Changes In High-energy Phosphates Research Articles

Investigation of possible high-energy phosphate concentration changes in the visual cortex for different stimulus frequencies

Purpose Many works have reported changes in the visual cortex regarding stimulation with different flickering frequencies using various neuroimaging techniques. Also, many phosphorus functional magnetic resonance spectroscopy (31P-fMRS) studies have reported high-energy phosphate (HEP) changes in the visual cortex during visual stimulation at 8 Hz, compared with rest periods. However, there have been no studies attempting to measure HEP changes during visual stimulation with different flickering frequencies. The aim of this work was to use the 31P-fMRS technique to assess possible HEP changes during visual stimulation experiments with stimuli flickering at 4 Hz or 8 Hz, and compare the results obtained with the different frequencies.

Gray matter-specific changes in brain bioenergetics after acute sleep deprivation: a 31P magnetic resonance spectroscopy study at 4 Tesla.

A principal function of sleep may be restoration of brain energy metabolism caused by the energetic demands of wakefulness. Because energetic demands in the brain are greater in gray than white matter, this study used linear mixed-effects models to examine tissue-type specific changes in high-energy phosphates derived using 31P magnetic resonance spectroscopy (MRS) after sleep deprivation and recovery sleep. Experimental laboratory study. Outpatient neuroimaging center at a private psychiatric hospital. A total of 32 MRS scans performed in eight healthy individuals (mean age 35 y; range 23-51 y). Phosphocreatine (PCr) and β-nucleoside triphosphate (NTP) were measured using 31P MRS three dimensional-chemical shift imaging at high field (4 Tesla) after a baseline night of sleep, acute sleep deprivation (SD), and 2 nights of recovery sleep. Novel linear mixed-effects models were constructed using spectral and tissue segmentation data to examine changes in bioenergetics in gray and white matter. PCr increased in gray matter after 2 nights of recovery sleep relative to SD with no significant changes in white matter. Exploratory analyses also demonstrated that increases in PCr were associated with increases in electroencephalographic slow wave activity during recovery sleep. No significant changes in β-NTP were observed. These results demonstrate that sleep deprivation and subsequent recovery-induced changes in high-energy phosphates primarily occur in gray matter, and increases in PCr after recovery sleep may be related to sleep homeostasis.

Historical Perspective on the Pathology of Myocardial Ischemia/Reperfusion Injury

A selective history of the pathophysiological, structural, and metabolic changes found during an episode of severe myocardial ischemia in the canine heart is presented. The changes that cause ischemic injury to become irreversible are discussed in detail because these changes are the target of any successful therapy designed to prevent ischemic cell death. Of these, the disruption of the sarcolemma, an injury the development of which is accelerated in vivo by the contraction of viable tissue elsewhere in the heart traumatizing the ischemic area, plus the changes in high-energy phosphate and the total adenine nucleotide pool are considered to be the critical events leading to the development of irreversibility. The discovery of preconditioning with ischemia is discussed, together with a brief description of postconditioning. Finally, reperfusion injury is discussed in a summary fashion. The evidence for the fact that myocytes are salvaged by reperfusion is presented, as is the evidence that myocytes become unsalvageable by reperfusion as the duration of ischemia increases. The concept that some of the myocytes that die after successful reperfusion with arterial blood actually are killed by changes initiated by reperfusion, so-called lethal reperfusion injury, is attractive in that prevention of this change would lead to greater salvage; however, the prevalence of this phenomenon in clinical practice remains to be determined.

Protective effects of antioxidants and anti-inflammatory agents against manganese-induced oxidative damage and neuronal injury

Exposure to excessive manganese (Mn) levels leads to neurotoxicity, referred to as manganism, which resembles Parkinson's disease (PD). Manganism is caused by neuronal injury in both cortical and subcortical regions, particularly in the basal ganglia. The basis for the selective neurotoxicity of Mn is not yet fully understood. However, several studies suggest that oxidative damage and inflammatory processes play prominent roles in the degeneration of dopamine-containing neurons. In the present study, we assessed the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates and associated neuronal dysfunctions both in vitro and in vivo. Results from our in vitro study showed a significant ( p < 0.01) increase in biomarkers of oxidative damage, F 2-isoprostanes (F 2-IsoPs), as well as the depletion of ATP in primary rat cortical neurons following exposure to Mn (500 μM) for 2 h. These effects were protected when neurons were pretreated for 30 min with 100 of an antioxidant, the hydrophilic vitamin E analog, trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), or an anti-inflammatory agent, indomethacin. Results from our in vivo study confirmed a significant increase in F 2-IsoPs levels in conjunction with the progressive spine degeneration and dendritic damage of the striatal medium spiny neurons (MSNs) of mice exposed to Mn (100 mg/kg, s.c.) 24 h. Additionally, pretreatment with vitamin E (100 mg/kg, i.p.) or ibuprofen (140 μg/ml in the drinking water for two weeks) attenuated the Mn-induced increase in cerebral F 2-IsoPs? and protected the MSNs from dendritic atrophy and dendritic spine loss. Our findings suggest that the mediation of oxidative stress/mitochondrial dysfunction and the control of alterations in biomarkers of oxidative injury, neuroinflammation and synaptodendritic degeneration may provide an effective, multi-pronged therapeutic strategy for protecting dysfunctional dopaminergic transmission and slowing of the progression of Mn-induced neurodegenerative processes.

Microvascular Tissue Oxygenation and Oxidative Metabolism Changes in the Pedicled Latissimus Dorsi Muscle During Graded Hypoxia: Correlation Between Near Infrared and 31P Nuclear Magnetic Resonance Spectroscopy

In this study, the microvascular tissue oxygenation and oxidative muscle metabolism during graded hypoxia and reoxygenation were examined in a rabbit model by near-infrared (NIR) spectroscopy and correlated with high-energy phosphates measured by (31)P nuclear magnetic resonance (NMR) spectroscopy. Graded hypoxia was performed in a New Zealand rabbit model (n = 20, 2.0 ± 0.4 kg) by a stepwise reduction of the fraction of inspired oxygen (FiO(2)) from 0.3 to 0.05 (intervention group versus control group). Recovery and reoxygenation were achieved using FiO(2) of 0.3. A noninvasive NIR spectroscopy sensor and NMR probe was positioned on the surface of the prepared pedicled latissimus dorsi muscle. Microvascular tissue oxygenation (oxyhemoglobin, HbO(2); deoxyhemoglobin, HHb) and redox state of cytochrome oxidase (CytOx) were measured by NIR spectroscopy and correlated with standard values of oxidative muscle metabolism (phosphocreatine, PCr; adenosine triphosphate, ATP) measured by time-resolved (31)P NMR spectroscopy (4.7T). Significant correlation was found between PCr and HbO(2) (r = 0.85, P < 0.001) and HHb (r = -0.75, P < 0.001). β-ATP levels correlated significantly with CytOx (r = 0.87, P < 0.001). The data suggest that changes in high-energy phosphates (PCr- and ATP-levels) correlate closely with microvascular tissue oxygenation (HbO(2), HHb, CytOx) measured by NIR spectroscopy.

Molecular neurodevelopment: an in vivo 31P-1H MRSI study.

Synaptic development and elimination are normal neurodevelopmental processes, which if altered could contribute to various neuropsychiatric disorders. 31P-1H magnetic resonance spectroscopic imaging (MRSI) and structural magnetic resonance imaging (MRI) exams were conducted on 105 healthy children ages 6-18 years old to identify neuromolecular indices of synaptic development and elimination. Over the age range studied, age-related changes in high-energy phosphate (phosphocreatine), membrane phospholipid metabolism (precursors and breakdown products), and percent gray matter volume were found. These neuromolecular and structural indices of synaptic development and elimination are associated with development of several cognitive domains. Monitoring of these molecular markers is essential for devising treatment strategies for neurodevelopmental disorders.

Oxidative damage and neurodegeneration in manganese-induced neurotoxicity

Exposure to excessive manganese (Mn) levels results in neurotoxicity to the extrapyramidal system and the development of Parkinson's disease (PD)-like movement disorder, referred to as manganism. Although the mechanisms by which Mn induces neuronal damage are not well defined, its neurotoxicity appears to be regulated by a number of factors, including oxidative injury, mitochondrial dysfunction and neuroinflammation. To investigate the mechanisms underlying Mn neurotoxicity, we studied the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates (HEP), neuroinflammation mediators and associated neuronal dysfunctions both in vitro and in vivo. Primary cortical neuronal cultures showed concentration-dependent alterations in biomarkers of oxidative damage, F 2-isoprostanes (F 2-IsoPs) and mitochondrial dysfunction (ATP), as early as 2 h following Mn exposure. Treatment of neurons with 500 μM Mn also resulted in time-dependent increases in the levels of the inflammatory biomarker, prostaglandin E 2 (PGE 2). In vivo analyses corroborated these findings, establishing that either a single or three (100 mg/kg, s.c.) Mn injections (days 1, 4 and 7) induced significant increases in F 2-IsoPs and PGE 2 in adult mouse brain 24 h following the last injection. Quantitative morphometric analyses of Golgi-impregnated striatal sections from mice exposed to single or three Mn injections revealed progressive spine degeneration and dendritic damage of medium spiny neurons (MSNs). These findings suggest that oxidative stress, mitochondrial dysfunction and neuroinflammation are underlying mechanisms in Mn-induced neurodegeneration.

Suppression of 5′-AMP-activated protein kinase activity does not impair recovery of contractile function during reperfusion of ischemic hearts

Activation of 5'-AMP-activated protein kinase (AMPK) may benefit the heart during ischemia-reperfusion by increasing energy production. While AMPK stimulates glycolysis, mitochondrial oxidative metabolism is the major source of ATP production during reperfusion of ischemic hearts. Stimulating AMPK increases mitochondrial fatty acid oxidation, but this is usually accompanied by a decrease in glucose oxidation, which can impair the functional recovery of ischemic hearts. To examine the relationship between AMPK and cardiac energy substrate metabolism, we subjected isolated working mouse hearts expressing a dominant negative (DN) alpha(2)-subunit of AMPK (AMPK-alpha(2) DN) to 20 min of global no-flow ischemia and 40 min of reperfusion with Krebs-Henseleit solution containing 5 mM [U-(14)C]glucose, 0.4 mM [9, 10-(3)H]palmitate, and 100 microU/ml insulin. AMPK-alpha(2) DN hearts had reduced AMPK activity at the end of reperfusion (82 +/- 9 vs. 141 +/- 7 pmol.mg(-1).min(-1)) with no changes in high-energy phosphates. Despite this, AMPK-alpha(2) DN hearts had improved recovery of function during reperfusion (14.9 +/- 0.8 vs. 9.4 +/- 1.4 beats.min(-1).mmHg.10(-3)). During reperfusion, fatty acid oxidation provided 44.0 +/- 2.8% of total acetyl-CoA in AMPK-alpha(2) DN hearts compared with 55.0 +/- 3.2% in control hearts. Since insulin can inhibit both AMPK activation and fatty acid oxidation, we also examined functional recovery in the absence of insulin. Functional recovery was similar in both groups despite a decrease in AMPK activity and a decreased reliance on fatty acid oxidation during reperfusion (66.4 +/- 9.4% vs. 85.3 +/- 4.3%). These data demonstrate that the suppression of cardiac AMPK activity does not produce an energetically compromised phenotype and does not impair, but may in fact improve, the recovery of function after ischemia.

31Phosphorus magnetic resonance spectroscopy study of tissue specific changes in high energy phosphates before and after sertraline treatment of geriatric depression

We investigated tissue specific differences in markers of energy metabolism, including high energy phosphate compounds (beta and total NTP, PCr) and pH, in older adults with depression compared with healthy controls, before and after a 12-week treatment trial of sertraline. Thirteen older adults, age > or =55, with Major Depressive Disorder (HAMD(17) score of > or =18) were recruited along with ten age-matched controls. The depression subjects had a pre- and post-treatment 4T (31)P-MRS scan using a three-dimensional chemical shift imaging sequence. The extracted brain images were segmented into white matter (WM), gray matter (GM) and CSF. A linear mixed effects model analyzed the effects of pre-treatment and post-treatment depression on phosphorus metabolite concentration estimates (including calculated pH and Mg(++)). Total tissue beta-NTP (-8%, t(18.66) = 3.50; p = 0.0024) and total tissue total NTP (-6%, t(17.41) = 2.68; p = 0.0156) were lower in subjects with geriatric depression compared with healthy controls. Total tissue levels of total-NTP changed significantly with treatment (-2%, t(14.84) = -2.47; p = 0.0259). Total NTP was reduced in the WM, but not the GM, in the pre-treatment depression group (t(51.65) = 4.02; p = 0.0002). Intracellular pH was higher in the GM of subjects with pre-treatment depression (t(1133.84) = -2.10; p = 0.0353) and decreased to approximate control levels after treatment (t(648.86) = -2.53; p = 0.0115). These findings demonstrate bioenergetic changes including tissue specific differences in (31)P-MRS metabolites in geriatric depression. Decreased white matter total NTP may reflect alterations in white matter function.

Short-term high-intensity interval training improves phosphocreatine recovery kinetics following moderate-intensity exercise in humans

Previous studies have shown that high-intensity training improves biochemical markers of oxidative potential in skeletal muscle within a 2-week period. The purpose of this study was to examine the effect of short-term high-intensity interval training on the time constant () of phosphocreatine (PCr) recovery following moderate-intensity exercise, an in vivo measure of functional oxidative capacity. Seven healthy active subjects (age, 21 +/- 4 years; body mass, 69 +/- 11 kg) performed 6 sessions of 4-6 maximal-effort 30 s cycling intervals within a 2-week period, and 7 subjects (age, 24 +/- 5 years; body mass, 80 +/- 15 kg) served as controls. Prior to and following training, phosphorous-31 magnetic resonance spectroscopy (31P-MRS; GE 3T Excite System) was used to measure relative changes in high-energy phosphates and intracellular pH of the quadriceps muscles during gated dynamic leg-extension exercise (3 cycles of 90 s exercise and 5 min of rest). A monoexponential model was used to estimate the of PCr recovery. The of PCr recovery after leg-extension exercise was reduced by 14% with high-intensity interval training (pretraining, 43 +/- 14 s vs. post-training, 37 +/- 15 s; p < 0.05) with no change in the control group (44 +/- 12 s vs. 43 +/- 12 s, respectively; p > 0.05). These findings demonstrate that short-term high-intensity interval training is an effective means of increasing functional oxidative capacity in skeletal muscle.

Cardiac 31P-MRS compared to echocardiographic findings in patients with hypertensive heart disease without overt systolic dysfunction—Preliminary results

Purpose To evaluate changes in high energy phosphate (HEP) metabolism in patients with hypertension and diastolic dysfunction but with normal LVEF > 55% assessed by echocardiography and tissue Doppler. Material and methods 20 patients (16 men and 4 women, mean age 57 ± 13 years) were studied with phosphorus magnetic resonance spectroscopy and echocardiography. MRS was performed at 1.5 T using an ECG-gated CSI sequence with nuclear Overhauser effect. According to echocardiographical findings 12 patients were found to have a diastolic dysfunction, whereas 8 patients were identified as normal, serving as control group in the following statistical analysis. All patients had normal systolic function (LVEF > 55%).Statistical analysis was made by using mean ± S.D. for description of the data, Spearman correlation and two-tailed Student's t-test for independent samples. Results No differences were found in weight, age, LVEF, endsystolic volume, end-diastolic volume, cardiac output and BNP levels between patients and control group. Myocardial mass at end-diastole correlated significantly with PCr/ATP ratio ( r = −0.66; p = 0.04) in patients and control group. Myocardial PCr/ATP ratio in patients was significantly decreased compared to controls (1.21 ± 0.22 vs. 1.54 ± 0.24; p = 0.006). Conclusions Cardiac 31P-MRS might offer a noninvasive means for detecting early states of heart failure in hypertensive patients.

Direct noninvasive quantification of lactate and high energy phosphates simultaneously in exercising human skeletal muscle by localized magnetic resonance spectroscopy

A novel method based on interleaved localized 31P- and 1H MRS is presented, by which lactate accumulation and the accompanying changes in high energy phosphates in human skeletal muscle can be monitored simultaneously during exercise and recovery. Lactate is quantified using a localized double quantum filter suppressing the abundant lipid signals while taking into account orientation dependent signal modulations. Lactate concentration after ischemic exercise directly quantified by DQF 1H spectroscopy was 24 +/- 3 mmol/L cell water, while 22 +/- 3 mmol/L was expected on the basis of 31P MRS acquired simultaneously. Lactate concentration in a sample of porcine meat was estimated to be 40 +/- 7 mmol/L by means of DQF quantitation, versus 39 +/- 5 mmol/L by biochemical methods. Excellent agreement is shown between lactate concentrations measured noninvasively by 1H MRS, measured biochemically ex vivo, and inferred indirectly in vivo from changes in pH, P(i), and PCr as obtained from 31P MRS data.

Mechanical load plays little role in contraction‐mediated glucose transport in mouse skeletal muscle

The factors responsible for control of glucose transport during exercise are not fully understood. We investigated the role of mechanical load in contraction-mediated glucose transport in an isolated muscle preparation. Mouse extensor digitorum longus muscles were stimulated with repeated contractions for 10 min with or without N-benzyl-p-toluene sulphonamide (BTS, an inhibitor of myosin II ATPase) to block crossbridge activity. BTS inhibited force production during repeated contraction to approximately 5% of control. In contrast, BTS had little effect on glucose transport in the basal state (control = 0.55 +/- 0.04; BTS = 0.47 +/- 0.09 micromol (20 min)(-1) ml(-1)) or after contraction (control = 2.27 +/- 0.15; BTS = 2.10 +/- 0.16 micromol (20 min)(-1) ml(-1)). BTS did not significantly alter the contraction-mediated changes in high-energy phosphates, glutathione status (a measure of oxidant status) or AMP-activated protein kinase activity. In conclusion, these data show that mechanical load plays little role in contraction-mediated glucose transport. Instead, it is likely that the increased glucose transport during contraction is a consequence of the increase in myoplasmic Ca(2+) and the subsequent alterations in metabolism, e.g. increased energy turnover and production of reactive oxygen species.

Effects of gamma ray irradiation on energy metabolism in the rat brain: a 31P nuclear magnetic resonance spectroscopy study

Gamma Knife surgery (GKS) is performed to treat patients with functional neurological diseases, but the neurophysiological mechanisms of GKS's biological effects with subnecrotic doses remain largely undefined. The purpose of the present study was to investigate the effects of gamma irradiation on energy metabolism in the rat brain by using 31P nuclear magnetic resonance spectroscopy (31P-NMRS). The whole brains of Wistar rats were irradiated with a subnecrotic (60-Gy) dose of radiation. One week after the irradiation, brain slices (400 microm thick) were incubated in standard artificial cerebrospinal fluid to undergo 31P-NMRS investigation. Changes in high-energy phosphate, phosphocreatine (PCr), and gamma-ATP, as well as inorganic phosphate levels before, during, and after ischemic stress for 64 minutes were measured. Histological findings were also evaluated using light and electron microscopy. The decrease in the PCr level was significantly slower during ischemia and recovery after reperfusion was significantly faster and greater in the gamma-irradiated rats than in the control animals. The gamma-ATP level after ischemia was also higher in the gamma-irradiated rats than in the controls. Neither neuronal damage nor astrocytosis was observed in the irradiated cerebral cortices. Gamma irradiation with a subnecrotic dose may have neuroprotective effects that maintain a more stable cellular phosphorylation potential after ischemic stress. Such effects of GKS on energy metabolism coupled with neurotransmission (glutamate-glutamine cycling between neurons and astrocytes) may play a role in the treatment of neurological disease.

Does blood flow restriction enhance hypertrophic signaling in skeletal muscle?

in the last decade, there was a dramatic increase in our knowledge of the molecular events that accompany changes in skeletal muscle mass in response to resistance exercise training or to chronic unloading. For example, the role of myostatin in limiting skeletal muscle growth during development was

Development of behavioural dysfunctions in accelerated-senescence OXYS rats is associated with early postnatal alterations in brain phosphate metabolism

We recently demonstrated that senescence-accelerated OXYS rats may represent a model adequate for studying aging processes. The animals of this strain have a particularly short life span; they display early cataract, macular dystrophy, hypertension, and changes in cognitive and emotional spheres. Mitochondrial dysfunctions have been suggested to be a causal factor for the accelerated senescence in these animals. In the present study we investigated whether behavioral alterations in OXYS rats could be associated with changes in high-energy phosphate and phospholipid metabolism of the brain in the early postnatal period. The development of behavioral dysfunction in OXYS rats relative to Wistar was investigated by measuring locomotor exploratory activity and the degree of anxiety at 4 and 12 weeks of age in open-field and elevated plus maze tests, respectively. Brain energy metabolism was evaluated at 2, 3, 4 and 12 weeks of age by calculating the ratios of PCr/Pi, PCr/ATP and phosphate potential (ATP/ADP×Pi) measured by 31P NMR spectroscopy. We found that the behavioral alterations in OXYS rats, i.e. the increased anxiety and the decreased exploratory activity, were not congenital but developed during the period from 4 to 12 weeks of age. The study of high-energy phosphates has not revealed any signs of energy deficiency in OXYS rat's brain but indicated changes in PCr metabolism at 2 and 3 weeks of age when compared with Wistar rats. Furthermore, alterations in phospholipids turnover were also found in young OXYS rats. The data suggest that the changes in phosphate metabolism may have impacts on the development of behavioral deficits in OXYS rats.

Direct action of T3on phosphorylation potential in the sheep heart in vivo

Thyroid acting through ligand binding to nuclear receptors modifies myocardial respiratory kinetics and oxidative phosphorylation in the heart. Direct nongenomic action of thyroid hormone on high-energy phosphate concentrations and respiratory kinetics has never been proven in vivo but might be responsible for observed changes in oxygen utilization efficiency immediately after triiodothyronine (T3) administration. We tested the hypothesis that T3 directly and rapidly modifies myocardial high-energy phosphate concentrations and phosphorylation potential in vivo. Anesthetized sheep (age 28-40 days) thyroidectomized shortly after birth (Thy) and euthyroid age-matched controls (Con) underwent median sternotomy and received T3 infusion (0.8 microg/kg), followed by epinephrine infusion to increase myocardial oxygen consumption (MVo2). 31P magnetic resonance spectra were monitored via a surface coil over the left ventricle. T3 increased phosphocreatine (PCr)/ATP and decreased ADP in Thy animals without causing a change in MVo2. T3 produced no changes in high-energy phosphates in Con animals. T3 did not modify the PCr/ATP or ADP response to epinephrine and elevation in MVo2 in either group. Cardiac mitochondria isolated from Thy and Con animals showed no change in respiratory rate or ADP/ATP exchange efficiency after T3 incubation. T3 infusion in a hypothyroid state decreases ADP concentration, thereby altering the equilibrium between phosphorylation potential and myocardial respiratory rate. These T3-induced effects are not due to changes in ADP/ATP exchange efficiency through action at the adenine nucleotide translocator but may be due to T3 mediation of substrate utilization, confirmed in other models.

Myocardial Ischemia Differentially Regulates LKB1 and an Alternate 5′-AMP-activated Protein Kinase Kinase

During myocardial ischemia, activation of 5'-AMP-activated protein kinase (AMPK) leads to the stimulation of glycolysis and fatty acid oxidation. Together these metabolic changes contribute to cardiac dysfunction. Although AMPK signaling in the ischemic heart is well characterized, the relative contribution of phosphorylation by AMPK kinase (AMPKK), and positive allosterism by the ratios of AMP:ATP and creatine (Cr):phosphocreatine (PCr), in stimulating AMPK during ischemia are unknown. In hearts subjected to severe ischemia, the ratios of AMP:ATP and Cr:PCr were significantly elevated as compared with aerobic hearts. Severe ischemia stimulated AMPK signaling, as demonstrated by an increase in both AMPK activity and acetyl-CoA carboxylase phosphorylation. Although AMPK phosphorylation was increased by severe ischemia, the protein abundance and activity of the recently identified AMPKK, LKB1, were similar between aerobic and severely ischemic hearts. However, in contrast to LKB1, the activity of AMPKK was stimulated in severely ischemic hearts. To further delineate the relative roles of positive allosterism and AMPKK in the regulation of AMPK during ischemia, hearts were subjected to mild ischemia. Although mild ischemia did not alter the ratios of AMP:ATP and Cr:PCr, mild ischemia increased AMPK activity and increased AMPK phosphorylation. Mild ischemia also stimulated the activity of AMPKK. In summary, we demonstrate that myocardial ischemia stimulates AMPK via an AMPKK other than LKB1. Additionally, we show that changes in high energy phosphates are not essential for the activation of AMPK by ischemia. Our data emphasize the critical role AMPKK plays in mediating AMPK signaling during myocardial ischemia.

Muscle dysfunction during exercise of a single skeletal muscle in rats with congestive heart failure is not associated with reduced muscle blood supply.

Inadequate muscle blood flow is a possible explanation for reduced fatigue resistance in patients with congestive heart failure (CHF). In rats with post-infarction CHF we electrically stimulated the soleus muscle (SOL) in situ with intact blood supply. Contractile properties, blood flow, high-energy phosphates and metabolites were measured during 30 min of intermittent stimulation, and in addition capillarization of SOL was recorded. During stimulation, SOL contracted more slowly in rats with CHF compared with sham-operated rats. However, the blood flow in SOL was unaltered and capillary density was maintained in CHF rats. Further, the content of ATP, ADP, AMP, NAD, CrP, P(i) and lactate in SOL was not different between the groups. The cause of contractile dysfunction in a single exercising skeletal muscle in rats with CHF cannot be explained simply by reduced blood supply. In addition, absence of changes in high-energy phosphates and metabolites indicate that the oxidative metabolism of SOL is intact in rats with CHF.

Organ-specific changes in high-energy phosphates after hemorrhagic shock and resuscitation in the rat.

Adenosine nucleotides provide energy for many essential cellular functions. Liver and intestinal ATP and energy charge are known to decrease during hemorrhagic shock, and the ability to regenerate high-energy phosphates may have important implications for recovery. We measured organ-specific changes in energy charge after hemorrhagic shock and after shock followed by resuscitation. Anesthetized Sprague-Dawley rats were bled and maintained at a mean arterial pressure (MAP) of 40 mmHg for 1, 2, 3, or 4 hours. Some animals were resuscitated with normal saline and shed blood (1:1) to a mean arterial pressure of 80 to 90 mmHg for 1 hour. Control animals were anesthetized, but not hemorrhaged. At the conclusion, blood gases and adenine nucleotides were measured. Arterial pO2 and pCO2 were normal in all groups. Unresuscitated hemorrhage caused metabolic acidosis, but bicarbonate was normal in controls and after hemorrhage followed by resuscitation. Energy charge (EC) in the gastrocnemius was unaffected by hemorrhage or resuscitation. Liver EC decreased after hemorrhage (p = 0.0001), but recovered partially after resuscitation. Kidney EC was decreased after only 3 hours of hemorrhage and 1 hour of resuscitation (p = 0.005), but not with shorter periods of hemorrhage. Lung EC decreased with shock, but was substantially worse after resuscitation (p < 0.05). After hemorrhage and resuscitation, EC decreased in lung, liver, kidney, and intestine, but the time course, extent of decline, and ability to recover after resuscitation varied from organ to organ. Inability to regenerate high-energy phosphates after hemorrhagic shock may be a marker for more severe cellular damage.