero-chromaffin cells.

Topics: Acetylcholine; Animals; Arginine; Atropine; Benzoates; Cholinesterase Inhibitors; Colon; Enzyme Inhibitors; Guinea Pigs; Imidazoles; In Vitro Techniques; Male; Muscarinic Antagonists; Nicotinic Antagonists; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Physostigmine; Serotonin

The effect of i.v. administration of the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NNA) on tumor blood flow compared with normal tissue blood flow was studied in anesthetized BD9 rats bearing subcutaneous P22 carcinosarcomas. Blood flow was measured by the tissue uptake of radiolabeled iodoantipyrine. The reversibility of blood flow changes was tested by subsequent administration of L-arginine, the natural substrate for NOS. The effect of L-NNA was compared to that of the imidazolineoxyl N-oxide C-PTIO, a carboxyl derivative of 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide and a nitric oxide scavenger. Drug-induced changes in mean arterial blood pressure (MABP) were monitored and used to calculate relative drug-induced changes in tissue vascular resistance. Heart rate was measured from blood pressure traces. L-NNA significantly decreased heart rate and increased MABP in a dose-dependent manner. Significant dose-dependent reductions in blood flow with L-NNA were observed in tumor, skeletal muscle, spleen, and skin overlying the tumor. No significant effect was found for normal skin, brain, heart, kidney, and small intestine. At 1 mg/kg, the effect of L-NNA was selective for the tumor, with a significant decrease in tumor blood flow to 0.45 of the control level and no significant effect in any of the normal tissues. Higher doses did not produce any further reduction in tumor blood flow, presumably due to an increase in tumor perfusion pressure arising from the increase in MABP at these doses. Vascular resistance was increased to some extent in all of the tissues studied but, overall, was greatest in the tumor. At 1 mg/kg, there was a 2-2.5-fold increase in tumor vascular resistance but no significant increase in any of the normal tissues. At the highest dose used (10 mg/kg), the increases in vascular resistance in the skeletal muscle and spleen were equivalent to that in the tumor. Administration of L-arginine 15 min after L-NNA completely reversed the decrease in tumor blood flow observed for 1 mg/kg L-NNA alone. In contrast to the effect of L-NNA, constant i.v. infusion of C-PTIO had no effect on tumor or normal tissue blood flow. These results indicate that nitric oxide is important for maintaining a vasodilatory tone in tumors and that inhibition of NOS may provide a means for enhancing therapeutic regimens that would benefit from a selective reduction in tumor blood flow.

Topics: Animals; Arginine; Benzoates; Blood Pressure; Enzyme Inhibitors; Heart Rate; Imidazoles; Male; Neoplasm Transplantation; Neoplasms, Experimental; Nitric Oxide Synthase; Nitroarginine; Rats; Regional Blood Flow

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.

Topics: Animals; Benzoates; Enzyme Inhibitors; Free Radical Scavengers; Gastric Mucosa; Histamine H2 Antagonists; Imidazoles; Male; Mucins; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Piperidines; Ranitidine; Rats; Rats, Wistar; Receptors, Histamine H2

This study was undertaken to determine whether atrial natriuretic peptide (ANP)-, C-type natriuretic peptide (CNP)-, and nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathways exist in the rat retina. Exposure of the retina to ANP (10(-7)M), CNP (10(-7)M), S-nitroso-N-acetylpenicillamine (10(-5)M, SNAP; a NO doner), A23187 (10(-5)M; a Ca2+ionophore), and carbachol (10(-5)M) caused 1.45-1.67 fold increases in cGMP content (p < 0.01). Carboxy-PTIO (10(-3)M; a NO scavanger) blocked the increase in cGMP induced by A23187. Both carboxy-PTIO (10(-3)M) and NG-nitro-L-arginine (10(-3)M, L-NNA; a NO inhibitor) blocked the increase in cGMP induced by carbachol. Atropine (10(-5)M; a muscarinic receptor antagonist) also blocked the cGMP increase induced by carbachol. These data demonstrate that ANP-, CNP- and NO-cGMP pathways exist in the retina and that the NO-cGMP pathway may be linked to the activation of the muscarinic receptor.

Topics: Animals; Atrial Natriuretic Factor; Atropine; Benzoates; Calcimycin; Carbachol; Cyclic GMP; Imidazoles; In Vitro Techniques; Ionophores; Male; Natriuretic Peptide, C-Type; Nitric Oxide; Nitroarginine; Penicillamine; Proteins; Rats; Rats, Wistar; Retina; S-Nitroso-N-Acetylpenicillamine