Cardiovascular manifestations of acute nitrite intoxication in laboratory rats

The systemic and peripheral hemodynamics was studied in male white rats under conditions of acute nitrite hypoxia (subcutaneous administration of sodium nitrite at doses of 1, 3, and 5 mg/100 g body mass). By the electrocardiographic, rheographic, and other methods there were recorded the heart rate (HR), minute circulation volume (MCV), cardiac output (CO), skeletal muscle circulation (SMC), brain circulation (BC), and systemic arterial pressure (AP). Nitrite was shown to produce a fast, dose-dependent AP fall accompanied by a decrease of MCV due to development of bradycardia and a fall of CO. At the phase of the steady hypotension, MCV increased due to a significant rise of CO on the background of the continuing bradycardia. The systemic circulatory effects of NaNO₂ were found to be accompanied by a redistribution of peripheral circulation in the form of a dose-dependent increase of BC and a sharp fall of MCV. It was shown that 1–1.5 h after the nitrite injection the parameters of systemic and peripheral hemodynamics approached the initial levels. Possible triggering mechanisms of the initial stage of the rat cardiovascular adaptation to conditions of acute nitrite hypoxia are discussed.     

Oxygen regime in rat brain tissues under conditions of acute nitrite methemoglobinemia

Oxygen regime in rat brain tissues was studied under conditions of nitrite hypoxia. The local brain circulation (LCC) and pO₂ were recorded by polargraphic method in microareas of the brain cortex one hour after a subcutaneous injection of NaNO₂ (3 mg/100 g body mass). A LCC decrease by 55% was shown by the 30th min of the nitrite intoxication, with its restoration to 85% of the initial blood-flow by the 60th min. In some brain microareas, a pO₂ increase by 40.7% was observed by the 45th min of the action and its decrease by 32.2% by the 60th min, whereas in other microareas, a pO₂ decrease by 24.5% with its subsequent increase to 78.7% of the initial level, respectively. A statistically significant correlation is revealed between changes of the oxygen pressure in the process of development of nitrite hypoxia and the LCC dynamics. It is concluded that the circulatory disturbances developing at the first moments of the nitrite action lead to an increase of the degree of the pO₂ differentiated distribution in the brain: to hyperoxygenation in some microareas and to severe hypoxia in others, what can be the cause of functional brain disturbances under the effect of nitrogen oxides.     

Oxygen supply of the brain cortex in acute nitrite hypoxia in rodents with different ecological specialization

Microhemodynamics and oxygen tension (pO₂) in the brain cortex tissues as well as the heart rate were studied in rodents with different ecological specialization during hypoxia produced by subcutaneous injection of sodium nitrite (3 mg/100 g body mass). It was shown that the blood flow in animals with low (rats) and high (muskrats) resistance to hypoxia decreased by the 30th min of the nitrite action, with its subsequent restoration to 85% and 83% of the initial level by the 60th min. The interspecies difference consisted in an increase of the brain blood flow (by 24%) in muskrats and a decrease (by 33%) in rats 15 min after the injection. In rats, simultaneously with the blood-flow dynamics, a pO₂ increase was observed in some brain cortex microareas, while in others—a pO₂ decrease 15 min after the NaNO₂ injection: meanwhile, in muskrats, at this time period a significant pO₂ decrease was observed on the background of a blood flow increase. In both animal species, the pO₂ minimal value was reached by the 45th min, while restoration almost to the initial levels—by the 60th min of the nitrite action. Changes in the rats, synchronous and unidirectional with the heart rate frequency, of the brain blood-flow, as well as tachycardia developing throughout the whole experiment in rats allow suggesting that restoration of the oxygen regime in the brain cortex microareas is provided by activation of systemic mechanisms of regulation of circulation.     

Peculiarities of myocardial electrogenesis in laboratory rats under conditions of acute nitrite intoxication

In anesthetized male rats the arterial blood pressure in femoral artery and electrocardiogram in standard leads were recorded uninterruptedly for 1–1.5 h under conditions of acute nitrite intoxication produced by a subcutaneous injection of water solution of sodium nitrite (donor of nitric oxide) at concentrations of 10, 30, and 50 mg/kg body mass. Results of the study have shown dose-dependent changes of arterial pressure as well as of time and amplitude characteristics of electrocardiogram under effect of NaNO₂. At the threshold hypoxic dose, an increase of amplitude of R and S waves was observed by the 30–45th min, while at the maximal NaNO₂ dose, amplitude of all waves rose by the 15th min of intoxication. High nitrite doses often caused an elevation of the ST segment above the isoelectric line and a rise of the amplitude of the T wave, on which a notch appeared in some cases. The change of the ECG time parameters was expressed in the dose-dependent development of bradycardia for the first 4–7 min; its level correlated with the progressively decreasing arterial pressure in the beginning (the 2–4th min) of nitrite intoxication. Variation analysis of the heart rate spectral characteristics by Baevskii’s method has revealed a rise of the total spectral power of pulse oscillations. Under effect of nitrite, in the specter of cardiointervals, the slower oscillations have been revealed with frequency of 0.15–0.2 Hz in the LF diapason with subsequent recovery of the normal ECG specter at the end of the experimental period. The maximal nitrite dose produced more pronounced shifts of the heart rate specter towards the LF and VLF diapasons that were not restored for 1 h of experiment. Transitory processes of readjustment of the cardiac rhythm had discrete character. The nitrite dose of 100 mg/kg body mass increased the RR-interval after 4–7 min with amplitude steps of 3–5 imp/s and the time constant of 20–40 s. The revealed ECG changes had the reflex (enhancement of parasympathetic tonus) and metabolic (the hypoxic and histotoxic damage of myocardium) nature.     

Combined hypoxia and sodium nitrite pretreatment for cardiomyocyte protection in vitro

Methods that increase cardiomyocyte survival upon exposure to ischemia, hypoxia and reoxygenation injuries are required to improve the efficacy of cardiac cell therapy and enhance the viability and function of engineered tissues. We investigated the effect of combined hypoxia/NaNO₂ pretreatment on rat neonatal cardiomyocyte (CM), cardiac fibroblast, and human embryonic stem cell‐derived CM (hESC‐CM) survival upon exposure to hypoxia/reoxygenation (H/R) injury in vitro. Cells were pretreated with and without hypoxia and/or various concentrations of NaNO₂ for 20 min, then incubated for 2 h under hypoxic conditions, followed by 2 h in normoxia. The control cells were maintained under normoxia for 4 h. Pretreatment with either hypoxia or NaNO₂ significantly increased CM viability but had no effect on cardiac fibroblast viability. Combined hypoxia/NaNO₂ pretreatment significantly increased CM viability but significantly decreased cardiac fibroblast viability. In rat neonatal CMs, cell death, as determined by lactate dehydrogenase (LDH) activity, was significantly reduced with hypoxia/NaNO₂ pretreatment; and in hESC‐CMs, hypoxia/NaNO₂ pretreatment increased the BCL‐2/BAX gene expression ratio, suggesting that hypoxia/NaNO₂ pretreatment promotes cell viability by downregulating apoptosis. Additionally, we found a correlation between the prosurvival effect of hypoxia/NaNO₂ pretreatment and the myoglobin content of the cells by comparing neonatal rat ventricular and atrial CMs, which express high and low myoglobin respectively. Functionally, hypoxia/NaNO₂ pretreatment significantly improved the excitation threshold upon H/R injury to the level observed for uninjured cells, whereas pretreatment did not affect the maximum capture rate. Hence, hypoxia/NaNO₂ pretreatment may serve as a strategy to increase CM survival in cardiac regenerative therapy applications and tissue engineering. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:482–492, 2015     

Autonomic nervous control of blood pressure and heart rate during hypoxia in the cod,Gadus morhua

Summary The autonomic nervous and possible adrenergic humoral control of blood pressure and heart rate during hypoxia was investigated in Atlantic cod. The oxygen tension in the water was reduced to 4.0–5.3 kPa (i.e.. P_wO₂=30–40 mmHg), and the fish responded with an immediate increase in ventral and dorsal aortic blood pressure (P _va P _da), as well as a slowly developing bradycardia. The plasma concentrations of circulating catecholamines increased during hypoxia with a peak in the plasma level of noradrenaline occurring before the peak for adrenaline. Bretylium was used as a chemical tool to differentiate between neuronal and humoral adrenergic control of blood pressure and heart rate (f _H) during hypoxia. The increase in P _va and P _da in response to hypoxia was strongly reduced in bretylium-treated cod, which suggests that adrenergic nerves are responsible for hypoxic hypertension. In addition, a small contribution by circulating catecholamines to the adrenergic tonus affecting P _va during hypoxia was suggested by the decrease in P _va induced by injection of the -adrenoceptor antagonist phentolamine. The cholinergic and the adrenergic tonus affecting heart rate were estimated by injections of atropine and the -adrenoceptor antagonist sotalol. The experiments demonstrate an increased cholicholinergic as well as adrenergic tonus on the heart during hypoxia.     

Sodium nitrite induces acute central nervous system toxicity in guinea pigs exposed to systemic cell-free hemoglobin

Systemic cell-free hemoglobin (Hb) released via hemolysis disrupts vascular homeostasis, in part, through the scavenging of nitric oxide (NO). Sodium nitrite (NaNO₂) therapy can attenuate the hypertensive effects of Hb. However, the chemical reactivity of NaNO₂ with Hb may enhance heme- or iron-mediated toxicities. Here, we investigate the effect of NaNO₂ on the central nervous system (CNS) in guinea pigs exposed to systemic cell-free Hb. Intravascular infusion of NaNO₂, at doses sufficient to alleviate Hb-mediated blood pressure changes, reduced the expression of occludin, but not zona occludens-1 (ZO-1) or claudin-5, in cerebral tight junctions 4 h after Hb infusion. This was accompanied by increased perivascular heme oxygenase-1 expression, neuronal iron deposition, increased astrocyte and microglial activation, and reduced expression of neuron-specific nuclear protein (NeuN). These CNS changes were not observed in animals treated with Hb or NaNO₂ alone. Taken together, these findings suggest that the use of nitrite salts to treat systemic Hb exposure may promote acute CNS toxicity.     

Production of aflatoxin by Aspergillus parasiticus NRRL-2999 during growth in the presence of curing salts

Aspergillus parasiticus NRRL-2999 was inoculated into meat mixtures with curing salts and into yeast extractsucrose (YES) and sucrose-ammonium salts (SAS) broth with and without curing salts to determine if the presence of curing salts significantly affected growth and aflatoxin production by the mold. The effect of individual curing salts or curing salt mixtures on growth and toxin elaboration by the aspergillus was substrate dependent. When YES broth contained 100 ppm of NaNO₂, 2% NaCl, or 1 or 2% NaCl plus 200 ppm of NaNO₂ or 200 ppm of NaNO₃, growth and/or aflatoxin production was depressed. Biosynthesis of aflatoxin B₁ was enhanced by presence of 1 and 4% NaCl in YES broth. The SAS broth containing only NaCl or NaCl combined with nitrite or nitrate yielded less aflatoxin than did control broth or no aflatoxin at all. When compared to the control, an increase in growth and amount of aflatoxin occurred in SAS broth which contained 200 ppm of NaNO₃. Sausages containing 100 and 200 ppm NaNO₂ and no NaCl supported more mold growth and aflatoxin production than did control sausage with 3 % NaCl and 100 ppm of NaNO₂. Addition of 2 and 3 % NaCl and no nitrite to sausage resulted in less aflatoxin than in control sausage.     

Effect of acute sodium nitrite intoxication on some essential biometals in mouse spleen

Background and aimSodium nitrite (NaNO₂) is an inorganic salt with numerous applications in a variety of industries, as well as in medicine. Nevertheless, exposure to high levels of NaNO₂ is toxic for animals and humans. Sodium nitrite intoxication is shown to decrease the activity of major antioxidant defence enzymes which is dependent on the maintenance of specific ion equilibrium. The aim of the present study was to investigate the effect of acute NaNO₂ intoxication on the content of the essential metals iron (Fe), calcium (Ca) and zinc (Zn) in mouse spleen.MethodsMature male ICR mice were divided into four groups and subjected to acute NaNO₂ exposure by a single intraperitoneal injection of 120 mg/kg body weight. Animals in each group were sacrificed at certain time interval after treatment (1 h, 5 h, 1 day and 2 days). Spleens were excised and processed for atomic absorption spectrometry analysis of Fe, Ca and Zn content.ResultsAt the first hour after treatment, a decrease in Fe and Ca levels was observed. One day following NaNO₂ administration, Zn concentration reached its lowest value and Ca levels remained lower, compared to the untreated controls. In contrast, Fe concentration increased on the first and second day after treatment.ConclusionThe results of the present study demonstrate that acute NaNO₂ intoxication provokes changes in the endogenous levels of Fe, Ca and Zn in mouse spleen. These findings suggest disruption of the ionic balance and impact on the activity of antioxidant defence enzymes.     

Effect of Sodium Nitrite on Ischaemia and Reperfusion-Induced Arrhythmias in Anaesthetized Dogs: Is Protein S-Nitrosylation Involved?

Background and Purpose

To provide evidence for the protective role of inorganic nitrite against acute ischaemia and reperfusion-induced ventricular arrhythmias in a large animal model.

Experimental Approach

Dogs, anaesthetized with chloralose and urethane, were administered intravenously with sodium nitrite (0.2 µmolkg^-1min^-1) in two protocols. In protocol 1 nitrite was infused 10 min prior to and during a 25 min occlusion of the left anterior descending (LAD) coronary artery (NaNO₂-PO; n = 14), whereas in protocol 2 the infusion was started 10 min prior to reperfusion of the occluded vessel (NaNO₂-PR; n = 12). Control dogs (n = 15) were infused with saline and subjected to the same period of ischaemia and reperfusion. Severities of ischaemia and ventricular arrhythmias, as well as changes in plasma nitrate/nitrite (NOx) levels in the coronary sinus blood, were assessed throughout the experiment. Myocardial superoxide and nitrotyrosine (NT) levels were determined during reperfusion. Changes in protein S-nitrosylation (SNO) and S-glutathionylation were also examined.

Key Results

Compared with controls, sodium nitrite administered either pre-occlusion or pre-reperfusion markedly suppressed the number and severity of ventricular arrhythmias during occlusion and increased survival (0% vs. 50 and 92%) upon reperfusion. There were also significant decreases in superoxide and NT levels in the nitrite treated dogs. Compared with controls, increased SNO was found only in NaNO₂-PR dogs, whereas S-glutathionylation occurred primarily in NaNO₂-PO dogs.

Conclusions

Intravenous infusion of nitrite profoundly reduced the severity of ventricular arrhythmias resulting from acute ischaemia and reperfusion in anaesthetized dogs. This effect, among several others, may result from an NO-mediated reduction in oxidative stress, perhaps through protein SNO and/or S-glutathionylation.     

Hemodynamics in the Microcirculation System of the Rat Cerebral Cortex in Nitrite Methemoglobinemia

Effects of sodium nitrite on the blood flow rate (V) in microvessels of rat cerebral cortex (5–15 µm in diameter), arterial pressure (AP), plasma osmotic pressure (P _osm), and hematological parameters were studied. The mean V and AP in 15 min after administration of NaNO₂ (3 mg/100 g mass) decrease by 36% and 45%, while in 30 and 45 min they increase by 14% and 7% and by 20% and 19% as compared with minimal values, respectively. At the end of the experiment, on the background of an elevation of P _osm (3%), a decrease of total hemoglobin concentration and of the number of erythrocytes was accompanied by a decrease of the discocyte number from 81 to 35% and a reduction of cell diameters by 7%. It is concluded that NaNO₂ produces block of local active mechanisms of the cerebral blood flow regulation. Compensatory responses in this case are provided by passive mechanisms (rheological blood properties) and systemic reactions.     

Sodium Nitrite Alone Protects the Brain Microsomal Ca2+-ATPase Against Potassium Cyanide-induced Neurotoxicity In Rats

The effect of a short-term oral administration of potassium cyanide (KCN) (200 ppm in diet) with or without sodium nitrite (NaNO₂) pretreatment on rat brain microsomal Ca^2± ATPase was investigated. The specific activity value of the enzyme significantly decreased (p<0.05) by 50% compared with control and by 63% for KCN-treated rats compared with KCN-treated rats pretreated with NaNO₂. There was no significant difference at the h=0.05 level between the values obtained for the control and KCN-treated rats pretreated with NaNO₂. These results show both that feeding lowers brain microsomal Ca²⁺-ATPase activity and that NaNO₂ has a protective role (antidote function) in that respect.     

Nitrite Uptake Patterns in Wheat Seedlings as Influenced by Nitrate and Ammonium

Nitrite and nitrate uptake by wheat (Triticum vulgare) from 0.5 mM potassium solutions both showed an apparent induction pattern characterized by a slow initial rate followed by an accelerated rate. The accelerated phase was more rapid for nitrate uptake, was initiated earlier, and was seriously restricted by the presence of equimolar nitrite. The accelerated phase of nitrite uptake was restricted by nitrate to a lesser extent. The two anions seem not to be absorbed by identical mechanisms. Ammonium pretreatments or prior growth with ammonium had relatively little influence on the pattern of nitrite uptake. However, prior growth with nitrate eliminated the slow initial phase and induced development of the accelerated phase of nitrite uptake. A beneficial effect was noted after 3 h nitrate pretreatment and full development had occurred by 12 h nitrate pretreatment. The evidence suggests that a small amount of tissue nitrite, which could be supplied either by absorption or by nitrate reduction, was specifically required for induction of the accelerated phase of nitrite uptake. Cycloheximide (2 μg ml^?1) seriously restricted development of the accelerated phase of nitrite uptake, but its effect was not as severe when it was added after the accelerated phase had been induced by prior exposure to nitrite or nitrate. However, translocation of ¹⁵N from the absorbed nitrite was sharply decreased under the latter conditions, indicating a difference in sensitivity of the uptake and translocation processes to cycloheximide. Potassium uptake was greater from KNO₃ than from KNO₂ and in both instances it was enhanced during the early stages of the accelerated phase of anion uptake. Moreover, addition of NaNO₃ to KNO₂ substantially increased potassium uptake. A coupling between anion and potassium uptake was therefore evident, but the coupling was not obligatory because the accelerated phase of nitrite uptake could occur in absence of rapid potassium uptake.     

Cardiovascular manifestations of acute nitrite intoxication in laboratory rats

The systemic and peripheral hemodynamics was studied in male white rats under conditions of acute nitrite hypoxia (subcutaneous administration of sodium nitrite at doses of 1, 3, and 5 mg/100 g body mass). By the electrocardiographic, rheographic, and other methods there were recorded the heart rate (HR), minute circulation volume (MCV), cardiac output (CO), skeletal muscle circulation (SMC), brain circulation (BC), and systemic arterial pressure (AP). Nitrite was shown to produce a fast, dose-dependent AP decrease accompanied by a decrease of MCV due to development of bradycardia and a fall of CO. At the phase of the steady hypotension, CO increased due to a significant rise of CO on the background of the continuing bradycardia. The systemic circulatory effects of NaNO2 were found to be accompanied by a redistribution of peripheral circulation in the form of a dose-dependent increase of BC and a sharp fall of MCV. It was shown that 1-1.5 h after the nitrite injection the parameters of systemic and peripheral hemodynamics approached the initial levels. Possible triggering mechanisms of the initial stage of the rat cardiovascular adaptation to conditions of acute nitrite hypoxia are discussed.     

Gamma Study of pH, Nitrite, and Salt Inhibition of Aeromonas hydrophila

The gamma hypothesis states that there are no interactions between antimicrobial environmental factors. The time to growth of Aeromonas hydrophila challenged with pH, NaNO₂, and salt combinations at 30°C was investigated. Data were examined using a model based on the gamma hypothesis (the gamma model), which takes into account variance-stabilizing transformations and which gives biologically relevant parameters. At high concentrations of NaNO₂ and at pHs of >6.0, the antimicrobial action of the nitrite ion has a strong influence (MIC = 2,033 mg liter⁻¹), whereas at pHs of <6, nitrous acid is dominant (MIC = 1.5 mg liter⁻¹). This change is not due to a “synergy” between pH and the nitrite ion but is due to the shift in the equilibrium concentrations of nitrous acid and nitrite in solution caused by pH. In combination with salt, the parameters found for the action of Na nitrite were identical to those found when it was examined in isolation. Therefore, pH, NaNO₂, and salt act independently on the growth of A. hydrophila. By expanding the gamma model with a cardinal temperature model, the results of fitting the model of Palumbo et al. (J. Food Prot. 54:429-435, 1994) to randomly produced environmental conditions could be reproduced, suggesting that temperature also has an independent effect.     

Mutation breeding of Emericella foeniculicola TR21 for improved production of tanshinone IIA

TR21, an original tanshinone IIA-producing endophytic fungus from the root of Salvia miltiorrhiza Bunge, produces low levels of tanshinone IIA. Three techniques were used to rapidly improve tanshinone IIA production: TR21 mutation by ultraviolet radiation (UV), TR21 mutation by sodium nitrite (NaNO₂) and TR21 mutation by a combination of both UV and NaNO₂. An improved mutant, labeled as NU152, was obtained from the combination of UV and NaNO₂. The content of tanshinone IIA produced by NU152 held a relative high value of 51.44 ± 0.22 μg per g, and the NU152 produced a more than 1.46-fold increase in tanshinone IIA yield, compared with the wild type TR21 (P < 0.05). The fungus NU152 showed a possible way for the sustainable production of tanshinone IIA.     

Improvement of NaNO2-Oxidizing Activity in Nitrobacter vulgaris by Coentrapment in Polyacrylamide Containing Polydimethylsiloxane Copolymer and DEAE-Sephadex

Removal of nitrite and nitrate from drinking water has attracted great attention in recent years because of the human health risk induced by the exposure to contaminated groundwater and surface water. We have therefore tested a model nitrite oxidation system by coentrapping the NaNO₂ oxidizer Nitrobacter vulgaris with polydimethylsiloxane (PDMS) copolymer and DEAE-Sephadex in a polyacrylamide gel. The copolymer and the anion exchanger facilitate the diffusion of oxygen and NaNO₂, respectively, into the gel matrix. To test the nitrite-oxidizing activity, the entrapped cells were coupled to a thermal sensor. Coentrapment of 5% (wt/vol) DEAE-Sephadex with Nitrobacter vulgaris increased the nitrite-oxidizing activity by a factor of 3.7 compared to entrapped cells alone, and by the addition of 0.86% (wt/vol) artificial oxygen carrier PDMS copolymer increased the activity further to 4.3 times higher. Operational and storage stability of the coentrapped N.vulgaris also improved. This suggests that this enhanced immobilized cell system can also be used for nitrite oxidation to nitrate in drinking water as an on-line thermally monitored bioreactor.     

Effects of NO2 − or NO3 − supply on polyamine accumulation and ethylene production of wheat roots at acidic and neutral pH: implications for root growth

Exposure of plant tissues to nitrite ion or nitrite-derived NO at acidic pH results in the degradation of important macromolecules and may lead to the formation of reactive molecular species. Polyamines as free radical scavengers protect plant tissues against membrane and DNA damage during stress and may contribute to the acclimation processes caused by nitrite as an abiotic stressor at acidic pH. The putrescine content of wheat roots grown under low salt conditions increased only transiently at pH 7.0 when the nutrient solution was replaced by 1mM KNO₂, KNO₃, NaNO₂ or NaNO₃, but the concentration of this diamine remained high after a 24-hour incubation at pH 4.0. The acid stress-induced putrescine accumulation was further enhanced by an external N source, especially by nitrite. The contents of spermine and spermidine in the 24-hour samples were also higher in N-supplied roots at acidic pH. Polyamine contents were not closely correlated with the ethylene production by the intact roots. Nitrite treatment, however, significantly decreased the ethylene release from the root apex, but not from the basal parts at pH 4.0. The peroxidative capacities of the tissues in the soluble fractions were also inhibited by nitrite in the apical zones, which might modify the H₂O₂-coupled oxidative processes. Nitrite ion at acidic pH may react directly with guaiacol-like phenolic compounds and in this way interfere with the lignification process. The low ethylene release by the apical zones in acidic environment may be a symptom of the nitrite-induced inhibition of root extension.     

Effects of hypoxic factors on cardiac chronotropic reactions in the muskrat Ondatra zibethicus in free behavior

Effects of natural and artificial hypoxic factors on cardiac chronotropic reactions were studied in the muskrat Ondatra zibethicus naturally adapted to underwater hypoxia under conditions of free behavior. To record cardiac activity, original implanted ECG sensors designed in the laboratory were used. Under observations were muskrats in the states of rest, movement, swimming on the water surface, diving, underwater swimming, forced underwater immersion, and artificial apnea, in the low-pressure chamber during changes of pressure from 100 to 25 kPa (ascent to an altitude of 11 km) and in the atmosphere of hypoxic mixtures with 5–10% O₂ as well as under conditions of hemic nitrite hypoxia after injection of 3 mg/kg NaNO₂. Heart rate (HR) in muskrats is labile and can change within the limits from 15 to 360 beats/min. A characteristic feature of hypoxic action is development in muskrats of bradycardia that can appear either instantly—both as a conditional reflex and from the nose lobe receptors—or gradually at a decrease of pO₂ in inhaled air. Before diving and after coming to the surface a brief tachycardia can also be observed. The gradual development of tachycardia takes place in nitrite hypoxia. Development of bradycardia was eliminated at blockade of M-cholinoreceptors by atropine, and of tachycardia—at blockade of β-adrenoreceptors by propranolol. Blockade of α-adrenoreceptors by phentolamine did not affect cardiac chronotropic reactions, which indicates the absence of their connection with vasoconstriction. Analysis of the cardiac rhythm variability has revealed a large spectrum of slow cardiointerval fluctuations connected with animal functional states. Regulation of cardiac chronotropic reactions in muskrats under effect of hypoxic factors operates along both sympathetic and parasympathetic pathways of the autonomic nervous system, the leading role in these processes being played by vagus influences. Original Russian Text. V. I. Shereshkov, T. E. Shumilova, D. A. Kuzmin, I. N. Yanvareva, and A. D. Nozdrachev, 2006, published in Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 2006, Vol. 42, No. 4, pp. 371–377.     

Decreases in Amino Acid and Acetylcholine Metabolism During Hypoxia

Abstract: Hypoxia impairs brain function by incompletely defined mechanisms. Mild hypoxia, which impairs memory and judgment, decreases acetylcholine (ACh) synthesis, but not the levels of ATP or the adenylate energy charge. However, the effects of mild hypoxia on the synthesis of the glucosederived amino acids [alanine, aspartate, γ-amino butyric acid (GABA), glutamate, glutamine, and serine] have not been characterized. Thus, we examined the incorporation of [U-¹⁴C]glucose into these amino acids and ACh during anemic hypoxia (injection of NaNO₂), hypoxic hypoxia (15 or 10% O₂), and hypoxic hypoxia plus hypercarbia (15 or 10% O₂ with 5% CO₂). In general, the synthesis of the amino acids and of ACh declined in parallel with each type of hypoxia we studied. For example, anemic hypoxia (75 mg/kg of NaNO₂) decreased the incorporation of [U-¹⁴C]glucose into the amino acids and into ACh similarly. [Percent inhibition: ACh (57.4), alanine (34.4), aspartate (49.2), GABA (61.9). glutamine (59.2), glutamate (51.0), and serine (36.7)]. A comparison of several levels (37.5, 75, 150, 225 mg/kg of NaNO₂) of anemic hypoxia showed a parallel decrease in the flux of glucose into ACh and into the amino acids whose synthesis depends on mitochondrial oxidation: GABA (r= 0.98), glutamate (r= 0.99), aspartate (r= 0.96), and glutamine (r= 0.97). The synthesis of the amino acids not dependent on mitochondrial oxidation did not correlate as well with changes in ACh metabolism: serine (r= 0.68) and alanine (r= 0.76). The decreases in glucose incorporation into ACh and into the amino acids with hypoxic hypoxia (15% or 10% O₂) or hypoxic hypoxia with 5% CO₂ were very similar to those with the two lowest levels of anemic hypoxia. Thus, any explanation of the brain's sensitivity to a decrease in oxygen availability must include the alterations in the metabolism of the amino acid neurotransmitters as well as ACh.