Recovery Of High-energy Phosphates Research Articles

Muscle Deoxygenation And Recovery During Repetitive Ice Shuttle Sprint Test In Elite Level Hockey Players

The ability to supply and utilize oxygen is a critical component of exercise performance. Near-infrared spectroscopy (NIRS) to measure muscle oxygenation (SmO2) has shown to be useful in both assessing maximal oxygen uptake, as well as the utilization and recovery of high-energy phosphates. Therefore, SmO2 dynamics should play an important role in performance during repetitive sprinting tasks and could provide valuable insights into sport-specific performance. PURPOSE: Assess the relationship between performance and SmO2 during a Repetitive Ice Shuttle Sprint test (RISS). METHODS: Twenty elite-level hockey players completed a RISS. The RISS consisted of 3 shifts of 4 x 30 m maximum intensity skating sprints with 3 min of passive recovery between shifts. Sprint time was documented and SmO2 data collected from both right and left leg quadriceps. SmO2 data was analyzed for maximal deoxygenation (SmO2min) and reoxygenation dynamics during the interspersed sprint and recovery periods and compared to sprint times. For shift comparisons, a repeated-measures ANOVA was used, and a Pearson Product-Moment correlation was used to assess the relationship between SmO2 and shift times. RESULTS: Both sprint time and SmO2min show a significant change between shifts respectively; F(2,38) = 5.018, p = .012, F(2,38) = 5.705, p = .007. All 3 shifts correlate with medium to large effects sizes, between time and SmO2min, respectively; r(19) = .411, p = .036, r(19) = .338, p = .072, r(19) = .516, p = .01. All 3 shifts show small to medium effects sizes for intra-shift recovery and time relationships, respectively; r(19) = .424, p = .031, r(19) = .214, p = .183, r(19) = .316, p = .087. Finally, oxidative capacity using NIRS can be assessed through both reoxygenation dynamics and SmO2min, which show strong correlations for all shifts; r(19) = .820, p < .001, r(19) = .784, p < .001, r(19) = .834, p < .001. CONCLUSIONS: SmO2min and reoxygenation dynamics appear to be related to repeated sprint performance during high-intensity skating. This understanding could benefit both athletic diagnostics and training guidance by better understanding local bioenergetic systems and their limitations.

Results of an explorative clinical evaluation suggest immediate and persistent post-reperfusion metabolic paralysis drives kidney ischemia reperfusion injury

Delayed graft function is the manifestation of ischemia reperfusion injury in the context of kidney transplantation. While hundreds of interventions successfully reduce ischemia reperfusion injury in experimental models, all clinical interventions have failed. This explorative clinical evaluation examined possible metabolic origins of clinical ischemia reperfusion injury combining data from 18 pre- and post-reperfusion tissue biopsies with 36 sequential arteriovenous blood samplings over the graft in three study groups. These groups included living and deceased donor grafts with and without delayed graft function. Group allocation was based on clinical outcome. Magic angle NMR was used for tissue analysis and mass spectrometry-based platforms were used for plasma analysis. All kidneys were functional at one-year. Integration of metabolomic data identified a discriminatory profile to recognize future delayed graft function. This profile was characterized by post-reperfusion ATP/GTP catabolism (significantly impaired phosphocreatine recovery and significant persistent (hypo)xanthine production) and significant ongoing tissue damage. Failing high-energy phosphate recovery occurred despite activated glycolysis, fatty-acid oxidation, glutaminolysis and autophagia, and related to a defect at the level of the oxoglutarate dehydrogenase complex in the Krebs cycle. Clinical delayed graft function due to ischemia reperfusion injury associated with a post-reperfusion metabolic collapse. Thus, efforts to quench delayed graft function due to ischemia reperfusion injury should focus on conserving metabolic competence, either by preserving the integrity of the Krebs cycle and/or by recruiting metabolic salvage pathways.

A modified protocol for retrograde cerebral perfusion: magnetic resonance spectroscopy in pigs

Retrograde cerebral perfusion (RCP) has been employed to protect the brain during cardiovascular surgery, requiring temporary hypothermic circulatory arrest (HCA). However, the protocol used for RCP remains to be modified if prolonged HCA is expected. The aim of this study was to determine the efficacy of a modified protocol for this purpose. After establishment of HCA at 15°C, 14 pigs were subjected to 90-min RCP using either the conventional protocol (i.e. alpha-stat strategy, 25-mmHg perfusion pressure and occluded inferior vena cava, Group I, n = 7) or the new protocol (i.e. pH-stat strategy, 40-mmHg perfusion pressure and unoccluded inferior vena cava, Group II, n = 7). After being rewarmed to 37°C, pigs were perfused for another 60 min. Phosphorus-31 magnetic resonance spectroscopy was used to track the changes of brain high-energy phosphates [i.e. adenosine triphosphate and phosphocreatine (PCr)] and intracellular pH (pHi). At the end, brain water content was measured. During RCP, high-energy phosphates decreased in both groups, whereas adenosine triphosphate decreased much faster in Group I (10.4 ± 4.3 vs 30.4 ± 4.4% of the baseline, P = 0.007, 60-min RCP). After rewarming, the recovery of high-energy phosphates and pHi was much slower in Group I (PCr: 55.7 ± 9.1 vs 78.4 ± 5.1% of the baseline, P = 0.046; adenosine triphosphate: 26.6 ± 10.6 vs 64.8 ± 4.6% of the baseline, P = 0.007; pHi: 6.5 ± 0.4 vs 7.1 ± 0.1, P = 0.021 at 30-min normothermic perfusion after rewarming). Brain tissue water content was significantly higher in Group I (81.1 ± 0.4 vs 79.5 ± 0.4%, P = 0.016). Application of the modified RCP protocol significantly improved cerebral energy conservation during HCA and accelerated energy recovery after rewarming.

Cellular Protection During Oxidative Stress: A Potential Role for D-ribose and Antioxidants

ABSTRACTA healthy cellular system involves the maintenance of an intracellular metabolic balance. Reactive oxygen species (ROS) are constantly produced as a normal product of cellular metabolism; however, during situations of cellular stress, these levels can increase dramatically with the potential to cause deleterious cellular structural and/or functional consequences. There is a significant elevation in these ROS following stressful situations, such as ischemia, hypoxia, high-intensity exercise, and in many diseases. To combat these ROS, neutralizing endogenous enzymes, as well as exogenous antioxidants, can aid in minimizing their potential untoward cellular effects. Exogenous reducing antioxidant agents, such as vitamin C and/or E, play a role in addressing these formed species; however, recent research has suggested that fruit seed extracts may provide additional cellular benefits beyond their antioxidant features. Furthermore, supplemental D-ribose enhances the recovery of high-energy phosphates following stress and appears to potentially offer additional benefits by reducing radical formation. Specifically, during periods of hypoxia/ischemia, supplemental D-ribose may play an inhibitory role in the breakdown of adenine nucleotides, influencing the subsequent formation of xanthine and uric acid compounds; and thereby affecting the release of superoxide anion radicals. The combination of D-ribose with reducing antioxidants may provide a more optimal state of cellular protection during and following times of oxidative stress.

A targeted metabolic protocol with D-ribose for off-pump coronary artery bypass procedures: a retrospective analysis

Coronary revascularization using cardiopulmonary bypass is an effective surgical procedure for ischemic coronary artery disease. Complications associated with cardiopulmonary bypass have included cerebral vascular accidents, neurocognitive disorders, renal dysfunction, and acute systemic inflammatory responses. Within the last two decades off-pump coronary artery bypass has emerged as an approach to reduce the incidence of these complications, as well as shorten hospital stays and recovery times. Many patients with coronary artery disease have insulin resistance and altered energy metabolism, which can exacerbate around the time of coronary revascularization. D-ribose has been shown to enhance the recovery of high-energy phosphates following myocardial ischemia. We hypothesized that patient outcomes could improve using a perioperative metabolic protocol with D-ribose. A perioperative metabolic protocol was used in 366 patients undergoing off-pump coronary artery bypass during 2004-2008. D-ribose was added in 308 of these 366 patients. Data were collected prospectively as part of the Society of Thoracic Surgeons database and retrospectively analyzed. D-ribose patients were generally similar to those who did not receive D-ribose. There was one death, two patients suffered strokes and renal failure requiring dialysis occurred in two patients postoperatively among the entire group of patients. D-ribose patients enjoyed a greater improvement in cardiac index postrevascularization compared with non-D-ribose patients (37% vs. 17%, respectively, p < 0.001). This metabolic protocol was associated with very low mortality and morbidity with a significant early postoperative improvement in cardiac index using D-ribose supplementation. These preliminary results support a prospective randomized trial using this protocol and D-ribose.

Can stunned hearts be resuscitated? Evaluation of aspartate/glutamate secondary blood cardioplegia using magnetic resonance spectroscopy.

Objectives: Reperfusion of ischemic hearts with warm, substrate-enriched, blood cardioplegia may alleviate post-ischemic metabolic and functional derangements. This study investigates this possibility using (31)P magnetic resonance (MR) spectroscopy. Methods: Fifteen blood-perfused Langendorff pig hearts were subjected to 30 min of total, normothermic ischemia. Control hearts (n=8) were reperfused with blood for 40 min. Experimental hearts (n=7) received 20 min of aspartate/glutamate (asp/glu) enriched blood cardioplegic solution, followed by 20 min of normal blood. (31)P MR spectroscopy was used to observe cellular energetics and intracellular pH (pHi) throughout the experiments. Left-ventricular function and myocardial oxygen consumption were evaluated before and after ischemia. Results: MR spectra showed no improvement in the rate or extent of high-energy phosphate recovery with asp/glu cardioplegia, but showed a transient increase in pHi during cardioplegic reperfusion (p<0.05). This, however, did not affect post-ischemic recovery of high energy metabolites, myocardial function or oxygen consumption. Conclusions: This study raises questions regarding the potential beneficial effects of asp/glu enriched secondary cardioplegic solution on functional or metabolic status of stunned pig hearts. Extrapolation of these results to humans should be viewed with caution. Keywords: Magnetic resonance; Pig heart; Aspartate; Glutamate; Cardioplegia; Myocardial stunning.

Effect of altitude on football performance

Altitude will impact football performance through two separate and parallel pathways related to the hypobaric (physical) and hypoxic (physiological) components of terrestrial altitude: (a) the decrease in partial pressure of oxygen reduces maximal oxygen uptake and impairs "aerobic" performance by reducing maximal aerobic power, increasing the relative intensity of any given absolute level of work, and delaying recovery of high-energy phosphates between high-intensity "interval" type efforts; (b) the decrease in air density reduces air resistance which will facilitate high-velocity running, but will also alter drag and lift thereby impairing sensorimotor skills. These effects appear to have their greatest impact very early in the altitude exposure, and their physiological/neurosensory consequences are ameliorated by acclimatization, though the extent of restoration of sea level type performance depends on the absolute magnitude of the competing and living altitudes.

Oral Administration of Amino Acidic Supplements Improves Protein and Energy Profiles in Skeletal Muscle of Aged Rats: Elongation of Functional Performance and Acceleration of Mitochondrial Recovery in Adenosine Triphosphate After Exhaustive Exertion

Sarcopenia is an inevitable age-related degenerative process chiefly characterized by decreased synthesis of muscle proteins and impaired mitochondrial function, leading to progressive loss of muscle mass. Here, we sought to probe whether long-term administration of oral amino acids (AAs) can increase protein and adenosine triphosphate (ATP) content in the gastrocnemius muscle of aged rats, enhancing functional performance. To this end, 6- and 24-month-old male Fisher 344 rats were divided into 3 groups: group A (6-month-old rats) and group B (24-month-old rats) were used as adult and senescent control group, respectively, while group C (24-month-old rats) was used as senescent treated group and underwent 1-month oral treatment with a mixture of mainly essential AAs. Untreated senescent animals exhibited a 30% reduction in total and fractional protein content, as well as a 50% reduction in ATP content and production, compared with adult control rats (p <0.001). Long-term supplementation with mixed AAs significantly improved protein and high-energy phosphate content, as well as the rate of mitochondrial ATP production, conforming their values to those of adult control animals (p <0.001). The improved availability of protein and high-energy substrates in the gastrocnemius muscle of treated aged rats paralleled a significant enhancement in functional performance assessed by swim test, with dramatic elongation of maximal exertion times compared with untreated senescent rats (p <0.001). In line with these findings, we observed that, after 6 hours of rest following exhaustive swimming, the recovery in mitochondrial ATP content was approximately 70% in adult control rats, approximately 60% in senescent control rats, and normalized in treated rats as compared with animals of the same age unexposed to maximal exertion (p <0.001). In conclusion, nutritional supplementation with oral AAs improved protein and energy profiles in the gastrocnemius of treated rats, enhancing functional performance and accelerating high-energy phosphate recovery after exhaustive exertion.

Effects of chronic heart failure in rats on the recovery of microvascular PO2 after contractions in muscles of opposing fibre type.

Chronic heart failure (CHF) impairs muscle O2 delivery (QO2) and, at a given O2 uptake (VO2), lowers microvascular O2 pressures (PmvO2: determined by the QO2-to-VO2 ratio), which may impair recovery of high-energy phosphates following exercise. Because CHF preferentially decreases QO2 to slow-twitch muscles, we hypothesized that recovery PmvO2 kinetics would be slowed to a greater extent in soleus (SOL: approximately 84% type I fibres) than in peroneal (PER: approximately 14% type I) muscles of CHF rats. PmvO2 dynamics were determined in SOL and PER muscles of control (CON: n= 6; left ventricular end-diastolic pressure, LVEDP: approximately 3 mmHg), moderate CHF (MOD: n= 7; LVEDP: approximately 11 mmHg) and severe CHF (SEV: n= 4; LVEDP: approximately 25 mmHg) following cessation of electrical stimulation (180 s; 1 Hz). In PER, neither the recovery PmvO2 values nor the mean response time (MRT; a weighted average of the time to 63% of the overall response) were altered by CHF (CON: 66.8 +/- 8.0, MOD: 72.4 +/- 11.8, SEV: 69.1 +/- 9.5 s). In marked contrast, SOL PmvO2, at recovery onset, was reduced significantly in the SEV group ( approximately 6 Torr) and PmvO2 MRT was slowed with increased severity of CHF (CON: 45.1 +/- 5.3, MOD: 63.2 +/- 9.4, SEV: 82.6 +/- 12.3 s; P < 0.05 CON vs. MOD and SEV). These data indicate that CHF slows PmvO2 recovery following contractions and lowers capillary O2 driving pressure in slow-twitch SOL, but not in fast-twitch PER muscle. These results may explain, in part, the slowed recovery kinetics (phosphocreatine and VO2) and pronounced fatigue following muscular work in CHF patients.

Recovery of Microvascular Po2 in Rats with Chronic Heart Failure

0181 Chronic heart failure (CHF) impairs muscle O2 delivery (Qo2) and thus reduces microvascular O2 pressures (Po2m: determined by the Qo2-to-O2 utilization ratio), which may impair the recovery of high-energy phosphates following exercise. PURPOSE: Because CHF preferentially impairs Qo2 to slow-twitch muscles (Musch & Terrell, Am. J. Physiol. 262: H411-419, 1992), we hypothesized that recovery Po2m kinetics would be slowed to a greater extent in soleus (SOL: ∼84% type I fibers) than peroneal (PER: ∼14% type I) muscles of CHF rats. METHODS:Po2m dynamics were determined in SOL and PER muscles of control (CON: n = 6; left ventricular enddiastolic pressure, LVEDP: 3±1 mmHg), moderate CHF (MOD: n = 7; LVEDP: 10±2 mmHg) and severe CHF (SEV: n = 4; LVEDP: 28±4 mmHg) CHF following cessation of electrical stimulation (180s; 1 Hz). RESULTS: In PER, neither the recovery Po2m values nor their recovery kinetics (mean response time, MRT; CON: 66.8±8.0, MOD: 72.4±11.8, SEV: 69.1±9.5s) were altered by CHF. In marked contrast, SOL Po2m was reduced significantly in the SEV group (∼6 Torr) and Po2m recovery kinetics were slowed progressively with increased severity of CHF (MRT, CON: 45.1±5.3, MOD: 63.2±9.4, SEV: 82.6±12.3s; P<0.05 CON vs SEV). CONCLUSION: These data indicate that CHF slows Po2m recovery and thus lowers capillary O2 driving pressure in slow-twitch SOL, but not fast-twitch PER muscle with SEV CHF. These results may explain, in part, the slowed recovery kinetics (phosphocreatine and Vo V2) and fatigue following muscular work in CHF patients. Supported by: NIH HL-50306, HL-67619, AG-19228

Recovery of Microvascular Po2 in Rats with Chronic Heart Failure

0181 Chronic heart failure (CHF) impairs muscle O2 delivery (Qo2) and thus reduces microvascular O2 pressures (Po2m: determined by the Qo2-to-O2 utilization ratio), which may impair the recovery of high-energy phosphates following exercise. PURPOSE: Because CHF preferentially impairs Qo2 to slow-twitch muscles (Musch & Terrell, Am. J. Physiol. 262: H411-419, 1992), we hypothesized that recovery Po2m kinetics would be slowed to a greater extent in soleus (SOL: ∼84% type I fibers) than peroneal (PER: ∼14% type I) muscles of CHF rats. METHODS:Po2m dynamics were determined in SOL and PER muscles of control (CON: n = 6; left ventricular enddiastolic pressure, LVEDP: 3±1 mmHg), moderate CHF (MOD: n = 7; LVEDP: 10±2 mmHg) and severe CHF (SEV: n = 4; LVEDP: 28±4 mmHg) CHF following cessation of electrical stimulation (180s; 1 Hz). RESULTS: In PER, neither the recovery Po2m values nor their recovery kinetics (mean response time, MRT; CON: 66.8±8.0, MOD: 72.4±11.8, SEV: 69.1±9.5s) were altered by CHF. In marked contrast, SOL Po2m was reduced significantly in the SEV group (∼6 Torr) and Po2m recovery kinetics were slowed progressively with increased severity of CHF (MRT, CON: 45.1±5.3, MOD: 63.2±9.4, SEV: 82.6±12.3s; P<0.05 CON vs SEV). CONCLUSION: These data indicate that CHF slows Po2m recovery and thus lowers capillary O2 driving pressure in slow-twitch SOL, but not fast-twitch PER muscle with SEV CHF. These results may explain, in part, the slowed recovery kinetics (phosphocreatine and Vo V2) and fatigue following muscular work in CHF patients. Supported by: NIH HL-50306, HL-67619, AG-19228

Glycolysis protects sarcolemmal membrane integrity during total ischemia in the rat heart.

Experimental evidence indicates that ischemic glycolysis improves myocardial tolerance to low flow ischemia and anoxia, and cellular membrane disruption signals and/or causes transition to irreversible ischemic injury. The objective of this study was to determine the impact of ischemic glycolysis on membrane integrity and myocardial viability during total ischemia. Phosphorus metabolites were measured by 31P NMR spectroscopy and cellular volumes were determined by 1H and 59Co NMR in conjunction with the extracellular marker cobalticyanide. Isolated rat hearts were submitted to 30 min of total ischemia, followed by 30 min of reperfusion. Glycogen contents were modulated by pre-ischemic perfusion with various substrates. Increased glycolytic activities, as determined from lactate production, delayed onset of ischemic contracture (p < 0.05), induced cytosolic acidification (p < 0.005) and cellular swelling during ischemia (p < 0.05), reduced post-ischemic diastolic tone (p < 0.05), improved recovery of high energy phosphates and contraction force (p < 0.005). Inhibition of glycolysis with iodoacetate and glycogen depletion with 2-deoxyglycose resulted in early onset of ischemic contracture (p < 0.005), elevated post-ischemic diastolic pressures (p < 0.05), reduced coronary flow rates and mechanical activities (p < 0.05). Cellular viability was evaluated by creatine kinase efflux, and membrane integrity was determined from cellular swelling during perfusion with hypoosmotic medium. High activities of ischemic glycolysis correlated with improved cellular viability and preserved membrane integrity, while low glycolytic fluxes were associated with membrane permeabilization (p < 0.05). The protective effect of ischemic glycolysis over sarcolemmal integrity was attributed to continuous provision of energy, undetected by 31P NMR spectroscopy. There was no evidence that ischemic swelling caused by glycolytic end-metabolites accumulation had detrimental consequences, and of excessive swelling during reperfusion. It is concluded that one of the cardio-protective mechanisms of ischemic glycolysis is energy-dependent preservation of sarcolemmal integrity and cellular viability.

Effect of poly(ADP-ribose) polymerase inhibitors on the ischemia-reperfusion-induced oxidative cell damage and mitochondrial metabolism in Langendorff heart perfusion system.

Ischemia-reperfusion induces reactive oxygen species (ROS) formation, and ROS lead to cardiac dysfunction, in part, via the activation of the nuclear poly(ADP-ribose) polymerase (PARP, called also PARS and ADP-RT). ROS and peroxynitrite induce single-strand DNA break formation and PARP activation, resulting in NAD(+) and ATP depletion, which can lead to cell death. Although protection of cardiac muscle by PARP inhibitors can be explained by their attenuating effect on NAD(+) and ATP depletion, there are data indicating that PARP inhibitors also protect mitochondria from oxidant-induced injury. Studying cardiac energy metabolism in Langendorff heart perfusion system by (31)P NMR, we found that PARP inhibitors (3-aminobenzamide, nicotinamide, BGP-15, and 4-hydroxyquinazoline) improved the recovery of high-energy phosphates (ATP, creatine phosphate) and accelerated the reutilization of inorganic phosphate formed during the ischemic period, showing that PARP inhibitors facilitate the faster and more complete recovery of the energy production. Furthermore, PARP inhibitors significantly decrease the ischemia-reperfusion-induced increase of lipid peroxidation, protein oxidation, single-strand DNA breaks, and the inactivation of respiratory complexes, which indicate a decreased mitochondrial ROS production in the reperfusion period. Surprisingly, PARP inhibitors, but not the chemically similar 3-aminobenzoic acid, prevented the H(2)O(2)-induced inactivation of cytochrome oxidase in isolated heart mitochondria, suggesting the presence of an additional mitochondrial target for PARP inhibitors. Therefore, PARP inhibitors, in addition to their important primary effect of decreasing the activity of nuclear PARP and decreasing NAD(+) and ATP consumption, reduce ischemia-reperfusion-induced endogenous ROS production and protect the respiratory complexes from ROS induced inactivation, providing an additional mechanism by which they can protect heart from oxidative damages.

The effect of duration of cerebral ischemia on brain pyruvate dehydrogenase activity, energy metabolites, and blood flow during reperfusion in gerbil brain

The objective of this study was to determine whether the duration of an ischemic insult effects the activity of the mitochondrial enzyme pyruvate dehydrogenase (PDH) in relation to the recovery of metabolites and regional cerebral blood flow (rCBF) immediately after ischemia and during reperfusion in gerbil cortex. Cerebral ischemia was induced, using the bilateral carotid artery occlusion method, for 20 or 60 min, followed by reperfusion up to 120 min. Immediately after ischemia PDH activity increased threefold regardless of ischemic duration. In the 60-min ischemic group, PDH remained activated, the recovery of high energy phosphates and the clearance of lactate were poor, and the rCBF was 48% of controls after 20-min reperfusion, decreasing gradually to 26% at 120-min reperfusion. In the 20-min ischemic group, PDH activity normalized quickly, the restoration of energy phosphates was good, there was a quick reduction in lactate within the first 60 min of reperfusion, and the rCBF was 65% of control at 20-min reperfusion, and remained over 48% of control throughout reperfusion. Recovery of metabolism after reperfusion did not parallel the changes in rCBF in either group, most noticeably in the 60-min ischemic group. The slow normalization of PDH activity reflected the poor recovery of metabolites in the 60-min ischemic group, indicating that PDH activity is important in the resynthesis of energy metabolites during reperfusion. In conclusion, prolonging the ischemic insult effected PDH activity during reperfusion, impaired recovery of energy metabolites, and worsened the recovery of rCBF.

Overexpression of human copper, zinc-superoxide dismutase (SOD1) prevents postischemic injury.

Superoxide and superoxide-derived oxidants have been hypothesized to be important mediators of postischemic injury. Whereas copper, zinc-superoxide dismutase, SOD1, efficiently dismutates superoxide, there has been controversy regarding whether increasing intracellular SOD1 expression would protect against or potentiate cellular injury. To determine whether increased SOD1 protects the heart from ischemia and reperfusion, studies were performed in a newly developed transgenic mouse model in which direct measurement of superoxide, contractile function, bioenergetics, and cell death could be performed. Transgenic mice with overexpression of human SOD1 were studied along with matched nontransgenic controls. Immunoblotting and immunohistology demonstrated that total SOD1 expression was increased 10-fold in hearts from transgenic mice compared with nontransgenic controls, with increased expression in both myocytes and endothelial cells. In nontransgenic hearts following 30 min of global ischemia a reperfusion-associated burst of superoxide generation was demonstrated by electron paramagnetic resonance spin trapping. However, in the transgenic hearts with overexpression of SOD1 the burst of superoxide generation was almost totally quenched, and this was accompanied by a 2-fold increase in the recovery of contractile function, a 2.2-fold decrease in infarct size, and a greatly improved recovery of high energy phosphates compared with that in nontransgenic controls. These results demonstrate that superoxide is an important mediator of postischemic injury and that increasing intracellular SOD1 dramatically protects the heart from this injury. Thus, increasing intracellular SOD1 expression may be a highly effective approach to decrease the cellular injury that occurs following reperfusion of ischemic tissues.

Aspartate/glutamate-enriched blood does not improve myocardial energy metabolism during ischemia-reperfusion: A 31p magnetic resonance spectroscopic study in isolated pig hearts

Objective: Our objective was to test the effects of exogenous l-aspartate and l-glutamate on myocardial energy metabolism during ischemia-reperfusion. Methods: Phosphorus 31–magnetic resonance spectroscopy was used to observe cellular energetics and intracellular pH in isolated pig hearts perfused with blood (group A, n = 8) or blood enriched with 13 mmol/L each of l-aspartate and l-glutamate (group B, n = 6). The hearts were subjected to 30 minutes of total normothermic ischemia and then reperfused for 40 minutes. Two hearts from each group were inotropically stimulated by titration with calcium after normokalemic reperfusion. Left ventricular function was measured with the use of a compliant balloon and oxygen consumption was calculated. Results: Magnetic resonance spectroscopy showed no decrease in the rate of energy decline during ischemia for group B versus group A. No significant differences were observed between the two groups in terms of myocardial function, oxygen consumption, or the rate or extent of high-energy phosphate recovery after normokalemic reperfusion or inotropic stimulation. Inotropic stimulation of postischemic hearts, however, led to dramatic improvement in myocardial function in both groups ( p < 0.05 for all parameters) and significant improvement in oxygen consumption ( p = 0.01). Conclusions: In a normal, isolated, blood-perfused pig heart subjected to 30 minutes of total normothermic ischemia, (1) enrichment of the perfusate with aspartate/glutamate before and after ischemia affects neither myocardial energy metabolism during ischemia-reperfusion nor postischemic recovery of myocardial function or oxygen consumption and (2) inotropic stimulation can recruit significant postischemic function and sufficient aerobic respiration to support it, irrespective of aspartate/glutamate enrichment. (J Thorac Cardiovasc Surg 1997;113:1068-80)

Effect of hyperglycemia on reperfusion-associated recovery of intracellular pH and high energy phosphates after transient cerebral ischemia in gerbils.

Hyperglycemia increases cerebral damage after transient cerebral ischemia. This study used in vivo 31P nuclear magnetic resonance spectroscopy to determine the relationship of intracellular tissue acidosis and delayed recovery of brain high-energy phosphates to increased damage during the reperfusion period. Mongolian gerbils were subjected to transient bilateral carotid ischemia for 20 min with 2 h reperfusion. All gerbils were pretreated intraperitoneally with equivalent volumes in saline of 0.003 units per kilogram of insulin or vehicle, or with 4 grams of glucose per kilogram. The gerbils were then scanned in a 4.7 Tesla Magnetic Resonance Imager-Spectrometer to determine levels of intracellular pH, inorganic phosphate, adenosine triphosphate, and phosphocreatine. In each group, intracellular pH decreased with ischemia, but most significantly in hyperglycemic animals (6.45 +/- 0.15), in which it had not recovered to preischemic levels by the end of the reperfusion period (6.8 +/- 0.1 vs 7.04 +/- 0.1, p < 0.05). High-energy phosphates phosphocreatine-inorganic phosphate and phosphocreatine-adenosine triphosphate showed partial recovery in all groups throughout the reperfusion period; the recovery was not significantly altered by glucose status. Hyperglycemia worsened pH but not the recovery of high-energy phosphates in animals reperfused after 20 min of transient cerebral ischemia. This sustained acidosis may be a primary event in transient damage in hyperglycemic animals.

Cerebral metabolic recovery from deep hypothermic circulatory arrest after treatment with arginine and nitro-arginine methyl ester

Background: Recent studies suggest that nitric oxide is important in the pathogenesis of ischemic brain injury and also has a role in controlling cerebrovascular tone. This study examines the net effects of nitric oxide on cerebral metabolic recovery after deep hypothermic circulatory arrest. Methods: Two-week-old piglets were supported by cardiopulmonary bypass and cooled to 15º C followed by 1 hour of deep hypothermic circulatory arrest, 45 minutes of reperfusion and rewarming, and then 3 hours of normothermic perfusion. Groups of 10 piglets received one of four treatments before bypass: l-nitro-arginine methyl ester, inhibitor of nitric oxide synthesis, 10 mg/kg intravenously; l-arginine, to enhance nitric oxide synthesis, 30 mg/kg intravenously before bypass and then 10 mg/kg per minute during the first hour of reperfusion; a combination of l-nitro-arginine methyl ester plus l-arginine at these same doses; and no pretreatment (controls). Cerebral high-energy phosphates and pH were measured by magnetic resonance spectroscopy in half the animals. Cerebral blood flow, metabolic rates for oxygen and glucose, and the oxidation/reduction state of cytochrome aa3 and oxygenated and deoxygenated hemoglobin measured by near-infrared spectroscopy were assessed in the other half of the piglets. Results: l-nitro-arginine methyl ester significantly increased cerebral vascular resistance and markedly reduced recovery of high-energy phosphates, pH, and oxidation state of cytochrome aa3. l-arginine increased cerebral blood flow, cerebral glucose and oxygen consumption, and recovery of cytochrome aa3 oxidation and high-energy phosphates. l-Arginine did not reverse completely the effects of l-nitro-arginine methyl ester on cerebral metabolic recovery. Conclusion: In a piglet model of deep hypothermic circulatory arrest, l-nitro-arginine methyl ester has a deleterious effect and l-arginine has a beneficial effect on cerebral metabolic recovery. The deleterious metabolic effects of l-nitro-arginine methyl ester are only partially reversed by l-arginine. This fact suggests that there may be mechanisms in addition to inhibition of nitric oxide synthesis contributing to the neurotoxicity of l-nitro-arginine methyl ester in this model. (J T HORAC C ARDIOVASC S URG 1996;112:698-707)

Pathways of adenine nucleotide metabolism: Degradation and resynthesis of IMP in ageing chicken heart

The activities of enzymes involved in adenine nucleotide metabolism and the concentration of their metabolic products were studied in the hearts of chickens from birth to advanced age. In particular, in order to investigate the main mechanisms which contribute to ensure availability of adenine nucleotides during ageing of the heart, IMP concentration and the activities of enzymes involved in its turnover were studied. In newborn animals, AMP degradation, though limited in amount, was found to lead to the final products of purine metabolism. In fact, the activity of hypoxanthine phosphoribosyl-transferase (HPRT)—the salvage enzyme of IMP—was not detected. On the contrary, in young chickens, the low concentration of final products of purine metabolism, together with a remarkable activity of HPRT and a high concentration of IMP, indicates that metabolic flux converges on the salvage pathway. In adult chickens, an increase of purine catabolism was observed. This, together with an optimal concentration of endogenous adenine nucleotides, is indicative of a particularly high AMP metabolism. Finally, in chickens of advanced age, a reduced purine catabolism appeared to take place, thus contributing to the maintenance of the adenine nucleotide pool. In ageing heart, a major role of IMP turnover probably consists in the preservation of adenine nucleotides and in the recovery of high-energy phosphates.

Hypothermia, circulatory arrest, and the pediatric brain

A review has been conducted of ongoing clinical and laboratory studies of hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (LFB) at a children's hospital in Boston. A prospective randomized clinical trial of HCA versus LFB has shown a higher incidence of perioperative seizures in patients randomized to HCA. At 1 year of age, neurologic and developmental studies have shown an association between seizures and worse outcome. Longer duration of HCA is associated with a worse score on the Bayley scale assessment of gross and fine motor function in particular, as well as a higher probability of neurologic abnormality. A retrospective review of development after HCA for Senning procedure has shown a correlation between more alkaline pH (alpha-stat strategy) during cooling before HCA and lower developmental score relative to a more acidotic strategy (pH stat). The institutional change to alpha-stat was accompanied by several cases of choreoathetosis after HCA. Currently, patients are being randomized between alpha-stat and pH-stat. Laboratory studies have used a piglet model with assessment of cerebral blood flow and metabolism as well as high-energy phosphates and cerebral pH determined by magnetic resonance spectroscopy. High-energy phosphates are maintained by a flow rate of 50 mL/kg/min but are undetectable after approximately 35 minutes of HCS. A pH-stat is associated with more rapid recovery of high-energy phosphates after HCA than alpha-stat. Recent studies have examined the role of nitric oxide in the causation of brain injury after HCA as well as the potential utility of cerebroplegia in increasing the safe duration of circulatory arrest.