Cytochrome Oxidase Levels Research Articles

Effect of Endurance Training on the Oxidative Capacity of Skeletal Muscle in Emphysema Hamster Model

Emphysema is a debilitating disease that is characterized by irreversible damage in the alveolar walls due to lung hyperinflation. One of the major consequences of this disease is diminished exercise capacity, thought to be caused by blood-gas imbalances, or from peripheral mechanisms such as reductions in skeletal muscle blood flow, or alterations in metabolism. PURPOSE: The purpose of this research was to determine the effects of endurance exercise training on the oxidative capacity of skeletal muscle in the elastase-induced emphysema hamster model. METHODS: Thirty-five adult male hamsters were utilized for this study. The hamsters were randomly divided by disease state; emphysema (EMP) or none (noEMP); activity level, endurance exercised trained (Ex), or sedentary (Sed); and dobutamine timing, prevention of diaphragm fatigue before simulated exercise stress (Prev), or treatments of diaphragm fatigue after simulated exercise (Tx). Cytochrome oxidase levels in the vastus lateralis, gastrocnemius, and soleus were analyzed. Group comparisons were made using an ANOVA. RESULTS: The emphysemic endurance trained hamsters showed significantly higher oxidative capacities (measured via μmol/min/g) in the vastus lateralis (Ex/EMP: 6.24 ± 2.68 vs. Sed/EMP: 3.56± 2.41, p<0.05). The endurance trained hamsters showed significantly higher oxidative capacities in both the treatment and prevention mechanisms of dobutamine administration in the vastus lateralis (Ex/Tx: 6.54 ± 2.30 vs. Sed/Tx: 4.34 ± 3.08 and, Ex/Prev: 5.45 ± 2.69 vs. Sed/Prev: 2.88 ± 1.55, p<0.05) and the soleus (Ex/Tx: 6.57 ± 2.92 vs. Sed/Tx: 6.09 ± 2.51 and, Ex/Prev: 5.83 ± 2.49 vs. Sed/Prev: 3.03 ± 0.68, p<0.05) when compared to those sedentary hamsters. However the hamsters that were sedentary were more responsive to the dobutamine treatment when compared to the dobutamine prevention in the vastus lateralis and soleus. CONCLUSION: Endurance training decreased the loss of oxidative capacity in hamster skeletal muscle that occurs with emphysema.

The effect of haem biosynthesis inhibitors and inducers on intestinal iron absorption and liver haem biosynthetic enzyme activities

The relation between haem biosynthesis and intestinal iron absorption is not well understood, we therefore investigated the effect of compounds that alter haem metabolism on duodenal iron absorption. CD1 mice were treated with either an inhibitor (succinyl acetone (SA)) or stimulator (2-allyl-2-isopropylacetamide (AIA)) of haem biosynthesis. 5-Aminolaevulinic acid (ALA) dehydratase and urinary ALA and porphobilinogen (PBG) levels, were determined. Intestinal iron absorption was assayed with in vivo and in vitro techniques. Liver hepcidin ( Hamp1) and duodenal iron transporter mRNA levels were measured using RT-PCR. AIA caused increased hepatic ALA synthase (1.6-fold) and ALA dehydratase (1.4-fold, both p < 0.005) activities and increased urinary ALA and PBG excretion (2.1- and 1.4-fold, p < 0.005, p < 0.05, respectively). In vivo intestinal iron absorption was reduced to 49% of control ( p < 0.005). Mice treated with SA showed decreased urinary ALA and PBG levels (75 and 55% control, both p < 0.005) and reductions in both ALA synthase and ALA dehydratase activities (77 and 56% control, p < 0.05, p < 0.005, respectively) in the liver. Liver and duodenal haem and cytochrome oxidase levels were not significantly decreased. Iron absorption was enhanced (1.26-fold, p < 0.05) and hepatic Hamp1 mRNA was reduced (53% of control, p < 0.05). In vitro duodenal iron uptake after mice were injected with SA also demonstrated an increase in Fe(III) reduction and uptake (1.27- and 1.41-fold, p < 0.01 respectively). Simultaneous injections of SA and ALA blocked the enhancing effect on iron absorption seen with SA alone. We conclude that alterations in haem biosynthesis can influence iron absorption and in particular, the intermediate ALA seems to be an inhibitor of iron absorption.

Sulfide, the first inorganic substrate for human cells

Hydrogen sulfide (H2S) is produced inside the intestine and is known as a poison that inhibits cellular respiration at the level of cytochrome oxidase. However, sulfide is used as an energetic substrate by many photo- and chemoautotrophic bacteria and by animals such as the lugworm Arenicola marina. The concentrations of sulfide present in their habitats are comparable with those present in the human colon. Using permeabilized colonic cells to which sulfide was added by an infusion pump we show that the maximal respiratory rate of colonocyte mitochondria in presence of sulfide compares with that obtained with succinate or L-alpha-glycerophosphate. This oxidation is accompanied by mitochondrial energization. In contrast, other cell types not naturally exposed to high concentration of sulfide showed much lower oxidation rates. Mitochondria showed a very high affinity for sulfide that permits its use as an energetic substrate at low micromolar concentrations, hence, below the toxic level. However, if the supply of sulfide exceeds the oxidation rate, poisoning renders mitochondria inefficient and our data suggest that an anaerobic mechanism involving partial reversion of Krebs cycle already known in invertebrates takes place. In conclusion, this work provides additional and compelling evidence that sulfide is not only a toxic compound. According to our study, sulfide appears to be the first inorganic substrate for mammalian cells characterized thus far.

P204 Cytochrome oxidase levels in chondrocytes during expansion and after return to 3-D culture

P204 Cytochrome oxidase levels in chondrocytes during expansion and after return to 3-D culture

In vitro cytotoxicity and mitochondrial toxicity of tenofovir alone and in combination with other antiretrovirals in human renal proximal tubule cells.

We assessed the in vitro toxicity of tenofovir (TFV) and compared it with those of zidovudine (AZT), didanosine (ddI), ritonavir (RTV), and lopinavir (LPV) alone and in combination in human renal proximal tubule epithelial cells (RPTECs). The cells were treated with various concentrations and combinations of the tested antiretrovirals for up to 22 days, and cytotoxicity was determined. In addition, we assessed the levels of mitochondrial DNA (mtDNA) and cytochrome oxidase II (COII) mRNA in RPTECs treated with reverse transcriptase inhibitors. TFV alone was not associated with significant cytotoxicity. ddI showed pronounced cytotoxicity that was greater than those of AZT (P = 0.002) and TFV (P = 0.0001). The combination of 10 muM RTV and 40 muM LPV significantly reduced RPTEC viability (P < 0.0001), and TFV tended to partially reduce this effect. TFV alone affected neither mtDNA nor COII mRNA levels, whereas ddI caused a profound depletion of mtDNA and a parallel reduction in COII mRNA expression. The effects of ddI, but not those of AZT, on mtDNA and COII mRNA were further enhanced in the presence of TFV, a finding consistent with the inhibition of ddI clearance by TFV. The addition of TFV to ddI or AZT appeared to slightly increase the COII mRNA/mtDNA ratio relative to that in cells treated with ddI or AZT alone. Together, these in vitro results indicate that combination with other antiretrovirals does not significantly increase the toxic potential of TFV in RPTECs.

Rewiring the adult brain (Reply)

We disagree with Calford . 1 that there is a consensus on adult plasticity in primate V1 cortex: for example, macaque area V1 cytochrome oxidase levels remained depressed for several months after binocular retinal lesions2; no reorganization in macaque V1 after monocular retinal lesions was found3; and no area V1 reorganization in a patient with macular degeneration was detected4.

Synergistic inhibition of respiration in brain mitochondria by nitric oxide and dihydroxyphenylacetic acid (DOPAC): Implications for Parkinson's disease

The inhibition of mitochondrial respiration by nitric oxide ( NO) at cytochrome c oxidase level has been established as a physiological regulatory mechanism of mitochondrial function. Given, on the one hand, the potential involvement of NO and dopamine metabolism in mitochondrial dysfunction associated with neurodegeneration and, on the other hand, the reported interaction of NO with dihydroxyphenylacetic acid (DOPAC), a major mitochondrial-associated dopamine metabolite, we examined the combined effects of NO and DOPAC on the respiratory chain of isolated rat brain mitochondria. Whereas dopamine or DOPAC induced no measurable effects on the mitochondrial respiration rate, a mixture of NO with DOPAC inhibited the rate in a way stronger than that exerted by NO. This effect was noticed with actively respiring (state 3) and resting (state 4) mitochondria. At variance with DOPAC, dopamine failed to potentiate NO inhibitory effects. The inhibition was dependent on the concentration of both compounds, NO and DOPAC, and exhibited characteristics similar to those exerted by NO, namely: it was reversible and dependent on the concentration of oxygen. Analysis of respiratory enzymatic activities demonstrated a selective inhibition at the level of cytochrome c oxidase (complex IV). Insights into the chemical mechanisms underlying the inhibitory effect were inferred from experiments using metmyoglobin (a ligand for NO and derived species, such as nitroxyl anion) and ferrocyanide (a reductant of NO, producing nitroxyl anion). Whereas metmyoglobin decreased the inhibition, ferrocyanide potentiated the inhibition. Moreover, a mixture of ferrocyanide with NO reproduced the effects exerted by the mixture of NO with DOPAC. The results are consistent with the notion of a reaction of NO with DOPAC producing a nitric oxide-derived compound(s), which inhibit O 2 uptake at the cytochrome oxidase level. Although the mechanism in question remains to be clearly elucidated it is suggested that the NO/DOPAC-dependent inhibition of cytochrome oxidase may involve nitroxyl anion. The significance of these observations for mitochondrial dysfunction inherent in Parkinson's disease is discussed.

Quantitative immuno-electron microscopic analysis of nuclear respiratory factor 2 alpha and beta subunits: Normal distribution and activity-dependent regulation in mammalian visual cortex

The macaque visual cortex is exquisitely organized into columns, modules, and streams, much of which can be correlated with its metabolic organization revealed by cytochrome oxidase (CO). Plasticity in the adult primate visual system has also been documented by changes in CO activity. Yet, the molecular mechanism of regulating this enzyme remains not well understood. Being one of only four bigenomic enzymes in mammalian cells, the transcriptional regulation of this enzyme necessitates a potential bigenomic coordinator. Nuclear respiratory factor 2 (NRF-2) or GA-binding protein is a transcription factor that may serve such a critical role. The goal of the present study was to determine if the two major subunits of NRF-2, 2alpha and 2beta, had distinct subcellular distribution in neurons of the rat and monkey visual cortex, if major metabolic neuronal types in the macaque exhibited different levels of the two subunits, and if they would respond differently to monocular impulse blockade. Quantitative immuno-electron microscopy was used. In both rats and monkeys, nuclear labeling of alpha and beta subunits was mainly over euchromatin rather than heterochromatin, consistent with their active participation in transcriptional activity. Cytoplasmic labeling was over free ribosomes, the Golgi apparatus, and occasionally the nuclear envelope, signifying sites of synthesis and possible posttranslational modifications. The density of both subunits was much higher in the nucleus than in the cytoplasm for all neurons examined, again indicating that their major sites of cellular action is in the nucleus.

Piscicidal activity of alcoholic extract of Nerium indicum leaf and their biochemical stress response on fish metabolism

Laboratory evaluations were made to assess the piscicidal activity of ethyl alcohol extract of Nerium indicum leaf against predatory fish Channa punctatus and their ultimate mode of action on fish metabolism. Toxicity experiments show there was significant negative correlation between LC values and exposure periods i.e. LC50 value decreased from 66.32 mg/L (24h) to 44.96 mg/L (96h). Biochemical studies show that after exposure to sub lethal doses of alcoholic extract, pyruvate level and activities of acetylcholinesterase and cytochrome oxidase significantly decreased while lactate level and activities of alanine aminotransferase and aspartate amino transferase were significantly enhanced in both liver and muscle tissues of Channa punctatus. The alterations in all the above biochemical parameters were significantly (P

Delayed ischemic preconditioning activates nuclear-encoded electron-transfer-chain gene expression in parallel with enhanced postanoxic mitochondrial respiratory recovery.

Delayed ischemic preconditioning promotes cardioprotection via genomic reprogramming. We hypothesize that molecular regulation of mitochondrial energetics is integral to this cardioprotective program. Preconditioning was induced by use of 3 episodes of 3-minute coronary artery occlusion separated by 5 minutes of reperfusion. Twenty-four hours later, infarct size was reduced by 58% after preconditioning compared with sham-operated controls (P<0.001). Cardiac mitochondria were isolated from sham and preconditioned rat hearts. Mitochondrial respiration and ATP production were similar between the groups; however, preconditioned mitochondria exhibit modest hyperpolarization of the inner mitochondrial membrane potential (> or =22% versus control, P<0.001). After 35-minute anoxia and reoxygenation, preconditioned mitochondria demonstrated a 191+/-12% improvement in ADP-sensitive respiration (P=0.002) with preservation of electron-transfer-chain (ETC) activity versus controls. This augmented mitochondrial recovery was eradicated when preconditioning was abolished by the antioxidant 2-mercaptopropionyl glycine (2-MPG). These biochemical modulations appear to be regulated at the genomic level in that the expression of genes encoding rate-controlling complexes in the ETC was significantly upregulated in preconditioned myocardium, with a concordant induction of steady-state protein levels of cytochrome oxidase, cytochrome c, and adenine nucleotide translocase-1. 2-MPG abolished preconditioning induction of these transcripts. Moreover, transcripts of nuclear regulatory peptides known to orchestrate mitochondrial biogenesis, nuclear respiratory factor-1 and peroxisome-proliferator-activated receptor gamma coactivator 1alpha, were significantly induced in preconditioned myocardium. Delayed preconditioned mitochondria display increased tolerance against anoxia-reoxygenation in association with modifications in mitochondrial bioenergetics, with concordant genomic induction of a mitochondrial energetic gene regulatory program. This program appears to be mediated by reactive oxygen species signaling.

Near-infrared spectroscopic assessment of mitochondrial oxygenation status—comparison during normothermic extracorporeal liver perfusion by buffer only or buffer fortified with washed red blood cells: an experimental study

Background Use of marginal and non–heart-beating donors leads to an increased incidence of complications after clinical liver transplantation. Normothermic extracorporeal liver perfusion (NELP) may allow resuscitation and evaluation of such organs. Despite recent success in long-term liver preservation by NELP, no methods of organ evaluation have been defined. Mitochondrial cytochrome oxidase (Cyt Ox) levels reflect oxygen and substrate delivery, and hence ATP production at the cellular level. This study used near-infrared spectroscopy (NIRS) to measure Cyt Ox levels during NELP. Methods Livers retrieved from New Zealand white rabbits were immediately perfused in an extracorporeal circuit with oxygenated buffer (group A, n = 4) or red blood cell (RBC)–fortified buffer (group B, n = 4). Perfusion was continued for 3 hours at 37°C pH 7.4, and perfusate was gassed with 95%O 2/5%CO 2 at 1 liter per minute. Cyt Ox levels were monitored continuously by NIRS and bile output was measured. Results Cyt Ox was reduced at the start of perfusion in both groups, but even more rapidly in the buffer-perfused group. After initial deterioration, Cyt Ox levels improved significantly ( P < .05) with perfusion in the RBG-perfused group, but remained impaired in the buffer group 5.74 ± 1.51 Δμmol/L and −25.77 ± 21.94 Δμmol/L for groups B and A, respectively, at 180 minutes. Differences in bile output were not significant (19.33 ± 9.50 and 25.00 ± 16.81 μmol/min/100 g for groups B and A respectively). Conclusions Cyt Ox levels may offer better viability markers than bile output. NIRS is a practical method to measure tissue oxygenation, and RBC-based perfusion provided better oxygenation during NELP.

Experience-dependent regulation of the zincergic innervation of visual cortex in adult monkeys.

Zinc is packaged in, and released from, a subset of glutamatergic synapses in the mammalian telencephalon where it has been shown to act as a potent neuromodulator. In order to establish the functional role for zincergic neurons in visual cortical function and plasticity we have compared the topographic distribution of zincergic terminals in the primary visual cortex (V1) of normal adult vervet monkeys (Cercopithicus aethiops) to that in monkeys monocularly deprived of visual input for short (24 h) or long (3 months) survival times. In normal animals, staining levels for zinc were highest in layers 1-3, 4b, 5 and 6 and lowest in layers 4a and 4c. The laminar and tangential patterns of zinc staining were complementary to staining patterns demonstrated using cytochrome oxidase (CO) histochemistry. Following 3 months of monocular deprivation by enucleation, levels of zinc staining in layers 3, 4calpha and 6a were heterogeneously reduced, clearly revealing the ocular dominance pattern in V1. When compared with the pattern of CO staining, levels of both CO and zinc were reduced in cortical territory innervated by the enucleated eye. Zinc histochemistry also revealed the ocular dominance pattern after only 24 h of monocular impulse blockade induced by enucleation or intravitreal tetrodotoxin infusion. However, by either means of deprivation for 24 h, levels of zinc were increased in deprived-eye stripes relative to nondeprived-eye stripes. These results indicate that zincergic terminals demarcate distinct compartments in the primate visual cortex. Furthermore, levels of synaptic zinc are rapidly and dynamically regulated, suggesting that zinc and/or zincergic neurons participate in mediating activity-dependent changes in the organization of the adult neocortex.

Oxidative stress and neuronal mitochondrial function. Factors dictating susceptibility

Oxidative stress and loss of neuronal mitochondrial function, particularly at the level of cytochrome oxidase has been implicated in the neurodegenerative process. Cell culture studies have revealed that neurones, in comparison to astrocytes, may be particularly susceptible, when cultured alone, to the action of oxidising species such as nitric oxide and peroxynitrite. An important factor in dictating such susceptibility appears to be the intracellular level of the antioxidant, glutathione (GSH). Whilst the coculture of neurones with nitric oxide generating astrocytes leads to neuronal mitochondrial damage, such damage appears to be initially limited due to the up‐regulation of neuronal GSH status by astrocytes. Other factors that may dictate the susceptibility of brain cell types to oxidative stress include the ability of cells to up‐regulate glycolysis in the face of mitochondrial damage and cellular ubiquinone availability.

SEASONAL THERMAL ACCLIMATIZATION IN SEDENTARY AND ACTIVE PIGEONS

Thermal and metabolic responses of pigeons maintained outdoors throughout the year in small cages (sedentary birds) or in large aviaries (active birds) were measured at three ambient temperatures (20, -10, -40 ° C) in midwinter and midsummer. In winter, all birds maintained a significantly lower heat production (measured as oxygen consumption and shivering), body temperature, and conductance than in summer at the two lower test temperatures. All birds maintained homeothermic body temperatures down to -40 ° C. Activity level had no effects on these thermoregulatory variables. Body mass was significantly higher in winter birds, and pectoral mass was correspondingly increased in winter. An additional specific increase in pectoral muscle mass was seen in sedentary birds. Muscle cytochrome oxidase levels were significantly higher in active birds, especially during winter. In winter, the birds had a higher plasma triiodothyronine level than in summer, and lowest values were found in active summer birds. We conc...

Subarachnoid hemorrhage induces dynamic changes in regional cerebral metabolism in rats.

Following a subarachnoid hemorrhage (SAH), adult rats exhibit dynamic regional changes in cerebral glucose metabolism characterized by an increase in metabolic rates and a subsequent upregulation of cytochrome oxidase (CO). We evaluated both local cerebral metabolic rates for glucose (ICMRglc: (mol/100 g/min) and CO in 23 brain regions of interest (ROI). Sham animals underwent anesthesia and superficial surgery; saline-controls received an injection of 0.9% saline into the cisterna magna; and SAH rats received an injection of autologous blood into the cisterna magna. This blood, measured by albumin labeled with radioactive carbon 14, distributed throughout the brain but predominated ventrally. After experimental animals were sacrificed at day 0 (3 h), 1, 3, and 7 days postinjection, ROI were analyzed using [14C]2-deoxy-D-glucose autoradiography and CO histochemistry. ICMRglc in SAH rats increased in many regions (ranging from 0.7% to 32.2% above sham levels). Cytochrome oxidase also increased from 1% to 9% above sham levels, peaking on day 3. Conversely, saline-controls exhibited prolonged depression of ICMRglc (ranging from 11% to 35% below sham levels) and CO (ranging from 4% to 11% below sham levels) from day 0 through day 7. All saline-control ROI for all time points showed this metabolic depression, and between 91% and 95% of saline-control ROI presented lower CO levels as compared to sham. Overall, ICMRglc and CO levels were greater in SAH than in saline-control ROI. However, when considering the influence of subarachnoid blood on metabolic changes in SAH animals, both CO and 2DG levels did not correlate well with the amount of 14C-albumin binding. While previous studies have measured both metabolic rates of glucose and CO soon after SAH, this is the first to simultaneously conduct these measurements in the same SAH rat model.

Cytochrome oxidase activity is increased in +/Lc Purkinje cells destined to die.

+/Lc Purkinje cells degenerate postnatally because of a gain-of-function mutation in the delta2 glutamate receptor (Grid2) that causes a constitutive Na+ current leak. The effect of the resulting chronic depolarization on Purkinje cell metabolism was investigated by measuring levels of cytochrome oxidase (COX) activity in Purkinje cell dendrites using quantitative densitometry. Analysis of wild type controls and +/Lc mutants at P10, P15 and P25 showed that levels of COX activity were significantly increased above control levels by P15 and continued to increase through P25. The increase in COX activity is likely to reflect an increase in oxidative phosphorylation to accommodate the energy demands of removing excess Na+ and Ca2+ entering the Purkinje cells in response to the Grid2 leak current.

Enzyme histochemical profile of immunohistochemically identified Renshaw cells in rat lumbar spinal cord

Activity levels of cytochrome oxidase, acid phosphatase, and NADPH diaphorase were examined in the perikarya of immunohistochemically identified Renshaw cells from sections of rat lumbar spinal cord. Renshaw cell profiles were identified on the basis of their characteristic anti-gephyrin-immunofluorescent labelling. Intrasomatic densities of enzyme histochemical reaction product were employed as indicators of relative mitochondrial activity (cytochrome oxidase), intracytoplasmic digestion (acid phosphatase), or putative nitrergic signalling (NAPDH-diaphorase). Approximately half of the Renshaw cell somata examined displayed moderate levels of cytochrome oxidase reaction product (142 of 262 Renshaw cells) or low levels of acid phosphatase activity (156 of 243 Renshaw cells). A majority (160 of 202 cells) of Renshaw cells contained low intrasomatic levels of NADPH-diaphorase activity but most of these cells were closely apposed by at least one NADPH-diaphorase reactive axonal varicosity. Our findings suggest that moderate levels of perikaryal oxidative metabolism and low levels of intracytoplasmic digestion are sufficient for, and support, the unique physiological capabilities of Renshaw cells. The presence of NADPH-diaphorase containing somatic close contacts indicate that nitric oxide may have at least a minor role in the regulation of Renshaw cell activity. These results are complementary and consistent with previous morphological and pharmacological demonstrations of Renshaw cell heterogeneity.

The Modulation of Oxygen Radical Production by Nitric Oxide in Mitochondria

Biological systems that produce or are exposed to nitric oxide (NO radical) exhibit changes in the rate of oxygen free radical production. Considering that mitochondria are the main intracellular source of oxygen radicals, and based on the recently documented production of NO(radical) by intact mitochondria, we investigated whether NO(radical), produced by the mitochondrial nitric-oxide synthase, could affect the generation of oxygen radicals. Toward this end, changes in H(2)O(2) production by rat liver mitochondria were monitored at different rates of endogenous NO(radical) production. The observed changes in H(2)O(2) production indicated that NO(radical) affected the rate of oxygen radical production by modulating the rate of O(2) consumption at the cytochrome oxidase level. This mechanism was supported by these three experimental proofs: 1) the reciprocal correlation between H(2)O(2) production and respiratory rates under different conditions of NO(radical) production; 2) the pattern of oxidized/reduced carriers in the presence of NO(radical), which pointed to cytochrome oxidase as the crossover point; and 3) the reversibility of these effects, evidenced in the presence of oxymyoglobin, which excluded a significant role for other NO(radical)-derived species such as peroxynitrite. Other sources of H(2)O(2) investigated, such as the aerobic formation of nitrosoglutathione and the GSH-mediated decay of nitrosoglutathione, were found quantitatively negligible compared with the total rate of H(2)O(2) production.

Cytochrome oxidase activity in rat retinal ganglion cells during postnatal development

In this study, the metabolic activity of rat retinal ganglion cells during postnatal development has been examined in vivo using cytochrome oxidase histochemistry. The intensity of staining was measured by optical densitometry. The activity of cytochrome oxidase in retinal ganglion cells progressively increased from postnatal day 0 (P0) and reached a peak during the second week of postnatal development (P10–P14) and declined thereafter. Our data show that the increased levels of cytochrome oxidase seen in developing retinal ganglion cells occur at the same time, when neuronal maturity and synaptogenesis reach their peaks.

Activity levels of enzymes of energy metabolism in heart and red muscle are higher in north-temperate-zone than in Amazonian teleosts

Fish living in the Amazon basin typically have body temperatures of about 30°C, whereas freshwater fishes of the north-temperate zone are eurythermal, with typical body temperatures of 10-20°C in summer. Enzyme activity levels in heart and red muscle of Amazonian species, which display various physiological mechanisms for dealing with hypoxic conditions, were compared with those in north-temperate-zone species. Five Amazonian species (acará-açu (Astronotus ocellatus), acari-bodó (Lipossarcus pardalis), tambaqui (Colossoma macropomum), tamoatá (Hoplosternum littorale), and pirarucu (Arapaima gigas)) and four north-temperate-zone species (American eel, bullhead, yellow perch, and rainbow trout) were studied. The Amazonian species included obligate and facultative air breathers. Activities of key indicator enzymes associated with carbohydrate metabolism, fatty acid metabolism, the citric acid cycle, and the electron-transport chain were determined. There was no obvious correlation between cardiac enzyme activity levels and the potential ability of fish to maintain blood oxygen levels in hypoxic water or the capacity of isolated heart preparations to survive anoxia. In heart, activity levels of hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase, citrate synthase, cytochrome oxidase, and β-hydroxyacyl CoA dehydrogenase were about twice as high in north-temperate-zone species than in Amazonian species. Activities of red-muscle enzymes, especially those associated with aerobic fatty acid metabolism, were significantly higher in comparable north-temperate-zone species relative to Amazonian species. Increased enzyme activity levels in north-temperate-zone species relative to Amazonian species is considered to be an adaptation to generally lower body temperatures. This finding is consistent with earlier comparisions of Antarctic and north-temperate-zone species and with the results of studies of cold acclimation within north-temperate-zone fishes.