Reduced Oxygen Supply Research Articles

Mitochondrial respiratory control can compensate for intracellular O(2) gradients in cardiomyocytes at low PO(2).

In isolated single cardiomyocytes with moderately elevated mitochondrial respiration, direct evidence for intracellular radial gradients of oxygen concentration was obtained by subcellular spectrophotometry of myoglobin (Mb). When oxygen consumption was increased by carbonyl cyanide m-chlorophenylhydrazone (CCCP) during superfusion of cells with 4% oxygen, PO(2) at the cell core dropped to 2.3 mmHg, whereas Mb near the plasma membrane was almost fully saturated with oxygen. Subcellular NADH fluorometry demonstrated corresponding intracellular heterogeneities of NADH, indicating suppression of mitochondrial oxidative metabolism due to relatively slow intracellular oxygen diffusion. When oxygen consumption was increased by electrical pacing in 2% oxygen, radial oxygen gradients of similar magnitude were demonstrated (cell core PO(2) = 2.6 mmHg). However, an increase in NADH fluorescence at the cell core was not detected. Because CCCP abolished mitochondrial respiratory control while it was intact in electrically paced cardiomyocytes, we conclude that mitochondria with intact respiratory control can sustain electron transfer with reduced oxygen supply. Thus mitochondrial intrinsic regulation can compensate for relatively slow oxygen diffusion within cardiomyocytes.

Gas tonometry for evaluation of gastrointestinal mucosal perfusion: experimental models of trauma, shock and complex surgical maneuvers - Part 1

Substantial clinical and animal evidences indicate that the mesenteric circulatory bed, particularly the gut mucosa, is highly vulnerable to reductions in oxygen supply and prone to early injury in the course of hemodynamic changes induced by trauma, shock, sepsis and several complex surgical maneuvers. Gut hypoxia or ischemia is one possible contributing factor to gastrointestinal tract barrier dysfunction that may be associated with the development of systemic inflammatory response and multiple organ dysfunction syndrome, a common cause of death after trauma, sepsis or major surgeries. Monitoring gut perfusion during experiments may provide valuable insights over new interventions and therapies highly needed to reduce trauma and sepsis-related morbidity and mortality. We present our experience with gas tonometry as a monitor of the adequacy of gastrointestinal mucosal perfusion in clinical and experimental models of trauma, shock and surgical maneuvers associated with abrupt hemodynamic changes, such as aortic occlusion and hepatic vascular exclusion. Next issue we will be presenting our experience with gas tonometry in experimental and clinical sepsis.

Endotoxin-Induced Liver Hypoxia: Defective Oxygen Delivery versus Oxygen Consumption

In vivo EPR was used to investigate liver oxygenation in a hemodynamic model of septic shock in mice. Oxygen-sensitive material was introduced either (i) as a slurry of fine particles which localized at the liver sinusoids (pO2 = 44.39 ± 5.13 mmHg) or (ii) as larger particles implanted directly into liver tissue to measure average pO2 across the lobule (pO2 = 4.56 ± 1.28 mmHg). Endotoxin caused decreases in pO2 at both sites early (5–15 min) and at late time points (6 h after endotoxin; sinusoid = 11.22 ± 2.48 mmHg; lobule = 1.16 ± 0.42 mmHg). The overall pO2 changes observed were similar (74.56% versus 74.72%, respectively). Blood pressures decreased transiently between 5 and 15 min (12.88 ± 8% decrease) and severely at 6 h (59 ± 9% decrease) following endotoxin, despite volume replacement with saline. Liver and circulatory nitric oxide was elevated at these times. Liver oxygen extraction decreased from 44% in controls to only 15% following endotoxin, despite severe liver hypoxia. Arterial oxygen saturation, blood flow (hepatic artery), and cardiac output were unaffected. Pretreatment with l-NMMA failed to improve endotoxin-induced oxygen defects at either site, whereas interleukin-13 preserved oxygenation. These site-specific measurements of pO2 provide in vivo evidence that the principal cause of liver hypoxia during hypodynamic sepsis is reduced oxygen supply to the sinusoid and can be alleviated by maintaining sinusoidal perfusion.

Nitrous oxide emissions from soil during freezing and thawing periods

In a laboratory investigation, the processes of N 2O emissions during freezing/thawing periods were studied. Four undisturbed soil columns from an agricultural site were subjected to two freeze/thaw cycles. Two periods of higher N 2O emissions were detected, a period of elevated N 2O emissions during continuous soil freezing and a period of brief peak emissions during thawing. Soil respiration indicated that microorganisms were still active in both periods. We concluded that N 2O was produced by microorganisms during continuous soil freezing in an unfrozen water film on the soil matrix. This thin liquid water film was covered by a layer of frozen water. The frozen water in form of an ice layer represents a diffusion barrier which reduces oxygen supply to the microorganisms and partly prevents the release of the N 2O. Peak emissions during soil thawing were explained by the physical release of trapped N 2O and/or denitrification during thawing.

Effects of acute hypoxemia on force and surface EMG during sustained handgrip.

Data on the consequences of acute hypoxemia on the strength of contraction are often contradictory. In healthy subjects, we tested the effects of hypoxemia (PaO(2) = 56 mmHg), maintained for a 30-min period, on static handgrip elicited by voluntary effort or direct electrical muscle stimulation, in order to separate the consequences of hypoxemia on central or peripheral factors, respectively. Force was measured during maximal voluntary contractions (MVCs), 60% MVCs sustained until exhaustion, and 1-min periods of electrical muscle stimulation at 60 HZ. The evoked compound muscle action potential (M wave) was recorded in resting muscle and after each period of 60-HZ stimulation or sustained 60% MVC. Power spectrum analysis of surface electromyogram (EMG) was performed during sustained 60% MVC. Compared to normoxemia, acute hypoxemia lowered MVC (-12%, P < 0.01) but enhanced (+38%, P < 0.01) the peak force elicited by electrical muscle stimulation. In resting muscle, hypoxemia had no influence on the M-wave amplitude but lengthened the neuromuscular transmission time(+740 micros, P < 0.05). Hypoxemia did not alter the M wave measured after 60 HZ stimulation and 60% MVC. During sustained 60% MVC, hypoxemia markedly depressed the EMG changes, abolishing the leftward shift of power spectra. These data show that acute hypoxemia reduces MVC through depression of the central drive, whereas it improves the peripheral muscle response to electrical stimulation. In addition, hypoxemia reduces the recruitment of slow firing motor unit, which are highly oxygen-dependent. This could constitute an adaptative muscle response to a reduced oxygen supply.

Fine sediment influence on salmonid spawning habitat in a lowland agricultural stream: a preliminary assessment

Spawning habitat utilized by Atlantic Salmon (Salmon salar) and Sea Trout (Salmo trutta) was characterized in a 1.6-km reach of the Newmills Burn, a small, highly canalized tributary of the River Don in Aberdeenshire. The Newmills Burn is typical of the intensively farmed lower sub-catchments of the major salmon rivers on the east coast of Scotland. Such streams have substantial potential in providing spawning and juvenile habitat for salmonids, with high redd densities resulting in egg deposition rates of >5 m2. However, in comparison with upland spawning tributaries draining less intensively managed catchments, canalization and intensive cultivation has seriously degraded the physical characteristics of aquatic habitats in many streams. In the Newmills Burn, spawning gravels have a relatively high (>20% by mass) fine sediment (<2 mm in size) content. The burn is characterized by hydraulic conditions that are suitable for salmonid spawning, with modal velocities of 0.50–0.65 m s−1 and depths of 0.20–0.25 m. However, infiltration of fine sediments into gravels is rapid during hydrological events in the winter months. Thus, complete siltation of open gravel matrices (simulated redds) can occur within a week, and probably within a single moderate to large storm event. Appreciable, but small, deposition of organic and silt/clay particles can also affect spawning gravels. Egg mortalities in redds following spawning are variable, but can be as high as 86% in the Newmills Burn. This may be related to fine sediment infiltration, reduced permeability of spawning gravels and reduced oxygen supply to ova. It appears that the main cause of high influx is sediment loads mobilized from intensively managed land. It is suggested that fundamental changes to the management of agricultural land is required if fish habitats are to be improved and degraded streams are allowed to re-naturalize. The need for closely focused investigations of the causal relationships between fine sediment infiltration and egg survival is stressed.

Use of thymidine analogues to indicate vascular perfusion in tumours

Temporary reduction in blood-flow within tumour blood vessels can reduce oxygen supply leading to transient perfusion-limited hypoxia. Consequent selection of cells with mutations and reduced radiosensitivity can lead to disease progression and treatment-resistance. In the present study, we investigated whether heterogeneity of labelling after thymidine analogue administration is related to perfusion variations, and if so, could it be quantified and used as a perfusion indicator. Perfusion in murine RIF1 tumours was reduced by hydralazine or increased by nicotinamide and the mice subsequently injected with IdUrd. Tumours were halved for analysis by both flow cytometry and immunohistochemistry. Tumour sections were stained for vasculature and IdUrd. Each blood vessel was scored for the density of IdUrd-labelled cells surrounding it, using a semi-quantitative scoring system. Flow cytometry showed that the IdUrd labelling index and intensity decreased by approximately 50% after hydralazine. In tumour sections of control animals, 2.9% of vessels showed no IdUrd label. In contrast, after hydralazine almost 50% of vessels had no surrounding IdUrd labelling, whereas after nicotinamide there were fewer vessels with low labelling and a higher median score. In conclusion, changes of tumour perfusion by pharmacological agents is reflected in changes in tumour-cell labelling by the thymidine analogue IdUrd, suggesting that IdUrd labelling could be used to indicate perfusion in individual vessels in human tumours. © 2000 Cancer Research Campaign

Effect of oxygen supply on metabolism of immobilized and suspended Escherichia coli

The effect of reduced oxygen supply on the production of a recombinant protein (plasmid-encoded beta-galactosidase) was investigated in Escherichia coli. A novel modified bubble tank reactor was used to provide a direct comparison between immobilized and suspended cells in identical environments except for the immobilization matrix. Decreased oxygen supply led to increased beta-galactosidase synthesis by both immobilized and suspended cells. Immobilized cells produced similar amounts of beta-galactosidase as the suspended cells. Lactose consumption and acetate production, on a per cell basis, were significantly higher in immobilized cells, suggesting that immobilized cells utilized fermentative metabolism. However, a transport analysis of the immobilized cell system showed that immobilized cells were not subject to either external or internal mass transfer gradients.

Placental Oxygen Consumption. Part II: In Vitro Studies—A Review

The human placenta in vivo consumes large amounts of oxygen. After delivery the placenta is exposed to anoxia and under in vitro experimental conditions oxygen consumption is only a fraction of in vivo estimates. In spite of a reduced oxygen supply, structural and functional integrity of the tissue is surprisingly well preserved. Special metabolic adjustments in the sense of ‘partial metabolic arrest’ may be the explanation for a remarkable survival capacity of placental tissue and reduction of protein synthesis seems to be an important component of metabolic slowdown. The potential significance of this special feature of placental metabolism for the in vivo situation is discussed.

The effects of exhaust gas recirculation on diesel combustion and emissions

An investigation was conducted with the aim of identifying and quantifying the effects of exhaust gas recirculation (EGR) on diesel engine combustion and exhaust emissions. Five effects of EGR were identified and investigated experimentally: the reduction in oxygen supply to the engine, participation in the combustion process of carbon dioxide and water vapour present in the EGR, increase in the specific heat capacity of the engine inlet charge, increased inlet charge temperature and reduction in the inlet charge mass flowrate arising from the use of hot EGR. The experimental methodology developed allowed each one of these effects to be investigated and quantified separately. The investigation was carried out on a high-speed, direct injection diesel engine, running at an intermediate speed and load. A limited number of tests were also conducted in an optically accessible diesel engine, which established the effects of EGR on local flame temperature. Finally, tests were conducted with simulated EGR being used additionally to the engine air supply. This contrasts with the conventional use of EGR, whereby EGR replaces some of the air supplied to the engine. It was found that the first effect of EGR (reduction in the oxygen flowrate to the engine) was substantial and resulted in very large reductions in exhaust NOx at the expense of higher particulate emissions. The second and third effects (participation of carbon dioxide and water vapour in the combustion process and increase in the charge specific heat capacity) were almost insignificant. The fourth effect (higher inlet charge temperature) increased both exhaust NOx and particulate emissions. The fifth effect (reduction in the inlet charge due to thermal throttling) reduced NOx but raised particulate emission. Finally, when EGR was used additionally to the inlet air charge (rather than displacing air), substantial reductions in NOx were recorded with little increase in particulate emission.

Perinatal brain injury.

Perinatal brain damage in the mature fetus is usually brought about by severe intrauterine asphyxia following an acute reduction of the uterine or umbilical circulation. The areas most heavily affected are the parasagittal region of the cerebral cortex and the basal ganglia. The fetus reacts to a severe lack of oxygen with activation of the sympathetic-adrenergic nervous system and a redistribution of cardiac output in favor of the central organs (brain, heart and adrenals). If the asphyxic insult persists, the fetus is unable to maintain circulatory centralization, and the cardiac output and extent of cerebral perfusion fall. Owing to the acute reduction in oxygen supply, oxidative phosphorylation in the brain comes to a standstill. The Na+/K+ pump at the cell membrane has no more energy to maintain the ionic gradients. In the absence of a membrane potential, large amounts of calcium ions flow through the voltage-dependent ion channels, down an extreme extra-/intracellular concentration gradient, into the cell. Current research suggests that the excessive increase in levels of intracellular calcium, so-called calcium overload, leads to cell damage through the activation of proteases, lipases and endonucleases. During ischemia, besides the influx of calcium ions into the cells via voltage-dependent calcium channels, more calcium enters the cells through glutamate-regulated ion channels. Glutamate, an excitatory neurotransmitter, is released from presynaptic vesicles during ischemia following anoxic cell depolarization. The acute lack of cellular energy arising during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to preischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. The inhibition of protein synthesis, therefore, appears to be an early indicator of subsequent neuronal cell death. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the postischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Part of the secondary neuronal cell damage may be caused by induction of a kind of cellular suicide programme known as apoptosis. Interestingly, there is increasing evidence from recent clinical studies that perinatal brain damage is closely associated with ascending intrauterine infection before or during birth. However, a major part of this damage is likely to be of hypoxic-ischemic nature due to LPS-induced effects on fetal cerebral circulation. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies with successful results in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of intravenous administration of magnesium or postischemic induction of cerebral hypothermia.

Responses of soil respiration and barley growth to modified supply of oxygen in the soil

Roots of dry-land plants are supplied with oxygen mainly by molecular diffusion from soil air. Roots may suffer from hypoxia if soil aeration is reduced by compaction and wetting. Although the mechanisms involved are well known, more research is needed to relate soil aeration status to plant growth. The effects of reduced oxygen supply on soil respiration and the growth of barley seedlings were studied in pot experiments with fine sand soil, where the soil air composition was varied by flushing the soil with gas streams containing 0%, 2%, 6%, 10% or 20% O2 independently of compactness (bulk density 1.4, 1.6 Mg m-3) and wetness (air space 0-5%, &gt;5%). Plant growth decreased only at 0-2% O2 in the loose moist soil but as early as 20% O2 in the wet soil. Soil compaction impaired plant growth regardless of wetting and aeration. In the loose moist soil cropped with barley, the respiration rate (emission of CO2) did not decrease at 6% O2 but decreased clearly at 0-2% O2. The results compared fairly well with the critical oxygen concentrations calculated by a simple multicylindrical model, in which the water-film thickness around the roots was estimated using soil water retention data.

Animal models of stroke: Compromise between consistency and clinical relevance?

Experimental stroke can be induced by permanent or temporal reduction of oxygen supply in focal brain regions of a variety of animal species in order to produce a reliable functional deficit with or without the formation of reproducible infarcts. The resulting lesion depends on the size of the occluded vessels and the territory that they supply. This can include a complete hemisphere, a major perfusion territory, specific functional regions or unpredictable lacunar fields. The outcome depends on the residual flow to the affected area and the timely restoration of blood supply. Areas of low flow, either in the occluded region or in the apposing penumbra, deserve attention for therapeutic rescue. This is also true for areas remote from the compromised structure. Since the progression of injury and the response of the different brain constituents are multifactorial and behave in a rather unpredictable and variable way, treatment is a complex matter. The evolution of acute or delayed neuronal injury and secondary phenomena such as edema formation, inflammatory reaction and retrograde degeneration may require well-timed approaches based on various mechanisms of action. In this paper current experimental models are reviewed and pharmacotherapeutic measures will be discussed in relation to the pathogenesis of stroke.

Effects of sessile Protozoa on intracapsular oxygen tension and embryonic shell calcification in the muricid Chorus giganteus

Clusters of egg capsules deposited by some common marine Mollusca may suffer problems of a low diffusive oxygen supply to the embryos they contain, especially if the capsules are exposed to hypoxic seawater or attachment and growth of marine biofouling organisms. The present study was undertaken to determine the effects of severe biofouling by sessile Protozoa on intracapsular oxygen tension (IPO 2 ) and the development of embryos contained in the egg capsules of the muricid snail Chorus giganteus. We also investigated the effects of ambient oxygen tension (EPO2) on IPO 2 . The presence of sessile Protozoa attached to the outer wall of the egg capsules significantly reduced the IPO 2 compared to capsules not fouled by Protozoa. Clean capsules containing embryos showed an IPO 2 of about 105 mm Hg, compared with about 92 mm Hg for protozoan-fouled capsules when both were immersed in air-saturated seawater at 12°C. The embryos in capsules without Protozoa grew normally, hatching in about 70 d as veliconch larvae, whereas the development of larvae in protozoan-fouled capsules showed impairment of shell formation and delay in hatching for up to 5 mo. Pre-hatch embryos at 60 d measured about 922 μm and had an ash content near 18 μg embryo -1 embryos in capsules covered by micro-organisms measured only about 783 pm, with an ash content of about 3 μg embryo -1 over the same time period. Our study suggested that the lack of larval calcification observed in the presence of sessile Protozoa on the outer wall of the egg capsules was probably related to reduced IPO 2 . Similarly, any factor reducing oxygen supply to encapsulated embryos (i.e. exposure to water masses with low oxygen content, biofouling, reduced water movement) could impair embryonic development, a significant phenomenon thus far not reported in C. giganteus.

Oxygen Uptake and Cardiac Performance in Obese and Normal Subjects during Exercise

Work capacity and cardiopulmonary performance were studied in a group of 11 young obese subjects (BMI 39.9 kg/m²) and a group of 10 young normal subjects (BMI 22 kg/m²). First of all they underwent an incremental cycle ergometer test up to exhaustion. Subsequently, every subject of the two groups performed a constant work rate test at different work loads to estimate cardiac output (q̇) below anaerobic threshold (AT) by a 20-second CO₂ rebreathing method. Obese subjects had a significantly lower AT (79 vs. 109 W). The ratio between oxygen uptake and heart rate (v̇O₂/HR) (O₂ pulse) was higher in the obese group; nevertheless, this variable became significantly lower if we took into consideration the ratio between O₂ pulse and kilogram fat-free body mass or kilogram body weight. Both these observations suggest that their reduced work tolerance is linked with a reduced oxygen supply to the muscles in activity. q̇ increased in similar ways in obese and normal subjects at the preset work rates. The ratio q̇/body surface (cardiac index; CI) that we considered in order to try to minimize the differences in body sizes between the two groups, increased less in response to increasing work rates in our obese subjects than in normal subjects. As a whole, these data appear to be in line with a relatively less efficient cardiac performance during progressive work rates in obese subjects.

Mechanisms of control of heart glycolysis.

This review focuses on the mechanisms of control of heart glycolysis under conditions of normal and reduced oxygen supply. The kinetic properties and the biochemical characteristics of control steps (glucose transporters, hexokinase, glycogen phosphorylase and phosphofructokinases) in the heart are reviewed in the light of recent findings and are considered together to explain the control of glycolysis by substrate supply and availability, energy demand, oxygen deprivation and hormones. The role of fructose 2,6-bisphosphate in the control of glycolysis is analysed in detail. This regulator participates in the stimulation of heart glycolysis in response to glucose, workload, insulin and adrenaline, and it decreases the glycolytic flux when alternative fuels are oxidized. Fructose 2,6-bisphosphate integrates information from various metabolic and signalling pathways and acts as a glycolytic signal. Moreover, a hierarchy in the control of glycolysis occurs and is evidenced in the presence of adrenaline or cyclic AMP, which relieve the inhibition of glycolysis by alternative fuels and stimulate fatty acid oxidation. Insulin and glucose also stimulate glycolysis, but inhibit fatty acid oxidation. The mechanisms of control underlying this fuel selection are discussed. Finally, the study of the metabolic adaptation of glucose metabolism to oxygen deprivation revealed the implication of nitric oxide and cyclic GMP in the control of heart glucose metabolism.

Sites and mechanism of adenosine formation in the cardiovascular system

This review summarizes recent developments on the mechanisms by which adenosine is formed in the cardiovascular system. The concept is developed that AMP is both a precursor of adenosine but also a product when rephosphorylated by adenosine kinase. The functional significance of this metabolic cycle is the amplification of changes in free cytosolic adenosine, which translates a minor decrease of cardiac energetics in a substantial rise in adenosine. Furthermore, the metabolism of adenosine is highly compartmentalized, and the vascular endothelium forms an important metabolic barrier, which significantly influences the dose-response curve for adenosine when this nucleoside is applied intervascularly. Inadequate supply of oxygen (critical Po 2 : 3 mm Hg) is the most important physiologic trigger for the formation of adenosine. In the range above the critical Po 2 , cardiomyocytes have the remarkable ability to down-regulate their oxygen consumption before metabolic signs of hypoxia occur. Therefore, a reduction in oxygen supply as such is not a sufficient cause for the formation of adenosine but the imbalance between ATP formation and consumption. Future studies must resolve which factors govern the in-vivo activity of adenosine kinase and 5'-nucleotidase and how this is linked to the known physiologic effects of adenosine. Furthermore, the molecular mechanisms by which ATP can permeate through cell membranes and gives rise to the extracellular formation of adenosine need to be resolved.

Real Time Monitoring of Rat Liver Energy State during Ischemia

Hepatic failure is one of the major problems developed during the posttransplantation period. A possible cause of hepatic failure is the prolonged ischemia induced during the implantation procedure. Hepatic ischemia leads to a reduction in oxygen supply, ATP level decline, liver metabolism impairment, and finally organ failure. The purpose of this study was to estimate the functional state of the liver by monitoring liver blood flow and the mitochondrial NADH redox state simultaneously and continuously duringin situliver ischemia followed by reperfusion. Measurements were performed using the multiprobe developed in our laboratory consisting of fibers for the measurement of relative liver blood flow (laser Doppler flowmetry) and mitochondrial redox state (NADH fluorescence). The experimental procedure included the temporary interruption of blood flow to the liver using three types of ischemia, hepatic artery occlusion, portal vein occlusion, and simultaneous occlusion of hepatic artery and portal vein, followed by a reperfusion period. These preliminary experiments showed a significant decrease in liver blood flow, following the three types of liver ischemia, and a significant increase in NADH levels. The probe used in this study incorporates the advantage of monitoring NADH and liver blood flow simultaneously and continuously from the same area on the surface of the liver. Since each of these two parameters is not calibrated in absolute units, the simultaneous monitoring decreases possible artifacts. Also, it will allow us to determine of the coupling between tissue blood flow and oxidative phosphorylation. It is believed that the measurements of respiratory chain dysfunction might predict organ viability in clinical organ transplantation situations. Using this probe may also help to decrease the variability in liver blood flow monitoring since liver blood flow monitoring is supported simultaneously with the mitochondrial redox state, which supplies the information on liver metabolic and functional state.

Decreased Susceptibility of Contractile Function to Hypoxia/Reoxygenation in Chronic Infarcted Rat Hearts

Cardiac hypertrophy is associated with modifications in Ca2+transport processes, enzymes of energy metabolism and antioxidant capacity. It is unknown whether these changes occur in infarct-induced hypertrophy with regard to an altered susceptibility to ischemia/reperfusion injury. We examined changes in sarcoplasmic reticulum (SR) Ca2+transport, creatine kinase (CK) system, and the antioxidant enzymes glutathionperoxidase (GSH-Px) and superoxide dismutase (SOD) in rats 6 weeks after infarction due to coronary ligation (MI). Phenotypic modificationsvsham operation (SHAM) were related to the contractile response of hypertrophied papillary muscle to hypoxia/reoxygenation for 30 min each. Under aerobic conditions we observed in MIvSHAM: decreases in isometric contraction and relaxation rate, a reduced Vmax-equivalent of sarcomeric shortening, a faster twitch-to-twitch decay of post-rest potentiation (PRC) which correlated closely to the decrease in SR Ca2+uptake (−25%), a decrease in CK activity (−20%), reduced CK-MI and CK-MM, increased CK-MB and CK-BB, and enhanced activities of SOD (40%) and GSH-Px (50%). During hypoxia, an initial increase in peak force (PF) was followed by a slower PF decline in MIvSHAM. Reoxygenation caused a recovery of PF to approximately 30% in both groups; rates of contraction and relaxation recovered better in MI. In SHAM but not MI, twitch-to-twitch decay of PRC was accelerated after reoxygenationvaerobic control. The results suggest that adaptive changes in SR Ca2+handling, CK isoenzymes and antioxidant enzymes may contribute to higher resistance against reduced oxygen supply and reoxygenation in hypertrophy due to MI.

Chronic Exposure of Rats to Hypoxic Environment Alters the Mechanism of Energy Transfer in Myocardium

We have investigated the effect of chronic exposure of rats to an hypoxic environment (10% O2; 3 weeks), on the first step of the intracellular energy transfer process in the myocardium, i.e. the transfer at mitochondrial level of high energy bonds from ATP to creatine. In the left ventricles from rats adapted to normobaric hypoxia, we observed, using the permeabilized fiber technique, that the stimulatory effect of creatine on the mitochondrial respiration in presence of a low ADP concentration (0.1 mm) was attenuated when compared to control. Furthermore, the creatine-induced decrease of the apparent Kmfor ADP of the mitochondrial respiration, which is observed in control, was significantly reduced. Both the basal and maximal respiratory rates of the fibers were unchanged by the hypoxic exposure of the rats. A significant decrease of the total creatine kinase activity from 755 to 630 IU/g wet weight (for control and hypoxic rats, respectively) was detected and was accompanied by a 25% decrease in mitochondrial isoform activity (mitoCK) and in the mitoCK/citrate synthase ratio. In the right ventricles, identical alterations in the effect of creatine on apparent Kmfor ADP were observed while we did not detect any changes in CK activity. The decrease in mitoCK activity and the fall in the reactivity of respiration to creatine could be interpreted as a mechanism for downregulating oxygen demand during chronic hypoxia. The consequences of such alterations on energy metabolism of cardiomyocytes under conditions of reduced oxygen supply are discussed.