Intracellular pH determination by a 31P-NMR technique. The second dissociation constant of phosphoric acid in a biological system

A study of nephrotoxin-induced acute tubular necrosis with 31P magnetic resonance spectroscopy

Phosphorus magnetic resonance spectroscopy (31P MRS) was used to obtain in vivo spectra from rat kidneys undergoing acute tubular necrosis induced by a nephrotoxic dose of cephaloridine (CLD). Spectra were obtained 0, 24, and 48 h after injection of CLD (experimental group, n = 6) or saline vehicle (control group, n = 6). The nephrotoxicity of CLD was demonstrated by severely increased serum creatinine levels and the development of extensive proximal tubular necrosis in the CLD-injected rats, and the lack of such changes in the controls. 31P MRS showed an increase in the inorganic phosphate region signal (Pi, p = 0.004) and a decrease in the phosphodiester region signal (PDE, p = 0.01) in the experimental group by 48 h, whereas these parameters did not vary significantly in the control group during the experiment. Significant correlations were found between serum creatinine and the same two 31P MRS parameters. In summary, rat kidneys which have developed severe CLD-induced proximal tubular necrosis exhibit changes in the 31P spectrum 48 h after administration of the drug. The causes of these changes were not determined.

Interleaved 1H and 31P spectroscopic imaging for studying regional brain injury

We present a new approach for in vivo localized spectroscopy which combines 1H and 31P one-dimensional spectroscopic imaging pulse sequences in an interleaved, time-shared manner using a surface coil. This approach was used to acquire metabolic information from a rat brain with regional ischemia at 4.7 Tesla. Spectra with very good signal-to-noise ratios, void of chemical shift artifacts, are obtainable from voxel sizes less than 0.3 cm3 in 40 min. Advantages and drawbacks of the proposed methodology are discussed.

Glycolysis in heart failure: a 31P-NMR and surface fluorometry study

Glycolysis is slow in the heart, especially in the cardiomyopathic heart. Glycolysis is partially rate-limited by phosphofructokinase (PFK), an enzyme which is inhibited by calcium (Ca2+)i and hydrogen ions (H+)i and activated by cAMP. (H+)i and (Ca2+)i are augmented in cardiomyopathy. With glucose as the only substrate (NADH)/(NAD) the phosphorylation potential and developed pressure were significantly lower, and concentrations of phosphomonoester sugars and hydrogen ions (H+)i were significantly higher in isolated cardiomyopathic hearts as compared to healthy hamster hearts. Pyruvate lowered diastolic (Ca2+)i in cardiomyopathic hamster hearts. With pyruvate as the substrate (NADH)/(NAD), the phosphorylation potential and developed pressure increased significantly and concentrations of phosphomonoester sugars (PME), (H+)i and diastolic (Ca2+)i decreased significantly in myopathic hamster hearts. The results suggest that late heart failure in the myopathic hamster is associated with calcium and/or hydrogen ion-induced inhibition of glycolysis.

pH standardization for phosphorus-31 magnetic resonance heart spectroscopy at different temperatures

Intracellular pH typically is measured by NMR using the calibrated chemical shift of the inorganic phosphate peak in phosphorus-31 spectra. Heart spectroscopy experiments often require measurements of intracellular pH at temperatures from 5 to 37 degrees C. This paper provides NMR pH calibrations for this range of temperatures, a summary of calibration data reported to date, and a discussion of the factors influencing pH standardization.

Correlations between in vivo 31P NMR spectroscopy measurements, tumor size, hypoxic fraction and cell survival after radiotherapy

Phosphorus metabolite levels were measured non-invasively using 31P magnetic resonance spectroscopy (MRS) in SCCVII/SF tumors, subcutaneously transplanted into the legs of unanesthetized C3Hf/Sed mice. Shortly after MRS measurements, tumors were irradiated with a single dose of 20 Gy, and cell survival and radiobiologic hypoxic fraction were determined with an in vitro cloning assay. Significant correlations were found between tumor size and surviving fraction, hypoxic fraction, pH, and phosphorus metabolite ratios. With increase of tumor size, surviving fraction and hypoxic fraction both increased, the ratios of inorganic phosphate and phosphomonoesters to nucleoside triphosphates (Pi/NTP and PME/NTP, respectively) and inorganic phosphate to phosphocreatine (Pi/PCr) increased and pH decreased. However, considerable heterogeneity of MRS spectral parameters, even in tumors of similar size, precluded accurate prediction of hypoxic fraction and cell survival after radiotherapy.

Postischemic recovery of mechanical performance and energy metabolism in the presence of left ventricular hypertrophy. A 31P-MRS study

The present study was undertaken to define the effects of left ventricular hypertrophy on postischemic recovery of myocardial performance and high energy phosphate metabolism. Hemodynamics and 31P-magnetic resonance spectra were monitored simultaneously in the isolated Langendorff-perfused rat heart during 30 minutes of ischemia and 30 minutes of reperfusion. Left ventricular hypertrophy was produced by either suprarenal aortic constriction or chronic thyroxine administration. In chronic pressure overload hypertrophy, minimal coronary resistance was significantly higher (p less than 0.001) and the loss of purine nucleosides in the coronary effluent during early reperfusion significantly larger (p less than 0.001) compared with both normal hearts and thyroxine-induced hypertrophied hearts. Postischemic recovery of the baseline values for left ventricular developed pressure and phosphorylation potential was 43 +/- 4% and 82 +/- 4%, respectively, in chronic pressure overload hypertrophied hearts; 86 +/- 4% and 91 +/- 3%, respectively, in normal hearts (chronic pressure overload hypertrophy versus normal hearts, p less than 0.001 and p less than 0.05); and 100 +/- 4% and 98 +/- 2%, respectively, in thyroxine-induced hypertrophied hearts (normal hearts versus thyroxine-induced hypertrophied hearts, p less than 0.05 and p less than 0.05). Recovery after reperfusion was not related to intracellular pH, ATP, phosphocreatine, or inorganic phosphate levels during ischemia. Also, recovery was not related to developed pressure or oxygen consumption before ischemia. However, recovery was inversely related to coronary resistance and directly related to coronary flow before ischemia. Thus, functional and/or anatomic alterations of the coronary vascular bed and a greater loss of purine nucleosides during reperfusion are likely responsible for the attenuated compensatory response to ischemia and reperfusion in left ventricular hypertrophy induced by chronic pressure overload. On the other hand, the excess muscle mass per se does not seem to alter recovery, since thyroxine-induced myocardial hypertrophied hearts responded at least as well as normal hearts.

Cerebral metabolite dynamics during temporary complete ischemia in rats monitored by time-shared 1H and 31P NMR spectroscopy

The changes in cerebral phosphorus metabolites, intracellular pH, and lactate during 30 min of complete global ischemia and 2 h of reperfusion were monitored by time-shared 1H and 31P in vivo NMR spectroscopy in rats. After the induction of ischemia, intracellular pH decreased from 7.14 +/- 0.01 to 6.32 +/- 0.10, and lactate concentration increased from 1.6 +/- 0.4 to 15.8 +/- 2.5 mumol/g; ATP and phosphocreatine were totally depleted, while inorganic phosphate increased 715 +/- 47%. Within 1 h after blood flow was restored, high-energy phosphates and lactate levels had recovered close to baseline levels. The changes in intracellular pH and lactate levels during ischemia and reperfusion correlated well.

The study of energy metabolism in denervated skeletal muscle with 31P-NMR

1. The denervated frog sartorius muscle showed a decrease in the energy store more than that in the control. 2. In the caffeine contractures, both the denervated and the innervated muscles showed similar sequential changes in the relative concentration of phosphocreatine (PCr) to beta-adenosine triphosphate (beta-ATP) and inorganic phosphate (Pi) to beta-ATP. Instead, the intracellular pH value of the denervated muscle was lower than that of the control. 3. It is suggested that phosphate metabolism of the denervated muscle during contracture shows little difference from that of the control, nevertheless, the buffering capacity is decreased in the early stage of atrophy.

An in vivo examination of rat brain during sepsis with 31P-NMR spectroscopy

Neurological symptoms including lethargy, obtundation, and confusion are early and common findings in patients with sepsis. The etiology of the mental status changes that occur during severe infection is not known. We investigated the effects of sepsis on the levels of high-energy phosphates to determine whether decreased energy metabolism was a factor in the depressed neurological state. The time course of changes in brain pH and brain high-energy phosphate metabolites during an Escherichia coli infusion was determined from sequential phosphorus-31 nuclear magnetic resonance (31P-NMR) spectra of ketamine-xylazine-anesthetized rats. A second group of rats received 0.9% saline infusion and served as a control group. Despite severe obtundation and near loss of righting reflex, the rats in the septic group had no significant differences in the brain pH, the ratio of phosphocreatine (PCr) to beta-adenosine 5'-triphosphate (beta-ATP), or in the ratio of PCr to Pi. The only significant decrease in brain high-energy phosphates or pH occurred terminally in the septic rat group and corresponded with a rapidly falling arterial blood pressure. We conclude that the severe neurological depression that is characteristic of sepsis is not due to decreased levels of brain high-energy phosphates or brain acidosis.

Study of acute renal ischemia in the rat using magnetic resonance imaging and spectroscopy

Magnetic resonance (MR) imaging and spectroscopy, chemical lactate measurements, and microscopic examinations were performed to investigate acute renal ischemia in rats. MR images (1H) and spectra (31P and 1H) were acquired on a 2.0-T superconducting small-bore magnet by using implanted coils. Occlusion of the renal artery induced a significant decrease in signal intensity of the renal parenchyma on T2-weighted images, which was most obvious in the outer medulla (-50 +/- 15%, n = 8, P less than 0.001) and was the result of venous congestion, as verified histologically, 31P spectroscopy demonstrated a drop in pH from 7.3 +/- 0.2 to 6.6 +/- 0.2 (n = 18, P less than 0.001), characterized by a time constant (Tc) in the same range as that of the depletion of ATP (2.3 +/- 1.3 min versus 1.9 +/- 1.2 min, n = 10, P = ns). By means of 1H spectroscopy, a lactate peak was detected within 1.5 to 4 min of ischemia, still increasing in intensity after 1 h of ischemia. The Tc of the lactate buildup (15.9 +/- 7.5 min, n = 8) was significantly longer than that of the drop in pH (P less than 0.005). The chemically measured intrarenal concentration of lactate was 1.3 +/- 0.5 mumol/g in control kidneys and 8.7 +/- 3.2 mumol/g (P less than 0.005) in kidneys made ischemic for 1 h. The present study demonstrated important features of acute renal ischemia: (a) acute ischemia induces venous congestion in the medulla; (b) accumulation of lactate is not the main cause of the intracellular acidification observed during ischemia.

Intracellular pH during secretion in the perfused rabbit mandibular salivary gland measured by 31P NMR spectroscopy

Intracellular pH (pHi) was measured in the isolated, perfused rabbit mandibular salivary gland by 31P NMR spectroscopy. In the unstimulated gland perfused with HCO3-/CO2-buffered Ringer's solution, pHi was 7.27 +/- 0.01. Continuous stimulation with acetylcholine elicited dose- and time-dependent changes in pHi. 10(-6) mol/l acetylcholine caused a brief intracellular acidosis (-0.19 +/- 0.06 pH units) followed by an increase in pHi to a more alkaline steady-state value (7.33 +/- 0.02). In the absence of perfusate HCO3- or in the presence of 10(-4) mol/l DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid), the transient acidosis was abolished and pHi increased rapidly to give a sustained alkalosis (7.49 +/- 0.03 and 7.44 +/- 0.03 respectively). In the presence of 10(-3) mol/l amiloride, the response to acetylcholine was a rapid decrease in pHi to 7.02 +/- 0.02. The data suggest that, during perfusion with HCO3-/CO2- buffered solutions, stimulation with acetylcholine results in a transient loss of HCO3- from the acinar cells (causing a transient acidosis), and, independently, the activation of Na+-H+ exchange (causing a sustained alkalosis). In the unstimulated gland, DIDS and the HCO3- -free perfusate caused decreases in pHi to 7.12 +/- 0.02 and 7.04 +/- 0.01 respectively. In contrast, amiloride had little effect. The relatively high value of pHi maintained by the unstimulated gland is therefore probably not due to Na+-H+ exchange.

In vivo [31P]NMR studies on the influence of age on rat brain hypoxia

In this paper the response of cerebral phosphate metabolism to mild hypoxia in young, medium and old rats has been studied via in-vivo [31P]nuclear magnetic resonance (NMR). It was found that the young adults (5-6 months) were more sensitive to this mild stress than either the mature adult (11-12 months) or senescent (23-24 months) rats even though the depth of hypoxia (paO2 = 45-55 mm Hg) was equal for all age groups. They displayed an earlier onset of acidosis, a greater fall in PCr and larger rise in Pi. This response is presumably an attempt to maintain adequate adenosine triphosphate (ATP) levels via anaerobic glycolysis. In contrast, mature adults and senescent adults appear to be able to maintain ATP levels by increasing mitochondrial rates. Acidosis is less severe as are drops in PCr and rises in Pi. Recovery is less complete for the young rats: Pi levels remain high while PCr and pHi levels stay low after normoxia has been reinstigated. All metabolite levels in the mature and senescent adults return to within 10% of control levels. All the data were analyzed and differences were found to be statistically significant. This study reveals that, contrary to popular belief, mature and old rats respond more favorably to reduced O2 than younger individuals. This is due to a more severe anaerobic acidosis in the latter age group. Speculations to explain this disparity are based on the fact that previous in-vitro studies involve systems that are totally or partially disconnected from the organism will not account for important feedback control present in an in-vivo system as studied here.

Acetylcholine-induced metabolic changes in the perfused rabbit mandibular salivary gland studied by 31P-NMR spectroscopy

Changes in the content of high-energy phosphates, intracellular pH (pHi) and the ratio of MgATP to total ATP ([MgATP]/[ATP]t) resulting from continuous stimulation with acetylcholine (10(-9) to 10(-4) M) were measured by 31P-NMR spectroscopy in the isolated, perfused rabbit mandibular gland at 37 degrees C. With 10(-9) to 10(-7) M acetylcholine, no significant changes in these parameters were observed. On stimulation with 10(-6) M acetylcholine, the optimal concentration for sustained secretion, the content of ATP decreased by 28 +/- 10% (mean +/- S.E.; n = 8) of its control value. pHi decreased initially by approx. 0.05 pH unit, then showed an alkalinization of 0.09 +/- 0.02 pH unit (n = 8). With 10(-5) and 10(-4) M acetylcholine, changes in ATP and pHi were similar to those induced by 10(-6) M acetylcholine: the total content of high-energy phosphates remained at approx. 70% of the control value and no decrease in [MgATP]/[ATP]t was observed. As possible causes of the reduced secretory rate observed with higher concentrations of acetylcholine (10(-5) to 10(-3) M), we can exclude depletion of high-energy phosphates, inhibition of metabolism caused by intracellular acidosis, and inhibition of ATP usage caused by a decrease in MgATP availability.

In vivo 31P NMR studies of rat salivary glands at 6.3 tesla

In vivo 31P NMR spectra of rat submandibular glands were obtained. The glands were exposed, leaving the neurovascular system intact, and placed in a solenoidal coil. Resonances of nine phosphate metabolites were identified in the spectra and metabolite concentrations were estimated from the corresponding integrals ([ATP] = 3.4 +/- 0.7 mM). Tissue pH, as deduced from the chemical shift of the inorganic phosphate resonance, was 7.26 (+/- 0.07). T1 relaxation times of ATP, phosphocreatine, inorganic phosphate, and phosphomonoester 31P spin systems were examined. The effect of hypoxia was followed as a function of time. 31P NMR spectra of the glands have also been obtained noninvasively by the use of a surface coil, adapted to the dimensions of the glands, and depth pulses.

Phosphorous compounds studied by 31P nuclear magnetic resonance spectroscopy in the taenia of guinea-pig caecum

1. In the isolated taenia (0.4-0.6 g) of guinea-pig caecum, the intracellular phosphorous compounds and pH were investigated using 31P nuclear magnetic resonance (NMR) under various metabolic conditions. 2. The ratios of the intracellular concentration of phosphocreatine ([ PCr]) and inorganic phosphate [( Pi]) to nucleotide triphosphate ([ NTP]) were 1.71 +/- 0.14 and 0.58 +/- 0.11 (n = 25), respectively, in normal solution (32 degrees C). The intracellular pH estimated from the chemical shift of Pi was 7.05 +/- 0.06 (n = 25), agreeing well with those previously obtained. 3. In the absence of glucose, the [PCr] and [NTP] were decreased to almost a half after 150 min exposure to 40 mM-K+ solution, while [Pi] was increased 3-fold. These changes were much faster than the rate of decline in tension. When glucose was readmitted, the contractile response to K+ fully recovered in 50 min. However, this was accompanied with only a partial recovery of [PCr] and [Pi], but no recovery of [NTP]. The intracellular pH was lowered by about 0.2 of a unit, suggesting an increase in glycolysis. 4. In Ca2+-free solution, respiratory inhibition with hypoxia or CN (1 mM) only decreased [PCr], leaving [NTP] nearly unchanged. On the other hand, respiratory inhibition in excess-K+ solution containing Ca2+ (2.4 mM) severely depleted PCr and decreased [NTP] to 40%. Increasing glucose to 50 mM did not prevent these changes, although it increased tension development. 5. The simultaneous decrease of [NTP] and [PCr] during K+ contracture suggests that the activity of creatine phosphokinase is low. The recovery from respiratory inhibition was much better for [PCr] than for [NTP]. Slow, but perfect, recovery of all NTP peaks was produced by adding 1 mM-adenosine to normal solution. 6. It was suggested that tension development is closely related to the turnover rate of ATP, and not to its concentration, and that deamination of adenosine is a limiting factor in the recovery of ATP after excessive consumption.

Considerations for brain pH assessment by 31P NMR

Recently in vivo NMR spectroscopy has been used to measure brain pH non-invasively. Both the inorganic orthophosphate (Pi) chemical shift (delta) and the difference between the chemical shifts of phosphocreatine (PCr) and Pi(delta delta PCr-Pi) have been proposed as indicators of brain pH. However, the precise delta of Pi may be difficult to determine under normoxic conditions as is the delta of PCr under hypoxic/ischemic conditions. Ideally one needs a NMR delta parameter that: (1) linearly changes between pH 6.0-8.0, (2) is either relatively unaffected or predictably affected by cations (e.g., Mg2+) other than H+, and that (3) comes from readily observable 31P NMR resonances whose delta's can be accurately assessed under all physiological conditions. Therefore, we undertook a systematic 31P NMR study of the pH and Mg2+ titration curves for 16 phosphorus-containing metabolites observed in brain by 31P NMR. On the basis of the titration curves, the delta delta's for PCr-Pi, phosphoethanolamine (PE)-Pi, and PCr-PE fulfill criteria (1) and (2), but not criterion (3). However, the delta delta of ATP gamma-alpha fulfills all three criteria and potentially provides information on the intracellular Mg2+ concentration.

Brain energy metabolism in two kinds of total asphyxia: an in vivo phosphorus nuclear magnetic resonance spectroscopic study

Brain energy metabolism was studied in vivo by means of 31P-NMR spectroscopy in newborn mice during and after 20-minutes exposure to either pure carbon dioxide gas or nitrogen gas. In the N2 group, the brain ATP concentration remained almost normal throughout the experiment, while it showed a 30% reduction in the CO2 group. The brain concentration of phosphocreatine dropped to about 20% of the control value during the asphyxia in both groups, and its recovery was significantly delayed in the CO2 group compared to in the N2 group. Tissue acidosis and Pi accumulation were more remarkable and prolonged in the CO2 group.

Intracellular acidosis during and after cerebral ischemia: in vivo nuclear magnetic resonance study of hyperglycemia in cats

In vivo 31P nuclear magnetic resonance spectroscopy was used to monitor the time course of intracellular pH in cat cerebral cortex subjected to global cerebral ischemia under control and hyperglycemic pretreatment conditions. Transient (16 minutes) global cerebral ischemia was induced in 14 cats using an inflatable cervical cuff combined with systemic arterial hypotension. Six cats were pretreated with infusion of 1.5 g/kg glucose prior to ischemia. Relative concentrations of high-energy phosphate metabolites and intracellular pH were continuously monitored before, during, and for 2 hours after cerebral reperfusion. During ischemia, intracellular pH fell to the same level and followed a similar time course in both groups. However, during initial reperfusion in the hyperglycemic group, there was a severe further decline (p less than 0.003) in intracellular pH. We suggest that the increased neurologic deficit and mortality found in hyperglycemic animals subjected to cerebral ischemia may be attributed to this transient severe tissue acidosis.

1H- and 31P-NMR studies on smooth muscle of bullfrog stomach

31P-NMR spectra of bullfrog stomach smooth muscle showed peaks for creatine phosphate (4.8 mumol X g-1 wet wt.), ATP (3.6), inorganic phosphate (Pi, 2.4), phosphomonoesters (3.0) and phosphodiesters (3.3). The intracellular pH was 7.3, and calculated from the chemical shift of Pi. 1H-NMR spectra of smooth muscle yielded peaks of 2.9 for lactate, 6.6 for total creatine (creatine phosphate + creatine) and methyl protons of choline tentatively assigned to glycerolphosphorylcholine or to membrane phospholipids. Creatine phosphate and ATP decreased under anaerobic conditions, and intracellular acidification was observed with the concomitant increase in lactate. 31P saturation transfer studies showed that saturation of the gamma-ATP resonance reduced the intensity of creatine phosphate to 60% of its control value, and the measured T1 value of creatine phosphate was 2.4 s with saturation. The calculated forward flux of the creatine kinase reaction (decomposition direction of creatine phosphate) was 0.77 mumol X g-1 wet wt. X s-1. The creatine kinase flux was approx. 100-times larger than the ATP turnover rate, calculated from the oxygen consumption rate with the assumption, P/O = 3. In conclusion, the creatine kinase reaction is at equilibrium in resting smooth muscle of bullfrog stomach.

31P magnetic resonance spectroscopy of mesenteric ischemia

31P magnetic resonance spectroscopy (MRS) was performed in vivo on normal and ischemic rat intestine. Within 3 min after induction of ischemia, there is a dramatic fall in adenosine triphosphate (ATP) and rise in inorganic phosphate (Pi). Our results suggest that MRS may prove useful in the early detection of mesenteric ischemia.

An in vivo 31P NMR study of cerebral hypoxic hypoxia in rats

Twenty minutes of hypoxic hypoxia in five anesthetized rats reversibly reduced cerebral PCr and pH while ATP stayed constant. Complete metabolic and neurologic recovery occurred after oxygen was restored. Careful control of physiological parameters resulted in metabolite changes that were the same, within errors, in each animal.

Application of high-field 1H-NMR spectroscopy for the study of perifused amphibian and excised mammalian muscles

Frog sartorius and gastrocnemius muscles were perifused at 20 degrees C, the intracellular pH (pHi) and the concentration of phosphocreatine were determined in the resting muscle by 1H-NMR spectroscopy at 470 MHz; values of pHi = 7.31 +/- 0.05 (n = 7) and concentration of phosphocreatine = 20.4 +/- 1.1 mumol/g wet wt. (n = 6) were found. The hydrolysis of phosphocreatine and the simultaneous increase in lactate upon perifusion with 10 mM caffeine (in Ringer's solution) was followed with a time resolution of 1 min. Lactate increased at a rate of 1.0 mumol/g per min, but no pHi change was recorded during the time monitored. The lower limit for the buffering capacity of the muscle cytosol was estimated to be 16.7 mumol/g muscle per pH unit from the uncertainty in pHi determination (+/- 0.03 pH units) and from the amount of lactate produced and phosphocreatine hydrolyzed. Changes in pHi, lactate concentration and fatty acyl chain intensity were monitored by 1H-NMR spectroscopy at 361 MHz in ischemic rat skeletal muscle, excised and stored at 20 degrees C. The resonances in the 1H-NMR spectrum of a human skeletal muscle perchloric acid extract are reported and tentatively assigned.

Comparison of in vivo 31P-MR spectra of the brain, liver, and kidney of adult and infant animals

In vivo 31P-magnetic resonance spectroscopy (MRS) was used to determine the phosphorus metabolite levels in the brain and kidney of infant rabbits and adult rats and in the liver of infant rabbits and adult and infant rats. For 31P-MRS of the brain, a surface, radiofrequency coil was placed on the anterosuperior region of the head; for 31P-MRS of the liver and kidney, a radiofrequency coil was chronically implanted either between the hepatic lobes or around the kidney. 31P-MR spectra were found to show large variations in the levels of the phosphorus metabolites depending on the species, the organ, and the age of the animal. The phosphate monoester (MP)/adenosine triphosphate (ATP) ratio was significantly higher and the phosphocreatine (PCr)/ATP ratio was significantly lower in the brains of infant rabbits than in the brains of adult rats. Comparison of these data with data reported for humans and other animals suggests that these differences are due mainly to differences in age and not to differences among species. The phosphodiester (PD)/ATP ratio was found to be significantly higher in the livers of infant rabbits than in the livers of adult and infant rats - a difference more likely related to the species than to age. The kidneys of the infant rabbits showed a higher PCr/ATP radio than the kidneys of the adult rats, but this difference might be due to the influence of PCr in the surrounding muscle.

Cerebral intracellular changes during supercarbia: an in vivo 31P nuclear magnetic resonance study in rats

31P nuclear magnetic resonance (NMR) spectroscopy was used noninvasively to measure in vivo changes in intracellular pH and intracellular phosphate metabolites in the brains of rats during supercarbia (PaCO2 greater than or equal to 400 mm Hg). Five intubated rats were mechanically ventilated with inspired gas mixtures containing 70% CO2 and 30% O2. Supercarbia in the rat was observed to cause a greater reduction in cerebral intracellular pH (pHi) and increase in PCO2 than observed in other experiments with rats after 15 min of global ischemia. Complete neurologic and metabolic recovery was observed in these animals, despite and average decrease in pHi of 0.63 +/- 0.02 pH unit during supercarbia episodes that raised PaCO2 to 490 +/- 80 mm Hg. No change was observed in cerebral intracellular ATP and only a 25% decrease was detected in phosphocreatine. The concentration of free cerebral intracellular ADP, which can be calculated if one assumes that the creatine kinase reaction is in equilibrium, decreased to approximately one-third of its control value. The calculated threefold decrease in the concentration of free ADP and twofold increase in the cytosolic phosphorylation potential suggest that there is increased intracellular oxygenation during supercarbia. Because a more than fourfold increase in intracellular hydrogen ion concentration was tolerated without apparent clinical injury, we conclude that so long as adequate tissue oxygenation and perfusion are maintained, a severe decrease in intracellular pH need not induce or indicate brain injury.

Intracellular pH in Dictyostelium discoideum: a 31P nuclear magnetic resonance study

We have used phosphorus-31 nuclear magnetic resonance to determine intracellular pH in the cellular slime mold Dictyostelium discoideum. We devised an air-lift circulator to maintain the dense cell suspensions in a well-oxygenated and well-stirred state while causing minimal perturbation to the sample flowing through the detector coils. Cells continued to develop normally in this set-up. Spectra acquired under these conditions typically show two peaks in the inorganic phosphate region corresponding to pH values of 7.16 +/- 0.03 and 6.48 +/- 0.02. These peaks are believed to represent the mitochondrial and cytosolic compartments respectively, based on a comparison of these values with published data and the collapse of the two compartments upon addition of the mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)-phenylhydrazone. Dictyostelium cells show a remarkable degree of intracellular pH homeostasis. Both mitochondrial and cytosolic pH remained unchanged as extracellular pH was varied from 4.3 to 8.1. There was also no apparent change in the pH of either compartment after up to 13.5 hours' development in suspension.

In vivo studies of energy metabolism in experimental cerebral ischemia using topical magnetic resonance. Changes in 31P-nuclear magnetic resonance spectra compared with electroencephalograms and regional cerebral blood flow

The energy state of the brain during and after transient cerebral ischemia was examined in rats by in vivo measurement of 31P-nuclear magnetic resonance (NMR) spectra using a topical magnetic resonance spectrometer. EEGs and regional CBF (rCBF) were monitored on the same ischemic models. Immediately after the induction of ischemia, the height of the ATP and phosphocreatine peaks in the spectrum began to decrease with a concurrent increase of the inorganic phosphate (Pi) peak. The calculated pH from the chemical shift of Pi decreased during ischemia. The EEG pattern became flat immediately after ischemic induction. The rCBF decreased below the sensitivity level of the measuring instrument. With 30-min ischemia, the 31P-NMR spectrum returned to a normal pattern rapidly after recirculation. However, recovery of the EEG was delayed. The rCBF after recirculation showed postischemic hyperemia followed by hypoperfusion. In cases of 120-min ischemia, none of the spectra showed recovery. Thus, we could investigate the dynamic process of pathophysiological changes occurring in the ischemic brain in vivo.

Observations of energy metabolism in neuroectodermal tumors using in vivo 31P-NMR

The energy metabolism of living tumors in rats and hamsters were investigated by obtaining in vivo 31P-NMR spectra, and the effects of chemotherapy on tumors were evaluated by observing the changes of these spectra. Tumor cells of rat glioma, human glioblastoma and human neuroblastoma were inoculated subcutaneously in the lumbar region of the animals. After the tumor grew to over 1.5 cm in diameter, in vivo 31P-NMR spectrum data was obtained selectively from the tumor with a TMR-32 spectrometer (Oxford Research Systems, U.K.). Several peaks (ATP, inorganic phosphate (Pi), phosphodiesters and phosphomonoesters (PME) were observed in the tumors. The heights of these peaks varied widely corresponding to the tumor growth. However, the spectrum pattern of each tumor in an active stage was found to be essentially the same regardless of histological type or tumor origin. The phosphocreatine (PCr) peak was small, ATP and PME peaks were large and tissue pH calculated from the chemical shift of Pi was low in each tumor group. After intravenous injection of a large dose of a chemotherapeutic agent, ATP peaks decreased and the Pi peak increased gradually, resulting in a dominant Pi peak pattern after several hours in all groups. With lower drug doses, spectrum changes were temporarily seen in the tumors. These findings indicated that drugs with a high dose have a selective and a direct action on the energy metabolism of tumor tissues. In vivo 31P-NMR spectra measurement is very valuable not only to investigate the energy metabolism in tumor tissue but also to evaluate the effects of chemotherapy on the tumor.

In vivo measurement of energy metabolism and the concomitant monitoring of electroencephalogram in experimental cerebral ischemia

The energy metabolites in rat brain in vivo were measured by using topical magnetic resonance (TMR) during the whole course of ischemia, in combination with the concomitant monitoring of electroencephalogram (EEG). Immediate loss of high energy phosphorus compounds, phosphocreatine (PCr) and ATP, resulted in the flattening of EEG after the induction of ischemia. PCr and ATP returned to almost normal level 30 min after recirculation of the ischemic brain, but EEG showed no recovery and the abnormality lasted for 12 h. The measurement of in vivo 31P-NMR is essential for the decision of the convalescence of cellular function in the brain.