Antihypoxic activity of cytochrome c heme peptides

A comparative study of antihypoxic activity of five and two cytochrome c derivatives was performed during their single prophylactic administration on the model of acute hypobaric hypoxia (AHBH) and during rehabilitation period after AHBH, respectively. Antihypoxic efficiency of cytochrome c derivatives was shown to be dependent on doses, time of drug administration, and type of experimental animal resistance. The heme-nonapeptide of cytochrome c proved to be of maximum efficiency during prophylactic administration and rehabilitation period after AHBH.     

Hypoxia-mediated prolonged elevation of sympathetic nerve activity after periods of intermittent hypoxic apnea.

Obstructive sleep apnea (OSA) is associated with transient elevation of muscle sympathetic nerve activity (MSNA) during apneic events, which often produces elevated daytime MSNA in OSA patients. Hypoxia is postulated to be the primary stimulus for elevated daytime MSNA in OSA patients. Therefore, we studied the effects of 20 min of intermittent voluntary hypoxic apneas on MSNA during 180 min of recovery. Also, we compared MSNA during recovery after either 20 min of intermittent voluntary hypoxic apneas, hypercapnic hypoxia, or isocapnic hypoxia. Consistent with our hypothesis, both total MSNA and MSNA burst frequency were elevated after 20 min of intermittent hypoxic apnea compared with baseline (P < 0.05). Both total MSNA and MSNA burst frequency remained elevated throughout the 180-min recovery period and were statistically different from time control subjects throughout this period (P < 0.05). Finally, MSNA during recovery from intermittent hypoxic apnea, hypercapnic hypoxia, and isocapnic hypoxia were not different (P = 0.50). Therefore, these data support the hypothesis that short-term exposure to intermittent hypoxic apnea results in sustained elevation of MSNA and that hypoxia is the primary mediator of this response.     

Recovery of the ventilatory response to hypoxia in normal adults

Recovery of the initial ventilatory response to hypoxia was examined after the ventilatory response had declined during sustained hypoxia. Normal young adults were exposed to two consecutive 25-min periods of sustained isocapnic hypoxia (80% O2 saturation in arterial blood), separated by varying interludes of room air breathing or an increased inspired O2 fraction (FIO2). The decline in the hypoxic ventilatory response during the 1st 25 min of hypoxia was not restored after a 7-min interlude of room air breathing; inspired ventilation (VI) at the end of the first hypoxic period was not different from VI at the beginning and end of the second hypoxic period. After a 15-min interlude of room air breathing, the hypoxic ventilatory response had begun to recover. With a 60-min interlude of room air breathing, recovery was complete; VI during the second hypoxic exposure matched VI during the first hypoxic period. Ventilatory recovery was accelerated by breathing supplemental O2. With a 15-min interlude of 0.3 FIO2 or 7 min of 1.0 FIO2, VI of the first and second hypoxic periods were equivalent. Both the decline and recovery of the hypoxic ventilatory response were related to alterations in tidal volume and mean inspiratory flow (VT/TI), with little alteration in respiratory timing. We conclude that the mechanism of the decline in the ventilatory response with sustained hypoxia may require up to 1 h for complete reversal and that the restoration is O2 sensitive.     

Selected Contribution: Regulation of sleep-wake states in response to intermittent hypoxic stimuli applied only in sleep.

Recurrent sleep-related hypoxia occurs in common disorders such as obstructive sleep apnea (OSA). The marked changes in sleep after treatment suggest that stimuli associated with OSA (e.g., intermittent hypoxia) may significantly modulate sleep regulation. However, no studies have investigated the independent effects of intermittent sleep-related hypoxia on sleep regulation and recovery sleep after removal of intermittent hypoxia. Ten rats were implanted with telemetry units to record the electroencephalogram (EEG), neck electromyogram, and body temperature. After >7 days recovery, a computer algorithm detected sleep-wake states and triggered hypoxic stimuli (10% O2) or room air stimuli only during sleep for a 3-h period. Sleep-wake states were also recorded for a 3-h recovery period after the stimuli. Each rat received an average of 69.0 +/- 6.9 hypoxic stimuli during sleep. The non-rapid eye movement (non-REM) and rapid-eye-movement (REM) sleep episodes averaged 50.1 +/- 3.2 and 58.9 +/- 6.6 s, respectively, with the hypoxic stimuli, with 32.3 +/- 3.2 and 58.6 +/- 4.8 s of these periods being spent in hypoxia. Compared with results for room air controls, hypoxic stimuli led to increased wakefulness (P < 0.005), nonsignificant changes in non-REM sleep, and reduced REM sleep (P < 0.001). With hypoxic stimuli, wakefulness episodes were longer and more frequent, non-REM periods were shorter and more frequent, and REM episodes were shorter and less frequent (P < 0.015). Hypoxic stimuli also increased faster frequencies in the EEG (P < 0.005). These effects of hypoxic stimuli were reversed on return to room air. There was a rebound increase in REM sleep, increased slower non-REM EEG frequencies, and decreased wakefulness (P < 0.001). The results show that sleep-specific hypoxia leads to significant modulation of sleep-wake regulation both during and after application of the intermittent hypoxic stimuli. This study is the first to determine the independent effects of sleep-related hypoxia on sleep regulation that approximates OSA before and after treatment.     

Anaerobic formation of succinate and facilitation of its oxidation -- possible mechanisms of cell adaptation to oxygen deficiency

An important role of anaerobic formation of succinate in anoxic and hypoxic states and the activation of succinate oxidation under hypoxia were shown. It was concluded that, for maintaining the energetics of animal cells under conditions of oxygen deficiency, it is advisable to use substrates capable of participating in the anaerobic formation of succinate, whereas under hypoxia it is reasonable to use succinate itself.     

Brain Lactate Is an Obligatory Aerobic Energy Substrate for Functional Recovery After Hypoxia: Further In Vitro Validation

Abstract: This study used the rat hippocampal slice preparation and the monocarboxylate transporter inhibitor, α-cyano-4-hydroxycinnamate (4-CIN), to assess the obligatory role that lactate plays in fueling the recovery of synaptic function after hypoxia upon reoxygenation. At a concentration of 500 µ M , 4-CIN blocked lactate-supported synaptic function in hippocampal slices under normoxic conditions in 15 min. The inhibitor had no effect on glucose-supported synaptic function. Of control hippocampal slices exposed to 10-min hypoxia, 77.8 ± 6.8% recovered synaptic function after 30-min reoxygenation. Of slices supplemented with 500 µ M 4-CIN, only 15 ± 10.9% recovered synaptic function despite the large amount of lactate formed during the hypoxic period and the abundance of glucose present before, during, and after hypoxia. These results indicate that 4-CIN, when present during hypoxia and reoxygenation, blocks lactate transport from astrocytes, where the bulk of anaerobic lactate is formed, to neurons, where lactate is being utilized aerobically to support recovery of function after hypoxia. These results unequivocally validate that brain lactate is an obligatory aerobic energy substrate for posthypoxia recovery of function.     

Age-related characteristics of cholinergic regulation of the biomechanical function of the rat heart in hypoxia

Hypoxia is shown to decrease chronotropic and inotropic responses of the isolated heart of mature rats to stimulation of M-choline receptors. In aged tissue hypoxia has no influence on the inotropic response to carbocholine effect. The results permit a conclusion to be made on the higher resistance of cholinergic mechanisms that regulate the cardiac function to hypoxic effects in aged animals.     

哺乳动物低氧应激代谢成因的研究进展

氧气是哺乳动物机体代谢稳态维持的物质基础,若代谢过程中氧气供给不足,可造成低氧应激。目前,环境低氧、代谢性低氧和携氧细胞功能障碍是造成动物低氧应激的重要成因。目前,低氧对动物机体代谢和组织功能的影响研究主要集中于肺脏、肝脏、消化道、肌肉和乳腺等部位。若处于低氧状态的哺乳动物形成了适应低氧的代谢模式,则可维持其代谢稳态;相反,若动物无法维持低氧状态下的代谢稳态,则会导致机体氧化应激甚至病变。目前,低氧应激在家畜方面的研究主要集中于高原动物代谢适应机制;然而,泌乳期动物机体代谢速率、氧气消耗和自由基水平均较高,但氧在泌乳动物代谢应激形成中的作用及其对泌乳性能的影响,仍有待探索。综述了哺乳动物产生低氧应激的代谢成因与作用结果,旨在探讨哺乳动物低氧应激生物学基础,为进一步从低氧应激调控角度为泌乳动物的健康状况维持提供理论依据。     

The effect of repeated intermittent hypoxia on pulmonary vasoconstriction in the newborn

The effect of repeated intermittent hypoxia upon the basal pulmonary vascular tone in the newborn period is unknown. We therefore studied the central hemodynamic response to seven repeated intermittent hypoxic challenges in acutely prepared piglets under 2 weeks of age. Catheters were placed in the aorta, pulmonary artery, and atria, and an electromagnetic flow probe was positioned around the main pulmonary artery. Each hypoxic challenge (Fio2 = 0.14) lasted 5 min, and was separated by an equal duration of ventilation with air. Nine control animals were ventilated with air for 90 min, a period of time equivalent to the seven challenges in the experimental group, and subjected to one hypoxic challenge at the end. Hypoxia uniformly induced pulmonary vasoconstriction. Repeated intermittent hypoxic challenges produced a progressive increase in pulmonary artery pressure and vascular resistance, both during air ventilation and hypoxia. For each challenge, the vascular resistance value achieved during hypoxia was directly related to the immediately preceding air ventilation one, and the magnitude of hypoxic pulmonary vasoconstriction, defined as the incremental change in resistance from air to hypoxia, was not different from the first to the last challenge in the experimental group. In the control group the pulmonary vascular tone did not change during the 90 min of air ventilation, and the single hypoxic challenge induced an increase in pulmonary vascular pressure and resistance similar in magnitude to the first challenge in the experimental group. Indomethacin administration to five experimental animals, after the last challenge, reversed the increase in air ventilation pulmonary artery pressure and vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlations of convulsive and hypoxic resistance in rats at different stages of ontogenesis

Hypoxic and convulsive resistances were studied in 3, 7, 14, 21, 40-day-old rats and in adults. Susceptibility to hypoxia was determined in pressure chamber by "lifting" the animals to the altitude of 12,000 metres. Convulsions were caused by intraabdominal injections of corazol. A correlation between hypoxic and convulsive resistances was found from 3 day after the birth. Their indexes were maximum at this period. Similar decrease of hypoxic and convulsive resistances was observed with the growth of the animals. Moreover the reduction in hypoxic resistance was more dramatic and reached its minimum on the 40th day. In grown up animals, resistance to hypoxia was higher, than in 40-day-old rats. Minimum latency period for development of status epilepticus was detected in 21-day-old rats.     

Hypoxic adaptation of the rat carotid body

Three types of hypoxia with different levels of carbon dioxide (hypocapnic, isocapnic, and hypercapnic hypoxia) have been called systemic hypoxia. The systemic hypoxic carotid bodies were enlarged several fold, but the degree of enlargement was different for each. The mean short and long axes of hypocapnic and isocapnic hypoxic carotid bodies were 1.6 (short axis) and 1.8-1.9 (long axis) times larger than normoxic control carotid bodies, respectively. Those of hypercapnic hypoxic carotid bodies were 1.2 (short axis) and 1.5 (long axis) times larger than controls, respectively. The rate of enlargement in hypercapnic hypoxic carotid bodies was lower than in hypocapnic and isocapnic hypoxic carotid bodies. The rate of vascular enlargement in hypercapnic hypoxic carotid bodies was also smaller than in hypocapnic and isocapnic hypoxic carotid bodies. Thus, the enlargement of hypoxic carotid bodies is mainly due to vascular dilation. Different levels of arterial CO2 tension change the peptidergic innervation during chronically hypoxic exposure. The characteristic vascular arrangement was under the control of altered peptidergic innervation. During the course of hypoxic adaptation, the enlargement of the carotid bodies with vascular expansion began soon after the start of hypoxic exposure. During the course of recovery, the shrinking of the carotid bodies with vascular contraction also started at a relatively early period after the termination of chronic hypoxia. These processes during the course of hypoxic adaptation and during the course of recovery were under the control of peptidergic innervation. These findings may provide a standard for further studies of hypoxic carotid bodies.     

Effect of past stress on the resistance of the myocardium to hypoxia

The effect of emotional painful stress on myocardial contractility and resistance to hypoxia was studied on the rat isolated atrium. It was established that in stress-exposed rats, myocardial resistance to hypoxia was reduced and contractility was depressed. It was manifested in accelerated development and greater degree of hypoxic contracture, as well as in a slower recovery of myocardial contractility under reoxygenation. The decreased myocardial resistance to hypoxia under stress is suggested to be related to the stress-induced alterations in glycolysis and calcium transport in cardiomyocytes.     

Hypoxia induced metabolism dysfunction of rat astrocytes in primary cell cultures

In order to study the astroglial contribution to hypoxic injury on brain tissue metabolism, modifications of glutamine synthetase (GS) lactate dehydrogenase (LDH) enolase and malate dehydrogenase activity produced by reduced oxygen supply have been determined in primary cultures of astrocytes prepared from newborn rat cerebral cortex. Enzymatic activities were measured immediately after the hypoxic treatment (9 h) and during post injury recovery. GS level is significantly decreased in response to low oxygen pressure and increased above control value during the post hypoxic recovery period. The magnitude of GS reduction by hypoxia depends on the age of the cells in culture. Lactate dehydrogenase and enolase levels were significantly enhanced during the two periods considered. No modification of the MDH level was observed. The synthesis of LDH isoenzymes containing mainly M subunits is specifically induced by hypoxia. Our results suggest that astroglial cells may represent a particularly sensitive target toward hypoxia injury in brain tissue. Low oxygen pressure available may modify some fundamental metabolical functions of these cells such as glutamate turnover and lactic acid accumulation.     

Attenuation of hypoxic pulmonary vasoconstriction by verapamil in intact dogs.

The hypothesis that hypoxic pulmonary vasoconstriction is mediated directly by depolarization of the vascular smooth muscle was tested in anesthetized dogs. Pulmonary vascular responses to hypoxia were first determined in eight dogs during 20-min exposures to 10% O2. Each animal was then treated with verapamil (0.5 mg/kg, iv), to block transmembrane Ca2+ influx in an attempt to abolish the vasoconstrictor responses to hypoxia. The hypoxic exposures were then repeated, and the pulmonary vascular responses were compared to the control responses. Verapamil administration attenuated hypoxic pulmonary vasoconstriction, but did not abolish the responses to hypoxia. Pulmonary vascular resistance increased 87% during the control hypoxic exposure, but increased only 38% during hypoxia after verapamil. The response to another vasoconstrictor, prostaglandin F2alpha, was not reduced by verapamil indicating a different mechanism of mediation. These results suggest that the pulmonary vasoconstrictor response to alveolar hypoxia, in the intact dog, involves transmembrane Ca2+ influx, and are consistent with the idea that hypoxia acts primarily by directly depolarizing vascular smooth muscle, rather than acting indirectly through a chemical mediator.     

Periods of intermittent hypoxic apnea can alter chemoreflex control of sympathetic nerve activity in humans

Obstructive sleep apnea is associated with sustained elevation of muscle sympathetic nerve activity (MSNA) and altered chemoreflex control of MSNA, both of which likely play an important role in the development of hypertension in these patients. Additionally, short-term exposure to intermittent hypoxic apneas can produce a sustained elevation of MSNA. Therefore, we tested the hypothesis that 20 min of intermittent hypoxic apneas can alter chemoreflex control of MSNA. Twenty-one subjects were randomly assigned to one of three groups (hypoxic apnea, hypercapnic hypoxia, and isocapnic hypoxia). Subjects were exposed to 30 s of the perturbation every minute for 20 min. Chemoreflex control of MSNA was assessed during baseline, 1 min posttreatment, and every 15 min throughout 180 min of recovery by the MSNA response to a single hypoxic apnea. Recovery hypoxic apneas were matched to a baseline hypoxic apnea with a similar nadir oxygen saturation. A significant main effect for chemoreflex control of MSNA was observed after 20 min of intermittent hypoxic apneas (P <0.001). The MSNA response to a single hypoxic apnea was attenuated 1 min postexposure compared with baseline (P <0.001), became augmented within 30 min of recovery, and remained augmented through 165 min of recovery (P <0.05). Comparison of treatment groups revealed no differences in the chemoreflex control of MSNA during recovery (P=0.69). These data support the hypothesis that 20 min of intermittent hypoxic apneas can alter chemoreflex control of MSNA. Furthermore, this response appears to be mediated by hypoxia.     

Effect of hypoxia on recovery from damage induced by heat and radiation in plateau-phase CHO cells

The effect of hypoxia on the induction of and recovery from damage by radiation alone and in combination with heat has been investigated using plateau-phase Chinese hamster ovary (CHO) cells. Postirradiation hypoxia reduced the potentially lethal damage recovery (PLDR) in cells irradiated under an euoxic state and completely eliminated PLDR in cells irradiated under hypoxia. Cells which were maintained under hypoxia during both irradiation and a 4-hr recovery period and then incubated for a further period of 4 hr under euoxic conditions showed PLDR, suggesting that the inhibition of PLDR by hypoxia is reversible. Oligomycin, an inhibitor of energy metabolism, completely eliminated PLDR when present at a concentration of 1 microM during the postirradiation period. Pre- or postirradiation heat treatment at 42.5 degrees C for 30 min appreciably sensitized the cells to the induction of lethality. Thermal enhancement ratio (TER) was 1.7 for cells irradiated and heat treated under hypoxic conditions. The same heat treatment reduced the oxygen enhancement ratio (OER) associated with gamma radiation from 3.1 to 2.5. Cells subjected to this postirradiation heat treatment showed a small extent of PLDR, whereas the pre-heat-treated cells showed as much recovery as non-heat-treated cells. When hypoxic conditions prevailed during the post-treatment incubation period, PLDR was reduced in preheated cells and completely eliminated in postheated cells. The kinetics of interaction between heat and radiation damage were studied by introducing a time gap of 4 hr between the treatments. Cells maintained under euoxic conditions between the treatments showed an appreciable decrease in interaction, suggesting recovery from damage induced by the first treatment. Hypoxic conditions intervening the two treatments largely inhibited the loss of sensitization. Analysis of the results suggests that cells fail to recover from sublethal heat damage when held for 4 hr under hypoxic conditions. Cells held under hypoxic conditions partly recover from the radiation damage which subsequently interacts with sublethal heat damage, resulting in cell lethality.     

The mechanism of neuronal resistance and adaptation to hypoxia

In this work we provide a theoretical explanation for the observations that: (i) young animals are more resistant to hypoxia than adult ones and (ii) repeated exposure to a hypoxic insult increases the tolerance of young animals and isolated brain tissue to that insult. Considered here is the role of taurine, a putative Ca2+ transport modulator, in attenuating Ca2+ influx and overload in brain tissue upon hypoxia. It is proposed that the higher resistance of young animals to hypoxia stems from their higher brain content of taurine as compared with adults. The increased resistance to lack of oxygen upon re-exposure to hypoxia may occur as a result of protein and coenzyme A (CoA) breakdown which leads to the accumulation of products like cystine, cysteine, cysteamine and other sulfur-containing compounds. Upon reoxygenation, these compounds are oxidized to form taurine, which in turn attenuates neuronal Ca2+ accumulation. The sulfur-containing compounds are considered to be natural scavengers of oxygen-derived free radicals which are formed upon reoxygenation and have been implicated as a major component in the process leading to ischemic/hypoxic brain damage. Repeated hypoxic insults bring about the formation of higher levels of taurine and hence the observed adaptation to oxygen lack. The hypothesis presented here is supported by experimental observations in our laboratory and those of others.     

Increased normoxic ventilation induced by repetitive hypoxia in conscious dogs.

To determine if a long-lasting increase in normoxic ventilatory drive is induced in conscious animals by repetitive hypoxia, we examined the normoxic [arterial O2 saturation (SaO2) > 93%] ventilatory response following successive episodes of 2-min eucapnic hypoxic challenges (SaO2 = 80%) in awake tracheotomized dogs. End-tidal CO2 was maintained at the resting level during and after repetitive hypoxia. The experimental protocol was performed twice in each of five dogs on separate days. To determine if changes in normoxic ventilation occurred between episodes of repetitive hypoxia, data were compared from six periods (epochs) for all experiments. The mean minute ventilation (VI) during three normoxic periods between episodes of intermittent hypoxia was 135, 154, and 169% of control (P < 0.05). VI during a 30-min recovery period was still higher at 183 and 172% of control (P < 0.05). Normoxic VI between hypoxic and recovery periods was significantly higher than the corresponding values in sham experiments. Our results indicate that a long-lasting increase in normoxic ventilation can be evoked in an awake unanesthetized dog by a short exposure to repetitive hypoxia.     

Testing drug effects against hypoxic damage of cultured neurons during long-term recovery

Cultured neurons of chick cerebral embryo hemispheres were used to study drug effects against neuronal damage caused by hypoxia during long-term recovery. Sodium cyanide (NaCN, 1 mmol/l) induces hypoxia-like conditions by inhibiting oxydative phosphorylation. The sensitivity of the cultured neurons against this type of hypoxia was determined after 3, 4, 5 and 6 days of cultivation followed by 4, 3, 2 days and 1 day of recovery, respectively. The ATP level and the viability of cells as well as the total cell number and the protein content of the cultures were used to characterize the extent of posthypoxic neuronal damage. A hypoxic period of 30 min after 4 days of cultivation followed by 3 days of recovery seemed to be appropriate for determining protective drug effects. The drug effects obtained were comparable to those from in vivo models of cerebral ischemia or hypoxia. The results suggest that cultured neurons exposed to hypoxia and to long-term recovery could be suitable for studying post-hypoxic neuronal damage as well as neuroprotective drug effects.