Effect of hyperoxia on liver necrosis induced by hepatotoxins

We have tested the effects of hyperbaric oxygen on necrosis of rat liver induced by the administration of several toxins. The extent of liver necrosis was determined 24 h after the administration of the toxins by measurement of serum levels of alanine and aspartate amino-transferases and by histologic and ultrastructural analyses. Treatment with hyperbaric oxygen decreases carbon tetrachloride (CCl4)-induced necrosis in a manner dependent upon duration and pressure of oxygen exposure. Pretreatment of rats with phenobarbital diminishes this protective effect. Hyperbaric oxygen treatment before or immediately after CCl4 intoxication is protective. Loss of protection is rapid; hyperbaric oxygen treatment 6 h after CCl4 intoxication augments the liver necrosis. No delayed necrogenic effects of CCl4 are seen in the animals treated with hyperbaric oxygen immediately. Hyperbaric oxygen augments the liver necrosis induced by acetaminophen, bromobenzene, dimethylnitrosamine or thioacetamide. This augmented necrosis is averted by prolonged treatment with hyperbaric oxygen. Hyperbaric oxygen has no effect on liver injury induced by galactosamine or lipopolysaccharide. We conclude that hyperoxia decreases the hepatic necrosis induced by compounds which undergo reductive biotransformation by the cytochrome P-450 monooxygenase system; hyperoxia augments the necrosis induced by compounds which undergo oxidative biotransformation by this system. Biotransformation of toxins appears to be nonspecifically inhibited by hyperoxic exposure of long duration.     

Inhibition of beta-1 receptor but not vagotomy can abolish the L-NAME evoked bradycardia in anesthetized rat

We reported previously that the nitric oxide synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) decreases cardiac output. Several studies have shown that inhibition of nitric oxide synthesis decreases the heart rate. In the present study, we investigated the effect of a single bolus administration of L-NAME on blood pressure and heart rate monitored for one hour in anesthetized rats and the influence of vagotomy and beta1-receptor blocker metoprolol on the L-NAME induced bradycardia. After L-NAME treatment, the blood pressure rose immediately after the injection of the drug (peak response in the third minute: +24%, p<0.001) and fell to the control level in the 20th minute. The heart rate decreased immediately after L-NAME administration, the lowest value being reached in the 10th minute (-14%, p<0.001). However, bradycardia was sustained even after the blood pressure had returned to the control level. Bilateral vagotomy failed to influence the negative chronotropic effect of L-NAME, but bradycardia was completely abolished by metoprolol pretreatment. We concluded that the bradycardia evoked by L-NAME is mainly due to the withdrawal of sympathetic tone upon the heart rate. However, the cause of sustained bradycardia after normalization of blood pressure cannot be elucidated.     

Comparison of Nitrogen Narcosis and Helium Pressure Effects on Striatal Amino Acids: A Microdialysis Study in Rats

Exposure to nitrogen–oxygen mixture at high pressure induces narcosis, which can be considered as a first step toward general anaesthesia. Narcotic potencies of inert gases are attributed to their lipid solubility. Nitrogen narcosis induces cognitive and motor disturbances that occur from 0.3 MPa in man and from 1 MPa in rats. Neurochemical studies performed in rats up to 3 MPa have shown that nitrogen pressure decreases striatal dopamine release like argon, another inert gas, or nitrous oxide, an anaesthetic gas. Striatal dopamine release is under glutamatergic and other amino acid neurotransmission regulations. The aim of this work was to study the effects of nitrogen at 3 MPa on striatal amino acid levels and to compare to those of 3 MPa of helium which is not narcotic at this pressure, by using a new technique of microdialysis samples extraction under hyperbaric conditions, in freely moving rats. Amino acids were analysed by HPLC coupled to fluorimetric detection in order to appreciate glutamate, aspartate, glutamine and asparagine levels. Nitrogen–oxygen mixture exposure at 3 MPa decreased glutamate, glutamine and asparagine concentrations. In contrast, with helium–oxygen mixture, glutamate and aspartate levels were increased during the compression phase but not during the stay at maximal pressure. Comparison between nitrogen and helium highlighted the narcotic effects of nitrogen at pressure. As a matter of fact, nitrogen induces a reduction in glutamate and in other amino acids that could partly explain the decrease in striatal dopamine level as well as the motor and cognitive disturbances reported in nitrogen narcosis.     

Serum erythropoietin levels in healthy humans after a short period of normobaric and hyperbaric oxygen breathing: the "normobaric oxygen paradox".

Renal (peritubular) tissue hypoxia is a well-known physiological trigger for erythropoietin (EPO) production. We investigated the effect of rebound relative hypoxia after hyperoxia obtained under normo- and hyperbaric oxygen breathing conditions. A group of 16 healthy volunteers were investigated before and after a period of breathing 100% normobaric oxygen for 2 h and a period of breathing 100% oxygen at 2.5 ATA for 90 min (hyperbaric oxygen). Serum EPO concentration was measured using a radioimmunoassay at various time points during 24-36 h. A 60% increase (P < 0.001) in serum EPO was observed 36 h after normobaric oxygen. In contrast, a 53% decrease in serum EPO was observed at 24 h after hyperbaric oxygen. Those changes were not related to the circadian rhythm of serum EPO of the subjects. These results indicate that a sudden and sustained decrease in tissue oxygen tension, even above hypoxia thresholds (e.g., after a period of normobaric oxygen breathing), may act as a trigger for EPO serum level. This EPO trigger, the "normobaric oxygen paradox," does not appear to be present after hyperbaric oxygen breathing.     

Acute alterations in stroke volume during exercise at 3,100 m altitude.

Following 3 weeks exposure to an altitude of 3,100 m, the cardiac output response to upright submaximal exercise was examined in 3 healthy subjects breathing ambient air and breathing 60% oxygen. The procedure allowed acute alteration of the 2 conditions within a single testing period of 30 min, 60% oxygen breathing either preceding or following breathing ambient air. Cardiac output was also measured in two of the subjects during maximal exercise under these two conditions. Administration of the high oxygen inspirate during exercise had little effect on the level of cardiac output but resulted in an immediate bradycardia and a dramatic increase of approximately 16% in stroke volume. Stroke volumes during maximal exercise were also increased by approximately 10% by the administration of high oxygen. It is suggested that the condition of decreases exercise stroke volume which develops with chronic exposure to altitude may be largely the result of diminished myocardial contractility stemming from a condition of myocardial hypoxia.     

Redox control of cardiac rhythm

The rhythm of cardiac beats is generated by pacemaker cells differing from other cardiomyocytes by the presence of slow diastolic depolarization. Consistently activated transmembrane ionic currents provide cyclic excitation of pacemakers, forming the original “membrane clocks”. A new concept has been forwarded in the last decade according to which periodic fluctuations in myoplasmic Ca²⁺ level (“calcium clocks”) not only influence a course of “membrane clocks”, but they also can serve as independent generators of the rhythm. Transport of Ca²⁺ in cells is under constant influence of active forms of oxygen and nitrogen. Both superoxide and NO in moderate doses facilitate Ca²⁺ output from the sarcoplasmic reticulum, accelerating the course of “calcium clocks”, but in higher doses they have opposite effect that may be neutralized mainly by reduced glutathione. The control of cardiac rhythm by active forms of oxygen and nitrogen represents a feedback mechanism by which mitochondria and NO-synthases support Ca²⁺ homeostasis in cells that can be temporarily disturbed under mechanical loads or hypoxia.     

Links in the histamine metabolism in the brain of rats with sequential exposure to low- and high-pressure oxygen

Histamine content and diamine oxidase activity in rat brain under hyperbaric oxygenation have been studied. Under 0,3 MPa histamine level decreases in brain of more sensitive rats, but it does not change in brain of more resistant animals in comparison with the control ones. High oxygen pressure (0,7 MPa) causes a significant increase of histamine concentration. Diamine oxidase activity decreases under hyperoxia. Under the consequent action of high and low pressure (0,3 MPa during 1 h and 0,7 MPa) convulsions in rats begin later and alterations of histamine content in brain are less than under 0,7 MPa oxygen action only. The role of histamine at compensate reaction and cause of increasing resistance of animals to hyperoxia are discussed.     

Effect of hyperbaric oxygenation on proton ATPase activity in mitochondria of various rat tissues

The H+-ATPase activity of mitochondria from the rat brain, liver heart and skeletal muscles was studied as affected by 1 at. of oxygen pressure (60 min), 5 at. (10 min) and 5 at. up to the convulsive and terminal states. The effect of 1 at. of oxygen pressure for 60 min and 5 at. for 10 min. causes an increase in the H+-ATPase activity of mitochondria of the investigated tissues. But under convulsive and terminal stages of 5 at. hyperbaric oxygenation the activity of H+-ATPase decreases, and to the greatest extent in the brain mitochondria.     

The cytochrome P-450 content and catalytic activity in rat liver microsomes during hyperbaric oxygenation]

The effect of different conditions of hyperbaric oxygenation (HBO) on content and catalytic activity of cytochrome P-450 in rat liver cytochrome has been studied. The intensity of lipid peroxidation in microsomal membranes has been determined by the content of dien conjugates and Schiff's bases. The rate of amidopyrine demethylation has been shown not to change, but the rate of aniline hydroxylation decreases on 34, 57 and 64% under increase of oxygen pressure up to 0.3, 0.5 and 0.7 MPa correspondingly. The level of dien conjugates increase on 66-87% under all studied conditions of HBO. Cytochrome P-450 content decreases on 45% under the action of 0.7 MPa, but content of Schiff's bases increases on 210% as compared with control.     

Effect of hyperbaric stress on yeast morphology: study by automated image analysis

The effects of hyperbaric stress on the morphology of Saccharomyces cerevisiae were studied in batch cultures under pressures between 0.1 MPa and 0.6 MPa and different gas compositions (air, oxygen, nitrogen or carbon dioxide), covering aerobic and anaerobic conditions. A method using automatic image analysis for classification of S. cerevisiae cells based on their morphology was developed and applied to experimental data. Information on cell size distribution and bud formation throughout the cell cycle is reported. The results show that the effect of pressure on cell activity strongly depends on the nature of the gas used for pressurization. While nitrogen and air to a maximum of 0.6 MPa of pressure were innocuous to yeast, oxygen and carbon dioxide pressure caused cell inactivation, which was confirmed by the reduction of bud cells with time. Moreover, a decrease in the average cell size was found for cells exposed for 7.5 h to 0.6 MPa CO₂.     

Slowing and attenuation of baroreflex heart rate control with nitrous oxide in exercising men.

The objective of the present study was to determine whether mild inert-gas narcosis impairs cardiovascular control mechanisms and contributes to the relative bradycardia that occurs in humans exercising in a hyperbaric environment. Eight healthy subjects were exposed to a normoxic 30% nitrous oxide (N(2)O) mixture and an air control during dynamic exercise of 100-W intensity. Beat-by-beat heart rate (HR) and invasive arterial blood pressure measurements were made. The sensitivity and the response latency of the arterial-cardiac-chronotropic baroreflex were determined from repeated blood pressure and HR transients induced by rapid tilts between the upright and supine posture. A significant increase (37%, P 相似文献   

Involvement of nitrogen oxide in the cerebral vasoconstriction during respiration with high pressure oxygen

High pressure oxygen evokes a cerebral vasoconstriction and diminishes cerebral blood flow with the aid of mechanisms which are not yet sufficiently studied. We were checking a hypothesis that the hyperbaric oxygen (HBO2) inactivates cerebral nitrogen oxide (NO), interrupts its basal relaxing effect, and evokes a vasoconstriction. In our experiments, HBO2 decreased cerebral blood flow depending on the pressure. Inhibiting the NO-synthase weakened basal vasorelaxation in breathing with atmosphere air and eliminated the vasoconstriction in exposure to the HBO2. Inactivation of O2 prevented the HBO2-induced vasoconstriction. The data obtained reveal that diminishing of cerebral blood flow in HBO is related to the NO inactivation and weakening of its basal vasorelaxing effect. Possible mechanisms of the NO inactivation may involve its reaction with oxygen and superoxide anion which lead to diminishing of the tissue NO concentration and weakening of its vasorelaxing effect.     

Level of ventilation influences the cardiovascular response to hypoxemia in lambs

Newborn animals of a number of species display a brisk increase in ventilation followed by a gradual drop toward or below baseline within minutes of exposure to acute hypoxemia. Heart rate and cardiac output (a determinant of systemic oxygen transport along with the arterial oxygen content) appear to follow a similar pattern, but whether or not the cardiovascular response is influenced by the respiratory response is unknown. We therefore carried out experiments in which the level of ventilation was controlled during normoxemia and hypoxemia to test the hypothesis that the level of ventilation influences the cardiovascular response to acute hypoxemia. Six lambs ranging in age from 17 to 22 days were anesthetized, tracheostomized, and instrumented for measurement of cardiovascular variables. A recovery period of at least 3 days was allowed before the study when each lamb was artificially ventilated with a mixture of 70% nitrous oxide and 30% oxygen in nitrogen. A control respiratory frequency (f) of 30 breaths per min was set and a control tidal volume (VT) was chosen to achieve normocapnia. Cardiovascular measurements were made during normoxemia and hypoxemia (FIO2 0.10) 5 min after f or VT was changed to simulate a decrease, no change, or an increase in ventilation. During normoxemia, the level of ventilation had little effect on the measured cardiovascular variables. At control levels of ventilation, hypoxemia caused an increase in cardiac output that was due solely to an increase in stroke volume as heart rate decreased; blood pressure was unchanged. Increasing ventilation during hypoxemia did not augment cardiac output or alter blood pressure as compared with that observed at control levels of ventilation. Decreasing ventilation during hypoxemia, however, decreased cardiac output due to a profound bradycardia; blood pressure increased significantly. Our data provide evidence that the level of ventilation significantly influences the cardiovascular response to hypoxemia in young lambs.     

Hyperbaric oxygen toxicity and ribosome destruction in Escherichia coli K12

The viability of resting suspensions of Escherichia coli K12 Ymel exposed to air plus 300 psi (1 psi = 6.895 kPa) oxygen (hyperbaric oxygen) decreased as an apparent first-order process after an initial period of constant viability. Control suspensions exposed to air plus 300 psi nitrogen (hyperbaric nitrogen) did not lose viability over the 96 h of the experiment. It was observed that a decrease in the refractive index of the cells preceded the loss of viability in hyperbaric oxygen. This finding together with electron micrographs, which showed extensive loss of ribosomal particles in bacteria incubated in hyperbaric oxygen, led us to suspect that ribosome injury or disassociation might be important in hyperbaric oxygen toxicity. In support of this we found that cellular RNA, labeled with [5-3H]uridine, was much more rapidly and more completely degraded in hyperbaric oxygen than in hyperbaric nitrogen. Furthermore, a far greater proportion of RNA was degraded than was DNA or protein. A direct assay for ribosome particles by sucrose gradient centrifugation showed that only 34% of the 70S ribosome particles was lost during the first 24 h in hyperbaric nitrogen whereas in hyperbaric oxygen 99.6% of the 70S particles was degraded during the same period. In hyperbaric oxygen the rate of viability loss between 24 and 72 h was equal to the rate of 70S ribosome degradation during the first 24 h. If 70S ribosome disassociation in hyperbaric oxygen continues at the same rate after first 24 h, then cumulative 70S ribosome disassociation or injury may lead to and provide an explanation for irreversible bacterial cell injury and the loss of viability.     

Change of Parameters of Functioning of the Cardiovascular and Respiratory Systems in Rats of Different Ages under Effects of Low Doses of the Cholinesterase Inhibitor Phosphacol

In the 4-day old rat pups and adult animals there were studied effects of subacute and acute phosphacol intoxication at the doses producing and not producing inhibition of aetylcholinesterase on ECG parameters and respiration rate. Analysis of the heart rhythm variability (HRV) was performed using an original program designed in the Labview media. The frequency diapason of cardiointervals was divided as follows: the high-frequency component (HF)-0.8-2.5 Hz, the low-frequency (LF, waves of the II order)-0.8-0.3 Hz; frequencies lower than 0.3 Hz-VLF (slow waves of the III order). Under the conditions of the subacute intoxication the heart rate frequency in the 4-day old and in adult rats increases by 36% and 13%, respectively, the respiration rate frequency increases by 73% in the newborn and does not change in adult rats. The VHR analysis indicates an increase of the tone of the parasympathetic nervous system. The level of the sympathetic activity somewhat increases in adults, but decreases in the 5-day old rat pups, which leads to an essential shift of the vagosympathetic balance towards predominance of parasympathetic influences. In adult rats, unlike the newborns, the role of the humoral-metabolic factors in regulation of the cardiac rhythm and vasomotor reactions increases significantly. Remarkably, the decrease of the nervous sympathetic effects in the rat pups leads to the positive chronotropic effect and stabilization of the cardiac rhythm. Acute phosphacol intoxication (doses of 0.25 and 1 µg/kg) is studied in the 4-day old rat pups. The low dose of the drug leads to development of a moderate bradycardia without disturbances of the cardiac rhythm. The high phosphacol dose produces pronounced bradycardia; on its background there develops a long-term transitory arrhythmia representing complexes of the heart rhythm, which alternate in the decasecond or nearminute rhythm and are separated by periodicity that is one order slower. We observed such rhythm earlier during activation of central N-cholinoreactive structures and development of bilateral pneumothorax. Results of the present study allow stating the paradoxical heart rhythm not as agonic, non-peculiar to the “living” organism, but as a special form of functioning of cardiac pacemakers due to disturbances of the heart regulatory mechanism.__________Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 41, No. 2, 2005, pp. 160–167.Original Russian Text Copyright © 2005 by Kuznetsov, Goncharov, Glashkina.     

Analysis of the effects of hyperbaric gases on S. cerevisiae cell cycle through a morphological approach

The effects of hyperbaric gases on the cell cycle of Saccharomyces cerevisiae were studied in batch cultures under pressures between 0.1 and 0.6 MPa and different gas compositions (air, oxygen, nitrogen or carbon dioxide). Classification of S. cerevisiae cells based on their morphology stages was obtained using an automatic image analysis procedure. Information on the distribution of different sub-populations along the cell cycle is reported. A structured morphological model was developed and used to describe the measured data. The results herein reported demonstrate that the bud separation phase is the limiting step in cell duplication. Additionally, the influence of the environmental conditions, specially the oxygen partial pressure, on the START event is reported. Under anaerobic conditions, no significant influence of hyperbaric gases on the cell cycle was verified.     

Immunomodulatory effect of oxygen and pressure

The immunomodulatory effect of hyperbaric oxygen, involving altered cytokine release by macrophages, is well described. Importantly, however, it is not known what the relative contribution is of the hyperbaric environment of the cells vs. increased oxygen tension on these hyperbaric oxygen-dependent effects. We compared, therefore, cytokine release by murine macrophages under hyperbaric oxygen, hyperpressure of normal air and normobaric conditions. We observed that hyperbaric oxygen enhanced cytokine release of both unstimulated as well as lipopolysaccharide (LPS)-challenged macrophages. Hyperpressure of normal air, however, enhanced LPS-induced cytokine production but did not elicit cytokine release in unstimulated macrophages. To further investigate the molecular details underlying the effects of hyperbaric oxygen, we investigated the effect of the p42/p44 mitogen-activated protein (MAP) kinase inhibitor PD98059 and the p38 MAP kinase inhibitor SB203580. Neither inhibitor, however, had a significant effect on the modulatory effects of hyperbaric oxygen on cytokine release. We concluded that the immunomodulatory effect of hyperbaric oxygen contains a component for which hyperpressure is sufficient and a component that apart from hyperpressure also requires hyperoxygenation.     

Study on mammal (rat) of the neuro-muscular synapse function under hyperbaric conditions (11 ata): effects of the curarization

Under hyperbaric conditions (11 ata) obtained with normoxic O2-N2 mixtures spontaneous EMG activity disappears, as do reactions to noise, but this phenomenon is reversible after the substitution of Helium for Nitrogen in the mixture. Analysis of EMG responses to sciatic nerve excitation has revealed no difference between the EMG tracings recorded under normobaric pressure and those obtained under hyperbaric conditions (O2-N2 or O2-He, 11 ata), and hyperbaric conditions do not seem to interfere with neuro-muscular synaptic transmission. Furthermore, the effect of Pavulon (an antidepolarising, acetyl-cholino-competitive curare-mimetic drug) is similar under normal and hyperbaric conditions: hyperbaria change neither the onset of neuro-muscular blockage nor its intensity or duration. The absence of a specific effect on synapse function of a change in the diluting gas from nitrogen to helium suggests that there was no change in post-synaptic receptor function. This result is not in accordance with the hypothesis that inert gas pressures of less than 10 ata modify molecular structures particularly at the neuro-muscular synapse level.     

Alteration of Striatal Dopamine Levels Under Various Partial Pressure of Oxygen in Pre-convulsive and Convulsive Phases in Freely-Moving rats

The purpose of this study was to investigate the change in the striatal dopamine (DA) level in freely-moving rat exposed to different partial pressure of oxygen (from 1 to 5 ATA). Some works have suggested that DA release by the substantia nigra pars compacta (SNc) neurons in the striatum could be disturbed by hyperbaric oxygen (HBO) exposure, altering therefore the basal ganglia activity. Such changes could result in a change in glutamatergic and GABAergic control of the dopaminergic neurons into the SNc. Such alterations could provide more information about the oxygen-induced seizures observed at 5 ATA in rat. DA-sensitive electrodes were implanted into the striatum under general anesthesia. After 1 week rest, awaked rats were exposed to oxygen–nitrogen mixture at a partial pressure of oxygen of 1, 2, 3, 4 and 5 ATA. DA level was monitored continuously (every 3 min) by in vivo voltammetry before and during HBO exposure. HBO induced a decrease in DA level in relationship to the increase in partial pressure of oxygen from 1 ATA to 4 ATA (?15 % at 1 ATA, ?30 % at 2 ATA, ?40 % at 3 ATA, ?45 % at 4 ATA), without signs of oxygen toxicity. At 5 ATA, DA level strongly decreases (?75 %) before seizure which occurred after 27 min ± 7 HBO exposure. After the epileptic seizure the decrease in DA level disappeared. These changes and the biphasic effect of HBO were discussed in function of HBO action on neurochemical regulations of the nigro striatal pathway.