phosphocreatine and Acidosis--Lactic

During heavy-intensity exercise, the mechanisms responsible for the continued slow decline in phosphocreatine concentration ([PCr]) (PCr slow component) have not been established. In this study, we tested the hypothesis that a reduced intracellular acidosis would result in a greater oxidative flux and, consequently, a reduced magnitude of the PCr slow component. Subjects (n = 10) performed isotonic wrist flexion in a control trial and in an induced alkalosis (Alk) trial (0.3g/kg oral dose of NaHCO3, 90 min before testing). Wrist flexion, at a contraction rate of 0.5 Hz, was performed for 9 min at moderate- (75% of onset of acidosis; intracellular pH threshold) and heavy-intensity (125% intracellular pH threshold) exercise. 31P-magnetic resonance spectroscopy was used to measure intracellular [H+], [PCr], [Pi], and [ATP]. The initial recovery data were used to estimate the rate of ATP synthesis and oxidative flux at the end of heavy-intensity exercise. In repeated trials, venous blood sampling was used to measure plasma [H+], [HCO3-], and [Lac-]. Throughout rest and exercise, plasma [H+] was lower (P < 0.05) and [HCO3-] was elevated (P < 0.05) in Alk compared with control. During the final 3 min of heavy-intensity exercise, Alk caused a lower (P < 0.05) intracellular [H+] [246 (SD 117) vs. 291 nmol/l (SD 129)], a greater (P < 0.05) [PCr] [12.7 (SD 7.0) vs. 9.9 mmol/l (SD 6.0)], and a reduced accumulation of [ADP] [0.065 (SD 0.031) vs. 0.098 mmol/l (SD 0.059)]. Oxidative flux was similar (P > 0.05) in the conditions at the end of heavy-intensity exercise. In conclusion, our results are consistent with a reduced intracellular acidosis, causing a decrease in the magnitude of the PCr slow component. The decreased PCr slow component in Alk did not appear to be due to an elevated oxidative flux.

Topics: Acid-Base Equilibrium; Acidosis, Lactic; Adenosine Diphosphate; Adenosine Triphosphate; Adult; Alkalosis; Exercise; Forearm; Humans; Lactic Acid; Male; Muscle, Skeletal; Oxidative Phosphorylation; Phosphocreatine; Protons; Sodium Bicarbonate

To determine whether epinephrine increases lactate concentration in sepsis through hypoxia or through a particular thermogenic or metabolic pathway.. Prospective, controlled experimental study in rats.. Experimental laboratory in a university teaching hospital.. Three groups of anesthetized, mechanically ventilated male Wistar rats received an intravenous infusion of 15 mg/kg Escherichia coli O127:B8 endotoxin. Rats were treated after 90 min by epinephrine ( n=14), norepinephrine ( n=14), or hydroxyethyl starch ( n=14). Three groups of six rats served as time-matched control groups and received saline, epinephrine, or norepinephrine from 90 to 180 degrees min. Mean arterial pressure, aortic, renal, mesenteric and femoral blood flow, arterial blood gases, lactate, pyruvate, and nitrate were measured at baseline and 90 and 180 min after endotoxin challenge. At the end of experiments biopsy samples were taken from the liver, heart, muscle, kidney, and small intestine for tissue adenine nucleotide and lactate/pyruvate measurements.. Endotoxin induced a decrease in mean arterial pressure and in aortic, mesenteric, and renal blood flow. Plasmatic and tissue lactate increased with a high lactate/pyruvate (L/P) ratio. ATP decreased in liver, kidney, and heart. The ATP/ADP ratio did not change, and phosphocreatinine decreased in all organs. Epinephrine and norepinephrine increased mean arterial pressure to baseline values. Epinephrine increased aortic blood flow while renal blood low decreased with both drugs. Plasmatic lactate increased with a stable L/P ratio with epinephrine and did not change with norepinephrine compared to endotoxin values. Nevertheless epinephrine and norepinephrine when compared to endotoxin values did not change tissue L/P ratios or ATP concentration in muscle, heart, gut, or liver. In kidney both drugs decreased ATP concentration.. Our data demonstrate in a rat model of endotoxemia that epinephrine-induced hyperlactatemia is not related to cellular hypoxia.

Topics: Acidosis, Lactic; Adenosine Diphosphate; Adenosine Triphosphate; Animals; Blood Gas Analysis; Disease Models, Animal; Drug Evaluation, Preclinical; Endotoxemia; Energy Metabolism; Epinephrine; Escherichia coli Infections; Glycolysis; Hemodynamics; Humans; Kidney; Lactic Acid; Liver; Myocardium; Nitrates; Norepinephrine; Phosphocreatine; Pyruvates; Rats; Rats, Wistar; Tissue Distribution

We compared responses of turtle heart at 20 degrees C to an anoxic lactic acidosis solution (LA) containing 35 mM lactic acid in an otherwise normal turtle Ringers equilibrated with 3% CO2/97% N2 at pH 7.0) to a solution simulating in vivo anoxic acidosis (VA), with elevated concentrations of lactate, Ca2+, Mg2+, and K+, and decreased Cl-, equilibrated with 10.8% CO2/89.2% N2 at pH 7.0. We examined mechanical properties on cardiac muscle strips and determined intracellular pH (pHi) and high energy phosphates on perfused hearts using 31P-NMR. Maximum active force (Fmax) and the maximum rate of force development (dF/dtmax) of muscle strips were significantly higher during VA than during LA superfusion. An elevation of Ca2+ alone (to 6 mM) in LA significantly increased both Fmax and dF/dtmax but the effects diminished toward the end of the exposure; however, hypercapnic anoxic lactic acidosis (addition of 20 mM HCO3- to LA, equilibrated with 10.8% CO2/89.2% N2, pH 7.0) did not significantly affect Fmax or dF/dtmax. During VA perfusion, pHi (6.73 +/- 0.01) was significantly higher than that during LA perfusion (pHi 6.69 +/- 0.013), but the difference is probably too small to have physiological significance. ATP, creatine phosphate, and inorganic phosphate were not significantly different in the two anoxic solutions. We conclude that the reduction of cardiac mechanical function in vivo is minimized by the integrated effects of changes of ionic concentrations, but the observed changes in Ca2+ and pHi cannot fully explain the effect.

Topics: Acidosis, Lactic; Adenosine Triphosphate; Animals; Calcium; Female; Heart; Hydrogen-Ion Concentration; Hypoxia; In Vitro Techniques; Magnetic Resonance Spectroscopy; Male; Myocardial Contraction; Myocardium; Perfusion; Phosphates; Phosphocreatine; Turtles

Newborn and 1-mo-old swine were exposed to identical durations (18 min) and degrees of hypoxia (O2 content = 4 mL/dL), to examine the effects of hypoxia on cerebral energy metabolism and intracellular pH (pHi) in vivo, using 31P and 1H nuclear magnetic resonance spectroscopy. Hypoxia produced the same extent of reductions in phosphocreatine (PCr) (63 +/- 28% and 65 +/- 10%, newborns and 1-mo-olds, respectively) and pHi (6.93 +/- 0.06 and 6.89 +/- 0.06, respectively) for either age group. The magnitude of changes in PCr, lactate, and pHi was larger for subgroups of data collected when cardiovascular instability was present, suggesting that hypotension and possibly reduced cerebral perfusion contributed to cerebral energy failure and lactic-acidosis for either age group. There were no correlations between the blood plasma glucose concentration at 18 min of hypoxia and the extent of change in PCr, lactate, or pHi for either age group. During a subsequent period of complete ischemia induced via cardiac arrest after 20 min hypoxia, the decline in PCr and nucleoside triphosphate (NTP), and increase in lactate followed similar rates compared with previously studied age-matched animals that were normoxic before ischemia. The rate constants for the change in PCr, NTP, and lactate followed similar rates compared with previously studied age-matched animals that were normoxic before ischemia. The rate constants for the change in PCr, NTP, and lactate during ischemia showed no correlation with the blood plasma glucose concentration measured immediately before cardiac arrest. These results suggest that cerebral glycolytic rates and energy utilization during ischemia are unaffected by a preceding interval of hypoxia and that hyperglycemia does not delay cerebral energy failure during hypoxia or combined hypoxic-ischemia.

Topics: Acidosis, Lactic; Animals; Animals, Newborn; Energy Metabolism; Glucose; Glycolysis; Hydrogen-Ion Concentration; Hypoxia; Ischemia; Phosphocreatine; Swine

In a patient with a mitochondrial myopathy, presenting with lactic acidosis, 31P-nuclear magnetic resonance spectroscopy in resting muscle showed half the creatine phosphate level of controls. The creatine phosphate resynthesis rate after aerobic exercise was only 18% of that in controls. However, the activities of complexes I to V catalyzing oxidative phosphorylation and the pyruvate and the 2-oxoglutarate dehydrogenase complexes showed a 2- to 20-fold increase. In line with this, the uncoupled mitochondrial respiration rate was significantly higher than in controls. In contrast, the respiration of the mitochondria from the patient was less stimulated by ADP than that of control mitochondria. This finding could point to a defect in complex V, the enzyme directly involved in ATP synthesis. The activity of complex V, measured as the mitochondrial ATPase activity, and its concentration, as judged from Western blots using antisera against the F1 part of complex V, were, however, also greatly increased in the patient. Alternatively, the transport system, importing ADP into and exporting ATP out of the mitochondrial matrix, the ADP/ATP or adenine nucleotide translocator, could be affected. Immunostaining of Western blots revealed a 4-fold decrease in the concentration of the adenine nucleotide translocator in the patient. Because oxidative phosphorylation was not disturbed in fibroblasts and lymphocytes, we conclude that this patient suffers from a muscle-specific deficiency of his mitochondrial adenine nucleotide translocator, a defect unknown so far.

Topics: Acidosis, Lactic; Adenosine Diphosphate; Adenosine Triphosphate; Child, Preschool; Energy Metabolism; Humans; Male; Mitochondria, Muscle; Mitochondrial ADP, ATP Translocases; Mitochondrial Myopathies; Oxidative Phosphorylation; Phosphocreatine

[31P]- and [1H]nuclear magnetic resonances recorded in an interleaved fashion were used in order to quantify high-energy phosphates, intracellular pH and lactate in cortical brain slices of the guinea-pig superfused in a CO2/HCO3(-)-buffered medium during and after anoxic insults. The volume-averaged intracellular pH and energy status of the preparation following anoxia were determined. In the presence of external Na+, intracellular pH normalized in 3 min and was significantly more alkaline from 10 to 12 min of recovery, but lactate remained elevated for 12 min of reoxygenation following anoxia. The amount of lactate removed was only 40% of the quantity of acid extruded showing operation of H+ neutralizing transmembrane mechanisms other than transport of lactic acid. Amiloride (1 or 2 mM) did not prevent the recovery of intracellular pH, but it blocked the "overshoot" of the alkalinization at 10-12 min of recovery. In a medium containing 70 mM K+, 60 mM Na+ and 0.1 mM Ca2+, the recovery of pH, but not lactate washout, was significantly delayed. Removal of external Na+ caused severe energetic failure, decreases both in oxygen uptake and in N-acetyl aspartate concentration, indicating loss of viable tissue. In Na(+)-free superfusion, lactic acidosis caused a more severe drop in intracellular pH than in the presence of Na+. Complexing of extracellular Ca2+ in the Na(+)-free medium inhibited the acidification by 0.38 pH units during anoxia which is as much as the acidification caused by lactate accumulation in the absence of Na+. In Na(+)-free medium intracellular pH recovered, however, from an anoxic level to a normoxic value in 6 min. Metabolic damage of the slice preparation induced by anoxia in the absence of Na+ was as profound in the presence as in the absence of Ca2+ showing that accumulation of Ca2+ is not the only reason for the damage. It is concluded that recovery of intracellular pH from lactic-acidosis can occur independently of energetic recovery and involves acid extrusion mechanism(s) that is(are) dependent on external Na+ and sensitive to high K+.

Topics: Acidosis, Lactic; Animals; Carrier Proteins; Cerebral Cortex; Extracellular Space; Guinea Pigs; Hydrogen-Ion Concentration; Hypoxia; In Vitro Techniques; Lactates; Magnetic Resonance Spectroscopy; Male; Oxygen Consumption; Phosphocreatine; Potassium; Sodium; Sodium-Hydrogen Exchangers

A quantitative analysis of taurine effect (facilitation of acid handling capacity of brain in response to anoxia/hypoxia by high levels of cytosolic taurine) was performed utilizing multinuclear (1H, 31P) in vivo nuclear magnetic resonance (NMR) spectroscopy and in vitro titration analysis. Taurine effects observed in vivo showed excellent quantitative agreement with the predicted values estimated based on brain taurine levels. The study confirmed that high levels of cytosolic taurine indeed facilitate acid buffering capacity of brain and this taurine effect can be readily explained by the physical, and need not involve metabolic, properties of taurine. Taurine appears to be a key component of the brain cytosol system in the fetus.

Topics: Acidosis, Lactic; Animals; Blood Glucose; Brain Chemistry; Chromatography, High Pressure Liquid; Female; Hydrogen-Ion Concentration; Lactates; Magnetic Resonance Spectroscopy; Phosphocreatine; Pregnancy; Rats; Rats, Sprague-Dawley; Taurine

To differentiate the effects of high energy phosphates, pH, and [H2PO4-] on skeletal muscle fatigue, intracellular acidosis during handgrip exercise was attenuated by prolonged submaximal exercise. Healthy human subjects (n = 6) performed 5-min bouts of maximal rhythmic handgrip (RHG) before (CONTROL) and after prolonged (60-min) handgrip exercise (ATTEN-EX) designed to attenuate lactic acidosis in active muscle by partially depleting muscle glycogen. Concentrations of free intracellular phosphocreatine ([PCr]), adenosine triphosphate ([ATP]), and orthophosphate ([P(i)]) and pH were measured by 31P nuclear magnetic resonance spectroscopy and used to calculate adenosine diphosphate [ADP], [H2PO4-], and [HPO4(2-)]. Handgrip force output was measured with a dynamometer, and fatigue was determined by loss of maximal contractile force. After ATTEN-EX, the normal exercise-induced muscle acidosis was reduced. At peak CONTROL RHG, pH fell to 6.3 +/- 0.1 (SE) and muscle fatigue was correlated with [PCr] (r = 0.83), [P(i)] (r = 0.82), and [H2PO4-] (r = 0.81); [ADP] was 22.0 +/- 5.7 mumol/kg. At peak RHG after ATTEN-EX, pH was 6.9 +/- 0.1 and [ADP] was 116.1 +/- 18.2 mumol/kg, although [PCr] and [P(i)] were not different from CONTROL RHG (P greater than 0.05). After ATTEN-EX, fatigue correlated most closely with [ADP] (r = 0.84). The data indicate that skeletal muscle fatigue 1) is multifactorial, 2) can occur without decreased pH or increased [H2PO4-], and 3) is correlated with [ADP] after exercise-induced glycogen depletion.

Topics: Acidosis, Lactic; Adenosine Diphosphate; Adenosine Triphosphate; Adult; Exercise; Female; Glycogen; Humans; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Male; Muscles; Phosphocreatine

Five siblings with autosomal dominant oculopharyngeal muscular dystrophy (OPMD) underwent P-31 Nuclear Magnetic Resonance Spectroscopy studies of forearm flexor muscles. Mean values of PCr/(PCr+Pi) in the patients were reduced (p = 0.01) and pH elevated (p = 0.02) in resting muscle when compared to controls. During exercise PCr/PCr+Pi) fell quickly to values less than controls (p less than 0.0001) despite submaximal exercise output and developed exercise-induced acidosis which exceeded that of controls (p = 0.05). Acidosis recovered slowly despite relatively normal recovery of PCr/(PCr+Pi) following exercise. Within the patient group, however, one member had normal resting, exercise and recovery values. The studies suggest that OPMD is a more widespread disorder of striated muscle than clinically appreciated. The pattern of findings observed in OPMD differs from those identified in denervation, disuse and mitochondrial myopathy.

Topics: Acidosis, Lactic; Aged; Exercise Test; Female; Forearm; Humans; Magnetic Resonance Spectroscopy; Male; Middle Aged; Muscular Dystrophies; Oculomotor Muscles; Pharyngeal Muscles; Phosphocreatine

We studied the effects of graded acidosis (both CO2 and lactic acid) and anoxia on intracellular pH (pHi) regulation, high-energy phosphates, and mechanical function of isolated perfused hearts of the turtle (Chrysemys picta bellii) at 20 degrees C using 31P-nuclear magnetic resonance (NMR) spectroscopy. During CO2 acidosis, anoxia had no effect on apparent nonbicarbonate buffer value (d[HCO3-]/dpHi = 71 and 89 mM/pH in normoxia and anoxia, respectively) or on pHi regulation (dpHi/dpHe = 0.52 and 0.43 in normoxia and anoxia, respectively, where pHe is extracellular pH). During normoxic lactic acidosis, dpHi/dpHe was similar to the values observed in CO2 acidosis and averaged 0.55 overall. During anoxic lactic acidosis, however, similar regulation occurred over only a narrow range of pHe, and then dpHi/dpHe increased to greater than 1.0 at pHe less than 7.1. Creatine phosphate (CP), calculated as the area of the NMR peak, fell more in response to normoxic CO2 acidosis than to normoxic lactic acidosis; in anoxia, the fall in CP was further increased but to similar extreme levels (10-20% of control) in both acid perfusions. Cardiac output and maximum rate of pressure development each fell during acidosis in similar fashion in all protocols, and the responses were similar in normoxic and anoxic hearts. Heart rate, in contrast, decreased during acidosis, but this effect was more pronounced when hearts were anoxic. We conclude that the effect of acidosis on cardiac function can depend on the type of acidosis imposed. Based on the heart's insensitivity to anoxia alone, we suggest that anoxia may normally depress function indirectly via its effect on intracellular acid-base state.

Topics: Acidosis, Lactic; Adenosine Triphosphate; Animals; Carbon Dioxide; Female; Heart; Heart Rate; Hydrogen-Ion Concentration; Hypercapnia; Hypoxia; Lactates; Lactic Acid; Magnetic Resonance Spectroscopy; Male; Myocardium; Oxygen; Phosphocreatine; Phosphorus; Turtles

A 34-year-old man affected by exercise intolerance, mild proximal weakness and severe lactic acidosis is described. Muscle biopsy revealed mitochondrial abnormalities and an increase of cytochrome c oxidase histochemical reaction. Biochemical investigations on isolated muscle mitochondria as well as polarographic studies revealed a mitochondrial NADH-CoQ reductase (complex I) deficiency. Mitochondrial dysfunction was confirmed by 31P nuclear magnetic resonance spectroscopy. Immunological investigation showed a generalized reduction of all complex I polypeptides. Genetic analysis did not reveal mitochondrial DNA deletions. The biochemical defect was not present in the patient's muscle tissue culture. Metabolic measurements and functional evaluation showed a reduced mechanical efficiency during exercise.

Topics: Acidosis, Lactic; Adenosine Triphosphate; Adult; Cells, Cultured; DNA, Mitochondrial; Enzyme-Linked Immunosorbent Assay; Exercise; Humans; Magnetic Resonance Spectroscopy; Male; Mitochondria, Muscle; Muscles; Muscular Diseases; NAD(P)H Dehydrogenase (Quinone); Oxygen Consumption; Phosphocreatine; Quinone Reductases

Topics: Acidosis, Lactic; Adenosine Triphosphate; Animals; Chemical Phenomena; Chemistry; Humans; Hydrogen-Ion Concentration; Hydrolysis; Lactates; Oxygen; Phosphocreatine; Protons

The main parameters of muscle acid-base, water and energy metabolism were studied in ten patients undergoing low-flux (1.5 l/min/m2), low-pressure (40 to 60 mmHg) hypothermic (26 degrees C) cardiopulmonary bypass (CPB) for aortocoronary grafting; absolute gas exchange and haemodynamic data were also measured throughout the entire CPB period. At the end of CPB a substantial preservation of water and energy metabolic indexes was found; a condition of extracellular metabolic acidosis was apparently sustained by muscle cell anaerobic glycolysis enhancement with a consequent increase of both muscle and plasma lactate content. Subnormal cell phosphocreatine levels as well as reduced bicarbonate buffer stores and decreased intracellular pH, were detected. Direct limiting effects of hypothermia on tissue O2 delivery and muscle oxidative metabolism as well as vasoconstriction and arteriovenous shunting associated with CPB procedures are likely to be involved in the above mentioned alterations of cell metabolism.

Topics: Acid-Base Equilibrium; Acidosis, Lactic; Adenosine Triphosphate; Cardiopulmonary Bypass; Coronary Artery Bypass; Female; Humans; Male; Middle Aged; Muscles; Oxygen Consumption; Phosphocreatine; Water-Electrolyte Balance

Progressive cerebral ischemia was induced in seven anesthetized hyperglycemic rats by carotid artery ligation and hemorrhagic hypotension. Phosphorus metabolites, intracellular pH, and lactate in the brain were monitored by 31P and 1H magnetic resonance spectroscopy. Under conditions in which blood flow was low, phosphocreatine (PCr) concentration and intracellular pH decreased and the concentration of lactate increased. The decrease in ATP was approximately one-third that of PCr until only 25% PCr remained, after which ATP was lost more rapidly than PCr. These changes were interpreted in terms of three regions observed by the magnetic resonance coil, one of complete ischemia, one of partial ischemia, and one of perfusion sufficient to maintain normal metabolite levels. The extent of the three regions was estimated quantitatively. Broadening and splitting of the inorganic phosphorus (Pi) peak into two components provided further evidence of distinct populations of cells, one very acidic and another less so. Apparent intracellular buffering capacity was calculated as 23.6 +/- 1.3 mumol lactate/g wet wt/pH.

Topics: Acidosis, Lactic; Adenosine Triphosphate; Animals; Brain Ischemia; Hydrogen; Hydrogen-Ion Concentration; Hyperglycemia; Lactates; Magnetic Resonance Spectroscopy; Phosphocreatine; Phosphorus; Rats; Rats, Inbred Strains