The aerobic physiology of the air-breathing blue gourami, Trichogaster trichopterus, necessitates behavioural regulation of breath-hold limits during hypoxic stress and predatory challenge

Physiological characteristics of the blood oxygen transport system and muscle metabolism indicate a high dependence on aerobic pathways in the blue gourami, Trichogaster trichopterus. Haemoglobin concentration and haematocrit were modest and the blood oxygen affinity (P50=2.31 kPa at pH 7.4 and 28 degrees C) and its sensitivity to pH (Bohr factor, phi=-0.34) favour oxygen unloading at a relatively high oxygen pressure (PO2). The intracellular buffering capacity (44.0 slykes) and lactate dehydrogenase (LDH) activity (154.3 iu g(-1)) do not support exceptional anaerobic capabilities. Air-breathing frequency in the blue gourami is expected to increase when aquatic oxygen tensions decline. Under threat of predation, however, this behaviour must be modified at a potential cost to aerobic metabolism. We therefore tested the hypothesis that metabolic responses to predatory challenge and aquatic hypoxia are subject to behavioural modulation. Computer-generated visual stimuli consistently reduced air-breathing frequency at 19.95, 6.65 and 3.33 kPa PO2. Bi-directional rates of spontaneous activity were similarly reduced. The metabolic cost of this behaviour was estimated and positively correlated with PO2 but not with visual stimulation thus indicating down-regulation of spontaneous activity rather than breath-holding behaviour. Neither PO2 nor visual stimulation resulted in significant change to muscle lactate and ATP concentrations and confirm that aerobic breath-hold limits were maintained following behavioural modulation of metabolic demands.     

Hypoxia induces anoxia tolerance in roots and shoots of lupine seedlings

Lupine seedlings were exposed to 4 kPa partial pressure oxygen (hypoxically pretreated) for 18 hours before treatment with strictly anaerobic conditions (anoxia). Seedlings previously exposed to hypoxia were more tolerant than the controls (not hypoxically pretreated) to anoxic stress in both roots and shoots. Hypoxic pretreatment induced roots and shoots survival in anoxia. Improved viability of roots, following hypoxic pretreatment, was associated with increased activity of ADH. In nonacclimated roots and shots significant increase in LDH activity occurd during the first hours under anoxia but the in vitro activity of LDH was two orders of magnitude lower than that of ADH. The results are discussed in relation to the ability of lupine seedlings to survive anoxia.     

Putative reaction mechanism of heterologously expressed octopine dehydrogenase from the great scallop, Pecten maximus (L)

cDNA for octopine dehydrogenase (ODH) from the adductor muscle of the great scallop, Pecten maximus, was cloned using 5'- and 3'-RACE. The cDNA comprises an ORF of 1197 nucleotides and the deduced amino acid sequence encodes a protein of 399 amino acids. ODH was heterologously expressed in Escherichia coli with a C-terminal penta His-tag. ODH-5His was purified to homogeneity using metal-chelate affinity chromatography and Sephadex G-100 gel filtration. Recombinant ODH had kinetic properties similar to those of wild-type ODH isolated from the scallop's adductor muscle. Site-directed mutagenesis was used to elucidate the involvement of several amino acid residues for the reaction catalyzed by ODH. Cys148, which is conserved in all opine dehydrogenases known to date, was converted to serine or alanine, showing that this residue is not intrinsically important for catalysis. His212, Arg324 and Asp329, which are also conserved in all known opine dehydrogenase sequences, were subjected to site-directed mutagenesis. Modification of these residues revealed their importance for the catalytic activity of the enzyme. Conversion of each of these residues to alanine resulted in strong increases in K(m) and decreases in k(cat) values for pyruvate and L-arginine, but had little effect on the K(m) and k(cat) values for NADH. Assuming a similar structure for ODH compared with the only available structure of a bacterial opine dehydrogenase, these three amino acids may function as a catalytic triad in ODH similar to that found in lactate dehydrogenase or malate dehydrogenase. The carboxyl group of pyruvate is then stabilized by Arg324. In addition to orienting the substrate, His212 will act as an acid-base catalyst by donating a proton to the carbonyl group of pyruvate. The acidity of this histidine is further increased by the proximity of Asp329.     

Energy metabolism during hypoxia in the isolated, perfused ventricle of the whelk,Busycon contrarium conrad

Summary Energy metabolism and endogenous contractile activity during hypoxia were investigated in the isolated, perfused ventricle of the whelk,Busycon contrarium Conrad. Perfusion under hypoxic conditions for 2 h resulted in only small changes in contractile amplitude, but further perfusion resulted in variable responses ranging from no change to near cessation of contractile activity. The adenylate energy charge decreased only slightly after four hours of hypoxia. Contractile activity during hypoxia appears to be sustained by utilization of arginine phosphate and an activation of anaerobic energy metabolism. Alanine, succinate and octopine accumulated during hypoxia. Since aspartate levels decreased to one-third of the aerobic level while glutamate levels remained unchanged, it appears that aspartate provides the amino group in alanine formation. The results of the present study onB. contrarium ventricle support the hypothesis that glycogen and aspartate are simultaneously mobilized during the early phases of hypoxia and anoxia in this species.Abbreviations ADH alanopine dehydrogenase - G3PDH glyceraldehyde-3-phosphate dehydrogenase - LDH lactate dehydrogenase - ODH octopine dehydrogenase - PEPCK phosphoenolpyruvate carboxykinase - PFK phosphofructokinase - PK pyruvate kinase Portions of this study were reported in brief in the form of an abstract which appeared in The Physiologist 23:40 (1980)     

Purification and characterization of two allozymic forms of octopine dehydrogenase from California populations ofMetridium senile

Summary In northern and southern California populations of the plumose sea anemone,Metridium senile, octopine dehydrogenase occurs in two allozymic forms and these forms are distributed in a highly population-specific manner; the frequency of the slow allele (ODH ¹⁰⁰) is 0.875 in the northern (Bodega Bay) population while the frequency of the fast allele (ODH ¹⁰³) in the southern population (Santa Barbara) is 0.125. Purification techniques resulted in an increase in purity of approximately 400 fold. The enzyme is a monomer ofM _r 35,000 to 40,000. Though there is some flexibility in the amino acid substrate which the enzyme uses (arginine and lysine react similarly), the specificity for the keto acid is limited to pyruvate.The kinetic characters of the two allozymes ofMetridium senile ODH are very different with respect to type of substrate saturation (Fig. 4 and 5) and apparent Michaelis constants (K _m) for pyruvate, lysine, arginine, and octopine (Table 5), product inhibition by octopine (Fig. 2), and optimal activity with respect to pH (Fig. 3). The properties of the slow and fast allozymes resemble the kinetic properties of cephalopod brain and muscle tissue-specific isozymes (Table 7). The kinetic data indicate that the slow allozyme would not allow a great deal of accumulation of octopine in vivo, while the fast allozyme is poised markedly towards octopine production.When the data presented in this study are compared to various physiological findings of other investigators, it becomes evident that the probable in vivo function of ODH in sea anemones is to act, in a manner analogous to vertebrate LDH, during the short-term anaerobiosis associated with muscle contraction and locomotion. The population-specific distribution and the different functional properties of the two ODH allozymes are most likely related to the different degree of tidal exposure which the two populations experience in nature. Only the slow allozyme possesses the regulatory properties which would allow a shift to the alternative anaerobic pathways utilized during these longer exposure periods.Abbreviations ODH octopine dehydrogenase - LDH lactate dehydrogenase - PHI phosphohexose isomerase     

Anaerobic induction in conifers: Expression of endogenous and chimeric anaerobically-induced genes

Alcohol dehydrogenase (ADH; EC 1.1.1.1) activity was measured in Picea glauca (Moench) Voss cell suspensions under differing conditions of hypoxia. ADH activity increased 4.5 fold after 48 h of induction. When cells were induced under different levels of hypoxia (2, 5 and 20% O₂) changes in ADH activity were found to increase with lower levels of oxygen. Alanine aminotransferase (AlaAT; EC 2.6.1.2) activity increased under hypoxia in a pattern similar to ADH, however lactate dehydrogenase (LDH; EC 1.1.1.27) activity did not increase under hypoxic conditions. The ability of white spruce cells to accurately regulate heterologous anaerobic promotors was tested by electroporating chimeric ADH reporter genes into protoplasts. While protoplasts were capable of anaerobically regulating a maize ADH reporter construct, constructs with dicotyledonous promoters (pea and Arabidopsis ) were not expressed.     

A comparative study on the responses of the gills of two mudskippers to hypoxia and anoxia

A comparison of branchial enzyme profiles indicates that the gills of Periophthalmodon schlosseri would have a greater capacity for energy metabolism through glycolysis than those of Boleophthalmus boddaerti. Indeed, after exposure to hypoxia, or anoxia, there were significant increases in the lactate content in the gills of P. schlosseri. In addition, exposure to hypoxia or anoxia significantly lowered the glycogen level in the gills of this mudskipper. It can be deduced from these results that the glycolytic flux was increased to compensate for the decrease in ATP production through anaerobic glycolysis. Different from P. schlosseri, although there was an increase in lactate production in the gills of B. boddaerti exposed to hypoxia, there was no significant change in the branchial glycogen content, indicating that a reversed Pasteur effect might have occurred under such conditions. In contrast, anoxia induced an accumulation of lactate and a decrease in glycogen in the gills of B. boddaerti. Although lactate production in the gills of these mudskippers during hypoxia was inhibited by iodoacetate, the decreases in branchial glycogen contents could not account for the amounts of lactate formed. The branchial fructose-2,6-bisphosphate contents of these mudskippers exposed to hypoxia or anoxia decreased significantly, leaving phosphofructokinase and glycolytic rate responsive to cellular energy requirements under such conditions. The differences in response in the gills of B. boddaerti and P. schlosseri to hypoxia were possibly related to the distribution of phosphofructokinase between the free and bound states.Abbreviations ADP adenosine diphosphate - ALD aldolase - ALT alanine transaminase - AST aspartate transaminase - ATP adenosine triphosphate - CS citrate synthase - EDTA ethylenediaminetetra-acetic acid - EGTA ethylene glycol tetra-acetic acid - F6P fructose-6-phosphate - F-1,6-P₂ fructose-1,6-bisphosphate - F-2,6-P₂ fructose-2,6-bisphosphate - FBPase fructose-1,6-bisphosphatese - GAPDH glyceraldehyde-3-phosphate dehydrogenase - GDH glutamate dehydrogenase - -GDH -glycerophosphate dehydrogenase - GPase glycogen phosphorylase - HK hexokinase - HOAD 3-hydroxyacyl-CoA dehydrogenase - IDH isocitrate dehydrogenase - IOA iodoacetic acid - LDH lactate dehydrogenase - LO lactate oxidizing activity - MDH malate dehydrogenase - 3-PG 3-phosphoglyceric acid - PEP phosphoenolpyruvate - PEPCK phosphoenolpyruvate carboxykinase - PGI phosphoglucose isomerase - PGK phosphoglycerate kinase - PFK 6-phosphofructo-1-kinase - PIPES piperazine-N, N-bis-(2-ethanesulphonic acid) - PK pyruvate kinase - PMSF phenylmethylsulphonyl fluoride - PR pyrurate reducing activity - SE standard error - SW seawater - TPI triosephosphate isomerase     

Anaerobic capacity of a crustacean sensitive to low environmental oxygen tensions,the freshwater amphipod Gammarus pulex (L.)

We investigated the accumulation of haemolymph L-lactate in response to anoxia, progressive hypoxia and activity, in a species that rarely encounters low PO₂ in its natural environment, the freshwater amphipod Gammarus pulex (L.). Individuals survived <1.5 h anoxia and accumulated L-lactate in the haemolymph at a rate of 10.26 mmol l^–1 h^–1. No lactate was excreted into the medium during this time. Despite the fact that most individuals of G. pulex were oxyconformers, exposure to acutely declining PO₂s did not result in a switch to anaerobic pathways until PO₂ < 4.4 kPa. Even then the concentrations accumulated remained very low until PO₂ < 0.46 kPa. There was no accumulation of L-lactate in the haemolymph as a result of exhaustive activity. Consequently, it was suggested that (a) it cannot be automatically assumed that anaerobic metabolism is switched on only at the point at which oxyregulation breaks down, (b) that the poor anaerobic capacity observed plays little, if any, role in the metabolic response to hypoxia by Gammarus pulex.     

Light-limitation on predator-prey interactions: consequences for metabolism and locomotion of deep-sea cephalopods

The present study attempts to correlate the metabolism and locomotory behavior of 25 species of midwater Cephalopoda from California and Hawaii with the maximal activities of key metabolic enzymes in various locomotory muscle tissues. Citrate synthase (CS) and octopine dehydrogenase (ODH) activities were used as indicators of aerobic and anaerobic metabolic potential respectively. CS activity in mantle muscle is highly correlated with whole-animal rates of oxygen consumption, whereas ODH activity in mantle muscle is significantly correlated with a species' ability to buffer the acidic end-products of anaerobic metabolism. Both CS and ODH activities in mantle muscle declined strongly with a species' habitat depth. For example, CS and ODH activities ranged respectively from 0.04 units g(-1) and 0.03 units g(-1) in the deep-living squid Joubiniteuthis portieri, to 8.13 units g(-1) and 420 units g(-1) in the epipelagic squid Sthenoteuthis oualaniensis. The relationships between enzymatic activities and depth are consistent with similar patterns observed for whole-animal oxygen consumption. This pattern is believed to result from a relaxation, among deep-living species, in the need for strong locomotory abilities for visual predator/prey interactions; the relaxation is due to light-limitation in the deep sea. Intraspecific scaling patterns for ODH activities may, for species that migrate ontogenetically to great depths, reflect the counteracting effects of body size and light on predator-prey detection distances. When scaled allometrically, enzymatic activities for the giant squid, Architeuthis sp., suggest a fairly active aerobic metabolism but little burst swimming capacity. Interspecific differences in the relative distributions of enzymatic activities in fin, mantle, and arm tissue suggest an increased reliance on fin and arm muscle for locomotion among deep-living species. We suggest that, where high-speed locomotion is not required, more efficient means of locomotion, such as fin swimming or medusoid arm propulsion, are more prevalent.     

Metabolic adjustments in two Amazonian cichlids exposed to hypoxia and anoxia

The effects of graded hypoxia on the physiological and biochemical responses were examined in two closely related species of cichlids of the Amazon: Astronotus crassipinnis and Symphysodon aequifasciatus. Ten fish of each species were exposed to graded hypoxia for 8 h in seven oxygen concentrations (5.92, 3.15, 1.54, 0.79, 0.60, 0.34, and 0.06 mg O(2) L(-)(1)), with the aim to evaluate hypoxia tolerance and metabolic adjustments, where plasma glucose and lactate levels, hepatic and muscle glycogen contents, and maximum enzyme activities (PK, LDH, MDH and CS) in skeletal and cardiac muscles were measured. Another experimental set was done to quantify oxygen consumption (MO(2)) and opercular movements in two oxygen concentrations. Hypoxia tolerance differed between the two species. Astronotus crassipinnis was able to tolerate anoxia for 178 min while S. aequifasciatus was able to withstand 222 min exposure in deep hypoxia (0.75 mg O(2) L(-)(1)). Suppressed MO(2) was observed during exposure to 0.34 (A. crassipinnis) and 0.79 mg O(2) L(-)(1) (S. aequifasciatus), while opercular movements increased in both species exposed to hypoxia. Higher levels of muscle and liver glycogen and larger hypoxia-induced increases in plasma glucose and lactate were observed in A. crassipinnis, which showed a higher degree of hypoxia tolerance. Changes in enzyme levels were tissue-specific and differed between species suggesting differential abilities in down-regulating oxidative pathways and increasing anaerobic metabolism. Based on the present data, we conclude that these animals are good anaerobes and highly adapted to their environment, which is allowed by their abilities to regulate metabolic pathways and adjust their enzyme levels.     

Pyruvate metabolism in rice coleoptiles under anaerobiosis

Relative importance of ethanolic, lactate and alanine fermentation pathways was estimated in coleoptiles of rice seedlings (Oryza sativa L.) subjected to anoxic stress. The in vitro activities of alcohol dehydrogenase (ADH, EC 1.1.1.1), pyruvate decarboxylase (PDC, EC 4.1.1.1) and alanine aminotransferase (AlaAT, EC 2.6.1.2) in the coleoptiles increased in anoxia, whereas no significant increase was measured in lactate dehydrogenase (LDH, EC 1.1.1.27) activity. At 48 h, the ADH, PDC and AlaAT activities in anoxic coleoptiles were 62-, 15- and 7.6-fold greater, respectively, than those in the presence of oxygen. Ethanol and alanine in the coleoptiles accumulated rapidly under anoxia, increasing by 48 h, 57- and 5.6-fold compared with those in the presence of oxygen, respectively. However, lactate concentration did not increase and no initial burst of lactate production was detected. The relative ratio of carbon flux from pyruvate to ethanol, lactate and alanine in anoxic coleoptiles was estimated to be 92, 1 and 7% of the total carbon flux, respectively. These results suggest that the potential carbon flux from pyruvate to ethanol may be much greater than the potential flux from pyruvate to lactate and alanine in rice coleoptiles during anoxia.     

Effect of reproduction on escape responses and muscle metabolic capacities in the scallop Chlamys islandica Müller 1776

In scallops, gametogenesis leads to mobilization of glycogen and proteins from the adductor muscle towards the gonad. This mobilization is likely to diminish the metabolic capacities of the adductor muscle and thereby the scallops' escape response. We examined the escape response in terms of number of valve claps until exhaustion, rate of clapping and the recovery during and after valve closure in adult scallops, Chlamys islandica, sampled at different stages in the reproductive cycle (immature, mature, before and after spawning). In parallel, we measured muscle glycogen, protein and phosphoarginine contents, the oxidative capacity of mitochondria isolated from the adductor muscle and levels of muscle enzymes which are active during exercise and recovery. The number of claps (24-26), rate of clapping ( approximately 13 clapsmin(-1)) and phosphoarginine and arginine kinase levels were similar during the different reproductive stages. All immature scallops responded to restimulation immediately after opening their valves, while only 62% of mature, 82% of prespawned and 38% of spawned scallops responded. Immature animals completely recovered their initial swimming capacity within 4 h of opening their valves, but mature, prespawned and spawned scallops needed 18, 12 and 18 h, respectively. Overall phasic adductor muscle from mature, prespawned and spawned animals showed decreased glycogen phosphorylase, phosphofructokinase, pyruvate kinase (except for prespawned), octopine dehydrogenase and citrate synthase levels, a deterioration of the oxidative capacity of mitochondria and a marked decrease in glycogen content compared to immature scallops. Therefore, during gonadal maturation and spawning, C. islandica did not change its clapping capacity, but slowed its recuperation from exhausting burst exercise, both during and after valve closure, likely due to the decreased metabolic capacity of the adductor muscle.     

Hypoxic induction of alcohol and lactate dehydrogenases in lupine seedlings

Seedlings of lupine (Lupinus luteus L. cv. Juno) were exposed for up to 96 hours to 1 to 2 kPa partial pressure oxygen (hypoxic treatment) and activities of alcohol dehydrogenase (ADH), lactate dehydrogenase (LDH) and their isoform profiles were determined. Roots of lupine seedlings were grown in a nitrogen flushed nutrient solution while their shoots were in air. Prolonged hypoxia led to a reduction of root elongation. This was accompanied by reduced increase in dry weight suggesting that insufficient carbohydrate supply was the cause of retarded growth of lupine roots. Hypoxically treated roots showed induction of ADH and LDH acivities. The maximum increase in LDH activity was low (2-fold) in contrast to ADH activity, which increased up to 7-fold. Hypoxic treatment of roots did not affect the activities of ADH and LDH in hypocotyls and cotyledons. Analysis of ADH and LDH activity gels indicated in roots 1 and 2 isoforms, respectively. The level of isozymes of both enzymes increased in roots upon exposure to hypoxic stress. Differences in isoenzymatic spectrum of ADH and LDH between roots, hypocotyls and cotyledons indicate organ specificity of isozymes of both enzymes. The importance of alcohol and lactate fermentation in roots to cope with hypoxic stress is discussed.     

Activity of biochemical pH-stat enzymes in cereal root tips under oxygen deficiency

The activity of the enzymes of alcoholic and lactic-acid fermentation: pyruvate decarboxylase (PDC, EC 4.1.1.1), alcohol dehydrogenase (ADH, EC 1.1.1.1), lactate dehydrogenase (LDH, EC 1.1.1.27) and the enzymes of malic acid metabolism: phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.23), NAD-dependent malate dehydrogenase (NAD-MDH, EC 1.1.1.37), and NADP-dependent malic enzyme (NADP-ME, EC 1.1.1.40) involved in the operation of biochemical pH-stat was investigated in the root tips of wheat (Triticum aestivum L.) and rice (Oryza sativa L.) under hypoxia and anoxia. Exposures lasted for 6, 12, and 18 h. The most pronounced response was detected for the enzymes of alcoholic fermentation. The activation of ADH and PDC in wheat occurred only under hypoxia, whereas in rice it was detected both under hypoxia and anoxia. The activation of LDH in wheat occurred under hypoxia, and in rice, the activity of this enzyme was slightly enhanced. The activity of the enzymes of malic acid metabolism did not change except in wheat root tips under hypoxia when PEPC activity decreased and NADP-ME activity simultaneously rose. The role of biochemical pH-stat in the regulation of cytoplasmic pH in plant cells under oxygen deficit and the mechanisms for regulating the activities of enzymes involved in biochemical pH-stat are discussed as well as the interaction between biochemical pH-stat and other mechanisms maintaining pH of plant cells. The results are analyzed within a context of intracellular pH regulation.     

Impact of exposure to bacteria on metabolism in the penaeid shrimp Litopenaeus vannamei

We hypothesized that aggregation of bacteria and hemocytes at the gill, which occurs as part of the shrimp's antibacterial immune defenses, would impair normal respiratory function and thereby disrupt aerobic metabolism. Changes in oxygen uptake and lactate accumulation were determined in Litopenaeus vannamei, the Pacific white shrimp, following injection with either saline (control) or a strain of the gram-negative bacterium Vibrio campbellii that is pathogenic in crustaceans. The rate of oxygen uptake was determined during the first 4 h after injection and after 24 h. Injection of bacteria decreased oxygen uptake by 27% (from 11.0 to 8.2 micromol g-1 h-1) after 4 h, while saline-injected shrimp showed no change. Decreased oxygen uptake persisted 24 h after Vibrio injection. In well-aerated water, resting whole-animal lactic acid levels increased in shrimp injected with bacteria (mean=2.59 micromol lactate g-1+/-0.39 SEM, n=8) compared to saline-injected control shrimp, but this difference did not persist at 24 h. Exposure to hypercapnic hypoxia (PCO2=1.8 kPa, PO2=6.7 kPa) also resulted in significant whole-body lactic acid differences (mean=3.99 and 1.8 micromol g-1 tissue in Vibrio and saline-injected shrimp, respectively). Our results support the hypothesis that the crustacean immune response against invading bacteria impairs normal metabolic function, resulting in depression of oxygen uptake and slightly increased anaerobic metabolism.     

Metabolic adaptations to environmental changes in Caenorhabditis elegans

Metabolic adaptations to environmental changes were studied in Caenorhabditis elegans. To assess adjustments in enzyme function, maximum activities of key enzymes of main metabolic pathways were determined. After a 12 h incubation at varying temperatures (10, 20°C) and oxygen supplies (normoxia or anoxia), the activities of the following enzymes were determined at two measuring temperatures in tissue extracts: lactate dehydrogenase (LDH; anaerobic glycolysis), 3-hydroxyacyl-CoA-dehydrogenase (HCDH; fatty acid oxidation), isocitrate dehydrogenases (NAD-IDH, NADP-IDH; tricarboxylic acid cycle) and isocitrate lyase (ICL; glyoxylate cycle). Incubation at 20°C induced a strong increase in maximum LDH activity. Anoxic incubation caused maximum HCDH and NADP-IDH activities and, at 10°C incubation, LDH activity to increase. Maximum NAD-IDH and ICL activities were not influenced by any type of incubation. In order to study the time course of metabolic adaptations to varying oxygen supplies, relative quantities of free and protein-bound NADH were determined in living C. elegans using time-resolved fluorescence spectroscopy. During several hours of anoxia, free and protein-bound NADH showed different time courses. One main result was that just at the moment when the protein-bound NADH had reached a constant level, and the free NADH started to increase rapidly, the worms fell into a rigor state. The data on enzyme activity and NADH fluorescence can be interpreted on the basis of a two-stage model of anaerobiosis.     

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.     

Reversibility of the lactate dehydrogenase isozyme shift induced by low oxygen tension

The shift of the lactate dehydrogenase (LDH) isoenzymes in experimental animals under hypoxia from B (aerobic) to A (anaerobic) is confirmed and its reversibility after removal of the animals to room air is reported. These experiments are interpreted as further supportive evidence of a physiological adaptive role for the lactate dehydrogenase enzyme system. The slow adaptive process observed in this experimental situation presumably requires de novo enzyme synthesis, however, in the emergency of a sudden deprivation of oxygen the liberation of preformed A LDH could be a link in the rapid chain of events resulting in depressed cardiac muscle contractility which follows myocardial infarction. A recently proposed comprehensive explanation of the role of LDH isozymes is thus extended.