sodium-nitrite and linsidomine

Peroxynitrite and heme peroxidases (or heme)-H

Topics: Acetophenones; Anthracenes; Antioxidants; Circular Dichroism; Flavonoids; Heme; Hydrogen Peroxide; Indicators and Reagents; Kinetics; Molsidomine; Oxidants; Oxidation-Reduction; Peroxynitrous Acid; Phytochemicals; Protein Processing, Post-Translational; Protein Structure, Secondary; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Sodium Nitrite; Triose-Phosphate Isomerase; Tyrosine

Falcipain-2 (FP2) is an important hemoglobinase from the malaria parasite Plasmodium falciparum and a suitable target for the development of an antimalarial chemotherapy. Many reports have indicated that radical nitrogen species (RNS) including nitric oxide (NO) are inhibitors of P. falciparum growth and promoters of recovery from malaria symptoms. In this scenario, FP2 emerges as a potential target of RNS, since its inhibition partially hinders the parasite growth. We report that in vitro FP2 did not undergo S-nitrosylation when exposed to the NO-donor GSNO. However, it was modified by a combined mechanism of methionine oxidation and tyrosine nitration in response to SIN-1, and NaNO2- H2O2 treatment. The treatments with the nitrating agents caused a pronounced decrease in protease activity most likely induced by a disruption on the secondary and tertiary structure of FP2. Our data also demonstrate that at least four tyrosine residues were nitrated and found on the surface of the enzyme, partially or completely exposed to the solvent. Although performed in vitro, these results suggest that falcipain-2 may be a target of RNS activity and its inhibition could explain the hindering of the parasite growth when exposed to these radicals. The understanding of the molecular mechanisms involving free radicals and its inhibition activity towards FP2 may be effective in the development of antimalarial therapies.

Topics: Antimalarials; Cysteine Endopeptidases; Hydrogen Peroxide; Molsidomine; Nitric Oxide; Oxidation-Reduction; Plasmodium falciparum; Protein Structure, Secondary; Sodium Nitrite; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization

The effects of a range of nitric oxide (NO)-related compounds on histamine release from human basophils and rat peritoneal mast cells were studied. Basal and immunologic histamine releases from human basophils were not affected by N(omega)-nitro-L-arginine, N(omega)-nitro-L-arginine methyl ester, aminoguanidine or methylene blue (all inhibitors of NO production), sodium nitroprusside (an NO donor), L-arginine (a substrate for NO synthase) or D-arginine (the inactive enantiomer of L-arginine). In rat peritoneal mast cells, NO donors such as sodium nitroprusside, sodium nitrite and sodium nitrate, and lipopolysaccharide (an inducer of NO synthase) had little effect on basal histamine release, while 3-morpholino-sydnonimine (SIN-1, an NO donor), L-arginine and D-arginine increased this release by up to threefold. None of the inhibitors of NO production had any striking effect on histamine release induced by anti-rat immunoglobulin E (IgE), compound 48/80, sodium fluoride, phospholipase C, 1,2-dioctanoyl-sn-glycerol or ionophore A23187. However, haemoglobin was found to inhibit histamine release by anti-rat IgE or A23187 by ca. 40%. Alone of the NO donors, low concentrations of L-arginine produced a mild inhibition of histamine release induced by anti-IgE, compound 48/80 and A23187, but not other ligands, while sodium nitroprusside dose-dependently inhibited (by a maximum of ca. 30%) histamine release by anti-rat IgE, sodium fluoride or A23187. Stimulation with a variety of secretagogues or treatment with L-arginine, D-arginine, lipopolysaccharide, SIN-1 or sodium nitroprusside had no effect on NO production. Similarly, L-arginine, D-arginine or sodium nitroprusside did not change intracellular cGMP levels. On the basis of these results, it is suggested that NO does not play a significant role in the modulation of histamine release from human basophils or rat peritoneal mast cells. The effects of L-arginine, D-arginine and sodium nitroprusside may involve mechanisms unrelated to NO.

Topics: Animals; Antibodies; Arginine; Basophils; Calcimycin; Dose-Response Relationship, Drug; Guanidines; Hemoglobins; Histamine; Humans; Immunoglobulin E; Male; Mast Cells; Methylene Blue; Molsidomine; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide; Nitric Oxide Donors; Nitroarginine; Nitroprusside; p-Methoxy-N-methylphenethylamine; Peritoneal Cavity; Rats; Rats, Sprague-Dawley; Sodium Fluoride; Sodium Nitrite

Nitric oxide reacts rapidly with superoxide to form the strong nitrating agent peroxynitrite, which is responsible for much of the tissue damage associated with diverse pathophysiological conditions such as inflammation. The occurrence of free or protein-bound nitrotyrosine (NTYR) has been considered as evidence for in vivo formation of peroxynitrite. However, various agents can nitrate tyrosine, and their relative significance in vivo has not been determined due to lack of a sensitive method to analyze NTYR in tissue proteins and biological fluids. We have developed a new HPLC-electrochemical detection method to analyze NTYR in protein hydrolyzates or biological fluids. The sample is injected directly into a reversed-phase HPLC column and NTYR is subsequently reduced by a platinum column to 3-aminotyrosine, which is quantified with an electrochemical detector. The method is simple, selective, and sensitive (detection limit, 0.1 pmol per 20-microl injection). We have applied this method to compare in vitro the ability of various nitrating agents to form NTYR in bovine serum albumin and human plasma. Yields of NTYR formed in human plasma proteins incubated with 1 or 10 mM nitrating agent decreased in the following order: synthetic peroxynitrite > 3-morpholinosydonimine, a generator of both NO and superoxide > Angeli's salt, which forms nitroxyl anion (NO-) > spermine-NONOate, which releases NO > sodium nitrite plus hypochlorite, which forms the nitrating agent nitryl chloride (NO2Cl). A simple purification method using a C18 Sep-Pak cartridge is also described for analysis of free NTYR in human plasma.

Topics: Chromatography, High Pressure Liquid; Electrochemistry; Humans; Hypochlorous Acid; Indicators and Reagents; Molsidomine; Nitrates; Nitrites; Nitrogen Oxides; Serum Albumin, Bovine; Sodium Nitrite; Spectrophotometry, Ultraviolet; Spermine; Tyrosine

Studies were conducted to clarify the effects of nitric oxide donors NOR 3 ((+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide, FK409), SIN-1 (3-morpholinosydnonimine) and SNAP (S-nitroso-N-acetylpenicillamine) on the accumulation of cGMP and cAMP and Ca2+ mobilization as well as ketogenesis from oleate in isolated rat hepatocytes. NOR 3 caused inhibition of ketogenesis from oleate along with stimulation of cGMP accumulation in rat hepatocytes, whereas SIN-1 and SNAP exerted no effect on ketogenesis despite their marked stimulation of cGMP accumulation. Although the nitric oxide trapping agent, carboxy-PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide), antagonized the stimulation by NOR 3 of cGMP accumulation, it failed to modulate the anti-ketogenic action of NOR 3. Furthermore, neither 8-bromoguanosine-3',5'-cyclic monophosphate nor N2,2'-O-dibutyrylguanosine-3',5'-cyclic monophosphate mimicked the anti-ketogenic action of NOR 3. It is concluded in the present study that NOR 3-induced inhibition of ketogenesis in rat hepatocytes is not mediated by cGMP. The present study revealed that the remaining structure of NOR 3 from which nitric oxide had been spontaneously released had no anti-ketogenic action. We first and clearly demonstrated that nitrite production was dramatically enhanced when NOR 3 was incubated in the presence of rat hepatocytes. The mechanism whereby NOR 3 inhibits ketogenesis in rat hepatocytes will be discussed.

Topics: Adenosine Triphosphate; Animals; Benzoates; Calcium; Cells, Cultured; Cyclic GMP; Imidazoles; Lactic Acid; Liver; Male; Molsidomine; Nitric Oxide; Nitro Compounds; Oleic Acid; Penicillamine; Rats; Rats, Wistar; S-Nitroso-N-Acetylpenicillamine; Sodium Nitrite; Vasodilator Agents

Nitric oxide (NO) or nitrite (NO2-) were assayed using the Werringloer's method or the Griess' method, respectively, in the presence or absence of various thiols, amino acids, or albumin. This has been done because both methods are used to determine the generation of endogenous NO from L-arginine or exogenous NO from drugs in vivo, paying little attention to biological constituents which may affect results of these assays. Albumin, reduced glutathione (GSH), cysteine and N-acetylcysteine, but not other amino acids lowered the amount of NO2- as detected by Griess' method no matter whether sodium nitrite or 3-morpholinosydnonimine (SIN-1) were used as a source of NO2-. This happened probably because at low pH of the reaction mixture the corresponding nitrosothiols were formed and thus NO2- was not accessible for detection. However, this phenomenon was not seen when instead of SIN-1 another NO donor--S-nitroso-N-acetylpenicillamine (SNAP) was used. SNAP is a nitrosothiol itself and physiological low molecular thiols (e.g. GSH or cysteine) displaced NO from SNAP. An increase in the amount of released NO was detectable by both Werringloer's and Griess' methods. Only the presence of 700 microns of albumin steadily suppressed the detection of NO or NO2- no matter what was the source of these species. It is concluded that low molecular thiols and albumin may differently influence the detection of both NO and NO2- which derive from various NO donors or sodium nitrite.

Topics: Amino Acids; Cysteine; Glutathione; Molsidomine; Nitric Oxide; Nitrites; Penicillamine; S-Nitroso-N-Acetylpenicillamine; Serum Albumin, Bovine; Sodium Nitrite; Sulfhydryl Compounds

Nitric oxide (NO.) is a free radical characterized by a high spontaneous chemical reactivity with many other molecules including the superoxide radical (O2.-). This complex interaction may generate a peroxynitrite anion (ONOO-), which behaves as an important mediator of oxidative stress in many pathological states. In the present study, in vitro experiments were performed to assess directly the O2.- and hydroxyl (.OH) radical scavenging effects of various NO. donor drugs, i.e. sodium nitroprusside (SNP), sodium nitrite (NaNO2), molsidomine and SIN 1, at pH 7.4, 7 or 6. Concentrations of NO. in the incubation medium containing the different NO. donor drugs were measured by the assay based on the reaction of Fe-N-methyl-D-glucamine dithiocarbamate (MGD) with NO. that yields a stable spin-adduct measured by electron paramagnetic resonance (EPR). O2.- and .OH generation was characterized by EPR spin trapping techniques, using the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). These free radicals were generated from the enzymatic system xanthine-xanthine oxidase, in phosphate buffer adjusted at pH 7.4, 7 and 6. Under these experimental conditions, SNP exhibited the strongest superoxide scavenging properties, characterized by IC50 values expressed in the micromolar range, which decreased at low pH. Addition of SNP (800 microM) to solution containing MGD and Fe2+ (5:1) at pH 7 4 produced a three line EPR spectrum which is identified to [(MGD)2-Fe2+-NO]. In control experiments no EPR signal was observed. We obtained the same results with NaNO2 and an augmentation of the spin-adduct level was noted with the prolongation of the incubation period. In return, molsidomine (2 mM) did not produce, in our conditions, a detectable production of NO.. NaNO2 displayed a significant superoxide scavenging effect only at pH 6, whilst neither molsidomine nor SIN 1 had any effect. Therefore, the superoxide scavenging properties of SNP, NaNO2, and molsidomine appeared to be closely related to their potential for NO release, which partially depends on the pH conditions. The behaviour of SIN 1 is more complicated, the speed of oxygen diffusion probably acting as a limiting factor in NO. formation in our conditions. The production of NO. was detected in presence of SIN 1. The intensity of the complex is comparable with the signal founded with NaNO2. By contrast, all molecules exhibited hydroxyl radical scavenging properties, highlighting the capacity of .OH to react with a wide r

Topics: Free Radicals; Hydrogen-Ion Concentration; Hydroxyl Radical; Molsidomine; Nitric Oxide; Nitroprusside; Oxidation-Reduction; Sodium Nitrite; Superoxides

Nitric oxide (NO) exerts microbicidal effects on a broad spectrum of pathogens, including viruses, but its antiretrovirus properties have not yet been described. The purpose of this study was to determine whether NO inhibits murine Friend leukemia virus (FV) replication in vitro and to what extent NO may play a role in defenses against FV infection in mice. Three NO-generating compounds were studied: 3-morpholino-sydononimine (SIN-1), sodium nitroprusside (SNP), and S-nitroso-N-acetylpenicillamine (SNAP). The effects of these three compounds were compared with those of their controls (SIN-1C, potassium ferricyanide, and N-acetylpenicillamine, respectively), which do not generate NO and with that of sodium nitrite (NaNO2). SIN-1, SNP, and SNAP inhibited FV replication in dunni cells in a concentration-dependent manner. In contrast, no significant inhibitory effect was observed with the three controls or NaNO2. Furthermore, the addition of superoxide dismutase did not alter the inhibitory effect of SIN-1, which is also known to generate superoxide anions. No dunni cell toxicity was observed in the range of concentrations tested. We also assessed the effect of NO produced by activated macrophages on FV replication. Macrophages activated by gamma interferon and lipopolysaccharide inhibited FV replication in a concentration-dependent manner. This inhibition was due in part to NO production, since it was reversed by NG-monomethyl L-arginine, a competitive inhibitor of NO synthase. In vivo administration of NG-nitro-L-arginine methyl ester, a competitive inhibitor of NO synthase, significantly increased the viral load in spleen cells of FV-infected mice. These results suggested that NO may play a role in defenses against the murine Friend leukemia retrovirus.

Topics: Animals; Antiviral Agents; Arginine; Cell Line; Dose-Response Relationship, Drug; Enzyme Inhibitors; Fibroblasts; Friend murine leukemia virus; Kinetics; Lipopolysaccharides; Macrophages, Peritoneal; Male; Mice; Mice, Inbred DBA; Molsidomine; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Penicillamine; S-Nitroso-N-Acetylpenicillamine; Sodium Nitrite; Virus Replication

Rat liver ADP-ribose pyrophosphatase-I (ADPRibase-I; EC 3.6.1.13) hydrolyzes ADP-ribose with high specificity and a low Km. Thus it can participate in the control of free ADP-ribose and nonenzymatic ADP-ribosylation of proteins. Here we show that ADPRibase-I was inactivated by acidified nitrite, whereas sodium nitroprusside (SNP) or 3-morpholinosydnonimine (SIN-1) at pH 7.5 produced a dose- and time-dependent Km increase from 0.5 microM to 2 microM. The effects of SNP and SIN-1 depended on the presence and concentration of dithiothreitol, pointing to S-nitrosylation of enzyme thiols. It is suggested that, by inhibiting ADPRibase-I, NO can stimulate nonenzymatic ADP-ribosylation of targets susceptible to micromolar free ADP-ribose. This is discussed in relation to apparently contradictory earlier reports on the role of NO in the ADP-ribosylation of actin.

Topics: Adenosine Diphosphate Ribose; Animals; Hydrogen-Ion Concentration; Kinetics; Molsidomine; Nitric Oxide; Nitroprusside; Pyrophosphatases; Rats; Sodium Nitrite; Vasodilator Agents

A role for nitric oxide (NO) in the regulation of hypothalamic neurohormone secretion has been suggested. The aim of the present study was to establish a direct involvement of this novel intracellular regulatory molecule in the control of GnRH release. For this purpose, the GT1-1 GnRH-secreting continuous cell line was treated with various agents that can modify the endogenous NO synthase activity or, alternatively, with substances that can liberate NO, mimicking an increased concentration of this molecule in the cell. Treatment of GT1-1 cells with increasing concentrations of L-arginine, the direct precursor of NO, produced a marked reduction of norepinephrine-stimulated GnRH release despite a lack of effect on basal secretion. Similarly, the NO donors SIN-1 and acidified NaNO2 potently reduced basal as well as KCl-stimulated GnRH secretion. Conversely, sodium nitroprusside caused a significant inhibition of KCl-stimulated, but not basal, GnRH secretion. Addition of these agents to GT1-1 cells resulted in a marked increase in intracellular cGMP accumulation. Addition of the NO synthase inhibitors N-nitro-L-arginine and N-nitro-L-arginine methyl ester stimulated basal GnRH secretion without modifying norepinephrine- or KCl-stimulated release. In addition, treatment of GT1-1 cells with both L-arginine analogs produced a significant inhibition of the basal cGMP concentration. Together, these data suggest an inhibitory role for NO in the control of GnRH secretion from GT1-1 cells.

Topics: Amino Acid Oxidoreductases; Animals; Arginine; Cell Line; Cyclic GMP; Gonadotropin-Releasing Hormone; Mice; Mice, Transgenic; Molsidomine; Neurons; Nitric Oxide; Nitric Oxide Synthase; Nitroprusside; Norepinephrine; Sodium Nitrite

A new fluorescence method using the dye FM1-43 was used to examine exocytotic release from hippocampal synaptosomes. Nitric oxide caused a marked transient stimulation of vesicle release. Several structurally unrelated nitric oxide donors, sodium nitroprusside, S-nitroso-N-acetylpenicillamine, 3-morpholino-sydnonimine, and acidified sodium nitrite, were effective. Release stimulated by nitric oxide and KCl were comparable in time course, using both the fluorescence assay and [3H]L-glutamate to monitor neurotransmitter release. Activation of guanylyl cyclase was not responsible for nitric oxide-stimulated release. Unlike release stimulated by KCl or A23187, nitric oxide-stimulated release was found to be independent of a rise in intrasynaptosomal Ca2+. Indo-1/AM measurements indicated that nitric oxide actually decreased intracellular Ca2+, and the Ca2+ channel blocker Cd2+ did not affect nitric oxide-stimulated vesicle release. Nitric oxide does, however, appear to act on the Ca(2+)-sensitive pool of vesicles. Nitric oxide may be the first physiological mediator that induces vesicle exocytosis without raising Ca2+ and may provide an interesting new tool for the study of molecules involved in vesicle exocytosis.

Topics: Animals; Calcium; Fluorescent Dyes; Glutamates; Glutamic Acid; Hippocampus; Indoles; Kinetics; Male; Molsidomine; Nitric Oxide; Nitroprusside; Penicillamine; Potassium Chloride; Pyridinium Compounds; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; S-Nitroso-N-Acetylpenicillamine; Sodium Nitrite; Spectrometry, Fluorescence; Synaptic Vesicles; Vasodilator Agents

We studied the effects of nitric oxide (NO)-producing agents on N-methyl-D-aspartate (NMDA) receptor activation in cultured neurons. 3-Morpholino-sydnonimine (SIN-1) blocked both NMDA-induced currents and the associated increase in intracellular Ca2+. The actions of SIN-1 were reversible and suppressed by hemoglobin. A degraded SIN-1 solution that did not release NO was unable to block NMDA receptors. This showed that the SIN-1 effects were due to NO and not to another breakdown product. Similar results were obtained with 1-nitrosopyrrolidine (an NO-containing drug) and with NO released from NaNO2. Pretreatment with hemoglobin potentiated NMDA-induced effects, demonstrating that endogenous NO modulates NMDA receptors. Since NMDA receptor activation induces NO synthesis, these results suggest a feedback inhibition of NMDA receptors by NO under physiological condition.

Topics: Animals; Calcium; Cyclic GMP; In Vitro Techniques; Mice; Molsidomine; N-Methylaspartate; N-Nitrosopyrrolidine; Nitric Oxide; Nitroso Compounds; Receptors, N-Methyl-D-Aspartate; Sodium Nitrite

The effects of 1 mM L-cysteine on sodium nitrite-, 3-morpholinosydnonimine (SIN-1)- and acetylcholine-induced relaxation and cyclic GMP accumulation were studied in isolated noradrenaline-precontracted rat mesenteric arterial rings. L-Cysteine augmented the relaxation and cyclic GMP increase induced by sodium nitrate and SIN-1 but not those induced by acetylcholine. The effects of L-cysteine on relaxation were independent of the presence of intact endothelium. The results suggest that L-cysteine protects exogenously released nitric oxide.

Topics: Acetylcholine; Animals; Cyclic GMP; Cysteine; Drug Synergism; Endothelium, Vascular; In Vitro Techniques; Male; Mesenteric Arteries; Molsidomine; Nitric Oxide; Rats; Rats, Inbred Strains; Sodium Nitrite; Vasodilation

1. In superfused precontracted strips of rabbit aorta, methylene blue (MeB) or pyocyanin (Pyo, 1-hydroxy-5-methyl phenazinum betaine) at concentrations of 1-10 microM inhibited relaxations induced by endothelium-derived relaxing factor (EDRF), glyceryl trinitrate (GTN), S-nitroso-N-acetyl-penicillamine (SNAP) or 3-morpholino-sydnonimine (SIN-1). However, the vasorelaxant actions of sodium nitroprusside (NaNP) or sodium nitrite (NaNO2) were enhanced by MeB or Pyo. Oxyhaemoglobin (HbO2, 1 microM) inhibited the activities of EDRF and all of the nitrovasodilators studied. Vascular preparations were not relaxed by Pyo unless pretreated with NaNP (0.05-10 microM). 2. In bathed, precontracted rings of rabbit aorta, Pyo (10 microM) produced a shift to the left of the cumulative concentration-response curve for NaNP (0.01-10 microM). The rise in guanosine-3':5'-cyclic monophosphate (cyclic GMP) content of aortic tissue was also enhanced. 3. The vasorelaxant potency of NaNP (30 microM) at pH 5-8 and at 37 degrees C remained unchanged over 2.5 h while a solution of SNAP (30 microM) progressively lost its biological activity over 60 min. The in vitro degradation of the biological activity of SNAP was accelerated by MeB (150 microM) or Pyo (150 microM), whereas the vasorelaxant potency NaNP (30 microM) was doubled when incubated with MeB or Pyo. 4. In human platelet-rich plasma, MeB or Pyo (0.3-3.0 microM) uncovered an anti-aggregatory action of subthreshold concentrations of NaNP (4-8 microM). This was abrogated by HbO2 (10 microM).5. We conclude that MeB or Pyo differ from HbO2 in their mode of interaction with nitrovasodilators.HbO2 scavenges nitric oxide that is released from all types of nitrovasodilators. MeB and Pyo exert a similar action towards organic nitrovasodilators (e.g. SNAP, SIN-1). However, the pharmacological actions of inorganic nitrovasodilators (e.g. NaNP or NaNO2) are potentiated by MeB and Pyo owing to facilitation of the intracellular release of nitric oxide from the inorganic nitrovasodilators.

Topics: Animals; Aorta; Cyclic GMP; Drug Interactions; In Vitro Techniques; Methylene Blue; Molsidomine; Nitric Oxide; Nitroglycerin; Nitroprusside; Penicillamine; Platelet Aggregation; Pyocyanine; Rabbits; S-Nitroso-N-Acetylpenicillamine; Sodium Nitrite; Vasodilator Agents

The effects of exogenous guanosine 5'-triphosphate (GTP) and guanosine on nitroglycerin-, sodium nitrite- and SIN-1-induced guanosine 3',5'-cyclic monophosphate (cyclic GMP) accumulation and smooth muscle relaxation were studied using endothelium-denuded rat mesenteric artery rings precontracted with noradrenaline. Preincubation of contracted artery rings with GTP (100 microM) or guanosine (100 microM) before eliciting relaxations with nitrovasodilators significantly shifted the dose-response curves of nitrocompounds to the left and augmented the increases in cyclic GMP. GTP and guanosine alone also induced cyclic GMP accumulation in pre-contracted artery rings. These effects of GTP and guanosine on nitrovasodilator responses were not related to the preincubation period (0-30 min). The present results raise the possibility of a cell membrane site of action for GTP and guanosine, which mediates the activation of soluble guanylate cyclase and leads to increased nitrovasodilator-induced cyclic GMP accumulation and arterial smooth muscle relaxation.

Topics: Animals; Cyclic GMP; Guanosine; Guanosine Triphosphate; In Vitro Techniques; Male; Molsidomine; Muscle, Smooth, Vascular; Nitroglycerin; Rats; Rats, Inbred Strains; Sodium Nitrite; Vasodilation

SIN-1, a metabolite of the vasodilating drug molsidomine, was found to stimulate dose dependently (0.01-1 mM) soluble guanylate cyclase from bovine coronary arteries up to 100-fold the control value. The stimulatory effect of SIN-1 increased with rising concentrations of MnC1(2) or MgC1(2) and was diminished in the presence of methylene blue or ferricyanide. The time course of SIN-1-induced guanylate cyclase stimulation was characterized by a lag phase which was not observed after preincubation of the enzyme with SIN-1. In contrast to nitroglycerin and sodium nitroprusside, SIN-1 did not require the presence of cysteine or other thiols to stimulate guanylate cyclase. The results presented in this study provide further evidence that SIN-1 exerts its dilating effect on coronary vessels via direct stimulation of guanylate cyclase.

Topics: Animals; Cations, Divalent; Cattle; Coronary Vessels; Cyclic GMP; Ferricyanides; Guanylate Cyclase; In Vitro Techniques; Methylene Blue; Molsidomine; Muscle Relaxation; Muscle, Smooth, Vascular; Nitroglycerin; Nitroprusside; Oxadiazoles; Sodium Nitrite; Sulfhydryl Compounds; Sydnones