Academic literature on the topic 'Methaemoglobin'

Calcium nitrate and urea were fed as a supplement on an isonitrogenous basis to Angus steers and their erythrocytic methaemoglobin concentrations and NADH- and NADPH-methaemoglobin reductase levels were measured over a 54-day period. Methaemoglobin concentrations remained elevated despite increases in NADH-methaemoglobin reductase activity. In a second experiment, Brahman cross steers were fed either calcium nitrate or urea supplements for 111 days. Blood cells were then taken, washed and exposed to sodium nitrite to convert all haemoglobin to methaemoglobin. The rates of glycolysis and methaemoglobin reduction were measured following incubation of these cells in buffers containing 1, 5 or 10 mM inorganic phosphate. Glucose consumption and methaemoglobin reduction were increased by inorganic phosphate and were more rapid in those animals supplemented with nitrate. Lactate production of erythrocytes was reduced in those animals fed nitrate. It is concluded that adaptation to chronic nitrite exposure occurs in the erythron, resulting in greater methaemoglobin reduction potential and that there is competition between NADH-methaemoglobin reductase and lactate dehydrogenase for NADH.

Methylene blue, at high concentrations, interferes with the estimation of methaemoglobin using the IL 282 CO-oximeter: the dye does not interfere with the method of Evelyn & Malloy for determination of methaemoglobin. In beagle bitches methylene blue causes both methaemoglobinogenesis and methaemoglobin reduction, the effect of the former being to delay the decline of methaemoglobin levels, when methylene blue is used to reverse the methaemoglobinaemia produced by sodium nitrite.

The ESR spectra of peroxidase systems of methaemoglobin-ascorbic acid-hydrogen peroxide and methaemoglobin-haptoglobin complex-ascorbic acid-hydrogen peroxide have been measured in the acetate buffer of pH 4.5. For the system with methaemoglobin an asymmetrical signal with g ~ 2 has been observed which is interpreted as the perpendicular region of anisotropic spectrum of superoxide radical. On the other hand, for the system with methaemoglobin-haptoglobin complex the observed signal with g ~ 2 is symmetrical and is interpreted as a signal of delocalized electron. After realization of three repeatedly induced peroxidase processes the ESR signal of the perpendicular part of anisotropic spectrum of superoxide radical is distinctly diminished, whereas the signal of delocalized electron remains practically unchanged. An amino acid analysis of methaemoglobin along with results of the ESR measurements make it possible to derive a hypothesis about the role of haptoglobin in increasing of the peroxidase activity of methaemoglobin.

Oral dosing of rats with the cyanide antidote 4-aminopropiophenone (PAPP), brought about peak methaemoglobin levels at 15-40 min, but peak levels were attained at 15-25 min after intravenous dosing. After both oral and intravenous administration at equimolar doses, 4-(N-hydroxy)aminopropiophenone (PHAPP), the putative methaemoglobin-producing metabolite of PAPP, produced higher peak levels of methaemoglobin than PAPP. Plasma from rats injected with PAPP was capable of forming methaemoglobin when added to naive rat erythrocytes. The identity of the metabolite responsible is discussed.

Twelve Bos indicus steers (liveweight ± s.d., 317.8 ± 28.5) kg were used in an experiment to examine two factors: daily nitrate dose (0, 30, 40 or 50 g of nitrate/day) and feeding frequency (once or twice a day) on methaemoglobin concentration, daily peak methaemoglobin concentration, rate of incline for methaemoglobin concentration, carboxyhaemoglobin concentration, oxyhaemoglobin concentration, total haemoglobin concentration, haematocrit and dry matter intake of Flinders grass hay. Increasing the dose rate of nitrate increased the fraction of methaemoglobin in the blood of steers (P = 0.014). A highly significant effect was demonstrated for the interaction of dose rate × day (P < 0.001). For once a day intake of nitrate, the dose rates of 40 and 50 g per day showed a greater increase in mean methaemoglobin values than for the 0 and 30 g of nitrate per day. Increasing the dose rate of nitrate also increased the daily peak methaemoglobin fraction and the rate of incline to peak methaemoglobin values for both once and twice a day feeding of the nitrate supplements. However, increasing the dose of nitrate had no significant overall effect on total haemoglobin, deoxyhaemoglobin, carboxyhaemoglobin, haematocrit or dry matter intake. Twice a day feeding of nitrate decreased the formation of methaemoglobin in the blood of Bos indicus steers. This study demonstrates that caution should be exercised when feeding nitrates as a non-protein nitrogen source to cattle grazing low quality pastures in northern Australia.

Methaemoglobin profiles have been studied by using ISIS, a simulation package, and NONLIN, a ion-linear least-squares analysis regression program. A simple kinetic model which satisfactorily describes methaemoglobin profiles after p-aminopropiophenone (PAPP) administration and 4-dimethylaminophenol (DMAP) administration has been developed. The two compounds differed nainly in their effective rates of elimination. The model less satisfactorily described methaemoglobin profiles after p-hydroxyaminopropiophenone (PHAPP) administration.

Concentrations of methaemoglobin (the oxidized non-functional ferric form of haemoglobin) in the blood of marine fish are poorly documented. Although high concentrations have been reported for fish maintained in captivity, baseline values for wild populations are unknown. Two techniques, the cyanide derivative method and the multiple wavelength method, were used to determine methaemoglobin concentrations in blood samples from 25 species of marine teleosts and elasmobranchs captured on the Australian Great Barrier Reef. Although methaemoglobin generally accounted for less than 2% of total haemoglobin, systematic errors occurred when these two standard methods, developed for mammalian blood, were applied to the blood of some fish species. Most problems arose from reactions of various blood components with the reagents used in the cyanide derivative method. Consequently, the multiple wavelength method generally was more reliable for estimating methaemoglobin in the blood of marine fish. The low methaemoglobin concentrations in fish studied on the Great Barrier Reef indicate high water quality and healthy physiological condition.

Recently, a family tree with a predisposition for the gene of multiple endocrine neoplasia Type 1 has been identified in Tasmania. As the surgical identification and localisation of parathyroid adenomas is facilitated by the administration of methylene blue, an opportunity has presented to measure the plasma concentration of methylene blue and methaemoglobin production. The study was undertaken to establish whether significant methaemoglobin concentrations were generated during the infusion and whether these concentrations could be related to the corresponding methylene blue concentrations. Mean peak methylene blue concentrations of 3.72 μgl−1, mean percentage methaemoglobin of 10.0 and a Pa.O2 within acceptable clinical ranges were found. No apparent relationship between methylene blue concentration and methaemoglobin production was found.

Simultaneous exposure to chemicals which can oxidize the haemoglobin of the red blood cell to methaemoglobin is common. Although the effects of some of these agents have been documented individually, little research considers the interactive effects. In-vitro experiments on the treated blood of female Dorset sheep assessed the interactive capacity of chlorite, copper and nitrite to affect methaemoglobin formation. All combinations of doses which produced 2.5, 5, 10% methaemoglobin were tested in all possible combinations (a total of 80), as were the controls. This included data on each chemical alone, each two-way combination and the three-way combination. The response is largely additive (the sum of the individual effects) except for one of the two-way interactions, chlorite/nitrite (P < . 01), which showed antagonism. Chlorite may oxidize nitrite which could explain the less-than-additive response. Overall, the result of combining these agents on methaemoglobin was additive.

Electron transport systems exist in the plasma membranes of all cells. Although not well characterised they play roles in cell growth and proliferation, hormone responses and other cell signalling events, but perhaps their most important role, especially in erythrocytes, is enabling the cell to respond to changes in both intra- and extracellular redox environments. Human erythrocytes possess a transmembrane electron transport capability that mediates the transfer of reducing equivalents from reduced intracellular species to oxidised extracellular species and is concomitant with proton extrusion. In the work for this thesis I showed that erythrocyte membranes contain a transmembrane WST-1 (water soluble tetrazolium-1) reductase activity that uses reducing equivalents from intracellular NADH to reduce extracellular WST-1. The rate of WST-1 reduction was increased by the presence of phenazine methosulfate and, although of low activity, it showed similar properties to a previously reported transmembrane NADH-oxidase activity. 1H NMR experiments showed that WST-1 was reversibly bound to the membrane and/or proteins in the membrane within the timeframe of the NMR experiment, confirming the location of the WST-1 reduction. Preliminary attempts to purify NADH:WST-1 reductase and NADH:ferricyanide reductase activities from the erythrocyte plasma membrane were inconclusive. The protein(s) responsible for the reduction of these oxidants appear to be of low abundance in the plasma membrane and may be part of a larger protein complex. Further work on the isolation of these redox activities is required before the protein(s) involved can be identified with any confidence. The ability of cells to export electrons suggests that an electron import mechanism might also exist to re-establish the cell�s redox-buffering equilibrium under conditions of oxidative stress. This hypothesis was tested in glucose-deprived erythrocytes using reduced glutathione and NADH as extracellular electron donors. It was shown that neither reduced glutathione nor NADH donated reducing equivalents through a transmembrane redox system. Extracellular NADH was, however, able to produce profound changes in starvation metabolism and methaemoglobin reduction rates. The addition of extracellular NADH caused a six-fold increase in the rate of lactate production above that observed in glucose-starved controls, together with a concomitant decrease in pyruvate production. In erythrocytes containing high levels of methaemoglobin, extracellular NADH increased the rate of methaemoglobin reduction in both the presence and absence of glucose. These results were explained by the leakage of lactate dehydrogenase from erythrocytes due to an admittedly low level of haemolysis. This caused the displacement of the intracellular pseudo-equilibrium of the lactate dehydrogenase reaction via transmembrane exchange of lactate, allowing the conversion of extracellular pyruvate to lactate and resulted in an increase in intracellular NADH concentrations. The latter increased the rate of methaemoglobin reduction. In conclusion, the work described in this thesis showed that erythrocyte membranes do not contain mechanisms for importing electrons or reducing equivalents from extracellular reduced glutathione or NADH. Erythrocytes do, however, contain an electron export system which can reduce extracellular oxidants such as WST-1 and the activity of this system depends on an intricate balance between intracellular antioxidants and enzyme activities. There is much still to be learnt about plasma membrane redox systems, little is known, for example, about the protein composition, mechanism of action, and the in vivo conditions under which these systems are most active.

Electron transport systems exist in the plasma membranes of all cells. Although not well characterised they play roles in cell growth and proliferation, hormone responses and other cell signalling events, but perhaps their most important role, especially in erythrocytes, is enabling the cell to respond to changes in both intra- and extracellular redox environments. Human erythrocytes possess a transmembrane electron transport capability that mediates the transfer of reducing equivalents from reduced intracellular species to oxidised extracellular species and is concomitant with proton extrusion. In the work for this thesis I showed that erythrocyte membranes contain a transmembrane WST-1 (water soluble tetrazolium-1) reductase activity that uses reducing equivalents from intracellular NADH to reduce extracellular WST-1. The rate of WST-1 reduction was increased by the presence of phenazine methosulfate and, although of low activity, it showed similar properties to a previously reported transmembrane NADH-oxidase activity. 1H NMR experiments showed that WST-1 was reversibly bound to the membrane and/or proteins in the membrane within the timeframe of the NMR experiment, confirming the location of the WST-1 reduction. Preliminary attempts to purify NADH:WST-1 reductase and NADH:ferricyanide reductase activities from the erythrocyte plasma membrane were inconclusive. The protein(s) responsible for the reduction of these oxidants appear to be of low abundance in the plasma membrane and may be part of a larger protein complex. Further work on the isolation of these redox activities is required before the protein(s) involved can be identified with any confidence. The ability of cells to export electrons suggests that an electron import mechanism might also exist to re-establish the cell's redox-buffering equilibrium under conditions of oxidative stress. This hypothesis was tested in glucose-deprived erythrocytes using reduced glutathione and NADH as extracellular electron donors. It was shown that neither reduced glutathione nor NADH donated reducing equivalents through a transmembrane redox system. Extracellular NADH was, however, able to produce profound changes in starvation metabolism and methaemoglobin reduction rates. The addition of extracellular NADH caused a six-fold increase in the rate of lactate production above that observed in glucose-starved controls, together with a concomitant decrease in pyruvate production. In erythrocytes containing high levels of methaemoglobin, extracellular NADH increased the rate of methaemoglobin reduction in both the presence and absence of glucose. These results were explained by the leakage of lactate dehydrogenase from erythrocytes due to an admittedly low level of haemolysis. This caused the displacement of the intracellular pseudo-equilibrium of the lactate dehydrogenase reaction via transmembrane exchange of lactate, allowing the conversion of extracellular pyruvate to lactate and resulted in an increase in intracellular NADH concentrations. The latter increased the rate of methaemoglobin reduction. In conclusion, the work described in this thesis showed that erythrocyte membranes do not contain mechanisms for importing electrons or reducing equivalents from extracellular reduced glutathione or NADH. Erythrocytes do, however, contain an electron export system which can reduce extracellular oxidants such as WST-1 and the activity of this system depends on an intricate balance between intracellular antioxidants and enzyme activities. There is much still to be learnt about plasma membrane redox systems, little is known, for example, about the protein composition, mechanism of action, and the in vivo conditions under which these systems are most active.