Search

We reported previously that plasma levels, urinary excretion, and metabolic production of cyclic guanosine 3',5'-monophosphate (cGMP) are increased in gravid rats, and postulated that endogenous nitric oxide (NO), a potent vasodilator and immune modulator, may mediate this change. Four lines of evidence are now presented demonstrating increased biosynthesis of NO during pregnancy in rats: 1) Urinary excretion and plasma levels of the stable NO metabolite, nitrate, are elevated in pregnant rats; urinary excretion of nitrate is increased in pseudopregnant rats. 2) The urinary excretion of cGMP also increases during pregnancy and pseudopregnancy, paralleling the rise in urinary nitrate excretion. 3) Chronic treatment with the NO synthase inhibitor, NG-nitroarginine methyl ester (NAME), inhibits the increase in urinary nitrate excretion. 4) Nitric oxide hemoglobin is detected by electron paramagnetic resonance spectroscopy in the blood of pregnant, but not in nonpregnant, rats. The results show endogenous NO production is increased in gravid rats. This finding raises the possibility that NO may contribute to maternal vasodilation and uterine immune suppression of normal pregnancy.

Sodium azide is a chemical of rapidly growing commercial importance with a high acute toxicity and an unknown mechanism of action. Although it has some chemical properties and biological effects in common with cyanide, its lethality does not appear to be due to inhibition of cytochrome oxidase. Unlike cyanide it is a potent vasodilator and inhibitor of platelet aggregation presumably by virtue of its conversion to nitric oxide in vivo and in isolated preparations of blood vessels and thrombocytes. It is not clear whether the high toxicity of azide is due to nitric oxide or to the parent anion. Of a number of possible azide antagonists tested in intact mice only phenobarbital in both anesthetic and subanesthetic doses afforded statistically significant protection against death. Diazepam, phenytoin, and an anesthetic dose of a ketamine/xylazine combination had no effect. Major motor seizures are sometimes seen in human azide poisoning, and these are a regular feature of azide poisoning in laboratory rodents. Solutions of nitric oxide given systemically to mice produced no signs of toxicity, but doses 1,000-fold lower placed in the cerebroventricular system of rats produced brief but violent tonic convulsive episodes. A dose of 0.61 mmol/kg azide as given systemically regularly produced convulsions whereas a dose of 6 mumol/kg given icv produced seizures in rats. The icv convulsive dose of azide was 50-fold larger than the icv dose of nitric oxide. These results suggest that azide lethality is due to enhanced excitatory transmission in the central nervous system perhaps after its conversion to nitric oxide.(ABSTRACT TRUNCATED AT 250 WORDS)

Mice given ip bacterial endotoxin (LPS) at 10 mg/kg showed a statistically significant decrease in plasma glucose and an increase in hematocrit at 2 h after injection. Glucose was still decreased at 4 h, but the hematocrit had returned to control values. Nitrosylated hemoglobin (HbNO) was detected at 3, but not at 2 h. By 4 h it had increased 5-fold. When N-monomethylarginine (NMMA) at 100 mg/kg, ip was given 2 h after LPS in mice, the HbNO concentration at 4 h was significantly reduced, but the hypoglycemia was worsened because NMMA itself produced a significant hypoglycemia. Rats given iv LPS, 20 mg/kg, showed a fleeting, transient rise in mean arterial pressure (MAP) lasting only a few min. Thereafter, the MAP tended to drift slowly downward over 4 h, but when the MAP at 30 min intervals was compared to the pre-LPS MAP, there were no significant differences. Plasma glucose in unanesthetized rats was significantly elevated at 1 h, back to control at 2 h, and significantly decreased at 3 h. HbNO was detected as early as 1 h after injection. By 2 h the HbNO concentrations exceeded the highest levels found in mice, and they were still increasing as late as 5 h after injection. Unanesthetized rats showed toxic signs and 3 12 rats died within 4 hours of LPS administration. These results are consistent with a model for endotoxic shock in which LPS stimulates an inducible pathway for NO synthesis.

Pairs of osmotic minipumps containing 400 mg/ml (6.15 m ) sodium azide in distilled water were subcutaneously implanted in timed pregnancy Syrian golden hamsters. The total delivered dose was calculated as 6 × 10 −2 mmol kg −1 hr −1 at the maximal pumping rate. Most dams exhibited obvious signs of toxicity during the period of pump implantation which was Days 7 through 9 of gestation. After removal of the pumps the dams were euthanized on Day 13 of gestation, and the uteri were removed for counting of the number of living, malformed, and resorbed fetuses. This dose rate resulted in a significantly increased incidence of resorptions of embryos over that in a control group implanted with pumps delivering only distilled water. The incidence of gross malformations exclusively in the form of encephaloceles was not different between control and azide-infused groups. The extent of nitrosylation of circulating hemoglobin was followed with time and found to involve only about 0.1% of the total blood pigment. Thus, this commercially important and widely distributed chemical with high acute toxicity is not considered to be teratogenic in hamsters, and it produces embryotoxicity only at dose rates that result in toxic signs in the dams.

Sodium nitroprusside (Na 2 [(CN) 5 FeNO], SNP), which is stable, diamagnetic, and not detectable by electron paramagnetic resonance (EPR) spectroscopy, can be activated by one-electron reduction. The initial product, which retains the five cyanides and is here called penta, has a distinctive EPR signal. Penta spontaneously dissociates the trans -cyanide ligand resulting in a second paramagnetic species called tetra, which has a different and distinctive EPR signal. Tetra is able to transfer its NO ligand to a suitable acceptor, and all four equatorial cyanides subsequently dissociate. However, excess free cyanide shifts the tetra-penta equilibrium in the direction of penta and prevents NO release. This study was an attempt to extend the above results on SNP reduction, which were obtained in a model hemoglobin system, to intact porcine cells by characterizing all EPR-detectable intermediates. When porcine aortic endothelial or smooth muscle cells in culture were incubated under anaerobic conditions with SNP, an EPR spectrum was obtained, which could be resolved into the signal for penta and a signal previously described as a nonheme iron-nitrosyl-sulfur complex, FeNOSR. Tetra was not detected. This FeNOSR has some differences in its stability and location from that described by others in activated macrophages. When incubations were carried out under air, penta could not be detected, but a somewhat diminished signal for FeNOSR was still detectable. When incubations were carried out in the presence of excess free cyanide, conditions under which reduced SNP does not nitrosylate hemoglobin, the penta signal became stronger and the FeNOSR signal, though decreased, was still observed. Depletion (95%) of intracellular reduced glutathione in endothelial cells had no effect on the FeNOSR signal strength. We conclude that SNP is activated in porcine endothelial cells by a one-electron reduction to penta, which apparently dissociates its trans -cyanide to form tetra which then goes on to form FeNOSR upon reaction with a membrane-bound thiol. Glutathione is not involved in any of these reactions.

N-Morpholino-N-nitrosoaminoacetonitrile (SIN-1), a nitrovasodilator metabolite of the drug, molsidomine, is widely used in studies on the pharmacology and toxicology of nitric oxide (NO) because solutions of SIN-1 'spontaneously' release NO in a pathway involving molecular oxygen. Preliminary results, however, suggested that SIN-1 could react with hemoglobin in anaerobic solutions to release NO and form NO-hemoglobin. Electron paramagnetic resonance (EPR) studies showed that heme(III) of methemoglobin was not being reduced, thereby not serving as the oxidant in the reaction generating NO-hemoglobin. When anaerobic solutions of SIN-1 and hemoglobin kept in the light and in the dark were compared, substantially more NO-hemoglobin was eventually generated in the dark, indicating that SIN-1 did not undergo photochemical decomposition to NO under the conditions used. Solutions of NO-hemoglobin were equally stable under these same conditions of light and dark. The initial pH (7.0) of stirred, unbuffered solutions of SIN-1 decreased at nearly the same rate whether or not oxygen was present. Anaerobic and aerobic solutions plateaued at the same pH, namely 5.4. Anaerobic solutions of SIN-1 in phosphate buffer, pH 7.4, released NO to the gas phase, where it was identified by trapping it with hemoglobin on agarose beads and deriving the characteristic NO-hemoglobin EPR spectrum. High pressure liquid chromatography revealed the presence of an unknown species with a retention time between that of SIN-1 and molsidomine. Samples from two different lots of SIN-1 contained this impurity which appears to oxidize SIN-1 to products that release NO in the absence of oxygen. This unknown impurity may be unstable toward light.

Sodium nitroprusside, Na2[Fe(CN)5NO], (SNP) has been recognized as a potent, directly acting vasodilator for over a half-century. More recently, it has been found also to inhibit blood platelet aggregation and adhesion. These biologicial activities are ascribed to the nitrosyl ligand on SNP which is thought to activate guanylate cyclase by binding to its critical heme group. c-GMP in turn initiates a cascade of kinase reactions which result in the utimate biological effects. Thus, SNP is one of the compounds known as the nitric oxide (NO) vasodilators (Ignarro, 1989) which mimic the effects of the so-called endothelium-derived relaxing factor (Furchgott and Zawadzki, 1980), an endogenous mediator which many are convinced is identical to NO. The same or a similar factor is believed to play in role in excitatory amino acid transmission in the central nervous system, and to be the cytotoxic factor synthesized by neutrophils and macrophages (Collier and Valiance, 1989).

The reaction of sodium nitroprusside (SNP) with deoxyhemoglobin (Hb) results in two distinct EPR-detectable species, the one-electron-reduced nitroprusside ion [(CN)5FeNO]3- and nitrosylhemoglobin (HbNO). In the presence of excess cyanide (CN-) only the signal for [(CN)5FeNO]3- is observed. Thus, while free CN- does not interfere with Hb reduction of SNP, it prevents transfer of the NO moiety to Hb. Electrolytic reduction of SNP under similar conditions, however, leads to [(CN)5FeNO]3- and a small amount of [(CN)4FeNO]2- resulting from loss of the CN- trans to the NO. Excess free CN- shifts the equilibrium between these two species toward [(CN)5FeNO]3-, thereby reducing the concentration of [(CN)4FeNO]2-. Thus, [(CN)4FeNO]2- appears to be responsible for the transfer of NO to Hb. Consistent with this mechanism, both [(CN)5FeNO]3- and [(CN)4FeNO]2- are observed when SNP is added to erythrocyte lysates. Under these conditions HbNO is formed more rapidly due to the higher concentration of the latter species with the labile NO. This observation suggests that red blood cell constituents capable of binding CN- shift the equilibrium between the reduced SNP ions toward [(CN)4FeNO]2-. In the reaction of reduced glutathione (GSH) with SNP, [(CN)5FeNO]3- is formed as well as low concentrations of an EPR-detectable GSH-SNP adduct. Excess free CN- introduces a lag in the appearance of these signals, suggesting that GSH mediates SNP reduction by a different mechanism from that of Hb, although it too is inhibited by CN-.(ABSTRACT TRUNCATED AT 250 WORDS)

We describe a simple method for measuring sodium azide concentrations in aliquots of blood and other tissues. Aliquots are acidified, converting azide to volatile hydrazoic acid (HN3) which is then trapped in sodium hydroxide. We analyze the resulting aliquots by ion chromatography, using a sodium tetraborate eluent and suppressed conductivity detection. The method is sensitive to at least 100 ng/mL.

Despite its many drawbacks the classic benzidine technique is the method most widely used for determining plasma hemoglobin. An additional disadvantage, reported here, is that the method measures hemoglobin in erythrocytes as well as in plasma. Thus, if plasma specimens are accidentally contaminated with erythrocytes, apparent free hemoglobin in plasma will be artifactually high. Although the present method lacks the sensitivity of the benzidine technique, it self-corrects for the presence of erythrocytes. We have found it particularly useful for specimens of rodent (rat mouse) blood, where some cells appear to resist centrifugation, where the small sample sizes frequently result in accidental contamination of plasma with cells, and where normal values may be higher than those for human plasma.

A series of compounds were synthesized from ruthenium trichloride, and their ip LD50s were determined in mice: pentamminenitrosylruthenium(II) chloride, 8.9; chloronitrobis(2,2'-dipyridyl)ruthenium(II), 55;dichlorobis(2,2'-dipyridyl)ruthenium(II), 63; ruthenium trichloride, 108; and potassium pentachloronitrosylruthenate(II), 127 mg/kg. The two bis-bipyridyl complexes produced death in convulsions within minutes, whereas the remaining compounds resulted in long, debilitating courses with death occurring in 4-7d. When given in massive overdoses, however, the compounds with inorganic ligands also produced rapid convulsive death in mice, and when given iv to anesthetized cats, they produced respiratory arrest. The major toxic effects of all the complexes appeared to be due to the metal and not to its associated ligands. Only complexes having nitrosyl ligand specifically relaxed vascular smooth muscle. Potassium pentabromoiridate(III) also relaxed rabbit aortic strips that had been contracted by adrenergic agonists, but potassium pentachloroiridate(III) did not. None of the complexes was as active as nitroprusside in relaxing aortic strips or in decreasing arterial blood pressure in cats. No compound tested was as potent as cisplatin in antitumor activity. The pentamminenitrosylruthenium(II) complex also relaxed guinea pig ileum and frog rectus abdominus when these isolated muscles had been contracted by acetylcho line. It appears that these organoruthenium compounds may produce death in central respiratory arrest, as do the inorganic complexes when given iv or ip in massive overdoses. In minimally lethal doses, the complexes with inorganic ligands may affect a variety of contractile tissues, perhaps by a general mechanism involving Ca. These complexes are apt to be generally cytotoxic as well.

Intraperitoneal doses of 4-dimethylaminophenol hydrochloride (DMAP), hydroxylamine hydrochloride (H2NOH) and sodium nitrite (NaNO2) were found where each converted a maximum of about 37% of the total circulating hemoglobin in mice to methemoglobin. Those doses in mmol/kg were: 0.29 for DMAP, 1.1 for H2NOH, and 1.1 for NaNO2. For DMAP and H2NOH the peak was sharp and at about 7 min after injection whereas for NaNO2 the peak was much broader and at about 40 min. The i.p. LD50's in mmol/kg were: 0.48 for DMAP, 1.8 for H2NOH and 2.3 for NaNO2. When mice pretreated with each of the methemoglobin-generating agents were challenged with sodium cyanide, the ratios of the LD50's in protected mice to those in control mice (protection index, PI) were 1.5 for H2NOH, 2.0 for DMAP and 3.1 for NaNO2. When sodium thiosulfate was also given in combination with each of the three methemoglobin-generating agents, the protective effect was at least additive. The PI against sodium sulfide was also significantly greater in mice pretreated with NaNO2 than in mice given H2NOH. Methemoglobins generated from human and mouse hemoglobins by either NaNO2 or by H2NOH had identical binding affinities (dissociation constants) for cyanide. When human red cells containing methemoglobin generated by exposure to either NaNO2 or H2NOH were injected into the peritoneal cavity of mice and then followed by cyanide challenges, there was no difference in the PI for the two kinds of methemoglobin. Not only was the PI the same in each case with human cells, but it was also identical with that in mice given NaNO2 systemically to generate the same total amount of methemoglobin. The difference in PI between NaNO2 and H2NOH (or DMAP) in mice appears to be related to the high rate of methemoglobin reductase activity in mouse RBC. It appears likely that cyanmethemoglobin is a substrate for mouse methemoglobin reductase activity, and that NaNO2 is an inhibitor of mouse methemoglobin reductase. No differences in cyanide antagonism between NaNO2 and H2NOH would be anticipated in humans because of the slow rates of methemoglobin reduction in human red cells.

Some mammalian hemoglobins, e.g., dog, cat and to lesser extents mouse and rat, exhibit a greatly increased rate of autoxidation in solutions containing low concentrations of a nonionic detergent. Human, rabbit and hamster hemoglobins were more stable toward detergent. Human hemoglobin was the most stable under these conditions, but even so its rate of autoxidation was at least five times faster with detergent than with saponin where the hemoglobins of all species appeared to be equally stable. Among the more unstable hemoglobins the rate of autoxidation in the presence of detergent was so rapid that it compromised the accuracy of methemoglobin analyses. The results of tests for detergent-induced heme loss suggested that the detergent did not significantly increase the thermolability of any of the hemoglobins tested.

Sodium nitroprusside relaxed guinea pig ileum after the segment had been submaximally contracted by either histamine or acetylcholine, intact isolated rabbit gall bladder after submaximal contraction by either acetylcholine or cholecystokinin octapeptide, and rat pulmonary artery helical strips after submaximal contraction with norepinephrine. In each of these cases the relaxation produced by nitroprusside was at least partially reversed by the subsequent addition of excess sodium cyanide. Cyanide, however, in nontoxic concentrations did not reverse the spasmolytic effects of hydroxylamine hydrochloride, sodium azide, nitroglycerin, sodium nitrite, or nitric oxide hemoglobin on guinea pig ileum, nor did cyanide alone in the same concentrations have any effect. The similar interaction between nitroprusside and cyanide on rabbit aortic strips is not dependent on the presence of an intact endothelial cell layer. Also, on rabbit aortic strips and like cyanide, sodium sulfide reversed the spasmolytic effects of azide and hydroxylamine, but it had little or no effect on the relaxation induced by papaverine. Unlike cyanide, however, sulfide augmented the relaxation induced by nitroprusside, and it reversed the effects of nitric oxide hemoglobin, nitroglycerin, and nitrite. A direct chemical reaction between sulfide and nitroprusside may account for the difference between it and cyanide. Although evidence was obtained also for a direct chemical reaction between sulfide and norepinephrine, that reaction does not seem to have played a role in these results. These observations suggest the existence of at least three distinct subclasses of so-called nitric oxide vasodilators. At least in some cases cyanide and sulfide cannot be acting by the same mechanism in their modifications of the responses to the agonists.

Human red blood cells (RBC) incubated under nitrogen with methylene blue and glucose at physiological temperature and pH can be used to test for the biotransformation of nitrogenous vasodilators to nitric oxide (NO). The NO generated was trapped as nitrosylated heme by reduced subunits (hemeII) on various hemoglobin valency species and quantified by electron paramagnetic resonance spectroscopy. It was possible to separate the various valency species of hemoglobin present in the mixture as (alpha 2 + beta 2)2, (alpha 2 + beta 3+)2, (alpha 3 + beta 2+)2, or (alpha 3 + beta 3+)2 by isoelectric focusing (IEF) unless cyanide (from nitroprusside) or azide was present in the mixture. These anions bind tenaciously to oxidized subunits (hemeIII) and prevent the separation of the various species by IEF. The fully oxidized tetramer, (alpha 3 + beta 3+)2, does not bind NO, but the other three species have hemeII units which can be nitrosylated. In the absence of cyanide or azide the valency species could be separated by IEF, and it was possible to quantify the degree of nitrosylation on each individual species. The various agents tested (nitrite, glyceryl trinitrate, hydroxylamine, hydralazine, nitroprusside, and azide) produced different patterns of valency species and degrees of nitrosylation of hemeII. When hemeIII ligands were present or in cases of very low yields, it was still possible to quantify the total concentration of NO-hemeII in the mixture. Thus, the method could still be used to test for NO formation. All of the so-called NO vasodilators tested yielded detectable amounts of NO in the system.

Oxygen (100% at 1 atmosphere) did not protect mice against death from acute sulfide poisoning as compared with animals maintained under air at 1 atmosphere. Sodium thiosulfate had a small, but statistically significant (P

When given IV in bolus doses to intact anesthetized dogs or cats, hydroxylamine hydrochloride produced transient but precipitous falls in the mean arterial blood pressure in a dose-related manner, as well as a significant methemoglobinemia. The half-time for recovery of the mean arterial pressure was also dose-related. These effects were very similar to those elicited by comparable doses of sodium nitrite, except that the half-recovery time for return to normal blood pressure was somewhat longer with the nitrite. Although hydroxylamine has long been known to relax vascular smooth muscle in vitro, we are not aware of previous demonstrations of hypotensive effects in vivo. Acute poisoning by either nitrite or hydroxylamine is apt to result in both an anemic hypoxia due to methemoglobinemia and a stagnat (hypokinetic) hypoxia due to direct vasodilation. Hydroxylamine, but not nitrite, also appeared to stimulate respiration possibly through an effect on the chemoreceptors of the carotid body.

Concurrent measurements of O 2 consumption and locomotor activity were made in adult female mice at 20 and 34°C. As anticipated, activity and O 2 consumption were positively correlated with a high degree of statistical significance. A 30-fold increase in spontaneous motor activity, however, was accompanied by only a 30% increase in O 2 consumption. Extrapolation of the regression relationship to zero activity provided a novel means of estimating the basal metabolic rate (BMR) of mice. That value agreed with traditional estimates based on resting or sleeping animals. Under our conditions the respiratory quotient for mice was 0.83 at 20°C and 1.0 at 34°C. Oxygen consumption averaged over all levels of spontaneous activity was 4.79 ml g −1 hr −1 at 20°C and 2.21 ml g −1 hr −1 at 34°C. These estimates are actually lower than those of others who employed physical restraint to control activity. Because the BMR of mice constitutes about 70% of the O 2 consumption at the highest levels of spontaneous motor activity, drug-induced changes in motor activity may not significantly affect O 2 consumption. Alternatively, it may be obvious that the two changes are not correlated. For example, in our hands pentobarbital decreased motor activity without affecting O 2 consumption, and amphetamine increased motor activity but decreased O 2 consumption. When the changes are in the same direction, the problem of distinguishing between a metabolic or respiratory effect of the drug and a change related to increased or decreased motor activity becomes more difficult. Analysis of covariance offers one possible approach to this problem.

Male and female mice were exposed to a simulated altitude of 5,500m for 10, 30 or 90 days. After exposure to altitude for 90 days one group of each sex was then returned to sea level pressures for 10 days. In addition to the expected increases in hematocrit and hemoglobin, altitude exposure increased the 2,3-DPG content of red cells. Maximum values of 2,3-DPG (μmoles/g hemoglobin) occurred after 10 days at altitude and thereafter declined to values comparable to those in sea level mice despite continued exposure to hypoxia.

The authors have confirmed previous observations that sodium cyanide (CN-) partially reverses the vasodilator effects of sodium nitroprusside (SNP) on vascular smooth muscle. As tested on rabbit aortic strips contracted by norepinephrine (NE), the final tension is independent of the order of addition of reagents. In the same concentration, CN- alone had no effect on tension also as reported by others. The ED50 values for relaxation of aortic strips for a series of directly acting agonists ("nitric oxide vasodilators") were: sodium azide (N-3) 2.1 X 10(-7) M; SNP 2.7 X 10(-7) M; hydroxylamine (H2NOH) hydrochloride 2.5 X 10(-6) M; human nitric oxide hemoglobin (HbNO) 3.5 X 10(-6) M; and sodium nitrite (NO-2) 1.2 X 10(-4) M. In addition to SNP, CN- antagonized the vasodilator effects of N-3 and H2NOH, but it failed to reverse relaxation by HbNO, NO gas, NO-2 (as observed by us), glyceryl trinitrate, adenosine, or papaverine (as observed by others). The only change noted in cyclic-adenosine monophosphate (c-AMP) concentrations in aortic strips exposed to 1) NE, 2) NE + NO-2 or SNP, or 3) NE + NO-2 or SNP + CN- was an increase due to NE. The only statistically significant change noted in cyclic-guanosine monophosphate (c-GMP) concentrations exposed to 1) NE, 2) NE + NO-2 or 3) NE + NO-2 + CN- was also an increase due to NE. In contrast, SNP resulted in further increases in c-GMP after NE, and when cyanide was added, a significant decrease in c-GMP followed. These results are only partially consistent with a role for c-GMP in relaxation of vascular smooth muscle, but cyanide may become a useful tool for the study of mechanisms of action of the nitric oxide vasodilators.

Most investigators agree that sodium nitroprusside (SNP) undergoes biotransformation in vivo to release free cyanide (CN-). Despite a demonstrated reactivity of SNP toward oxyhemoglobin (HbO2) in vitro, that reaction is probably not the major cause for CN- release in vivo. An unknown reaction in various vascular beds inactivates SNP more rapidly than the reaction in blood, but both result in the release of free CN-. Recently it has been claimed that SNP is stable in blood and that the apparent CN- release is an artifact due to photodecomposition of SNP during CN- analyses. In this study the release of free CN- from SNP was followed over 3 hr of incubation in plain buffer, in suspensions of red blood cells (RBC), in lysates, and in solutions of HbO2 purified by isoelectric focusing and shown to be free of methemoglobin (MetHb), valency hybrid species, and reduced glutathione (GSH). In each case the mixtures containing HbO2 released significantly more CN- than plain buffer where CN- release was at the limit of sensitivity of the method. Moreover, in the order of RBC, purified HbO2 solutions and lysates, each preparation released significantly more CN- in 1 hr than the preceding one. In lysates the reaction had gone to completion by 3 hr. Using 13C nuclear magnetic resonance (NMR) spectroscopy, SNP was shown to be inert to CN- exchange in solutions of Na13CN, but when GSH or MetHb was added, an exchange reaction occurred between the trans-CN- of SNP and 13CN- in solution. The same reaction proceeded even more rapidly in the presence of HbO2. The results of this study show that in the presence of GSH, MetHb and particularly in the presence of HbO2, SNP readily exchanges its trans-CN- ligand with excess free CN-. This reaction is believed to represent an obligatory precursor step in the total decomposition of SNP which occurs in the absence of free CN-, but in the presence of RBC, solutions of HbO2, and lysates. It appears that excess free CN- halts total decomposition at the stage of trans-CN- labilization.

Excerpt To the editor: Since we (RS, RG) were responsible for the suggestion that the therapeutic induction of methemoglobinemia might be of value in acute azide poisoning (1, 2), we are naturally ...