phosphocreatine and Acidosis

Topics: Acid-Base Equilibrium; Acidosis; Adenine Nucleotides; Animals; Bicarbonates; Carbon Dioxide; Diet; Glycolysis; Hydrolysis; Ketone Bodies; Kidney; Lung; Muscles; Oxidation-Reduction; Phosphocreatine; Proteins

Topics: Acidosis; Adenosine Triphosphate; Animals; Calcium; Cell Membrane; Electrophysiology; Heart Septum; Hypoxia; Myocardial Contraction; Phosphates; Phosphocreatine; Rabbits

Little is known about the metabolic differences that exist among different muscle groups within the same subjects. Therefore, we used (31)P-magnetic resonance spectroscopy ((31)P-MRS) to investigate muscle oxidative capacity and the potential effects of pH on PCr recovery kinetics between muscles of different phenotypes (quadriceps (Q), finger (FF) and plantar flexors (PF)) in the same cohort of 16 untrained adults. The estimated muscle oxidative capacity was lower in Q (29 ± 12 mM min(-1), CV(inter-subject) = 42%) as compared with PF (46 ± 20 mM min(-1), CV(inter-subject) = 44%) and tended to be higher in FF (43 ± 35 mM min(-1), CV(inter-subject) = 80%). The coefficient of variation (CV) of oxidative capacity between muscles within the group was 59 ± 24%. PCr recovery time constant was correlated with end-exercise pH in Q (p < 0.01), FF (p < 0.05) and PF (p < 0.05) as well as proton efflux rate in FF (p < 0.01), PF (p < 0.01) and Q (p = 0.12). We also observed a steeper slope of the relationship between end-exercise acidosis and PCr recovery kinetics in FF compared with either PF or Q muscles. Overall, this study supports the concept of skeletal muscle heterogeneity by revealing a comparable inter- and intra-individual variability in oxidative capacity across three skeletal muscles in untrained individuals. These findings also indicate that the sensitivity of mitochondrial respiration to the inhibition associated with cytosolic acidosis is greater in the finger flexor muscles compared with locomotor muscles, which might be related to differences in permeability in the mitochondrial membrane and, to some extent, to proton efflux rates.

Topics: Acidosis; Adenosine Triphosphate; Adult; Exercise; Female; Humans; Hydrogen-Ion Concentration; Intracellular Space; Kinetics; Magnetic Resonance Spectroscopy; Male; Muscle, Skeletal; Oxidation-Reduction; Phosphocreatine; Phosphorus Isotopes; Phosphorylation; Protons; Rest

The effects of prior moderate- and prior heavy-intensity exercise on the subsequent metabolic response to incremental exercise were examined. Healthy, young adult subjects (n = 8) performed three randomized plantar-flexion exercise tests: 1) an incremental exercise test (approximately 0.6 W/min) to volitional fatigue (Ramp); 2) Ramp preceded by 6 min of moderate-intensity, constant-load exercise below the intracellular pH threshold (pHT; Mod-Ramp); and 3) Ramp preceded by 6 min of heavy-intensity, constant-load exercise above pHT (Hvy-Ramp); the constant-load and incremental exercise periods were separated by 6 min of rest. (31)P-magnetic resonance spectroscopy was used to continuously monitor intracellular pH, phosphocreatine concentration ([PCr]), and inorganic phosphate concentration ([P(i)]). No differences in exercise performance or the metabolic response to exercise were observed between Ramp and Mod-Ramp. However, compared with Ramp, a 14% (SD 10) increase (P < 0.01) in peak power output (PPO) was observed in Hvy-Ramp. The improved exercise performance in Hvy-Ramp was accompanied by a delayed (P = 0.01) onset of intracellular acidosis [Hvy-Ramp 60.4% PPO (SD 11.7) vs. Ramp 45.8% PPO (SD 9.4)] and a delayed (P < 0.01) onset of rapid increases in [P(i)]/[PCr] [Hvy-Ramp 61.5% PPO (SD 12.0) vs. Ramp 45.1% PPO (SD 9.1)]. In conclusion, prior heavy-intensity exercise delayed the onset of intracellular acidosis and enhanced exercise performance during a subsequent incremental exercise test.

Topics: Acid-Base Equilibrium; Acidosis; Adult; Exercise; Foot; Humans; Hydrogen-Ion Concentration; Intracellular Fluid; Magnetic Resonance Spectroscopy; Male; Muscle Contraction; Muscle Fatigue; Muscle, Skeletal; Phosphates; Phosphocreatine; Phosphorus Isotopes; Physical Endurance; Time Factors

Onset of intracellular acidosis during muscular exercise has been generally attributed to activation or hyperactivation of nonoxidative ATP production but has not been analyzed quantitatively in terms of H(+) balance, i.e., production and removal mechanisms. To address this issue, we have analyzed the relation of intracellular acidosis to H(+) balance during exercise bouts in seven healthy subjects. Each subject performed a 6-min ramp rhythmic exercise (finger flexions) at low frequency (LF, 0.47 Hz), leading to slight acidosis, and at high frequency (HF, 0.85 Hz), inducing a larger acidosis. Metabolic changes were recorded using (31)P-magnetic resonance spectroscopy. Onset of intracellular acidosis was statistically identified after 3 and 4 min of exercise for HF and LF protocols, respectively. A detailed investigation of H(+) balance indicated that, for both protocols, nonoxidative ATP production preceded a change in pH. For HF and LF protocols, H(+) consumption through the creatine kinase equilibrium was constant in the face of increasing H(+) generation and efflux. For both protocols, changes in pH were not recorded as long as sources and sinks for H(+) approximately balanced. In contrast, a significant acidosis occurred after 4 min of LF exercise and 3 min of HF exercise, whereas the rise in H(+) generation exceeded the rise in H(+) efflux at a nearly constant H(+) uptake associated with phosphocreatine breakdown. We have clearly demonstrated that intracellular acidosis in exercising muscle does not occur exclusively as a result of nonoxidative ATP production but, rather, reflects changes in overall H(+) balance.

Topics: Acidosis; Adult; Anaerobiosis; Bicarbonates; Creatine Kinase; Exercise; Glycogen; Humans; Hydrogen; Kinetics; Magnetic Resonance Spectroscopy; Male; Muscle, Skeletal; Phosphocreatine; Rest

The precise origin of phosphate that is removed during hemodialysis remains unclear; only a minority comes from the extracellular space. One possibility is that the remaining phosphate originates from the intracellular compartment, but there have been no available data from direct assessment of intracellular phosphate in patients undergoing hemodialysis.. We used phosphorus magnetic resonance spectroscopy to quantify intracellular inorganic phosphate (Pi), phosphocreatine (PCr), and. During the first hour of hemodialysis, mean phosphatemia decreased significantly (-41%;. Phosphorus magnetic resonance spectroscopy examination of patients with ESKD during hemodialysis treatment confirmed that depurated Pi originates from the intracellular compartment. This finding raises the possibility that excessive dialytic depuration of phosphate might adversely affect the intracellular availability of high-energy phosphates and ultimately, cellular metabolism. Further studies are needed to investigate the relationship between objective and subjective effects of hemodialysis and decreases of intracellular Pi and. Intracellular Phosphate Concentration Evolution During Hemodialysis by MR Spectroscopy (CIPHEMO), NCT03119818.

Topics: Acidosis; Adenosine Triphosphate; Adult; Aged; Calcium; Energy Metabolism; Female; Hemodynamics; Humans; Hydrogen-Ion Concentration; Kidney Failure, Chronic; Kinetics; Magnetic Resonance Spectroscopy; Male; Middle Aged; Phosphates; Phosphocreatine; Phosphorus; Phosphorus Isotopes; Pilot Projects; Prospective Studies; Renal Dialysis

What is the central question of this study? The aim of this study was to evaluate the potential beneficial effects of endurance training during an ischaemia-reperfusion protocol in a mouse model of sickle cell disease (SCD). What is the main finding and its importance? Endurance training did not reverse the metabolic defects induced by a simulated vaso-occlusive crisis in SCD mice, with regard to intramuscular acidosis, mitochondrial dysfunction or anatomical properties. Our results suggest that endurance training would reduce the number of vaso-occlusive crises rather than the complications related to vaso-occlusive crises.. The aim of this study was to investigate whether endurance training could limit the abnormalities described in a mouse model of sickle cell disease (SCD) in response to an ischaemia-reperfusion (I/R) protocol. Ten sedentary (HbSS-SED) and nine endurance-trained (HbSS-END) SCD mice were submitted to a standardized protocol of I/R of the leg, during which ATP, phosphocreatine and inorganic phosphate concentrations and intramuscular pH were measured using magnetic resonance spectroscopy. Forty-eight hours later, skeletal muscles were harvested. Oxidative stress markers were then measured. Although the time course of protons accumulation was slightly different between trained and sedentary mice (P < 0.05), the extent of acidosis was similar at the end of the ischaemic period. The initial rate of phosphocreatine resynthesis measured at blood flow restoration, illustrating mitochondrial function, was not altered in trained mice compared with sedentary mice. Although several oxidative stress markers were not different between groups (P > 0.05), the I/R-related increase of uric acid concentration observed in sedentary SCD mice (P < 0.05) was not present in the trained group. The spleen weight, generally used as a marker of the severity of the disease, was not different between groups (P > 0.05). In conclusion, endurance training did not limit the metabolic consequences of an I/R protocol in skeletal muscle of SCD mice, suggesting that the reduction in the severity of the disease previously demonstrated in the basal state would be attributable to a reduction of the occurrence of vaso-occlusive crises rather than a decrease of the deleterious effects of vaso-occlusive crises.

Topics: Acidosis; Adenosine Triphosphate; Anemia, Sickle Cell; Animals; Biomarkers; Disease Models, Animal; Endurance Training; Ischemia; Mice; Muscle, Skeletal; Oxidative Stress; Phosphocreatine; Physical Conditioning, Animal

Sickle cell disease (SCD) is associated with an impaired oxygen delivery to skeletal muscle that could alter ATP production processes. The present study aimed to determine the effects of sickle hemoglobin (HbS) on muscle pH homeostasis in response to exercise in homozygous (HbSS,

Topics: Acidosis; Anemia, Sickle Cell; Animals; Disease Models, Animal; Hemoglobin, Sickle; Homeostasis; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Male; Mice; Muscle, Skeletal; Phosphocreatine; Physical Conditioning, Animal; Rest

Clinical effectiveness of metabolic support in surgical treatment of patients, suffering stenotic affection of carotid arteries, was estimated. Neoton intraoperative injection inside internal carotid artery have promoted improvement of metabolism in ischemized brain tissues, reduction of metabolic acidosis severity, and preservation of normal bioelectrical activity of the brain. Expediency of prolongation of clinical investigation for intraoperative prophylaxis of reperfusional brain tissue damage, while surgical treatment of patients, suffering stenotic affection of carotid arteries, using metabolic support, was discussed.

Topics: Acidosis; Brain; Brain Ischemia; Cardiotonic Agents; Carotid Artery, Internal; Carotid Stenosis; Catheters, Indwelling; Electroencephalography; Endarterectomy, Carotid; Female; Humans; Lactic Acid; Male; Middle Aged; Phosphocreatine

Reduced myofibrillar ATP availability during prolonged myocardial ischemia may limit post-ischemic mechanical function. Because creatine kinase (CK) is the prime energy reserve reaction of the heart and because it has been difficult to augment ATP synthesis during and after ischemia, we used mice that overexpress the myofibrillar isoform of creatine kinase (CKM) in cardiac-specific, conditional fashion to test the hypothesis that CKM overexpression increases ATP delivery in ischemic-reperfused hearts and improves functional recovery. Isolated, retrograde-perfused hearts from control and CKM mice were subjected to 25 min of global, no-flow ischemia and 40 min of reperfusion while cardiac function [rate pressure product (RPP)] was monitored. A combination of (31)P-nuclear magnetic resonance experiments at 11.7T and biochemical assays was used to measure the myocardial rate of ATP synthesis via CK (CK flux) and intracellular pH (pH(i)). Baseline CK flux was severalfold higher in CKM hearts (8.1 ± 1.0 vs. 32.9 ± 3.8, mM/s, control vs. CKM; P < 0.001) with no differences in phosphocreatine concentration [PCr] and RPP. End-ischemic pH(i) was higher in CKM hearts than in control hearts (6.04 ± 0.12 vs. 6.37 ± 0.04, control vs. CKM; P < 0.05) with no differences in [PCr] and [ATP] between the two groups. Post-ischemic PCr (66.2 ± 1.3 vs. 99.1 ± 8.0, %preischemic levels; P < 0.01), CK flux (3.2 ± 0.4 vs. 14.0 ± 1.2 mM/s; P < 0.001) and functional recovery (13.7 ± 3.4 vs. 64.9 ± 13.2%preischemic RPP; P < 0.01) were significantly higher and lactate dehydrogenase release was lower in CKM than in control hearts. Thus augmenting cardiac CKM expression attenuates ischemic acidosis, reduces injury, and improves not only high-energy phosphate content and the rate of CK ATP synthesis in postischemic myocardium but also recovery of contractile function.

Topics: Acidosis; Adenosine Triphosphate; Animals; Creatine Kinase, MM Form; Disease Models, Animal; Energy Metabolism; Hydrogen-Ion Concentration; Kinetics; L-Lactate Dehydrogenase; Magnetic Resonance Spectroscopy; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Myocardial Contraction; Myocardial Ischemia; Myocardial Reperfusion Injury; Myocardium; Phosphocreatine; Up-Regulation

The phosphocreatine (PCr) recovery overshoot in skeletal muscle is a transient increase of PCr concentration above the resting level after termination of exercise. In the present study [PCr], [ATP], [P(i)] and pH were measured in calf muscle during rest, during plantar flexion exercise until exhaustion and recovery, using the (31)P NMR spectroscopy. A significantly greater acidification of muscle cells and significantly lower phosphorylation potential (DeltaG (ATP)) at the end of exercise was encountered in the group of subjects that evidenced the [PCr] overshoot as well as [ADP] and [P(i)] undershoots than in the group that did not. We postulate that the role of the PCr overshoot-related transiently elevated [ATP]/[ADP(free)] ratio is to activate different processes (including protein synthesis) that participate in repairing numerous damages of the muscle cells caused by intensive exercise-induced stressing factors, such as extensive muscle acidification, a significant decrease in DeltaG (ATP), an elevated level of reactive oxygen species or mechanical disturbances.

Topics: Acidosis; Adult; Body Mass Index; Exercise; Humans; Leg; Male; Muscle, Skeletal; Phosphocreatine; Phosphorylation; Young Adult

Indirect data suggest that delayed recovery of intracellular pH (pHi) during reperfusion is involved in postconditioning protection, and calpain activity has been shown to be pH-dependent. We sought to characterize the effect of ischaemic postconditioning on pHi recovery during reperfusion and on calpain-dependent proteolysis, an important mechanism of myocardial reperfusion injury.. Isolated Sprague-Dawley rat hearts were submitted to 40 min of ischaemia and different reperfusion protocols of postconditioning and acidosis. pHi was monitored by (31)P-NMR spectroscopy. Myocardial cell death was determined by lactate dehydrogenase (LDH) and triphenyltetrazolium staining, and calpain activity by western blot measurement of alpha-fodrin degradation. In control hearts, pHi recovered within 1.5 +/- 0.24 min of reperfusion. Postconditioning with 6 cycles of 10 s ischaemia-reperfusion delayed pHi recovery slightly to 2.5 +/- 0.2 min and failed to prevent calpain-mediated alpha-fodrin degradation or to elicit protection. Lowering perfusion flow to 50% during reperfusion cycles or shortening the cycles (12 cycles of 5 s ischemia-reperfusion) resulted in a further delay in pHi recovery (4.1 +/- 0.2 and 3.5 +/- 0.3 min, respectively), attenuated alpha-fodrin proteolysis, improved functional recovery, and reduced LDH release (47 and 38%, respectively, P < 0.001) and infarct size (36 and 32%, respectively, P < 0.001). This cardioprotection was identical to that produced by lowering the pH of the perfusion buffer to 6.4 during the first 2 min of reperfusion or by calpain inhibition with MDL-28170.. These results provide direct evidence that postconditioning protection depends on prolongation of intracellular acidosis during reperfusion and indicate that inhibited calpain activity could contribute to this protection.

Topics: Acidosis; Animals; Apoptosis; Calpain; Carrier Proteins; Disease Models, Animal; Hydrogen-Ion Concentration; L-Lactate Dehydrogenase; Male; Microfilament Proteins; Myocardial Reperfusion Injury; Phosphocreatine; Rats; Rats, Sprague-Dawley

It has been proposed that intracellular acidosis may be the basis of the cardioprotection of different interventions, including postconditioning. However, contradictory reports exist on the effects of acidic reperfusion on myocardial salvage. Here we characterized the effect of lowering the pH of the reperfusion media (pHo) on intracellular pH (pHi) and cell death.. The effect of acidic perfusion on reperfusion injury was studied in isolated rat hearts submitted to 40 min of ischaemia and 30 min of reperfusion, and its effect on the Na(+)/Ca(2+)-exchanger (NCX) was analysed in isolated myocytes. pHi and phosphocreatine (PCr) were monitored by nuclear magnetic resonance spectroscopy. Lowering pHo to 6.4 during the initial 3 min of reperfusion delayed pHi normalization, improved PCr recovery, and markedly reduced (P < 0.001) lactate dehydrogenase release and infarct size (tetrazolium reaction). This cardioprotection was attenuated as pHo was increased, and was lost at pH0 7.0. Extending acidic reperfusion to the first 15 or 30 min of reflow did not result in further delay of pHi normalization and abolished the protection afforded by the initial 3 min of acidic reperfusion unless the Na(+)/H(+)-exchanger (NHE) blocker cariporide was added to the acidic perfusate and HCO(3)(-) substituted for N-[2-hydroxyethyl]piperazine-N'-[2-ethanesulphonic acid]. In experiments performed in fura-2-loaded myocytes exposed to low Na(+) buffer adjusted to pH 6.4, the lower Ca(2+) uptake indicated an inhibitory effect of acidosis on NCX.. Acidic reperfusion for 3 min delays normalization of pHi and enhances myocardial salvage, but extending it beyond this period fails to further delay pHi recovery. This is probably due to persisting NHE and Na(+)/HCO(3)(-)-cotransporter activities, and it is detrimental, possibly through prolonged NCX inhibition.

Topics: Acidosis; Animals; Buffers; Cell Death; Energy Metabolism; Hydrogen-Ion Concentration; In Vitro Techniques; L-Lactate Dehydrogenase; Magnetic Resonance Spectroscopy; Male; Myocardial Infarction; Myocardial Reperfusion; Myocardial Reperfusion Injury; Myocardium; Myocytes, Cardiac; Phosphocreatine; Rats; Rats, Sprague-Dawley; Sodium-Bicarbonate Symporters; Sodium-Calcium Exchanger; Sodium-Hydrogen Exchangers; Time Factors

The purpose of this study was to examine the kinetics of phosphocreatine (PCr) breakdown in repeated bouts of heavy-intensity exercise separated by three different durations of resting recovery. Healthy young adult male subjects (n = 7) performed three protocols involving two identical bouts of heavy-intensity dynamic plantar flexion exercise separated by 3, 6, and 15 min of rest. Muscle high-energy phosphates and intracellular acid-base status were measured using phosphorus-31 magnetic resonance spectroscopy. In addition, the change in concentration of total haemoglobin (Delta[Hb(tot)]) and deoxy-haemoglobin (Delta[HHb]) were monitored using near-infrared spectroscopy. Prior exercise resulted in an elevated (P < 0.05) intracellular hydrogen ion ([H(+)](i)) after 3 min (182 +/- 72 (SD) nM; pH 6.73) and 6 min (112 +/- 19 nM; pH 6.95) but not after 15 min (93 +/- 8 nM; pH 7.03) compared to pre-exercise in Con (90 +/- 3 nM; pHi 7.05). The on-transient time constant (tau) of the PCr primary component was not different amongst the exercise bouts. However, in each of the subsequent bouts the amplitude of the PCr slow component, total PCr breakdown, and rise in [H(+)](i) were reduced (P < 0.05). At exercise onset, Delta[Hb(tot)] was increased (P < 0.05) and the Delta[HHb] kinetic response was slowed (P < 0.05) in the exercise after 3 min, consistent with improved muscle perfusion. In summary, neither the level of acidosis or muscle perfusion at the onset of exercise appeared to be directly related to the time course of the on-transient PCr primary component or the magnitude of the PCr slow component during subsequent bouts of exercise.

Topics: Acid-Base Equilibrium; Acidosis; Adult; Exercise; Hemoglobins; Humans; Hydrogen-Ion Concentration; Kinetics; Magnetic Resonance Spectroscopy; Male; Muscle Contraction; Muscle, Skeletal; Myoglobin; Oxygen; Oxygen Consumption; Phosphocreatine; Recovery of Function; Regional Blood Flow; Spectroscopy, Near-Infrared

(31)P magnetic resonance spectroscopy provides the possibility of obtaining bioenergetic data during skeletal muscle exercise and recovery. The time constant of phosphocreatine (PCr) recovery (tau(PCr)) has been used as a measure of mitochondrial function. However, cytosolic pH has a strong influence on the kinetics of PCr recovery, and it has been suggested that tau(PCr) should be normalized for end-exercise pH. A general correction can only be applied if there are no intersubject differences in the pH dependence of tau(PCr). We investigated the pH dependence of tau(PCr) on a subject-by-subject basis. Furthermore, we determined the kinetics of proton efflux at the start of recovery. Intracellular acidosis slowed PCr recovery, and the pH dependence of tau(PCr) differed among subjects, ranging from -33.0 to -75.3 s/pH unit. The slope of the relation between tau(PCr) and end-exercise pH was positively correlated with both the proton efflux rate and the apparent proton efflux rate constant, indicating that subjects with a smaller pH dependence of tau(PCr) have a higher proton efflux rate. Our study implies that simply correcting tau(PCr) for end-exercise pH is not adequate, in particular when comparing patients and control subjects, because certain disorders are characterized by altered proton efflux from muscle fibers.

Topics: Acidosis; Adenosine Diphosphate; Adult; Cytoplasm; Exercise; Female; Humans; Hydrogen-Ion Concentration; Kinetics; Magnetic Resonance Spectroscopy; Male; Mitochondria, Muscle; Models, Biological; Muscle Contraction; Phosphocreatine; Phosphorus Isotopes; Protons; Quadriceps Muscle; Recovery of Function; Reproducibility of Results

Energy for muscle contractions is supplied by ATP generated from 1) the net hydrolysis of phosphocreatine (PCr) through the creatine kinase reaction, 2) oxidative phosphorylation, and 3) anaerobic glycolysis. The effect of old age on these pathways is unclear. The purpose of this study was to examine whether age may affect ATP synthesis rates from these pathways during maximal voluntary isometric contractions (MVIC). Phosphorus magnetic resonance spectroscopy was used to assess high-energy phosphate metabolite concentrations in skeletal muscle of eight young (20-35 yr) and eight older (65-80 yr) men. Oxidative capacity was assessed from PCr recovery after a 16-s MVIC. We determined the contribution of each pathway to total ATP synthesis during a 60-s MVIC. Oxidative capacity was similar across age groups. Similar rates of ATP synthesis from PCr hydrolysis and oxidative phosphorylation were observed in young and older men during the 60-s MVIC. Glycolytic flux was higher in young than older men during the 60-s contraction (P < 0.001). When expressed relative to the overall ATP synthesis rate, older men relied on oxidative phosphorylation more than young men (P = 0.014) and derived a smaller proportion of ATP from anaerobic glycolysis (P < 0.001). These data demonstrate that although oxidative capacity was unaltered with age, peak glycolytic flux and overall ATP production from anaerobic glycolysis were lower in older men during a high-intensity contraction. Whether this represents an age-related limitation in glycolytic metabolism or a preferential reliance on oxidative ATP production remains to be determined.

Topics: Acidosis; Adenosine Triphosphate; Adult; Aged; Aging; Creatine Kinase; Energy Metabolism; Glycolysis; Humans; Hydrogen-Ion Concentration; Male; Muscle Fatigue; Muscle, Skeletal; Oxidative Phosphorylation; Phosphocreatine

Electrical muscle stimulation (Mstim) at a low or high frequency is associated with failure of force production, but the exact mechanisms leading to fatigue in this model are still poorly understood. Using 31P magnetic resonance spectroscopy (31PMRS), we investigated the metabolic changes in rabbit tibialis anterior muscle associated with the force decline during Mstim at low (10 Hz) and high (100 Hz) frequency. We also simultaneously recorded the compound muscle mass action potential (M-wave) evoked by direct muscle stimulation, and we analyzed its post-Mstim variations. The 100-Hz Mstim elicited marked M-wave alterations and induced mild metabolic changes at the onset of stimulation followed by a paradoxical recovery of phosphocreatine (PCr) and pH during the stimulation period. On the contrary, the 10-Hz Mstim produced significant PCr consumption and intracellular acidosis with no paradoxical recovery phenomenon and no significant changes in M-wave characteristics. In addition, the force depression was linearly linked to the stimulation-induced acidosis and PCr breakdown. These results led us to conclude that force failure during 100-Hz Mstim only results from an impaired propagation of muscle action potentials with no metabolic involvement. On the contrary, fatigue induced by 10-Hz Mstim is closely associated with metabolic changes with no alteration of the membrane excitability, thereby underlining the central role of muscle energetics in force depression when muscle is stimulated at low frequency. Finally, our results further indicate a reduction of energy cost of contraction when stimulation frequency is increased from 10 to 100 Hz.

Topics: Acidosis; Action Potentials; Animals; Electric Stimulation; Electrophysiology; Energy Metabolism; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Muscle Contraction; Muscle Fatigue; Phosphocreatine; Phosphorus; Rabbits; Reaction Time

This study tested the hypothesis that acidic pH inhibits oxidative ATP supply during exercise in hand (first dorsal interosseus, FDI) and lower limb (leg anterior compartment, LEG) muscles. We measured oxidative flux and estimated mitochondrial capacity using the changes in creatine phosphate concentration ([PCr]) and pH as detected by 31P magnetic resonance (MR) spectroscopy during isometric exercise and recovery. The highest oxidative ATP flux in sustained exercise was about half the estimated mitochondrial capacity in the LEG (0.38 +/- 0.06 vs. 0.90 +/- 0.14 mM ATP s(-1), respectively), but at the estimated capacity in the FDI (0.61 +/- 0.05 vs. 0.61 +/- 0.09 mM ATP s(-1), respectively). During sustained exercise at a higher contraction rate, intracellular acidosis (pH < 6.88) prevented a rise in oxidative flux in the LEG and FDI despite significantly increased [ADP]. We tested whether oxidative flux could increase above that achieved in sustained exercise by raising [ADP] (> 0.24 mM) and avoiding acidosis using burst exercise. This exercise raised oxidative flux (0.69 +/- 0.05 mM ATP s(-1)) to nearly twice that found with sustained exercise in the LEG and matched (0.65 +/- 0.11 mM ATP s(-1)) the near maximal flux seen during sustained exercise in the FDI. Thus both muscles reached their highest oxidative fluxes in the absence of acidosis. These results show that acidosis inhibits oxidative phosphorylation in vivo and can limit ATP supply in exercising muscle to below the mitochondrial capacity.

Topics: Acidosis; Adenosine Diphosphate; Adenosine Triphosphate; Adult; Algorithms; Exercise; Exercise Test; Female; Hand; Humans; Hydrogen-Ion Concentration; Kinetics; Leg; Magnetic Resonance Spectroscopy; Male; Middle Aged; Muscle Contraction; Muscle, Skeletal; Oxidative Phosphorylation; Phosphocreatine; Rest

The possible relationships between intracellular Na(+) (Na(i)(+)), bioenergetic status and intracellular pH (pH(i)) in the mechanism for ischemic preconditioning were studied using (23)Na and (31)P magnetic resonance spectroscopy in isolated Langendorff perfused rat heart. The ischemic preconditioning (three 5-min ischemic episodes followed by two 5-min and one 10-min period of reperfusion) prior to prolonged ischemia (20 min stop-flow) resulted in a decrease in ischemic acidosis and faster and complete recovery of cardiac function (ventricular developed pressure and heart rate) after 30 min of reperfusion. The response of Na(i) during ischemia in the preconditioned hearts was characterized by an increase in Na(i)(+) at the end of preconditioning and an accelerated decrease during the first few minutes of reperfusion. During post-ischemic reperfusion, bioenergetic parameters (PCr/P(i) and betaATP/P(i) ratios) were partly recovered without any significant difference between control and preconditioned hearts. The reduced acidosis during prolonged ischemia and the accelerated decrease in Na(i)(+) during reperfusion in the preconditioned hearts suggest activation of Na(+)/H(+) exchanger and other ion transport systems during preconditioning, which may protect the heart from intracellular acidosis during prolonged ischemia, and result in better recovery of mechanical function (LVDP and heart rate) during post-ischemic reperfusion.

Topics: Acidosis; Animals; Energy Metabolism; Hydrogen-Ion Concentration; Intracellular Membranes; Ischemic Preconditioning, Myocardial; Magnetic Resonance Spectroscopy; Male; Myocardial Ischemia; Myocardial Reperfusion Injury; Myocardium; Oxazoles; Perfusion; Phosphates; Phosphocreatine; Pyrimidinones; Rats; Rats, Sprague-Dawley; Sodium; Sodium-Hydrogen Exchangers

The mechanism underlying the fatal complications in jaundiced states after shock has not been fully clarified. The present study was designed to examine the effect of hemorrhagic shock on myocardial high-energy phosphate stores and the arterial ketone body ratio (AKBR:acetoacetate/beta-hydroxybutyrate), which reflects the redox state of the liver mitochondria, in normal and jaundiced rats.. At 1 week after ligation of the common bile duct, hemorrhagic shock was induced by exsanguination (mean arterial blood pressure = 40 mmHg) and maintained for 2 h. Serial changes in AKBR were measured. The myocardial adenine nucleotides phosphocreatine (PCr) and inorganic phosphate (Pi) were determined before and after hemorrhagic shock.. Before shock, myocardial ATP in the jaundiced group was lower than that in the sham group. However, the myocardial PCr levels in the two groups did not differ. After reinfusion of the shed blood, ATP and PCr recovered to the preshock levels in the sham group. However, ATP and PCr were further increased in the jaundiced group. At 60 min after reinfusion, AKBR recovered to the normal level in the sham group, but decreased below 0.7 in the jaundiced group. Metabolic acidosis was more severe in the jaundiced group than in the sham group.. The decrease in AKBR indicated irreversible metabolic acidosis. As a result, fatal circulatory failure occurred, although the phosphoenergetic level in the myocardium was sufficiently maintained.

Topics: Acidosis; Adenosine Triphosphate; Animals; Blood Pressure; Heart Rate; Jaundice; Ketone Bodies; Liver; Male; Myocardium; Oxidation-Reduction; Phosphocreatine; Rats; Rats, Wistar; Shock, Hemorrhagic; Time Factors

We investigated temporal differences in the protective action of three types of Ca2+ channel blockers in myocardial ischemia, focusing particularly on the blocking ability under depolarizing conditions. The effects of diltiazem, verapamil, and nifedipine on extracellular potassium concentration ([K+]e), acidosis, and level of metabolic markers were examined during 30-min global ischemia and postischemic left ventricular (LV) function in isolated guinea pig hearts. Diltiazem and verapamil, but not nifedipine, inhibited the late phase (15-30 min) of [K+]e elevation, whereas all three blockers delayed the onset of the early phase (0-8 min) of [K+]e elevation. Diltiazem and verapamil inhibited ischemic contracture and improved postischemic LV function to a greater extent. These differences appeared to be linked to preservation of ATP and creatine phosphate and delay of cessation of anaerobic glycolytic activity. Maneuvers to preserve energy sources during ischemia (decrease in external Ca2+ concentration or pacing at a lower frequency) attenuated the late phase of [K+]e elevation. Inhibition of LV pressure was potentiated 12- and 8.2-fold by diltiazem and verapamil, respectively, at 8.9 mM K+ as compared with 2.9 mM K+, whereas that by nifedipine was unchanged. These results indicate that the differential cardioprotection of Ca2+ channel blockers in the late period of ischemia correlates with preservation of high-energy phosphates as a result of different Ca2+ channel blocking abilities under high [K+]e conditions.

Topics: Acidosis; Adenosine Triphosphate; Animals; Calcium Channel Blockers; Depression, Chemical; Diltiazem; Extracellular Space; Guinea Pigs; Heart; Heart Rate; Hydrogen-Ion Concentration; In Vitro Techniques; Lactic Acid; Male; Myocardial Contraction; Myocardial Ischemia; Myocardium; Nifedipine; Phosphocreatine; Potassium; Time Factors; Verapamil

It has been previously suggested that alterations in sodium homeostasis, leading to calcium overload may play a part in the mediation of cardiac ischemic injury. It has been demonstrated that the Na+-H+ exchanger plays an important role with regard to the regulation of intracellular sodium during ischemia and reperfusion and that inhibition of the Na+-H+ exchanger during ischemia protects hearts from ischemic injury. Studies using chemically-induced diabetic animals have suggested that the cardiac Na+-H+ exchanger in the diabetic heart is impaired and is responsible for limiting the increase in sodium during ischemia. The extent to which the Na+-H+ exchanger contributes to increases in intracellular sodium during ischemia in diabetic hearts is unclear as direct measurements of exchanger activity have not been made in genetically diabetic hearts. Therefore, this paper aims to address the following issues: (a) is the Na+-H+ exchanger impaired in a genetically diabetic rat heart: (b) does this impairment result in lower [Na]i or [Ca]i during ischemia; and (c) does Na+-H+ exchanger inhibition limit injury and functional impairment in diabetic hearts during ischemia and reperfusion? These issues were examined by inhibiting the Na+-H+ exchanger with ethylisopropylamiloride (EIPA) in isolated perfused hearts from both genetically diabetic (BB/W) and non-diabetic rats. Levels of intracellular sodium, intracellular calcium, intracellular pH and high energy phosphates (using 23Na,19F, 31P NMR spectroscopies, respectively) during global ischemia and reperfusion were also measured. The impact of diabetes on Na+-H+ exchanger activity was assessed by measuring pH recovery of these hearts after an acid load. Creatine kinase release during reperfusion was used as a measure of ischemic injury. This study demonstrated that the Na+-H+ exchanger is impaired in diabetic hearts. Despite this impaired activity, inhibition of Na+-H+ exchanger protected diabetic hearts from ischemic injury and was associated with attenuation of the rise in sodium and calcium, and limitation of acidosis and preservation of ATP during ischemia. The data presented here favor the use of Na+-H+ exchanger inhibitors to protect ischemic myocardium in diabetics. Also, the data provides possible mechanisms for the altered susceptibility of diabetic hearts to ischemic injury.

Topics: Acidosis; Adenosine Triphosphate; Amiloride; Animals; Calcium; Diabetes Mellitus, Type 1; Hydrogen-Ion Concentration; In Vitro Techniques; Intracellular Fluid; Magnetic Resonance Spectroscopy; Myocardial Reperfusion Injury; Phosphocreatine; Quaternary Ammonium Compounds; Rats; Rats, Inbred BB; Sodium; Sodium-Hydrogen Exchangers

Iron-catalyzed radical generation is a potentially significant mechanism by which extensive tissue acidosis exacerbates brain injury during ischemia/reperfusion. We hypothesized that levels of low-molecular-weight (LMW) iron increase during in vivo global cerebral ischemia in a pH-dependent manner, potentially catalyzing oxidant injury. The present study quantified regional differences in LMW iron during global cerebral incomplete ischemia and determined whether augmenting the fall in ischemic tissue pH with hyperglycemia also amplifies free iron availability.. Dogs anesthetized with pentobarbital-fentanyl were treated with 30 minutes of global incomplete cerebral ischemia produced by intracranial pressure elevation. Cerebral energy metabolites (ATP, phosphocreatine) and intracellular pH (pHi) were measured by 31P magnetic resonance spectroscopy. Preischemic plasma glucose level was manipulated to titrate end-ischemic pHi. After ischemia, brains were perfused with cold phosphate-buffered saline solution; then 16 different brain areas were sampled, filtered to separate the LMW fraction (<30000 D), and assayed by rapid colorimetric assay for tissue iron. Total iron, LMW iron, and protein in each sample were measured in sham-operated (no ischemia, n=8), normoglycemic ischemia (ISCH [glucose 7+/-4 mmol/L], n=7), and hyperglycemic (GLU-ISCH [glucose 31+/-3 mmol/L], n=9) groups.. High-energy phosphates fell to near zero values in both ISCH and GLU-ISCH groups by 30 minutes but remained unchanged in the sham-operated group. As expected, pHi decreased during ischemia but to a greater extent in GLU-ISCH (6.20+/-0.05 in ISCH, 6.08+/-0.04 in GLU-ISCH, P<.05). Iron could be detected in all areas of the brain in sham-operated animals, with the highest amounts obtained from subcortical areas such as the hippocampus, pons, midbrain, and medulla. Total iron was higher in ISCH relative to sham-operated animals and higher in cortex and pons relative to GLU-ISCH. Regional LMW (as a percentage of total iron; LMW/total iron) was elevated in numerous brain areas in ISCH, including cortical gray matter, cerebellum, hippocampus, caudate, and midbrain. LMW/total iron was higher in GLU-ISCH versus ISCH in cortical gray matter only. In other brain areas, ischemic LMW/total iron was equivalent in glucose-treated or normoglycemic animals (white matter, thalamus, pons, medulla) or lower in the glucose-treated group (cerebellum, hippocampus, caudate, midbrain).. These data demonstrate that levels of total and LMW iron increase with global cerebral ischemia in the majority of cortical and subcortical regions of normoglycemic brain. However, exacerbation of ischemic acidosis via glucose administration does not increase tissue iron and produces a greater increase in the LMW fraction in cortical gray matter only. In other brain regions, total and LMW iron availability is similar to that of nonischemic animals.

Topics: Acidosis; Adenosine Triphosphate; Animals; Blood Glucose; Blood Pressure; Body Temperature; Brain; Carbon Dioxide; Dogs; Hydrogen-Ion Concentration; Hyperglycemia; Intracranial Pressure; Iron; Ischemic Attack, Transient; Male; Organ Specificity; Oxygen; Partial Pressure; Phosphocreatine; Reference Values; Time Factors

The question was investigated whether cardiomyocytes can be resuscitated after extreme energy depletion, i.e. after loss of ATP >70%. Isolated ventricular cardiomyocytes of the adult rat were exposed to metabolic inhibition with dinitrophenol and cyanide (DNP 0.2 mm; KCN 2 mm). After rapid energy depletion, cells were "reoxygenated" by wash-out of DNP and KCN. Intracellular calcium, cell length, ATP and creatine phosphate (CrP) of the cardiomyocytes were monitored. Metabolic inhibition resulted in a depletion of the stores of ATP and CrP by more than 95% of the normoxic values and caused a cytosolic Ca2+ overload. Parameters of metabolic recovery were: (i) resynthesis of CrP; (ii) recovery of a normal cytosolic Ca2+ control; and (iii) the elicitation of energy-dependent hypercontracture. "Reoxygenation", i.e. wash-out of metabolic inhibitors, reactivated oxidative phosphorylation. Consecutively, CrP levels recovered to 76.0+/-7.3%, ATP levels recovered to 10. 4+/-2.3% (means+/-s.dn=10) of the initial normoxic values, a normoxic intracellular calcium level was re-established and hypercontracture was elicited. Prolongation of metabolic inhibition with KCN (2 mm) or inhibition of the Na+/K+ pump with ouabain (0.5 mm) disabled the cardiomyocytes to recover from cytosolic Ca2+ overload and prevented hypercontracture. It is concluded that even after extensive energy depletion metabolic resuscitation of the myocardial cell remains possible and a critical range of ATP for recovery, i.e. a "threshold" of a 70% loss of ATP, does not exist.

Topics: Acidosis; Adenosine Triphosphate; Animals; Calcium; Cells, Cultured; Dinitrophenols; Energy Metabolism; Heart Ventricles; Kinetics; Male; Myocardial Contraction; Myocardium; Ouabain; Oxidative Phosphorylation; Phosphocreatine; Potassium Cyanide; Rats; Rats, Wistar

The relationships between oxygen consumption (Q(O2)) and calculated cytoplasmic ADP concentration ([ADP]) and the free energy of ATP hydrolysis (deltaG(ATP)) were examined in ex vivo arterially perfused cat soleus muscles during repetitive twitch stimulation under normocapnic (5% CO2) and hypercapnic (70% CO2) conditions. Hypercapnia decreased extra- and intracellular pH by over 0.5 but had no significant effect on Q(O2) or phosphocreatine (PCr)/ATP in muscles at rest. The maximum Q(O2) measured during stimulation and the rate constant for PCr recovery after stimulation both decreased during hypercapnic compared with normocapnic perfusion, but the estimated ATP/O2 was unchanged. The change in PCr and deltaG(ATP) with increasing Q(O2) was greater during hypercapnic compared with normocapnic stimulation, as expected from the decrease in maximum Q(O2). However, the relationships between Q(O2) and [ADP] and deltaG(ATP) were both shifted to the left during hypercapnia compared with normocapnia. The results show that changes in cytoplasmic adenine nucleotides and phosphate are not sufficient to explain the control of respiration in skeletal muscle. However, in the context of thermodynamic models of respiratory control, the results can be explained by increased intramitochondrial potential for ATP synthesis at low pH.

Topics: Acidosis; Animals; Cats; Electric Stimulation; Homeostasis; Hydrogen-Ion Concentration; Hypercapnia; Magnetic Resonance Spectroscopy; Muscle, Skeletal; Oxygen Consumption; Phosphocreatine

Pharmacologic inhibition of the Na-H exchanger prior to and during ischemia has been shown to protect the ischemic heart by reducing Na-H exchange. However, pH regulation in the ischemic heart is primarily mediated by other pH regulatory mechanisms, such as metabolite efflux and sodium-coupled HCO3-influx, which may compensate for a reduction in Na-H exchange by increasing proton efflux. We hypothesized that short-term pharmacologic inhibition of the Na-H exchanger would result in increases in other compensatory pH regulatory mechanisms and thereby limit acidosis during ischemia and reduce ischemic injury.. In order to test this hypothesis, we exposed isolated perfused rat hearts to ethylisopropylamiloride (EIPA, 3 micro M) for 40 min, followed by 10 min of EIPA-free perfusate and 30 min of global ischemia (termed CTL/EIPA hearts). The effects of this intervention were compared to hearts perfused with either glucose alone (CTL) or EIPA 3 micro M for 10 min before ischemia (EIPA). Ischemic injury was measured using creatine kinase (CK) release on reperfusion, while pH and metabolic effects were measured using 31P nuclear magnetic resonance spectroscopy. The effect of this intervention on recovery from an acid load was assessed using an NH4Cl pre-pulse in bicarbonate-containing Krebs-Henseleit as well as a HEPES buffer.. Both CTL/EIPA and EIPA hearts had marked reduction in ischemic injury (CK control 1191 +/- IU/g dry weight: CTL/EIPA 406 +/- 42 IU/gdw; EIPA 333 +/- 78 IU/gdw), as well as significantly reduced end-diastolic pressure on reperfusion. Intracellular pH was higher in the CTL/EIPA hearts (end-ischemic pH = 6.34 +/- 0.05) compared to either control (5.86 +/- 0.02) or EIPA hearts (6.01 +/- 0.02), while pH recovery on reperfusion was markedly slowed in the CTL/EIPA hearts. CTL/EIPA hearts had rapid ATP depletion during ischemia, but PCr recovery comparable to EIPA hearts. Acidification on exposure to NH4Cl was increased in the presence of HEPES, but ph recovery was not altered by short-term exposure to EIPA.. These data show that short-term inhibition of the Na-H altered pH regulation in the ischemic heart, resulting in reduced acidosis and slow pH recovery on reperfusion, coupled with reduction in ischemic injury and end-diastolic pressure on a reperfusion. These findings are consistent with short-term exposure to EIPA accelerating ATP depletion during ischemia, as well as limiting proton efflux during reperfusion.

Topics: Acidosis; Adenosine Triphosphate; Amiloride; Ammonium Chloride; Animals; Anti-Arrhythmia Agents; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Male; Myocardial Ischemia; Myocardium; Perfusion; Phosphocreatine; Rats; Rats, Sprague-Dawley; Sodium-Hydrogen Exchangers; Time Factors

To analyze metabolic changes associated with a fulminant malignant hyperthermia (MH) crisis developed spontaneously in an MH susceptible pig which was part of 12 pigs undergoing metabolic investigation (six MH susceptible and six controls) and had been anaesthetized with a non-triggering agent (pentobarbitone).. The pig was placed in a cradle and then inserted into a 4.7 T magnet bore. The semi-membranous muscle was submitted to three repetitive stimulation-recovery sessions. 31-P magnetic resonance spectra and mechanical data were recorded.. The pig developed a non-rigid MH crisis during recovery from the second set of experiments. Although no mechanical work was performed, dramatic metabolic changes were noted. Twitch tension decreased progressively reaching zero while mouth temperature continuously increased to 44.5 degrees C. Phosphocreatine (PCr) consumption was coupled to Pi accumulation. Also, a marked intracellular acidosis and a large accumulation of phosphomonoesters (PME) were observed, probably as a result of massive glycolysis activation. Interestingly, ATP level remained constant.. These irreversible mechanisms may constitute a metabolic dead-end coupling calcium pumping ATP-consuming processes and ATP synthesis through PCr breakdown and anaerobic glycolysis. They do not differ from metabolic changes previously reported in rigid forms of MH crisis.

Topics: Acidosis; Adenosine Triphosphate; Adjuvants, Anesthesia; Animals; Body Temperature; Calcium-Transporting ATPases; Disease Models, Animal; Glycolysis; Male; Malignant Hyperthermia; Muscle Fatigue; Muscle, Skeletal; Pentobarbital; Phosphocreatine; Swine

The aim of this prospective study was to explore muscular metabolism in arterial occlusive disease (AOD) by dynamic phosphorus-31 (31P) magnetic resonance spectroscopy (MRS).. The authors examined 56 patients with AOD. Acquisition of up to 60 consecutive phosphorus spectra of the quadriceps muscle was done by "time series" in 36 seconds each. In this way, the authors achieved uninterrupted monitoring of muscle metabolism during rest, exhaustion, and recovery. During 31P MRS, the volunteers performed an isometric and an isotonic exercise until exhaustion of the quadriceps muscle. Spectroscopic results of 56 patients with AOD were correlated with clinical and angiographic findings and were compared with spectroscopic results of 10 age-matched healthy volunteers.. There were no significantly differing spectroscopic results between patients and volunteers at rest, except for an elevated ratio phosphomonoester (PME)/beta-adenosine triphosphate (ATP) in patients with AOD (0.66 +/- 0.19 versus 0.48 +/- 0.09). Despite a sixfold duration of both of the exercises until exhaustion in healthy volunteers, exercise-induced changes of inorganic phosphate (P1)/phosphocreatine (PCr), PME/beta-ATP, and pH were similar in healthy volunteers and patients with AOD. Compared with maximal exercise-induced values of Pi/PCr, acidosis was relatively increased in AOD, resulting in a steeper slope of linear regression line (-0.33 +/- 0.06 versus -0.14 +/- 0.06) between these parameters. Recovery rate of Pi/PCr was markedly prolonged in AOD (time of half recovery: 80 seconds versus 25 seconds [isometric exercise] and 70 seconds versus 37 seconds [isotonic exercise]), whereas recovery rate of pH was not significantly slowed down in our patients (192 seconds versus 166 seconds [isometric exercise] and 234 seconds versus 220 seconds [isotonic exercise]).. Dynamic 31P MRS provides a direct judgment of muscular metabolism, which is not only influenced by macro-, but also by microangiopathia. Results of 31P MRS suggest a reduced mitochondrial oxidative phosphorylation in AOD.

Topics: Acidosis; Adenosine Triphosphate; Angiography, Digital Subtraction; Aorta, Abdominal; Arterial Occlusive Diseases; Energy Metabolism; Exercise; Female; Femoral Artery; Humans; Iliac Artery; Magnetic Resonance Spectroscopy; Male; Middle Aged; Muscle, Skeletal; Phosphocreatine; Phosphorus Isotopes; Prospective Studies

Acidosis may contribute to ischemic injury by mobilizing iron because the iron chelator deferoxamine improves early metabolic recovery from hyperglycermic ischemia. Mobilized iron may then promote oxygen radical-induced lipid peroxidative injury during reperfusion. We tested the hypothesis that administration of the antioxidant tirilazad at the start of reperfusion improves early metabolic recovery after severe acidotic ischemia and ameliorates depletion of the endogenous antioxidant glutathione.. In anesthetized dogs, arterial glucose concentration was increased to 500 to 600 mg/dL and global incomplete cerebral ischemia was produced for 30 minutes by ventricular fluid infusion to reduce perfusion pressure to 10 to 12 mm Hg. Metabolic recovery and intracellular pH were measured by phosphorus MR spectroscopy. In the first experiment, four groups of eight dogs each received either vehicle or 0.25, 1, or 2.5 mg/kg of tirilizad mesylate at reperfusion. Cerebral blood flow was measured with microspheres. In the second experiment, two groups of eight dogs each each received either vehicle or 2.5 mg/kg of tirilazad at reperfusion, and cortical glutathione was measured at 3 hours of reperfusion.. Cerebral blood flow decreased to approximately 6 mL/min per 100 g and intracellular pH decreased to approximately 5.6 during ischemia in all groups. In the vehicle group, ATP recovery was transient and pH remained less than 6.0. Cerebral blood flow, O2 consumption, and ATP eventually declined to near-zero levels by 3 hours. Recovery was improved by tirilazad posttreatment in a dose-dependent fashion. At the highest dose, cerebral blood flow and O2 consumption were sustained near preischemic levels, and five of eight dogs had recovery of ATP greater than 50% and of pH greater than 6.7. Recovery of ATP and phosphocreatine became significantly greater than that in the vehicle group by 17 minutes of reperfusion despite similar levels of early hyperemia, indicating that the drug was acting before the onset of hypoperfusion. Cortical glutathione concentration in the vehicle group was 27% less than that in the tirilazad group and 34% less than that in nonischemic controls.. Decreased depletion of the endogenous antioxidant glutathione is consistent with tirilazad acting as an antioxidant in vivo. Improvement in high-energy phosphate recovery 17 minutes after starting tirilazad infusion during reperfusion is consistent with an early onset of a functionally significant oxygen radical injury. Thus, severe acidosis appears to contribute to early ischemic injury through an oxygen radical mechanism sufficient to impede metabolic recovery.

Topics: Acidosis; Adenosine Triphosphate; Animals; Antioxidants; Brain; Brain Ischemia; Cerebrovascular Circulation; Dogs; Dose-Response Relationship, Drug; Free Radical Scavengers; Glutathione; Hydrogen-Ion Concentration; Hyperemia; Hyperglycemia; Iron; Lipid Peroxidation; Magnetic Resonance Spectroscopy; Male; Oxygen Consumption; Phosphocreatine; Phosphorus; Pregnatrienes; Reperfusion

Metabolic and mechanical properties of female rat skeletal muscles, submitted to endurance training on a treadmill, were studied by a 60-min in vivo multistep fatigue test. 31P-NMR was used to follow energy metabolism and pH. Mechanical performance was greatly improved in trained muscles. The oxidative capacity of the skeletal muscles was evaluated from the relationship between ADP calculated from the creatine kinase equilibrium and work and from the measure of the rate of phosphocreatine (PCr) resynthesis following exercise. In trained muscles, ADP production was lower per unit of mechanical performance, showing an improvement of oxidative metabolism. However, the PCr resynthesis rate was not modified. Slight acidosis and ATP depletion were observed from the beginning of the fatigue test. These modifications suggest changes of the creatine kinase equilibrium favoring mitochondrial ATP production. Our results indicate that muscle status improvement could be accompanied by ATP depletion and minimal acidosis during contraction; this would be of particular importance for objective evaluation of muscle regeneration processes and of gene therapy in muscle diseases.

Topics: Acidosis; Adenosine Diphosphate; Adenosine Triphosphate; Animals; Energy Metabolism; Exercise Test; Female; Magnetic Resonance Spectroscopy; Muscle Fatigue; Muscle, Skeletal; Oxygen Consumption; Phosphocreatine; Phosphorus Isotopes; Physical Exertion; Rats; Rats, Wistar

The effects of 5-(N,N-dimethyl)amiloride, a potent and specific Na(+)-H+ exchange inhibitor, were investigated in isolated perfused rabbit hearts subjected to ischemia and reperfusion. Phosphorus 31-nuclear magnetic resonance spectroscopy was used to monitor intracellular pH, creatine phosphate, beta-adenosine triphosphate, and inorganic phosphate. After cardioplegic arrest with St. Thomas' Hospital solution, normothermic (37 degrees C) global ischemia was induced for 45 minutes, and the hearts were reperfused for 50 minutes. Dimethyl amiloride at 10 mumol/L, which has minimal inotropic and chronotropic effects on the nonischemic heart, was added to the cardioplegic solution. Treatment with dimethyl amiloride reduced the elevation of left ventricular end-diastolic pressure during and after the ischemia and improved the postischemic recovery of developed pressure from 76% +/- 3.2% at 30 minutes of reperfusion in control hearts (n = 6) up to 99% +/- 1.9% in hearts treated with dimethyl amiloride (n = 8). Dimethyl amiloride did not affect the decline in intracellular pH during ischemia for up to 30 minutes but enhanced the intracellular acidosis thereafter. The intracellular pH at the end of ischemia was 6.21 +/- 0.05 in control hearts compared with 5.24 +/- 0.17 in hearts treated with dimethyl amiloride (p < 0.05). During reperfusion, intracellular pH of hearts treated with dimethyl amiloride was less than control for 5 minutes, but subsequent recovery of intracellular pH was similar to control. Treatment with dimethyl amiloride did not affect creatine phosphate breakdown, inorganic phosphate accumulation, and beta-adenosine triphosphate depletion during 45 minutes of ischemia. The creatine phosphate resynthesis and inorganic phosphate reduction during reperfusion were also unaffected. These findings suggest that Na(+)-H+ exchange plays an important role not only during reperfusion but also during ischemia for the development of postischemic cardiac dysfunction most likely by inducing primary Na+ and secondary Ca2+ overload. Specific Na(+)-H+ exchange inhibitors like dimethyl amiloride would have a potential therapeutic profile in cardiac surgery, especially if added before ischemia.

Topics: Acidosis; Adenosine Triphosphate; Amiloride; Animals; Bicarbonates; Calcium; Calcium Chloride; Cardioplegic Solutions; Diastole; Energy Metabolism; Heart; Heart Arrest, Induced; Hydrogen-Ion Concentration; Ischemia; Magnesium; Magnetic Resonance Spectroscopy; Myocardial Contraction; Myocardial Reperfusion; Myocardial Reperfusion Injury; Myocardium; Phosphates; Phosphocreatine; Phosphorus Isotopes; Potassium Chloride; Rabbits; Sodium; Sodium Chloride; Sodium-Hydrogen Exchangers; Ventricular Function, Left; Ventricular Pressure

We studied the intracellular pH in rat cerebral cortex of rats subjected to reversible total cerebral ischemia by cardiac arrest and resuscitation. Brain acidoses was more pronounced during ischemia in hyperglycemic rats (6.21 +/- 0.14) than in normoglycemic rats (6.56 +/- 0.07). Brain tissue lactate accumulated proportionally. Nevertheless, within 5 min of reperfusion, pHi in both normoglycemic and hyperglycemic groups had recovered to baseline levels, i.e. near 7.1-7.2, despite the fact that lactate concentrations were still elevated. These results demonstrate a rapid reversal of ischemic acidosis during recovery from 10 min of cardiac arrest, and suggest that acidosis, per se, may not be responsible for neuronal damage following cardiac arrest and resuscitation, even in hyperglycemic conditions.

Topics: Acidosis; Adenosine Triphosphate; Animals; Body Temperature; Brain Chemistry; Cardiopulmonary Resuscitation; Heart Arrest; Hydrogen-Ion Concentration; Lactates; Lactic Acid; Male; Neutral Red; Phosphocreatine; Rats; Rats, Wistar

A 2.9 degrees C reduction in the intraischemic rectal temperature of neonatal piglets is associated with less brain damage compared with animals with normothermic rectal temperatures. This investigation studied one potential mechanism for this observation: better maintenance of energy stores and less brain acidosis secondary to reduced metabolic activity associated with modest hypothermia.. 31P MR spectroscopy was used to study piglets before, during, and after 15 minutes of partial brain ischemia with intraischemic rectal temperatures of either 38.3 +/- 0.4 degrees C (n = 10, normothermic) or 35.4 +/- 0.5 degrees C (n = 10, hypothermic). Animals were followed up for up to 72 hours after ischemia and were evaluated clinically and by brain histology.. Values for pHi remained 0.15 to 0.20 pH units greater in modestly hypothermic than in normothermic piglets during ischemia and the initial 30 minutes after ischemia (P = .049, group effect). Phosphocreatine, beta-ATP, and inorganic phosphorus were similar between groups. The relationship between the intraischemic energy state and subsequent clinical evidence of brain damage (irrespective of group assignment) revealed lower pHi over the last 7 minutes of ischemia for abnormal compared with normal piglets (5.98 +/- 0.22 versus 6.39 +/- 0.24, respectively; P = .002). In contrast, intraischemic beta-ATP (41 +/- 19% versus 57 +/- 21% of control) and inorganic phosphorus (273 +/- 31% versus 224 +/- 92% of control) for abnormal and normal piglets, respectively, did not differ between groups.. Intraischemic modest hypothermia attenuates the severity of brain acidosis during and 30 minutes after ischemia compared with normothermic animals and supports the concept that attenuated brain acidosis is a potential mechanism by which hypothermia may reduce ischemic brain damage.

Topics: Acidosis; Adenosine Triphosphate; Animals; Animals, Newborn; Body Temperature; Brain; Brain Damage, Chronic; Brain Diseases; Brain Ischemia; Energy Metabolism; Follow-Up Studies; Hydrogen-Ion Concentration; Hypothermia, Induced; Magnetic Resonance Spectroscopy; Phosphates; Phosphocreatine; Phosphorus Isotopes; Swine; Time Factors

In vitro working hearts of the turtle, Chrysemys picta bellii, paced at 30 beats/min, were studied over a range of input pressures in the following sequence of perfusion conditions: control normoxia, control anoxia, lactacidotic normoxia, and lactacidotic anoxia. Two such series of experiments were performed. In series 1 (n = 12), ventricular pressure (PV) and cardiac output were measured, and power output and dPV/dt were calculated. In series 2 (n = 5), intracellular phosphorus metabolites and intracellular pH (pHi) were also measured using 31P-nuclear magnetic resonance (31P-NMR) spectroscopy. In series 1 all mechanical variables increased with input pressure in generally similar fashion, except during anoxic acidosis, during which mechanical performance was depressed and was increased less or not at all by input pressure. Creatine phosphate (CP) and pHi fell significantly in anoxia and anoxic acidosis, but neither these variables, ATP, CP/ATP, nor, presumably, ADP changed as a function of input pressure with any perfusate despite often large increments in mechanical output. We conclude that anoxia and acidosis act synergistically to depress cardiac function in turtle hearts. Also, the insensitivity of NMR variables to changes in input pressure and cardiodynamics suggests that changes in these variables are unimportant for controlling energy turnover in this preparation.

Topics: Acidosis; Adenosine Diphosphate; Adenosine Triphosphate; Animals; Blood Pressure; Cardiac Output; Energy Metabolism; Female; Heart; Hemodynamics; Hydrogen-Ion Concentration; Hypoxia; In Vitro Techniques; Intracellular Fluid; Magnetic Resonance Spectroscopy; Male; Myocardium; Perfusion; Phosphocreatine; Phosphorus; Turtles

Tissue acidosis is believed to be a key element in ischemic injury of neural tissue. The goal of this study was to determine whether persisting postischemic acidosis or the extent of acidosis would affect metabolic recovery following an ischemic event. Intracellular pH (pHi), adenosine triphosphate, phosphocreatine, and lactate levels were measured in the cerebral cortex during the early stages of reperfusion, following either 5 or 10 minutes of global ischemia in both normo- and hyperglycemic gerbils. A total of 130 gerbils were injected with a solution containing 1.5 ml Neutral Red (1%) (+/- 2.5 gm/kg glucose); 30 minutes later, the gerbils were placed under halothane anesthesia, and the carotid arteries were occluded for either 5 or 10 minutes. The brains were frozen in liquid nitrogen at 0, 15, 30, 60, and 120 seconds after reperfusion; they were sectioned and the block face was photographed to determine the pHi by using Neutral Red histophotometry. At the conclusion of the ischemia, the pHi in all groups had decreased significantly from a control value of 7.05 +/- 0.03) (mean +/- standard error of the mean). In normoglycemic brains, the pHi values fell to 6.71 +/- 0.04 and 6.68 +/- 0.11 after 5 and 10 minutes of ischemia, respectively. Hyperglycemic brains were more acidotic; values fell to 6.57 +/- 0.10 and 6.52 +/- 0.24 after 5 and 10 minutes of ischemia, respectively. Lactate levels were approximately fivefold greater than those of control tissue in normoglycemic brains, while lactate levels in hyperglycemic brains were increased eightfold. The adenosine triphosphate and phosphocreatine levels were depleted at the end of ischemia in all groups. After 2 minutes of reflow activity, the pHi levels in both normo- and hyperglycemic brains were restored to those of control values in the '5-minute ischemic group, while the pHi levels remained significantly depressed in the 10-minute ischemic group. Restoration of high-energy phosphates was similar in normoglycemic brains regardless of ischemic duration, recovering to only 20% of the restoration obtained in control tissue at 2 minutes. In hyperglycemic brains, however, there was complete recovery of high-energy phosphates by 2 minutes of reflow activity following 5 minutes of ischemia. Extending the ischemic period to 10 minutes in hyperglycemic brains slowed the rate of metabolic recovery to that observed in normoglycemic brains. The results indicate that the reflow period permits the rapid restoration o

Topics: Acidosis; Adenosine Triphosphate; Animals; Blood Glucose; Brain Ischemia; Cerebral Cortex; Cerebrovascular Circulation; Energy Metabolism; Gerbillinae; Hydrogen-Ion Concentration; Lactates; Male; Phosphocreatine; Reperfusion; Vascular Patency

Phosphoenergetic and pH images in human calf muscles before and after ischemic exercise were generated by 31P NMR chemical shift imaging (CSI) with a 1.5 T standard clinical MR machine using a home-built volume coil. Acquisition of data was repeated four times with 8 x 8 phase-encoding steps and 1 s repetition time. The total acquisition time was 4 min 16 s. After 3-dimensional (3D) Fourier transformation with zero-filling, 2-dimensional (2D) images with 32 x 32 matrices of phosphocreatine (PCr), inorganic phosphate (Pi), PCr/(PCr + Pi) and pH were constructed. These metabolic images were overlaid with concurrently observed 1H MRI to locate the areas showing metabolic response. After 3 min exercise consisting of repeated plantarflexion of the foot under ischemic conditions, decreases in phosphoenergetic levels and acidosis were the most severe in the peroneus muscles, moderate in the tibialis anterior muscle, and slight in the triceps muscle of the calf. Under maintained ischemic conditions, phosphoenergetic level further decreased, but the acidosis in each muscle did not progress further. Heterogeneous metabolic and pH changes throughout the entire calf muscle were clearly demonstrated in detail by these images.

Topics: Acidosis; Adult; Energy Metabolism; Fourier Analysis; Humans; Hydrogen-Ion Concentration; Image Processing, Computer-Assisted; Ischemia; Leg; Magnetic Resonance Spectroscopy; Male; Middle Aged; Muscle Contraction; Muscle Fatigue; Muscle, Skeletal; Phosphates; Phosphocreatine; Phosphorus Isotopes; Physical Exertion

Bioenergetic and metabolic status of murine FSaII tumours were evaluated using 31P MRS, acid extracts ('global' techniques) and quantitative bioluminescence ('microregional' assay). Data obtained from s.c. tumours of varying sizes (44-600 mm3) have been correlated with the oxygenation status evaluated using O2-sensitive needle electrodes. beta-NTP/Pi and phosphocreatine (PCr)/Pi ratios derived from 31P MRS were positively correlated to the median tissue pO2 values. pH declined during growth with intracellular acidosis being evident in tumours > 350 mm3. Whereas lactic acid formation greatly contributed to this decline in small- and medium-sized tumours, ATP hydrolysis and slowing down of the activities of pumps involved in pHi regulation seem to be major factors responsible for intracellular acidification in bulky tumours. PCr levels decreased at an early growth stage, whilst ATP concentrations dropped in bulky malignancies only, coinciding with a decrease in adenylate energy charge and a substantial rise in the levels of total Pi. MRS observable (mobile) Pi was consistently lower than [Pi] measured in acid extracts. On average, median pO2 values of ca 10 mmHg represent a critical threshold for energy metabolism. At higher median O2 tensions, levels of ATP, phosphomonoester and total Pi were relatively constant. This coincided with intracellular alkalosis or neutrality and stable adenylate ratios. On average, median pO2 values < 10 mmHg coincided with intracellular acidosis, ATP depletion, a drop in energy charge and rising Pi levels.

Topics: Acidosis; Adenosine Triphosphate; Animals; Cell Hypoxia; Energy Metabolism; Female; Fibrosarcoma; Glucose; Hydrogen-Ion Concentration; Lactates; Lactic Acid; Magnetic Resonance Spectroscopy; Mice; Mice, Inbred C3H; Oxygen; Phosphates; Phosphocreatine

The new non-NMDA (N-methyl-D-aspartate) receptor antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) has previously been shown to exert a neuroprotective effect in animal models of cerebral ischemia when administered in the post-ischemic phase. In this investigation the effect of NBQX on acidosis and energy recovery in early reperfusion after 10 min of transient forebrain ischemia with the 2-vessel occlusion model in the rat was studied with 31P NMR spectroscopy. In the intervention group the animals received a bolus dose of NBQX 30 mg.kg-1 i.v. at the start of reperfusion. 31P NMR spectroscopy was used to measure intracellular pH, ATP and phosphocreatine continuously in-vivo during, and after, the ischemic event. The recovery of high energy phosphates and pH was followed during 30 min of reperfusion. Pre-ischemic levels of phosphocreatine were reached after approximately 9-10 min in both groups. Although a slight improvement could be seen in the intervention group there was no significant difference in the rate of recovery between the two groups. ATP reached 90% of preischemic levels after about 8 min without significant difference between the two groups. With respect to the recovery of intracellular pH, no difference could be shown. Our results do not contradict previously published results, but suggest that the potential protective effect of NBQX is not mediated through improved recovery of energy metabolism in early reperfusion.

Topics: Acidosis; Adenosine Triphosphate; Animals; Energy Metabolism; Hydrogen-Ion Concentration; Ischemic Attack, Transient; Magnetic Resonance Spectroscopy; Male; Phosphocreatine; Phosphorus; Prosencephalon; Quinoxalines; Rats; Rats, Wistar; Receptors, AMPA; Reperfusion; Time Factors

The cerebral metabolic changes elicited by kainate-induced seizures in the rat were investigated by in vivo combined NMR spectroscopy of 31P and 1H. Systemic injection of kainate induced no significant changes in cerebral ATP or PCr levels during up to 90 min of continuous, generalised seizures, and the cerebral 31P spectra showed only a transient mild cerebral acidosis 30 min after kainate administration. In parallel with the changes in intracellular cerebral pH, the 1H spectra showed a significant increase in lactate, which remained elevated throughout the seizures. These findings indicate that oxidative metabolism does not completely match the increased glycolysis during seizures though the energy homeostasis is maintained. This suggests that oxidative metabolism has a limited capacity to satisfy the brain's energy needs during the kainate-induced seizures, but that the different pathways of energy production in the brain cells can overcome this limitation. Thus the brain damage associated with this experimental model of epilepsy is not due to extended major failure of the energy supply.

Topics: Acidosis; Adenosine Triphosphate; Animals; Blood Pressure; Brain; Carbon Dioxide; Energy Metabolism; Fourier Analysis; Glycolysis; Homeostasis; Hydrogen; Hydrogen-Ion Concentration; In Vitro Techniques; Kainic Acid; Lactates; Magnetic Resonance Spectroscopy; Oxygen; Partial Pressure; Phosphocreatine; Phosphorus; Rats; Seizures; Time Factors

Capacity for ATP resynthesis during recovery from ischemia or hypoxia is limited to the size of the adenine nucleotide pool, which is determined in part by the activity of cytosolic 5'-nucleotidase (5'-NT): AMP-->adenosine plus inorganic phosphate (Pi). To define in vivo regulation of 5'-NT, we used the tools of 31P nuclear magnetic resonance (NMR), spectroscopy and chemical assay to measure the substrates (AMP), products (Pi, adenosine, and its catabolites), and inhibitors (Pi and H+) of 5'-NT in isolated perfused rat hearts exposed to hypoxia (where pH remains near 7) and no flow, global ischemia (where pH falls to 6.1). We estimated 5'-NT reaction velocity, assessed the relative contributions of Pi and H+ to enzyme inhibition, and defined the consequences of changes in 5'-NT activity on ATP resynthesis after hypoxia and ischemia. We conclude that (a) 5'-NT is activated during hypoxia and early ischemia but is inhibited during prolonged ischemia, (b) H+ (pH < 6.2) is a potent inhibitor of 5'-NT, and (c) differences in AMP accumulation are sufficient to explain the differences in the capacity for net ATP resynthesis in ischemic and hypoxic tissue. These observations have implications for our understanding of heterogeneity of ischemic injury and myocardial protection during ischemia.

Topics: 5'-Nucleotidase; Acidosis; Adenosine Triphosphate; Animals; Blood Pressure; Coronary Circulation; Heart; Heart Rate; In Vitro Techniques; Kinetics; Magnetic Resonance Spectroscopy; Male; Myocardial Ischemia; Myocardial Reperfusion; Myocardium; Phosphates; Phosphocreatine; Rats; Rats, Sprague-Dawley; Time Factors

1. Intracellular pH (pHi) and phosphorus metabolites were measured in isolated ferret hearts with 31P nuclear magnetic resonance (NMR). 2. The application of cyanide (to mimic hypoxia) produced a fall of the concentration of phosphocreatine ([PCr]) and a rise of those of inorganic phosphate ([Pi]) and sugar phosphates. These were accompanied by an intracellular acidosis. 3. If glycolysis was partly inhibited by prior exposure to a glucose-free solution then the application of cyanide also produced a fall of [ATP]. The acidosis was similar to that observed in the presence of glucose. 4. If glycolysis was completely inhibited by iodoacetate then the acidosis produced by subsequent addition of cyanide developed more quickly. 5. The results are reproduced by a model which incorporates lactic acid production as well as the effects of protons released and absorbed by the changes in metabolite concentrations. The results suggest that the acidosis produced by cyanide (without inhibition of glycolysis) is largely due to lactic acid production. When glycolysis is partly inhibited (glucose-free solution) the acidosis produced by cyanide is partly due to protons released by ATP breakdown. Finally, when glycolysis is entirely inhibited the acidosis is completely due to ATP breakdown. There is no need to postulate a contribution on this time scale from inhibition of pH regulating mechanisms.

Topics: Acidosis; Adenosine Triphosphate; Animals; Cyanides; Ferrets; Glycolysis; Heart; Hydrogen-Ion Concentration; Hypoxia; In Vitro Techniques; Intracellular Fluid; Iodoacetates; Iodoacetic Acid; Lactates; Lactic Acid; Models, Cardiovascular; Myocardial Contraction; Myocardium; Phosphates; Phosphocreatine

The aim of the present study was to identify components of ischaemia involved in the induction of preconditioning. Isolated rat hearts (n = 8 per group) were perfused with bicarbonate buffer. Following 10 min aerobic perfusion they were randomised and subjected to 5 min periods during which the perfusion conditions were: (i) normal aerobic perfusion (controls); (ii) zero flow ischaemia; (iii) low flow ischaemia (10% of control O2 delivery); (iv) hypoxia (10% of control O2 delivery); or (v) acidosis (pH 6.4). After these periods of "preconditioning", all hearts underwent 5 min aerobic perfusion followed by 40 min zero flow global ischaemia and 35 min reperfusion. Contractile function was measured at the beginning and at the end of the experiment. Despite profound differences in coronary flow during preconditioning, substantial and similar protection was observed in all groups preconditioned by transiently limiting oxygen delivery. Recovery of cardiac output was 66.7 +/- 6.3%, 58.7 +/- 5.1% and 62.6% +/- 3.3% in the zero flow, low flow and hypoxic groups, respectively, vs 31.0 +/- 3.0% in controls (all P < 0.05). In hearts subjected to acidosis there was no protection (recovery of cardiac output 38.1 +/- 2.7%). Impairment of oxygen delivery appears to be the principle component of ischaemia responsible for the induction of preconditioning. Metabolite accumulation appears to play no significant role.

Topics: Acidosis; Adenosine Triphosphate; Animals; Creatine Kinase; Extracellular Space; Heart; Hypoxia; Male; Myocardial Contraction; Myocardial Ischemia; Myocardium; Oxygen; Phosphocreatine; Rats; Rats, Wistar; Regional Blood Flow; Reperfusion Injury

In this study, the physiological and metabolic effects of Carbicarb administered as an isotonic (150 mmol/L Na[n[]I+) or hypertonic (1 mol/L Na[n[]I+) solution over 2 minutes in the acidotic isolated heart were compared. Physiological monitoring as well as 31P and 23Na nuclear magnetic resonance spectroscopy were performed. Both isotonic and hypertonic Carbicarb induced comparable dose-dependent increases in intracellular pH as well as decreases in inorganic phosphate and increases in creatine phosphate concentrations, which were sustained for 20 minutes. However, immediate functional improvement was greater in hearts receiving isotonic Carbicarb. Metabolic acidosis conditions resulted in a 27% increase in cytosolic sodium by 30 minutes (P < .05). In this setting, hypertonic Carbicarb induced a large transient increase in cytosolic sodium, whereas isotonic Carbicarb caused immediate and sustained decreases in cytosolic sodium. These data suggest that isotonic Carbicarb may have more beneficial effects on cardiac function than hypertonic Carbicarb. These effects may be related to associated changes in cytosolic sodium.

Topics: Acidosis; Animals; Blood Gas Analysis; Carbonates; Cytosol; Dose-Response Relationship, Drug; Drug Combinations; Heart Rate; Hydrogen-Ion Concentration; Hypertonic Solutions; In Vitro Techniques; Isotonic Solutions; Magnetic Resonance Spectroscopy; Myocardium; Oxygen Consumption; Phosphates; Phosphocreatine; Rats; Rats, Sprague-Dawley; Sodium; Sodium Bicarbonate

Experimental and clinical studies suggest that the calcium channel blocker nimodipine may reduce cerebral ischemic injury. Using rapid acquisition phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy, we examined the effect of nimodipine on cerebral energy metabolism during severe ischemia in gerbils. High-energy phosphates and intracellular pH were characterized at baseline and at 2-min intervals following bilateral common carotid artery (CCA) ligation. Serial forebrain spectroscopy was continued until phosphocreatine (PCr) and adenosine triphosphate (ATP) resonances disappeared. Controls (n = 10) were compared to gerbils receiving intraperitoneal nimodipine 30 min prior to carotid ligation, at the following doses: 0.5 mg/kg (n = 8), 1.0 mg/kg (n = 10), 2.0 mg/kg (n = 8), or 4.0 mg/kg (n = 4). In the control group, PCr and ATP peaks were undetectable after a mean of 5.4 +/- 0.47 min following CCA ligation. Compared with controls, the mean time for depletion of high-energy phosphates following carotid ligation was prolonged at nimodipine doses of 0.5 mg/kg and 1.0 mg/kg, but the differences did not reach statistical significance. In the 2.0 mg/kg group, however, ATP was preserved until 9.8 +/- 1.0 min following the onset of ischemia, significantly longer than the control group (p = 0.005, Mann-Whitney test). Nimodipine had no effect on the time course or severity of intracellular acidosis. In this model of severe ischemia, relatively high doses of nimodipine slowed the depletion of high-energy phosphates without altering intracellular acidosis. This suggests that nimodipine may provide cerebral protection by directly altering ischemic cellular metabolism.

Topics: Acidosis; Adenosine Triphosphate; Animals; Brain Ischemia; Carotid Artery, Common; Energy Metabolism; Gerbillinae; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Male; Nimodipine; Phosphates; Phosphocreatine

Although hypoxia and metabolic acidosis have both been shown to impair cardiac function, some workers have suggested that acidosis during a period of hypoxia will actually accelerate physiologic recovery from this insult. To address the interactions of metabolic acidosis and hypoxia further, isolated isovolumic rat hearts were exposed to normal perfusion conditions for 30 min to establish baseline conditions, then either continued normal conditions, metabolic acidosis, hypoxia, or combined acidosis and hypoxia for 30 min and subsequently reperfused under normal perfusion conditions for an additional 30 min. We observed that acidosis + hypoxia impaired recovery of cardiac contraction more than acidosis or hypoxia alone following experimental perfusion. The combination of acidosis and and hypoxia also impaired cardiac energy metabolism more than acidosis or hypoxia alone as assessed by increases in tissue inorganic phosphate during experimental perfusion as well as during reperfusion. These data suggest that during hypoxia, acidosis appears to primarily impair cardiac energy production as we have previously observed in the normoxic isolated rat heart. Therefore, in the intact beating heart, acidosis may not protect from hypoxic injury as has been suggested in simpler systems but may not protect from hypoxic injury as has been suggested in simpler systems but rather may exacerbate at.

Topics: Acidosis; Animals; Heart Rate; Hypoxia; In Vitro Techniques; Magnetic Resonance Spectroscopy; Myocardial Contraction; Myocardium; Phosphates; Phosphocreatine; Rats; Rats, Sprague-Dawley

Postischemic evoked potential recovery correlates with acidosis during ischemia and early reperfusion. Acidosis promotes lipid peroxidation in vitro. We tested the hypothesis that the 21-aminosteroid tirilazad mesylate (U74006F), an inhibitor of lipid peroxidation in vitro, ameliorates somatosensory evoked potential recovery and acidosis during reperfusion after severe incomplete cerebral ischemia.. Cerebral perfusion pressure was reduced to 11 +/- 1 mm Hg (+/- SEM) for 30 minutes by cerebral ventricular fluid infusion in anesthetized dogs. Cerebral intracellular pH and high-energy phosphates were measured by magnetic resonance spectroscopy. Dogs were randomized to receive vehicle (citrate buffer; n = 8) or tirilazad (1 mg/kg; n = 8) before ischemia in a blinded study.. Cerebral blood flow was reduced to 6 +/- 1 mL/min per 100 g during ischemia, resulting in nearly complete loss of high-energy phosphates and an intracellular pH of 6.0-6.1 in both groups. Initial postischemic hyperemia was similar between groups but lasted longer in the vehicle group. Tirilazad accelerated mean recovery time of intracellular pH from 31 +/- 5 to 15 +/- 3 minutes and of inorganic phosphate from 13 +/- 2 to 6 +/- 1 minutes. Recovery of somatosensory evoked potential amplitude was greater with tirilazad (49 +/- 3%) than vehicle (33 +/- 6%). Fractional cortical water content was less with tirilazad (0.819 +/- 0.003) than vehicle (0.831 +/- 0.002).. Tirilazad attenuates cerebral edema and improves somatosensory evoked potential recovery after incomplete ischemia associated with severe acidosis. Accelerated pH and inorganic phosphate recovery indicates that this antioxidant acts during the early minutes of reperfusion.

Topics: Acidosis; Adenosine Triphosphate; Animals; Bicarbonates; Brain; Brain Edema; Brain Ischemia; Cytoplasm; Dogs; Drug Evaluation, Preclinical; Evoked Potentials, Somatosensory; Hydrogen-Ion Concentration; Male; Phosphocreatine; Pregnatrienes; Reactive Oxygen Species; Reperfusion Injury

The pH management that provides optimal organ protection during hypothermic circulatory arrest is uncertain. Recent retrospective clinical data suggest that the pH-stat strategy (maintenance of pH at 7.40 corrected to core temperature) may improve brain protection during hypothermic cardiopulmonary bypass with a period of circulatory arrest in infants. The impact of alpha-stat (group A) and pH-stat (group P) strategies on recovery of cerebral high-energy phosphates and intracellular pH measured by magnetic resonance spectroscopy (A, n = 7; P, n = 5), organ blood flow measured by microspheres, cerebral metabolic rate measured by oxygen and glucose extraction (A, n = 7; P, n = 6), and cerebral edema was studied in 25 4-week-old piglets undergoing core cooling and 1 hour of circulatory arrest at 15 degrees C. Group P had greater cerebral blood flow during core cooling (54.3% +/- 4.7% versus 34.2% +/- 1.5% of normothermic baseline, respectively; p = 0.001). The intracellular pH during core cooling showed an alkaline shift in both groups but became more alkaline in group A than in group P at the end of cooling (7.08 to 7.63 versus 7.09 to 7.41, respectively; p = 0.013). Recovery of cerebral adenosine triphosphate (p = 0.046) and intracellular pH (p = 0.014) in the initial 30 minutes of reperfusion was faster in group P. The cerebral intracellular pH became more acidotic during early reperfusion in group A, whereas it showed continuous recovery in group P. Brain water content postoperatively was less in group P (0.8075) than in group A (0.8124) (p = 0.05). These results suggest that compared with alpha-stat, the pH-stat strategy provides better early brain recovery after deep hypothermic cardiopulmonary bypass with circulatory arrest in the immature animal. Possible mechanisms include improved brain cooling by increased blood flow to subcortical areas, improved oxygen delivery, and reduction of reperfusion injury, as well as an alkaline shift in intracellular pH with hypothermia in spite of a stable blood pH.

Topics: Acidosis; Adenosine Triphosphate; Animals; Body Temperature; Brain; Cerebrovascular Circulation; Energy Metabolism; Glucose; Heart Arrest, Induced; Hydrogen-Ion Concentration; Hypothermia, Induced; Kidney; Lactates; Magnetic Resonance Spectroscopy; Oxygen; Oxygen Consumption; Phosphates; Phosphocreatine; Regional Blood Flow; Reperfusion; Swine; Swine, Miniature; Vascular Resistance

The authors investigated early human focal ischemia with phosphorus-31 nuclear magnetic resonance spectroscopy at 1.89 T to characterize the temporal evolution and relationship of brain pH and phosphate energy metabolism. Data from 65 symptomatic patients were prospectively studied; none of the patients had had ischemic stroke in the internal carotid artery territory before. Twenty-eight neurologically normal individuals served as control subjects. Serial ischemic brain pH levels indicated a progression from early acidosis to subacute alkalosis. When acidosis was present there was a significant elevation in the relative signal intensity of inorganic phosphate (Pi) and significant reductions in signal intensities of alpha-adenosine triphosphate (ATP) and gamma-ATP compared with those of control subjects. Ischemic brain pH values directly correlated with the relative signal intensity of phosphocreatine (PCr) and the PCr index and inversely correlated with the signal intensity of Pi. There was a general lack of correlation between either ischemic brain pH or phosphate energy metabolism and the initial clinical stroke severity. The data suggest a link between high-energy phosphate metabolism and brain pH, especially during the period of ischemic brain acidosis, and the authors propose that effective acute stroke therapy should be instituted during this period.

Topics: Acidosis; Adenosine Triphosphate; Adult; Aged; Aged, 80 and over; Brain; Cerebral Infarction; Cerebrovascular Disorders; Energy Metabolism; Female; Humans; Hydrogen-Ion Concentration; Ischemic Attack, Transient; Magnetic Resonance Spectroscopy; Male; Middle Aged; Phosphates; Phosphocreatine; Phosphorus

31-phosphorous magnetic resonance spectroscopy was used in a rat model of 10 min severe incomplete forebrain ischemia (two-vessel occlusion with hypotension) to assess the effect of hyperglycemia on intracellular pH and high energy phosphates during ischemia and early reperfusion. One group (n = 8) with preischemic hyperglycemia (serum glucose 20 mmol.l-1) showed an increased intracellular acidosis (pH 6.35) during ischemia compared to 6.55 in the normoglycemic control group (n = 7, P less than 0.001), but the recovery of phosphocreatine and ATP in early reperfusion was the same in the two groups. Another group (n = 7) was normoglycemic during ischemia, but received an i.v. bolus of glucose during the first minute of reperfusion. In this group the recovery of intracellular pH in early reperfusion was slower than in the control group (0.034 +/- 0.006 pH units per minute compared to 0.052 +/- 0.11 in the controls, +/- s.d. and P less than 0.01).

Topics: Acidosis; Adenosine Triphosphate; Animals; Blood Glucose; Brain Ischemia; Hydrogen-Ion Concentration; Hyperglycemia; Magnetic Resonance Spectroscopy; Male; Phosphates; Phosphocreatine; Phosphorus; Rats; Rats, Inbred Strains; Reperfusion; Time Factors

To investigate the mechanisms by which acidosis depresses cardiac function, a Langendorff isolated perfused rat heart preparation was studied using 31P magnetic resonance spectroscopy. Isolated hearts were subjected to normal perfusion conditions or experimental manipulations simulating severe metabolic acidosis, substrate depletion, impairment of oxidative metabolism, or low perfusate calcium concentrations. All maneuvers resulted in marked reductions in oxygen consumption and the force of myocardial contraction (dP/dt). Metabolic acidosis had bioenergetic changes suggestive of impaired energy production, specifically, increases in Pi and decreases in phosphocreatine concentrations, which did not occur in hearts subjected to low perfusate calcium concentrations. In acidotic perfusions as well as substrate depletion and impairment of oxidative metabolism, the change in dP/dt correlated best with the change in the intracellular concentration of monovalent Pi (P(im)) (r = 0.70, P less than 0.01), whereas in hearts subjected to a low perfusate calcium concentration, there was no relationship between dP/dt and the change in Pim concentrations. More detailed analysis of the time course of the metabolic and physiological changes with metabolic acidosis revealed a discordance between changes in Pim and the decreases in dP/dt during the first 20 min of the induction of acidosis and the first 10 min of recovery from acidosis. These data suggest that metabolic acidosis has a major direct effect on energy metabolism in this model. Moreover, impairment of oxidative metabolism in concert with decreases in intracellular pH may be important in the contractile failure associated with prolonged metabolic acidosis.

Topics: Acidosis; Animals; Coronary Circulation; Energy Metabolism; Heart; Heart Rate; Hydrogen-Ion Concentration; In Vitro Techniques; Magnetic Resonance Spectroscopy; Myocardial Contraction; Myocardium; Perfusion; Phosphates; Phosphocreatine; Rats; Rats, Inbred Strains

Peak tetanic tension was measured during acidosis resulting from either hypercapnia or repetitive tetanic stimulation in isolated, arterially perfused cat biceps brachii (predominantly fast twitch) or soleus (slow twitch) muscles. Phosphocreatine (PCr), Pi, intracellular pH (pHi), and extracellular pH (pHo) were monitored by 31P-nuclear magnetic resonance spectroscopy. During repetitive stimulation under normocapnic conditions (5% CO2, pHo 7.4) Pi increased, pHi decreased from 7.1 to 6.3, and there were significant correlations between both pHi and calculated [H2PO4-] vs. peak tetanic force in both muscle types. However, hypercapnic perfusion (70% CO2, pHo, 6.7, pHi 6.4-6.5) had no effect on peak tetanic force, and there was no significant correlation between pHi or [H2PO4-] during hypercapnia in either muscle. The results indicate that decreased peak tetanic force during repetitive stimulation is not directly due to changes in pHi or diprotonated phosphate.

Topics: Acidosis; Adenosine Triphosphate; Animals; Cats; Female; Hydrogen-Ion Concentration; Hypercapnia; In Vitro Techniques; Kinetics; Magnetic Resonance Spectroscopy; Male; Muscle Contraction; Muscles; Perfusion; Phosphates; Phosphocreatine

The effect of pH of the reperfusion buffer on postischemic changes in tissue Ca and Na was examined in isolated Langendorff-perfused Sprague-Dawley rat hearts. Reperfusion began after 15-, 25-, or 60-min ischemia at 37 degrees C. After 60-min ischemia, reperfusion at pH 6.4 or 6.6 attenuated the reperfusion-induced Ca gain so long as the acidotic conditions were maintained (3.08 +/- 0.22, 1.37 +/- 0.41, and 16.96 +/- 1.18 mumol Ca gain/g dry wt for pH 6.4, 6.6, and 7.4, respectively after 15-min reperfusion). Conversely, reperfusion under alkalotic conditions (pH 7.9) after 60-min ischemia exacerbated the gain (27.45 +/- 4.75 and 8.92 +/- 1.53 mumol Ca gain/g dry wt during 5-min reperfusion at pH 7.9 and 7.4, respectively). Similar, but less pronounced Ca gains occurred during reperfusion after 15- or 25-min ischemia. Sodium content during reperfusion, but not during aerobic perfusion, was also found to be pH sensitive with acidosis causing a reduction and alkalosis an increase. These results could not be explained in terms of an effect of pH on recovery of high-energy phosphates, percentage "reflow" during reperfusion, or reperfusion-induced increases in tissue water or resting tension. The results are in agreement with the hypothesis that the "inhibitory" effect of acidosis on postischemic Ca overload could involve an effect of pH on the Na(+)-H+ exchanger and intracellular Ca storage.

Topics: Acidosis; Acidosis, Respiratory; Adenosine Triphosphate; Alkalosis; Alkalosis, Respiratory; Animals; Biomechanical Phenomena; Buffers; Coronary Disease; Female; Hydrogen-Ion Concentration; In Vitro Techniques; Mitochondria, Heart; Myocardial Reperfusion; Perfusion; Phosphocreatine; Rats; Rats, Inbred Strains; Time Factors

Metabolic events were followed by 31-P NMR spectroscopy during mechanical exhaustion of directly stimulated rat gastrocnemius. During mechanical fatigue, phosphocreatine (PCr) and pH first declined but although stimulation continued high values were recovered without mechanical recovery. Total recovery was only observed after cessation of stimulation. Partial mechanical recovery was elicited by lowering stimulation rhythm; it was accompanied by decrease in PCr to a steady-state level without pH alteration. When exhaustive exercise was induced immediately after nonexhaustive exercise, failure of mechanical function occurred without decrease in pH. Major findings were: first, during exhaustive stimulations, the greater the muscle fatigue, and the higher the PCr level at the end of stimulation. Secondly, PCr and force levels did not depend on preceding levels of PCr and pH. Thirdly, acidosis was observed transiently during the first minutes of the first exercise period. These findings strongly suggested that electrical events and/or excitation-contraction (EC) coupling play a crucial role in this type of fatigue.

Topics: Acidosis; Animals; Electric Stimulation; Fatigue; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Male; Muscle Contraction; Muscles; Phosphocreatine; Rats; Rats, Inbred Strains

We used 31P-nuclear magnetic resonance (NMR) spectroscopy to measure intracellular pH (pHi) and high-energy phosphate levels in hearts of turtles (Chrysemys picta bellii) during either 4 h of anoxia [extracellular pH (pHo) 7.8, 97% N2-3% CO2], 4 h of lactic acidosis (pHo 7.0, 97% O2-3% CO2), or 1.5 h of combined anoxia + lactic acidosis (pHo 7.0, 97% N2-3% CO2) followed by 2 h of oxygenated recovery (pHo 7.8) at 20 degrees C. We also measured heart rate, maximum ventricular-developed pressure, and rate of pressure development (dP/dtmax). 31P-NMR spectra were characterized by the seven peaks typical of mammalian hearts, although turtle spectra were dominated by a large phosphodiester peak. Anoxia caused an increase in Pi to 165% and a decrease in creatine phosphate (CP) to 42% of control, whereas ATP levels remained unchanged. pHi declined from 7.37 +/- 0.01 to 7.22 +/- 0.03 at 1 h of anoxia and remained unchanged through hour 4. Lactic acidosis caused a 59% decrease in Pi, whereas CP and ATP levels remained unchanged. pHi fell to 6.88 +/- 0.04 by hour 1 and then climbed steadily to 7.14 +/- 0.05 at hour 4. During recovery from acidosis, pHi exceeded control values and returned to control by 2 h. Combined anoxia + acidosis caused profound decreases in CP to 14% and pHi to 6.56 +/- 0.03. In anoxic hearts, cardiodynamic variables remained at control levels through hour 3, after which cardiac output, heart rate, and dP/dtmax declined. Cardiodynamic variables were essentially unchanged from control throughout 4 h of acidosis except for dP/dtmax, which declined rapidly. In the combined protocol, all measures of cardiac function decreased. Recovery in all three cases was complete by approximately 2 h. We conclude that turtle hearts were relatively resistant to the stresses imposed in all three protocols compared with mammalian hearts, although anoxia + acidosis depressed the measured cardiac variables more profoundly than predicted from responses to the conditions imposed separately. Our results from the anoxia protocol suggest no direct causal relationship between myocardial CP (or ATP) levels and cardiac function.

Topics: Acidosis; Adenosine Triphosphate; Animals; Heart; Heart Ventricles; Hydrogen-Ion Concentration; Hypoxia; In Vitro Techniques; Intracellular Membranes; Magnetic Resonance Spectroscopy; Myocardium; Phosphocreatine; Phosphorus; Pressure

Amlodipine is a long-acting dihydropyridine-based Ca2+ channel blocker, developed for use on a once-daily basis. Experiments using hearts from amlodipine-pretreated rats were undertaken to further test the hypothesis that Ca2+ channel blockers can be used as prophylactic therapy to reduce the severity of the mechanical and biochemical consequences of ischemia and reperfusion. Amlodipine was given intravenously, 0.25 mg/kg, 5 hours before excising the hearts. Ischemia (global) was induced at 37 degrees C for 10, 30 or 60 minutes, and was followed by reperfusion. Protection was quantitated in terms of functional recovery, adenosine triphosphate and creatine phosphate retention, tissue acidosis and Ca2+ gain. The results show that amlodipine pretreatment supplied protection, provided that the ischemic episode did not exceed 30 minutes. The protection resulted in improved recovery of peak developed tension on reperfusion, reduced Ca2+ gain, retention of tissue adenosine triphosphate and creatine phosphate, and reduced acidosis.

Topics: Acidosis; Adenosine Triphosphate; Amlodipine; Animals; Calcium; Calcium Channel Blockers; Coronary Disease; Heart Rate; In Vitro Techniques; Male; Myocardial Contraction; Myocardial Reperfusion Injury; Myocardium; Nifedipine; Phosphocreatine; Rats; Rats, Inbred Strains; Reperfusion; Time Factors

Chronic administration of the NADH-CoQ reductase inhibitor, diphenyleneiodonium to rats at two dose levels, 1.0 and 1.5 mg/kg per day, caused a 40% and 60% reduction, respectively, in the in vitro rate of NAD-linked respiration by skeletal muscle mitochondria. At the highest dose, muscle fatigue, lactic acidosis and an over-utilization of phosphocreatine was observed in the gastrocnemius muscle during mild stimulation of 1 Hz frequency. The resynthesis of phosphocreatine following muscle stimulation was about 2 fold slower in the treated animal group. At the low dose, no significant biochemical changes were observed during muscle stimulation at 4 Hz. The results are discussed in terms of skeletal muscle "oxidative reserve", twitch tension maintenance and the relevance to the human diseased state of mitochondrial myopathy.

Topics: Acidosis; Animals; Dose-Response Relationship, Drug; Male; Mitochondria, Muscle; Muscles; Muscular Diseases; NAD(P)H Dehydrogenase (Quinone); Onium Compounds; Phosphocreatine; Quinone Reductases; Rats; Rats, Inbred Strains; Time Factors

We investigated the effect of mild whole-body hyperthermia before and after 16 minutes of global cerebral ischemia on metabolic recovery during recirculation in cats using in vivo phosphorus-31 nuclear magnetic resonance spectroscopy. Hyperthermia (temperature 40.6 +/- 0.2 degrees C) was induced greater than or equal to 1 hour before ischemia and was maintained during 1.5-2 hours of recirculation in nine cats; four cats were subjected to hyperthermia without cerebral ischemia, six to hyperthermia during recirculation (after return of intracellular pH to preischemic values), and 14 to normothermic ischemia and recirculation. Our data indicate that preischemic hyperthermia results in an intracellular cerebral pH during recirculation significantly lower than that in normothermic cats. In hyperthermic cats beta-ATP and phosphocreatine (PCr) concentrations and the ratio of PCr to inorganic phosphate failed to return to preischemic levels during recirculation in contrast to normothermic cats. Hyperthermia without ischemia and hyperthermia during recirculation had no significant effect on intracellular pH. Thus, preischemic hyperthermia has a detrimental effect on metabolic recovery after transient global cerebral ischemia.

Topics: Acidosis; Adenosine Triphosphate; Animals; Brain Ischemia; Cats; Fever; Phosphates; Phosphocreatine

When exposed to hypercapnia, several muscles deteriorate with respect to their mechanical performance. Exposure to metabolic acidosis and, perhaps surprisingly, to compensated metabolic acidosis has the same effect on the diaphragm. The mechanisms involved in these effects remain unclear. If the diaphragmatic intracellular pH (pHi) is assumed to decrease with hypercapnia, to remain unchanged during metabolic acidosis, and to increase during compensated metabolic acidosis, it would appear that different mechanisms must be responsible for the depreciation in the diaphragm's mechanical performance. The present experiments using 31P nuclear magnetic resonance (31P-NMR) spectroscopy were undertaken to determine the effect of metabolic acidosis and compensated metabolic acidosis on pHi and on high-energy phosphate metabolites in the resting rat diaphragm. A whole diaphragm was slightly stretched while being stitched onto a fiberglass mesh. The area approximated that at functional residual capacity. It was superfused in the NMR sample tube with a phosphate-free Krebs-Ringer bicarbonate solution [( HCO3-] = 6 meqO equilibrated with either 95% O2-5% CO2 or 98.75% O2-1.25% CO2). Spectra were acquired during 15-min intervals for control (30 min of normal Krebs-Ringer bicarbonate superfusate, equilibrated with 95% O2-5% CO2), for 120 min of exposure to either form of acidosis and for 60 min of recovery with normal superfusate. The pHi decreased rapidly during metabolic acidosis but did not change significantly during compensated metabolic acidosis. In both forms of acidosis, phosphocreatine declined gradually but not significantly, whereas ATP and inorganic phosphate did not change at all. The results suggest that HCO3- passes freely through the diaphragmatic sarcolemma, very much like the cardiac sarcolemma.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acidosis; Adenosine Triphosphate; Animals; Diaphragm; Hydrogen-Ion Concentration; In Vitro Techniques; Magnetic Resonance Spectroscopy; Muscle Relaxation; Phosphates; Phosphocreatine; Rats; Rats, Inbred Strains

This paper describes a method by which antianginal drugs can be evaluated in the dog heart in situ. Myocardial pH was measured continuously by a micro glass pH electrode inserted in the left ventricular endocardial layers of the dog anesthetized with pentobarbital. Occlusion of the left anterior descending coronary artery (LAD) decreased myocardial pH, and release of the LAD restored the pH. The myocardial acidosis induced by ischemia was metabolic in nature and accompanied by a decrease in the levels of adenosine triphosphate and creatine phosphate and an increase in the levels of lactate in the myocardium. Drugs were injected intravenously 30 min after incomplete (partial) occlusion ot the LAD, lasting until 60 min after drug injection. Propranolol, atenolol, and sotalol markedly attenuated the myocardial pH that had been decreased by LAD occlusion. Nitroglycerin, diltiazem, and nicorandil also attenuated the pH, but these drugs were less active in attenuating myocardial acidosis. Dipyridamole, nifedipine, and beta-2 adrenoceptor antagonists were least active in this regard. It is concluded that myocardial pH can be used as an indicator of myocardial regional ischemia and utilized for evaluation of antianginal drugs.

Topics: Acidosis; Adenosine Triphosphate; Adrenergic beta-Antagonists; Angina Pectoris; Animals; Coronary Disease; Dogs; Hydrogen-Ion Concentration; Lactates; Lactic Acid; Myocardium; Phosphocreatine; Time Factors; Vasodilator Agents

Phosphorus magnetic resonance spectroscopy (P MRS) affords and innovative approach to the study of the oxidative enzyme content of normal and diseased muscles. Examples of the evaluation of the enzyme content of normal muscles by an exercise protocol are provided. The protocol affords a hyperbolic work/cost profile, the Vmax of which is calculated by the reciprocal plots giving the enzyme content and the "effective Michaelis constant" with an evaluation of the resting metabolism. This steady state protocol clearly illustrates enzyme adaptation, on the one hand, and tissue atrophy particularly in the case of tissue injury, Duchenne's dystrophy, and genetic deletion of specific enzymes, on the other hand. The method is rapid, safe, and affords a quantitative evaluation of the disease process and possibilities for following appropriate therapies. So far, approx 1000 examinations of normal and diseased human limbs have been carried out in our laboratory in over the past four years.

Topics: Acidosis; Adenine Nucleotides; Age Factors; Animals; Cattle; Cytochrome b Group; Energy Metabolism; Humans; Immobilization; Kinetics; Magnetic Resonance Spectroscopy; Mitochondria, Muscle; Muscles; Muscular Diseases; Muscular Dystrophies; NAD; Phosphates; Phosphocreatine; Phosphofructokinase-1; Physical Exertion

Three types of metabolic control of oxidative metabolism are observed in the various tissues that have been studied by phosphorous magnetic resonance spectroscopy. The principal control of oxidative metabolism in skeletal muscle is by ADP (or Pi/phosphocreatine). This conclusion is based upon studies of arm muscles of humans during steady-state exercise. A work-cost (Vm vs. Pi/phosphocreatine) relationship follows a Michaelis-Menten rectangular hyperbola, where Km values from 0.5 to 0.6 and Vmax values from 50 to 200 (at nearly constant pH) are found in linearized plots of the equation V/Vmax = 1/(1 + 0.6 phosphocreatine/Pi) where V is work level (which is equal to the velocity of the enzymatic reaction) and Vmax is the maximal work capacity that is a measure of the enzyme activity (E) of oxidative metabolism. Adaptation to exercise enhances the slope of the work-cost relationship and causes large changes in Vmax or E. A second metabolic control may enhance the slope of the work-cost relationship but not Vmax. For example, the initiation of exercise can lead to an improved characteristic that can be explained by 2-fold increased substrate delivery, for example, increased oxygen delivery by microcirculatory control. Cardiac tissue of the adult dog affords an example of optimal endurance performance adaptation and exhibits the steepest work-cost relationship observed and is attributed to a coordinated control of substrate delivery that may involve Ca2+ and inorganic phosphate control of NADH; control of O2 delivery may also be involved. The calculated work-cost relationship is similar to that observed in the beagle heart. The theoretical curve illustrates that the liability of multiple controls is a sharp break point in metabolic control at the end of the multiple control range--a possible cause of instability of cardiac performance at high V/Vmax.

Topics: Acidosis; Adenine Nucleotides; Adenosine Diphosphate; Energy Metabolism; Humans; Kinetics; Magnetic Resonance Spectroscopy; Muscles; Myocardium; NAD; Oxygen; Phosphocreatine; Physical Endurance; Physical Exertion

Exhaustive 'burst-type' exercise in the rainbow trout resulted in a severe acidosis in the white muscle, with pHi dropping from 7.21 to a low of 6.62, as measured by DMO distribution. An accumulation of lactate and pyruvate, depletions of glycogen, ATP and CP stores, and a fluid shift from the extracellular fluid to the intracellular fluid of white muscle were associated with the acidosis. The proton load was in excess of the lactate load by an amount equivalent to the drop in ATP, suggesting that there was an uncoupling of ATP hydrolysis and glycolysis. Initially, lactate was cleared more quickly than protons from the muscle, a difference that was reflected in the blood. It is suggested that during the early period of recovery (0-4 h), the bulk of the lactate was oxidized in situ, restoring pHi to a point compatible with glyconeogenesis. At that time, lactate and H+ were used as substrates for in situ glyconeogenesis, which was complete by 24 h. During this time, lactate and H+ disappearance could account for about 75% of the glycogen resynthesized. The liver and heart showed an accumulation of lactate, and it is postulated that this occurred as a result of uptake from the blood. Associated with the lactate load in these tissues was a metabolic alkalosis. Except for an apparent acidosis immediately after exercise, the acid-base status of the brain was not appreciably affected. Despite the extracellular acidosis, red cell pHi remained nearly constant.

Topics: Acid-Base Equilibrium; Acidosis; Adenosine Triphosphate; Animals; Body Fluids; Carbon Radioisotopes; Female; Glycogen; Glycolysis; Hydrogen-Ion Concentration; Intracellular Fluid; Lactates; Male; Muscles; Phosphocreatine; Physical Exertion; Tritium; Trout

The metabolism and performance of a perfused rat hindquarter preparation was examined during heavy exercise in three conditions: control (C), metabolic acidosis (MA, decreased bicarbonate concentration), and respiratory acidosis (RA, increased CO2 tension). A one-pass system was used to perfuse the hindquarters for 30 min at rest and 20 min during tetanic stimulation via the sciatic nerve. The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded, and biopsies were taken pre- and postperfusion. Initial isometric tensions were similar in all conditions, but the rate of tension decay was largest in acidosis; the 5-min tensions for C, MA, and RA were 1,835 +/- 63, 1,534 +/- 63, and 1,434 +/- 73 g, respectively. O2 uptake in C was greater than in MA and RA (23.4 +/- 1.3 vs. 17.0 +/- 1.4 and 16.5 +/- 2.3 mumol X min-1), paralleling the tension findings. Hindquarter lactate release was greatest in C, least in MA, and intermediate in RA. Acidosis resulted in less muscle glycogen utilization and lactate accumulation than during control. Muscle creatine phosphate utilization and ATP levels were unaffected by acidosis. Acidosis decreased the muscle's ability to generate isometric tension and depressed both aerobic and anaerobic metabolism. During stimulation in this model lactate left the muscle mainly as a function of the production rate, although a low plasma bicarbonate concentration at pH 7.15 depressed muscle lactate release.

Topics: Acidosis; Acidosis, Respiratory; Adenosine Triphosphate; Animals; Bicarbonates; Carbon Dioxide; Electric Stimulation; Energy Metabolism; Glycogen; Hindlimb; Hydrogen-Ion Concentration; Lactates; Lactic Acid; Male; Muscle Contraction; Muscles; Oxygen Consumption; Perfusion; Phosphocreatine; Physical Exertion; Rats; Time Factors

The recovery of the EEG and somatosensory evoked responses (SER) as compared with recovery of the cerebral energy state was studied in rats during recirculation following different degrees of brain ischemia with varying tissue lactic acidosis. Reversible complete and incomplete ischemia was induced either by increasing the intracranial pressure (compression ischemia) or by carotid artery clamping combined with arterial hypotension. In incomplete ischemia the degree of tissue lactic acidosis was varied by manipulations of blood and brain glucose levels. Animals with an increase in brain lactate to about 25 mumol X g-1 (whole brain wet weight) during ischemia showed persistent failure of both cerebral energy metabolism and neurophysiologic restitution during the recirculation phase; if less than 20 mumol X g-1 metabolic recovery was almost complete. Despite a similar restitution of tissue energy metabolism in these animals, neurophysiologic recovery was inversely proportional to brain lactate concentrations during ischemia. At similar levels of ischemic tissue lactic acidosis, and despite a similar recovery of cortical energy state, the neurophysiologic restitution was clearly inferior after complete ischemia to that following incomplete ischemia. Three conclusions were drawn: (i) neurophysiologic variables were more sensitive indicators of postischemic persistent cerebral dysfunction than the cerebral energy state; (ii) the degree to which lactate accumulated in the ischemic brain influenced neurophysiologic restitution even if concentrations critical for metabolic recovery were not attained; and (iii) incomplete ischemia was less harmful than complete ischemia provided that tissue lactic acidosis was not excessive.

Topics: Acidosis; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Brain Ischemia; Cerebral Cortex; Electroencephalography; Energy Metabolism; Evoked Potentials, Somatosensory; Lactates; Male; Phosphocreatine; Rats; Rats, Inbred Strains

Isolated extensor digitorum longus muscles from rat were exposed to atmospheres of 30% CO2 (high-CO2 muscles) or 6.5% CO2 (control muscles) in O2 for 95 min. Muscle contraction characteristics were studied before and after the incubation. Tetanic tension decreased in high-CO2 muscles to 55% of initial value but remained unchanged in control muscles. Relaxation time was prolonged in high-CO2 muscles but not in control muscles. Intracellular pH was 6.67 +/- 0.04 (SD) in high-CO2 muscles and 7.01 +/- 0.04 in control muscles. CO2-induced acidosis had a marked influence on the intermediary energy metabolism as shown by a fourfold increase of glucose 6-phosphate, a 14% increase of ADP, and a decrease of phosphocreatine to 44% of the control value. Lactate and pyruvate contents were unchanged. The observed metabolic changes can be explained by an effect of H+ on the activity of phosphofructokinase and on the creatine kinase equilibrium. It can be concluded that H+ concentration causes muscular fatigue. It is, however, uncertain whether this is an effect of increased H+ per se or by high-energy phosphate depletion induced by acidosis.

Topics: Acidosis; Adenine Nucleotides; Animals; Body Water; Carbon Dioxide; Electrolytes; Fatigue; Muscle Contraction; Muscles; Phosphocreatine; Rats; Rats, Inbred Strains

A 16-year-old boy with myopathy, ophthalmoplegia, and raised basal metabolic rate was examined by the non-invasive technique of phosphorus-31 nuclear magnetic resonance (31 P NMR). The muscles of the forearm showed an abnormal 31P NMR spectrum with a high inorganic phosphate (Pi) content in relation to phosphocreatine (PCr) (PCr/Pi = 4; control = 10). This finding was compatible with the abnormality of mitochondrial function already established by biopsy and offers in addition an explanation for the raised oxygen consumption in this patient. The method of 31P NMR is suited to rapid non-invasive diagnosis in various muscle disorders.

Topics: Acidosis; Adolescent; Humans; Hydrogen-Ion Concentration; Lactates; Magnetic Resonance Spectroscopy; Male; Mitochondria, Muscle; Muscular Diseases; Oxygen Consumption; Phosphates; Phosphocreatine; Phosphorus Radioisotopes

During vigorous, strong contractions there is a rapid decline in the mechanical output or tension development in skeletal muscle. Several studies have indicated that this rapid decline in force development (often referred to as fatigue), is caused by metabolic changes in the muscles. During brief intense exercise there is a rapid breakdown of phosphocreatine and glycogen and a concomitant increase in the lactate and hydrogen ion concentration. The muscle lactate concentration is increased from about 1-2 mmol kg-1 wet weight at rest before exercise to approximately 25-30 mmol kg-1 wet weight immediately after intensive brief exercise to exhaustion. The muscle pH (i.e. the pH of muscle homogenates) falls from about 7.0 at rest to approximately 6.4 at exhaustion. The changes in the concentrations of ATP, ADP, and AMP are small. It is suggested that the changes in intracellular pH might affect the force generation of skeletal muscle by two different mechanisms: (1) The fall in intracellular pH reduces the activity of key enzymes in glycolysis, thus reducing the rate of ATP resynthesis, and (2) the increased hydrogen ion concentration has a direct effect on the contractile processes, thus reducing the rate of ATP utilization. It is suggested that the increased hydrogen ion concentration might be the common regulator for the maximal rate at which ATP is being utilized and the maximal rate at which it is being resynthesized.

Topics: Acidosis; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Glycogen; Humans; Hydrogen-Ion Concentration; Lactates; Muscle Contraction; Muscle Tonus; Muscles; Phosphocreatine; Physical Exertion; Time Factors

There are conflicting reports regarding the effects of hypoxemia on the cerebral metabolic rate for oxygen (CMRO2). Accordingly, we examined the changes in CMRO2 during normoxia, progressive hypoxia (PaO2 of 37, 27, and 23 mm Hg), and normoxic recovery from hypoxia. Measurements were made in dogs anesthetized with nitrous oxide (60-70%) and halothane (less than 0.1%) in oxygen. Arterial-cerebral venous blood oxygen content differences and cerebral blood flow (CBF) were measured simultaneously, the latter by a technique (collection of sagittal sinus outflow) previously validated for conditions of near-maximal CBF. The duration of each of the three hypoxic exposures was approximately 10 min. CMRO2 was significantly decreased (14%) only when the arterial blood oxygen tension was reduced to 23 mm Hg. CBF increased progressively to a maximum of 153% of control. Posthypoxemic brain biopsy values for cerebral metabolites obtained 40 min after normoxemia had been restored were normal. These results, in conjunction with an unchanged CMRO2 at 40 min normoxic recovery, suggest that no gross irreversible brain cell damage occurred. We conclude that with progressive hypoxemia, CMRO2 remains stable until oxygen demand exceeds oxygen delivery, resulting thereafter in a progressive reduction in CMRO2.

Topics: Acidosis; Adenine Nucleotides; Animals; Brain; Dogs; Electroencephalography; Glucose; Hypoxia; Lactates; Lactic Acid; Oxygen; Phosphocreatine; Pyruvates; Pyruvic Acid

This study explores the influence of severe lactic acidosis in the ischemic rat brain on postischemic recovery of the tissue energy state and neurophysiological parameters. Severe incomplete brain ischemia (cerebral blood flow below 5% of normal) was induced by bilateral carotid artery clamping combined with hypovolemic hypotension. We varied the production of lactate in the tissue by manipulating the blood glucose concentrations. A 30-min period of incomplete ischemia induced in food-deprived animals caused lactate to accumulate to 15-16 mumol g-1 in cortical tissue. Upon recirculation these animals showed: (1) a considerable recovery of the cortical energy state as evaluated from the tissue concentrations of phosphocreatine, ATP, ADP, and AMP; and (2) return of spontaneous electrocortical activity as well as of somatosensory evoked response (SER). In contrast, administration of glucose to food-deprived animals prior to ischemia caused an increase in tissue lactate concentration to about 35 mumol g-1. These animals did not recover energy balance in the tissue and neurophysiological functions did not return. In other experiments the production of lactate during 30 min of complete compression ischemia was increased from about 12 mumol g-1 (normoglycemic animals) to 20-30 mumol g-1 by preischemic hyperglycemia and, in separate animals, combined hypercapnia. The recovery of the cortical energy state upon recirculation was significantly poorer in hyperglycemic animals. It is concluded that a high degree of tissue lactic acidosis during brain ischemia impairs postischemic recovery and that different degrees of tissue lactic acidosis may explain why severe incomplete ischemia, in certain experimental models, is more deleterious than complete brain ischemia.

Topics: Acidosis; Adenosine Triphosphate; Animals; Blood Glucose; Brain; Brain Ischemia; Cerebral Cortex; Electroencephalography; Energy Metabolism; Fasting; Ketone Bodies; Lactates; Male; Phosphocreatine; Rats; Rats, Inbred Strains

The deamination of AMP by AMP aminohydrolase (EC 3.5.4.6.) serves as the major source of ammonia production in skeletal muscle. It has been suggested that the ammonia may serve either in a buffering capacity to combat acidosis due to the accumulation of lactic acid produced during prolonged muscular activity, or as a substrate for glutamine formation which can ultimately be utilized by the kidney in adapting to metabolic acidosis. In view of this proposal, the properties of the enzyme obtained from skeletal muscle of acidotic rats have been compared with the enzyme from normal muscle. The specific activity of AMP deaminase in crude homogenates of acidotic muscle was not significantly different from normal levels. The enzyme from acidotic muscle was purified to homogeneity and was found to be identical to the enzyme obtained from normal muscle by the criteria of electrophoretic mobility, pH optimum, molecular weight, sedimentation coefficient, subunit composition, amino acid composition, monovalent cation requirement, substrate saturation, and inhibition by ATP, Pi and creatine-P. Thus, if the enzyme functions to prevent acidosis, the ability to respond to changes in the intracellular environment which accompany acidosis must be built into the structure of the enzyme normally found in skeletal muscle. Three lines of evidence strongly support this viewpoint: (a) the rate of deamination is approximately 2-fold higher at pH 6.5 than at pH 7.0, (b) the activity increases linearly with a decrease in the adenylate energy charge, and (c) within the normal physiological range of the adenylate energy charge, the enzyme is operating at only 10--20% of its maximum capacity.

Topics: Acidosis; Adenine Nucleotides; Adenosine Triphosphate; AMP Deaminase; Animals; Cations, Monovalent; Hot Temperature; Hydrogen-Ion Concentration; Kinetics; Male; Muscles; Nucleotide Deaminases; Phosphates; Phosphocreatine; Rats

Topics: Acidosis; Adenosine Triphosphate; Animals; Calcium; Coronary Circulation; Heart Rate; Hydrogen-Ion Concentration; Hypoxia; Male; Mitochondria, Heart; Myocardial Contraction; Myocardium; Oxygen; Oxygen Consumption; Phosphocreatine; Rabbits

1. Phosphorus-nuclear-magnetic-resonance measurements were made on perfused rat hearts at 37 degrees C. 2. With the improved sensitivity obtained by using a wide-bore 4.3 T superconducting magnet, spectra could be recorded in 1 min. 3. The concentrations of ATP, phosphocreatine and Pi and, from the position of the Pi resonance, the intracellular pH (pHi) were measured under a variety of conditions. 4. In a normal perfused heart pHi = 7.05 +/- 0.02 (mean +/- S.E.M. for seven hearts). 5. During global ischaemia pHi drops to 6.2 +/- 0.06 (mean +/- S.E.M.) in 13 min in a pseudoexponential decay with a rate constant of 0.25 min-1. 6. The relation between glycogen content and acidosis in ischaemia is studied in glycogen-depleted hearts. 7. Perfusion of hearts with a buffer containing 100 mM-Hepes before ischaemia gives a significant protective effect on the ischaemic myocardium. Intracellular pH and ATP and phosphocreatine concentrations decline more slowly under these conditions and metabolic recovery is observed on reperfusion after 30min of ischaemia at 37 degrees C. 8. The relation between acidosis and the export of protons is discussed and the significance of glycogenolysis in ischaemic acid production is evaluated.

Topics: Acidosis; Adenosine Triphosphate; Animals; Coronary Disease; Glycogen; Hydrogen-Ion Concentration; In Vitro Techniques; Intracellular Fluid; Kinetics; Magnetic Resonance Spectroscopy; Male; Myocardium; Perfusion; Phosphocreatine; Phosphorus; Rats

Topics: Acidosis; Adenosine Triphosphate; Animals; Calcium; Hypoxia; Mitochondria, Heart; Oxygen Consumption; Phosphocreatine; Rabbits

Topics: Acidosis; Adenosine Triphosphate; Animals; Creatine Kinase; Hypoxia; Myocardium; Phosphocreatine; Rabbits

Topics: Acidosis; Adenosine Diphosphate; Adenosine Triphosphate; Animals; Bicarbonates; Blood Flow Velocity; Brain; Carbon Dioxide; Cats; Cerebrovascular Circulation; Dogs; Electric Stimulation; Energy Metabolism; Epilepsy; Flurothyl; Hydrogen-Ion Concentration; Lactates; Mice; NAD; Oxygen; Oxygen Consumption; Pentylenetetrazole; Phosphocreatine; Pyruvates; Rats; Seizures

Topics: Acidosis; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Anemia; Animals; Asphyxia; Brain; Brain Diseases; Carbon Dioxide; Dogs; Energy Metabolism; Glucose; Hemoglobins; Humans; Hypoxia; Ischemia; Ischemic Attack, Transient; Lactates; Oxygen; Oxygen Consumption; Partial Pressure; Phosphocreatine; Rats; Time Factors

Topics: Acidosis; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Blood Glucose; Blood Pressure; Body Temperature; Brain; Creatine; Energy Metabolism; Glucosephosphates; Glycogen; Hydrogen-Ion Concentration; Hyperglycemia; Hypoglycemia; Ischemia; Lactates; Phosphocreatine; Pyruvates; Rats

Topics: Acidosis; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Brain; Brain Chemistry; Carbon Dioxide; Cerebrovascular Circulation; Disease Models, Animal; Glucosephosphates; Hypoxia; Hypoxia, Brain; Ischemic Attack, Transient; Keto Acids; Lactates; Ligation; Malates; Nitrogen; Oxygen; Oxygen Consumption; Partial Pressure; Phosphocreatine; Rats

Topics: Acidosis; Adenosine Triphosphate; Alkalosis; Animals; Bicarbonates; Carbon Dioxide; Creatine Kinase; Female; Guinea Pigs; Heart; Heart Ventricles; Hydrogen-Ion Concentration; Male; Myocardium; Perfusion; Phosphates; Phosphocreatine; Tromethamine

Topics: Acidosis; Adenosine Triphosphatases; Adenosine Triphosphate; Amino Acids; Animals; Blood Glucose; Blood Pressure; Blood Proteins; Blood Transfusion; Blood Volume; Disease Models, Animal; Dogs; Fructose; Glycogen; Hydrogen-Ion Concentration; Hyperbaric Oxygenation; Hypotension; Lactates; Methods; Phosphates; Phosphocreatine; Pulse; Pyruvates; Respiration

Topics: Acidosis; Adenosine Triphosphate; Alkalosis; Animals; Brain; Carbon Monoxide Poisoning; Glycolysis; Hemoglobins; Lactates; Mice; Phosphocreatine; Pyruvates; Sodium; Succinates

Topics: Acidosis; Adenosine Triphosphate; Alanine Transaminase; Alcoholism; Aspartate Aminotransferases; Catalase; Cholinesterases; Coenzymes; Fatty Acids; Fructose-Bisphosphate Aldolase; Hepatitis; Hepatitis A; Humans; Hyperlipidemias; Hyponatremia; Liver Cirrhosis; Liver Diseases; NAD; Pathology; Peroxidases; Phosphocreatine