Sexual differences and steroid-induced changes in metabolic activity in toadfish sonic muscle

Since the male oyster toadfish (Opsanus tau) is more active in sound production than the female, we hypothesized that sonic muscles of the male are biochemically specialized to perform more work. In order to categorize the muscle biochemically and test for sexual differences, we measured the activity of two anaerobic enzymes, 3-phosphoglyceraldehyde dehydrogenase (3PG) and lactic dehydrogenase (LDH), and two aerobic enzymes, malate dehydrogenase (MDH) and glutamic oxaloacetic transaminase (GOT). Males exhibited greater 3PG and GOT activity than females (p less than 0.05). Both MDH and LDH showed little activity in either sex. High 3PG and low LDH levels indicate a sustained level of glycolysis, with pyruvate shuttled into aerobic metabolism, and high GOT activity indicates a high level of aerobic metabolism. From this and other data, we conclude that toadfish sonic muscle can be classified as fast-twitch oxidative glycolytic or fast-twitch fatigue resistant. The endocrine basis for these sexual differences was examined by implanting steroid pellets into ovariectomized females. Testosterone induced a doubling of 3PG activity (p less than 0.02), and dihydrotestosterone induced an eight-fold increase (p less than 0.0005) in GOT concentration over controls. The steroids had no effect on LDH and MDH activities. Hormones, therefore, trigger one of the fundamental sexual differences underlying toadfish communication, namely a difference in metabolism, providing the male with the capacity for increased sound production.     

Activity of some enzymes of energy metabolism in striated muscle of obese subjects with respect to body composition.

The effect of obesity on the activity of some enzymes of energy supplying metabolism was studied in male and female groups of different body weight, using tissue samples of m. quadriceps femoris obtained by a biopsy needle. Both obese males and females displayed a distinct tendency towards anaerobic metabolism (high lactate dehydrogenase activities). The assumption that cytoplasm has an increased capacity in the muscle of the obese for reduction syntheses is supported by the increased ratio of malate dehydrogenase to citrate synthase activities. Compared with controls, less activity of enzymes associated with fatty acid and glucose degradation (hexokinase, hydroxyacyl-CoA dehydrogenase, citrate synthase) was observed in obese males. In obese females the latter enzyme activities did not differ from those in the controls; however, lactate dehydrogenase and triosophosphate dehydrogenase activities were significantly higher. Significant inverse correlations between hexokinase and hydroxyacyl- CoA dehydrogenase activities, on the one hand, and indicators of body composition and body weight, on the other, were found in males. The female group did not display analogous significant relations between the enzymatic organization and indicators of body composition.     

Activities of citrate synthase and NAD+-linked and NADP+-linked isocitrate dehydrogenase in muscle from vertebrates and invertebrates.

1. The activities of citrate synthase, NAD+-linked and NADP+-linked isocitrate dehydrogenase were measured in muscles from a large number of animals, in order to provide some indication of the importance of the citric acid cycle in these muscles. According to the differences in enzyme activities, the muscles can be divided into three classes. First, in a number of both vertebrate and invertebrate muscles, the activities of all three enzymes are very low. It is suggested that either the muscles use energy at a very low rate or they rely largely on anaerobic glycolysis for higher rates of energy formation. Second, most insect flight muscles contain high activities of citrate synthase and NAD+-linked isocitrate dehydrogenase, but the activities of the NADP+-linked enzyme are very low. The high activities indicate the dependence of insect flight on energy generated via the citric acid cycle. The flight muscles of the beetles investigated contain high activities of both isocitrate dehydrogenases. Third, other muscles of both vertebrates and invertebrates contain high activities of citrate synthase and NADP+-liniked isocitrate dehydrogenase. Many, if not all, of these muscles are capable of sustained periods of mechanical activity (e.g. heart muscle, pectoral muscles of some birds). Consequently, to support this activity fuel must be supplied continually to the muscle via the circulatory system which, in most animals, also transports oxygen so that energy can be generated by complete oxidation of the fuel. It is suggested that the low activities of NAD+-linked isocitrate dehydrogenase in these muscles may be involved in oxidation of isocitrate in the cycle when the muscles are at rest. 2. A comparison of the maximal activities of the enzymes with the maximal flux through the cycle suggests that, in insect flight muscle, NAD+-linked isocitrate dehydrogenase catalyses a non-equilibrium reaction and citrate synthease catalyses a near-equilibrium reaction. In other muscles, the enzyme-activity data suggest that both citrate synthase and the isocitrate dehydrogenase reactions are near-equilibrium.     

Carboxylate metabolism changes induced by Fe deficiency in barley, a Strategy II plant species

The effects of iron (Fe) deficiency on carboxylate metabolism were investigated in barley (Hordeum vulgare L.) using two cultivars, Steptoe and Morex, which differ in their Fe efficiency response. In both cultivars, root extracts of plants grown in Fe-deficient conditions showed higher activities of enzymes related to organic acid metabolism, including citrate synthase, malate dehydrogenase and phosphoenolpyruvate carboxylase, compared to activities measured in root extracts of Fe-sufficient plants. Accordingly, the concentration of total carboxylates was higher in Fe-deficient roots of both cultivars, with citrate concentration showing the greatest increase. In xylem sap, the concentration of total carboxylates was also higher with Fe deficiency in both cultivars, with citrate and malate being the major organic acids. Leaf extracts of Fe-deficient plants also showed increases in citric acid concentration and in the activities of glucose-6-phosphate dehydrogenase and fumarase activities, and decreases in aconitase activity. Our results indicate that changes in root carboxylate metabolism previously reported in Strategy I species also occur in barley, a Strategy II plant species, supporting the existence of anaplerotic carbon fixation via increases in the root activities of these enzymes, with citrate playing a major role. However, these changes occur less intensively than in Strategy I plants. Activities of the anaerobic metabolism enzymes pyruvate decarboxylase and lactate dehydrogenase did not change in barley roots with Fe deficiency, in contrast to what occurs in Strategy I plants, suggesting that these changes may be Strategy I-specific. No significant differences were observed in overall carboxylate metabolism between cultivars, for plants challenged with high or low Fe treatments, suggesting that carboxylate metabolism changes are not behind the Fe-efficiency differences between these cultivars. Citrate synthase was the only measured enzyme with constitutively higher activity in Steptoe relative to Morex leaf extracts.     

Allometric scaling of maximal enzyme activities in the axial musculature of striped bass, Morone saxatilis (Walbaum)

It had been suggested that the activity of anaerobic enzymes in the white muscle of fish increases exponentially with body size to meet the increasing hydrodynamic costs of burst swimming. We tested whether this relationship holds across a very large size range of striped bass, spanning a nearly 3,000-fold range in body mass. We examined the scaling of marker enzymes of anaerobic (lactate dehydrogenase and pyruvate kinase) and aerobic (citrate synthase and malate dehydrogenase) metabolism in the red and white locomotor muscles. In white muscle, we found positive scaling of anaerobic enzymes only in smaller fishes. Positive scaling of anaerobic enzymes was not found among the samples that included fishes >1,000 g despite having a sufficiently large sample size to detect such scaling. The absence of positive scaling in the white muscles of large bass suggests that they are unable to generate sufficient power to sustain relative burst swimming performance. Enzymes from aerobic pathways had activities that were mass independent in both red and white muscle. Red and white muscles were metabolically distinct except among the smallest fishes. Among young of the year, the anaerobic capacity of red muscle approached that of white muscle and also showed positive scaling. This unusual pattern suggests that red muscle might augment white muscle during burst swimming and add to the total power generated by these small fish. Maximizing burst swimming performance may be critical for small fishes vulnerable to predation but unimportant for large fishes.     

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.     

The effect of endurance-training on the maximum activities of hexokinase, 6-phosphofructokinase,citrate synthase,and oxoglutarate dehydrogenase in red and white muscles of the rat

Adult female rats were subjected to an eleven-week endurance-training programme, and, for the first time, the maximum activities of enzymes that can indicate the quantitative capacities of both anaerobic glycolysis and the Krebs cycle in muscle (viz. 6-phosphofructokinase and oxoglutarate dehydrogenase respectively) were measured in heart plus white and fast-oxidative skeletal muscle. No changes were observed in heart muscle. In fast-oxidative skeletal muscle, activities of hexokinase, citrate synthase, and oxoglutarate dehydrogenase were increased by 51, 26, and 33% respectively but there was no effect on 6-phosphofructokinase. These results demonstrate that in red muscle there is no effect of this training programme on the anaerobic capacity but that of the aerobic system is increased by one third. In white skeletal muscle, only the activity of citrate synthase was increased, which indicates that this activity may not provide even qualitative information about changes in capacity of the Krebs cycle.     

Flight muscle enzyme activities do not differ between pelagic and near-shore foraging seabird species

Common terns (Sterna hirundo), sooty terns (S. fuscata) and brown noddies (Anous stolidus) are phylogenetically related seabirds that differ in field activity levels and daily energy expenditure. To test whether muscle metabolic capacities co-evolve with activity levels and energy expenditure, we collected pectoral muscle biopsies from members of each species, and measured the activities of key enzymes in oxidative metabolism (citrate synthase, CS), anaerobic metabolism (lactate dehydrogenase, LDH), glycolysis (pyruvate kinase, PK), fatty acid oxidation (3-hydroxyacyl CoA dehydrogenase) and phosphocreatine hydrolysis (creatine phosphokinase, CPK). We hypothesized that temperate-breeding common terns would have higher enzyme activities than the two tropical species (sooty terns and brown noddies); consistent with the higher activity level of common terns. There were no differences in enzyme activities among adults of the three species. Common tern chicks within 2-3 days of flight had two-fold higher pyruvate kinase activity than adults, suggesting an increased glycolytic capacity in the chicks. Given the lack of difference among species at the enzymatic level, our results support the notion that behavior and whole organism performance can evolve considerably before there are detectable changes in underlying lower-level physiological/biochemical traits.     

粘虫飞行肌中与能量代谢有关的酶活性研究

该文报道粘虫Mythimna separata (Walker ) 蛹及不同日龄成虫飞行肌中与3 种代谢途径有关的5 种酶,即3-磷酸甘油醛脱氢酶(GAPDH)、3-磷酸甘油脱氢酶(GDH)、乳酸脱氢酶(LDH)、3-羟酰辅酶A 脱氢酶(HOAD)、柠檬酸合成酶(CS)活性的变化。成虫羽化后,这5 种酶的活性大多数都高于蛹期,表明成虫飞行肌与能量代谢有关的活动比蛹期高。不同日龄成虫飞行肌的能量代谢特点为：成虫羽化后糖酵解循环的活性增加;1 日龄进行糖酵解的能力较强,2 日龄即具备较强的脂肪代谢能力,2～5日龄糖及脂肪代谢的能力基本相当,但7日龄脂肪代谢的能力较强。1～7日龄粘虫蛾飞行肌具有较高的GDH 和LDH活性,这既是粘虫蛾飞行肌能进行高度有氧代谢的重要标志,也是其具有一定无氧代谢能力的最好说明,而飞行肌中较高的CS活性则是粘虫蛾具有较强飞行能力的重要保证。对成虫GAPDH∶HOAD 活性进行分析比较的结果还显示,粘虫蛾持续飞行的能源物质既有脂类也有糖类,而不仅仅只限于脂类。     

Effects of sleep deprivation on the activity of selected metabolic enzymes in skeletal muscle

The effect of 120-h sleep deprivation on the activity of selected enzymes of energy metabolism in skeletal muscle was studied in seven healthy volunteers. The results showed a significant decrease in the activity of malate dehydrogenase, citrate synthase, glycerol-3-phosphate dehydrogenase and lactate dehydrogenase. Triosephosphate dehydrogenase, hexokinase, and hydroxyacyl-CoA-dehydrogenase activities showed an insignificant decrease. The findings are indicative of (1) decreased aerobic oxidation capacity; (2) reduced function of reducing-equivalent carriers from cytosol across the mitochondrial membrane; (3) relative accentuation of the non-aerobic glycolytic pathway; (4) a prediabetic type of muscle metabolism.     

Enzymes of the tricarboxylic acid cycle in Obeliscoides cuniculi (Nematoda; Trichostrongylidae) during parasitic development

The specific activities of the enzymes of the tricarboxylic acid cycle; citrate synthase, aconitase, isocitrate dehydrogenase, succinate dehydrogenase, fumarase, and malate dehydrogenase, were determined in early fifth-stage, young and mature adult Obeliscoides cuniculi, the rabbit stomach worm. ∝-Ketoglutarate dehydrogenase activity could not be determined in any fraction. Fumarate reductase activity was found only in the mitochondrial fraction while all other enzymes, including an NADP-dependent malic enzyme were localized in the cytoplasm. Glutamate dehydrogenase, acid and alkaline phosphatase activities were also recorded. High levels of those enzymes acting in the “reversed” direction, i.e. MDH and fumarase relative to the enzymes of the “forward” direction, i.e. citrate synthase, aconitase and isocitrate dehydrogenase suggests that under anaerobic conditions a modified tricarboxylic acid cycle can operate. Some variations in specific activities were apparent as the worms matured but no qualitative differences were observed.     

Organization of Krebs tricarboxylic acid cycle enzymes in mitochondria

Sonic oscillation of mitochondria usually leads to the release of a number of Krebs tricarboxylic acid cycle enzymes. These enzymes have, therefore, been referred to as soluble matrix enzymes. In the present report, we show that gentle sonic or osmotic disruption can be used to obtain a mitochondrial preparation where these enzymes appear to be organized in a large complex of proteins. Using citrate synthase as a marker for these enzymes, we show that the proposed complex is easily sedimented at 32,000 X g in 30 min. The exposed citrate synthase in these complexes can be inhibited by its antibody, indicating that the enzymes are not merely entrapped in substrate-permeable vesicles. The effects of pH, temperature, ionic strength, and several metabolites on the ability to obtain the sedimentable citrate synthase have been tested. These studies indicate that the complex is stable at conditions presumed to exist in situ. Electron microscopic studies show that gentle sonic oscillation gives rise to an efflux of mitochondrial matrix contents which tend to remain attached to the original membranes. The sedimentable fraction also contained four other presumably soluble Krebs tricarboxylic acid cycle enzymes: aconitase, NAD+-isocitrate dehydrogenase, fumarase, and malate dehydrogenase.     

Physical training under the influence of beta-blockade in rats. III. Effects on muscular metabolism

Rats were trained by daily running exercises for 7 weeks. In addition, one group of rats was trained under the influence of propranolol, while another group received daily injections of propranolol only. None of the treatments used had influence on the activities of myocardial enzymes: 3-hydroxyacyl-CoA - dehydrogenase (HADH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH), and citrate synthase (CS) which were assayed for estimating oxidative capacity, or lactate dehydrogenase (LDH) which was used as a measure of anaerobic capacity. Training without propranolol resulted in elevated activities of the oxidative enzymes in M. extensor digitorum and in M. soleus. The corresponding changes in the rat group trained with propranolol always were much smaller, despite an equal amount of training. Only the trend for lowered activity of LDH was observable in skeletal muscle of the rat groups trained both with and without propranolol. Long-term beta-blockade alone did not induce enzymatic changes. It is concluded that a functioning sympathetic nervous system is necessary for the adaptive responses of muscular metabolism to training. Blockade of the sympathetic influence during exercise periods also hampers the training-induced responses.     

Enzyme profiles in two wing polymorphic soapberry bug populations (Jadera haematoloma: Rhopalidae)

Wing-polymorphic insects are excellent models for asking questions about trade-offs in physiology and life-history because of the existence of multiple morphs exhibiting numerous strategies living in one environment. We measured activities of select key enzymes in oxidative metabolism (citrate synthase), glycolysis (hexokinase, pyruvate kinase) and fatty acid oxidation (?-hydroxyacyl CoA dehydrogenase, HOAD) in flying and non-flying long-winged bugs from two populations (ancestral and derived) of the wing-polymorphic soapberry bug (Jadera haematoloma). In the ancestral population, flyers had significantly greater activities of citrate synthase, hexokinase, pyruvate kinase, and HOAD than non-flyers. In contrast, in the derived population, flyers and non-flyers showed no significant differences in the activities of any of the enzymes tested. There were no significant differences in activities of citrate synthase as a function of adult age (3-20 d) for either population. Short-winged bugs in the derived population had significantly lower citrate synthase activities than either of the two derived, long-winged morphs, however, they were analogous to the ancestral long-winged non-flyer. These results suggest an evolution of alternative flight strategies between the two populations.     

Metabolic and cyclic nucleotide enzyme activities in muscle and nonmuscle cells of rat heart during perinatal development

Enzyme activities related to aerobic metabolism and cyclic nucleotides were evaluated in muscle and nonmuscle cells of rat heart. The perinatal period from weaning to adult was studied. Malate dehydrogenase, citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase activities of nonmuscle cells equal or exceed muscle cell activities in the weanling heart. Aerobic enzymes remain unchanged in nonmuscle cells during growth; however, muscle cell activities are enhanced. Adenylate cyclase and guanylate cyclase activities are higher in heart homogenates of weanling than adult rats. Despite elevated adenylate cyclase activity, cyclic AMP levels are identical in weanling and adult rats. Cyclic GMP levels are twofold higher in weanling than in adult rats. Muscle cell metabolism and cyclic nucleotide levels are associated with growth-related changes in heart function and cellularity, respectively.     

Relation between growth rate and metabolic organization of white muscle,liver and digestive tract in cod,Gadus morhua

To determine whether the aerobic capacity of tissues required for growth specifically reflects growth rates, we monitored the activities of key enzymes of oxidative, glycolytic and amino acid metabolism in muscle, liver and intestine of Atlantic cod (Gadus morhua) growing at different rates. Fish were maintained individually in small tanks at 10°C and fed on rations that allowed growth rates ranging from-0.6 to 1.6% per day. The correlation between growth rate and muscle enzyme activity was pronounced for the glycolytic enzymes (LDH, PFK and PK). The activities of glycolytic enzymes were more than four times higher for fish having higher growth rates compared to those that did not grow. Mitochondrial enzyme (cytochrome c oxidase, citrate synthase and -hydroxyacyl-CoA dehydrogenase) activities remained unchanged in fish with positive growth. The liver seems to respond to requirements of growth by an increase in size. In the liver, the activities of the enzymes of amino acid metabolism expressed as units · g DNA^-1 specifically increases with growth rate. In contrast to the two other tissues, the specific activities of mitochondrial enzymes in the intestine increased with growth rate while the relative mass of the intestine remained constant. Intestinal cytochrome c oxidase activity increased from a minimum of about 2 to more than 8 units · g intestine^-1. Cytochrome c oxidase activity increased in parallel with the food conversion efficiency. This suggests that the aerobic capacity of the intestine may initially limit the rates of digestion and growth in this species.Abbreviations AA amino acid(s) - BM body mass - CCO cytochrome c oxydase - CS citrate synthase - DTNB 5,5 dithiobis-2-nitrobenzoic acid - GDH glutamate dehydrogenase - GOT glutamate oxalacetate transaminase - GPT glutamate pyruvate transaminase - GR growth rate(s) - HOAD -hydroxyacyl-CoA dehydrogenase - HSI hepatosomatic index - LDH lactate dehydrogenase - MR metabolic rate(s) - PCA perchloric acid - PFK phosphofructokinase - PK pyruvate kinase - PMSF phenylmethylsulphonyl fluoride; TRIS     

Genetic and biochemical analysis of anaerobically-induced enzymes during seed germination of Echinochloa crus-galli varieties tolerant and intolerant of anoxia

To compare the regulation of anaerobic metabolism during germination in anoxia-tolerant and intolerant plants, enzymes associated with anaerobic metabolism such as sucrose synthase, aldolase, enolase, pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH), and aldehyde dehydrogenase (ALDH) were assayed in two varieties of Echinochloa crus-galli, formosensis (tolerant) and praticola (intolerant). The initial and intervening enzymes of the pathway (sucrose synthase and aldolase) and enzymes in the last part of the pathway (PDC, ADH and ALDH) revealed similar changing patterns in activities during germination. This implies that each group of enzymes may be controlled by an identical regulatory mechanism. During anoxia, activities of all enzymes increased 1.5-30-fold in both varieties compared to their activities under aerobic conditions. Activities of sucrose synthase, enolase and ADH exhibited the same induction patterns under anoxia in formosensis and praticola. However, the activities of aldolase, ALDH and PDC were more strongly induced in formosensis under anoxia (1.2-2-fold) than in praticola. These enzymes were also assayed in F(3) families which varied in their anaerobic germinability. For PDC, activities under anoxia in anoxia-tolerant families were similar to those of an anoxia-intolerant family during the whole period although the family did not exhibit anaerobic germinability. This suggests that there is no correlation between PDC activity and anaerobic germinability. For ALDH, activities were more strongly induced under anoxia in anoxia-tolerant families than in anoxia-intolerant families, a trend also exhibited by the parents. This indicates that ALDH may play a role in detoxifying acetaldehyde formed through alcoholic fermentation during anaerobic germination.     

High swimming and metabolic activity in the deep-sea eel Synaphobranchus kaupii revealed by integrated in situ and in vitro measurements

Several complementary studies were undertaken on a single species of deep-sea fish (the eel Synaphobranchus kaupii) within a small temporal and spatial range. In situ experiments on swimming and foraging behaviour, muscle performance, and metabolic rate were performed in the Porcupine Seabight, northeast Atlantic, alongside measurements of temperature and current regime. Deep-water trawling was used to collect eels for studies of animal distribution and for anatomical and biochemical analyses, including white muscle citrate synthase (CS), lactate dehydrogenase (LDH), malate dehydrogenase (MDH), and pyruvate kinase (PK) activities. Synaphobranchus kaupii demonstrated whole-animal swimming speeds similar to those of other active deep-sea fish such as Antimora rostrata. Metabolic rates were an order of magnitude higher (31.6 mL kg(-1) h(-1)) than those recorded in other deep-sea scavenging fish. Activities of CS, LDH, MDH, and PK were higher than expected, and all scaled negatively with body mass, indicating a general decrease in muscle energy supply with fish growth. Despite this apparent constraint, observed in situ burst or routine swimming performances scaled in a similar fashion to other studied species. The higher-than-expected metabolic rates and activity levels, and the unusual scaling relationships of both aerobic and anaerobic metabolism enzymes in white muscle, probably reflect the changes in habitat and feeding ecology experienced during ontogeny in this bathyal species.     

Enzyme Activities in Regions of the Hypothalamus

Abstract: The activities of certain key enzymes have been measured in the ventral medial and ventral lateral areas of the hypothalamus, which are implicated in feeding behaviour, and compared with enzyme activities in the cortex and brainstem. The enzymes measured are concerned with glucose metabolism [hexokinase (EC 2.7.1.1) and glucosesphosphate dehydrogenase (EC 1.1.1.49)], ketone body metabolism [3-hydroxybutyrate dehydrogenase (EC 1.1.1.30)], fatty acid utilisation [carnitine palmitoyl transferase (EC 2.3.1.7)], citric acid cycle activity [pyruvate dehydrogenase (EC 1.2.4.2) and citrate synthase (EC 4.1.3.7)] and neurotransmitter synthesis [glutamate dehydrogenase (EC 1.4.1.3)].     

Oxidative stress reversibly inactivates myocardial enzymes during cardiac arrest

Oxidative stress during cardiac arrest may inactivate myocardial enzymes and thereby exacerbate ischemic derangements of myocardial metabolism. This study examined the impact of cardiac arrest on left ventricular enzymes. Beagles were subjected to 5 min of cardiac arrest and 5 min of open-chest cardiac compressions (OCCC) before epicardial direct current countershocks were applied to restore sinus rhythm. Glutathione/glutathione disulfide redox state (GSH/GSSG) and a panel of enzyme activities were measured in snap-frozen left ventricle. To test whether oxidative stress during arrest inactivated the enzymes, metabolic (pyruvate) or pharmacological (N-acetyl-l-cysteine) antioxidants were infused intravenously for 30 min before arrest. During cardiac arrest, activities of phosphofructokinase, citrate synthase, aconitase, malate dehydrogenase, creatine kinase, glucose-6-phosphate dehydrogenase, and glutathione reductase fell by 56, 81, 55, 34, 42, 55, and 45%, respectively, coincident with 50% decline in GSH/GSSG. OCCC effected full recovery of glutathione reductase and partial recovery of citrate synthase and aconitase, in parallel with GSH/GSSG. Phosphofructokinase, malate dehydrogenase, creatine kinase, and glucose-6-phosphate dehydrogenase recovered only after cardioversion. Antioxidant pretreatments augmented phosphofructokinase, aconitase, and malate dehydrogenase activities before arrest and enhanced these activities, as well as those of citrate synthase and glucose-6-phosphate dehydrogenase, during arrest. In conclusion, cardiac arrest reversibly inactivates several important myocardial metabolic enzymes. Antioxidant protection of these enzymes implicates oxidative stress as a principal mechanism of enzyme inactivation during arrest.