Cerebral Acid Buffering Capacity at Different Ages Measured In Vivo by ³¹P and ¹H Nuclear Magnetic Resonance Spectroscopy

Abstract

Cerebral acidosis occurring during ischemia has been proposed as one determinant of tissue damage. Newborn animals appear to be less susceptible to ischemic tissue damage than adults. One possible component of ischemic tolerance could derive from maturational differences in the extent of acid production and buffering in newborns compared to adults. The purpose of this study was to measure the dependency of acid production on the blood plasma glucose concentrations and acid buffering capacity of piglets at different stages of development. Complete ischemia was induced in 29 piglets ranging in postconceptual age from 111 to 156 days (normal term conception, 115 days). Brain buffering capacity during the first 30 min of ischemia was quantified in vivo, via 31P and 1H nuclear magnetic resonance (NMR) spectroscopy, by measuring the change in intracellular brain pH for a given change in the concentration of compounds that contribute to the production of hydrogen ions. Animals from all four age groups showed a similar linear correlation between preischemia blood glucose concentration and intracellular pH after 30 min of ischemia. For each animal the slope of the plot of intracellular pH versus cerebral buffer base deficit was used to calculate the buffer capacity. Using data obtained over the entire 30 min of ischemia, there was no difference in the mean buffer capacity of the different age groups, nor was there a significant correlation between buffer capacity and age. However, there was a significant increase in buffer capacity for the intracellular pH range 6.6-6.0, compared to 7.0-6.6, for all age groups. No significant differences in buffer capacity for these two pH ranges were observed between any of the age groups. Acid buffering capacity was also measured by performing pH titrations on brain tissue homogenized in the presence of inhibitors of glycolysis and creatine kinase. Plots of homogenate pH versus buffer base deficit showed a nonlinear trend similar to that seen in vivo, indicating an increase in buffer capacity as intracellular pH decreases. A comparison of newborn and 1-month-old brain tissue frozen under control conditions or after 45 min of ischemia revealed no differences that could be attributed to age and a slight decrease in buffer capacity of ischemic brain compared to control brain tissue homogenates. There was no difference between the brain buffering capacity measured in vivo using 31P and 1H NMR and that measured in vitro using brain homogenates.

Non-Invasive Methods for Studying Brain Energy Metabolism: What They Show and What It Means

“…First, the initial PCr + ATP depletion rate gives an estimate of pre-ischaemic ATP turnover [17] similar to those obtained from PET. Second, the cellular proton-buffering capacity can be estimated as the slope against intracellular pH of a calculated cerebral 'base deficit': this increases with decreasing pH (as in skeletal muscle [19]) and agrees with results of titration of brain homogenate [104]. Another observation recalling muscle work is that during recovery from acute ischaemia, as in muscle recovering from exercise [105], pH recovery is faster than that of lactate [106], although the transporters involved in net proton efflux are not well understood in the brain.…”

31P NMR Relaxation Does Not Affect the Quantitation of Changes in Phosphocreatine, Inorganic Phosphate, and ATP Measured In Vivo During Complete Ischemia in Swine Brain

“…A total of 16 piglets were studied between the ages of 1 day and 1 month. The choice of species and age span reflects our ongoing interest in the study of age-related changes in cerebral metabolism and acid homeostasis using NMR spectroscopy (Corbett et al, 1992). The TI relaxation times during control conditions and from 30-45 rnin following complete ischemia were determined in six animals using the saturation recovery pulse sequence described by Evelhoch and Ackerman (1983).…”

“…In 10 additional animals, 31P NMR spectra using long and short interpulse delays were acquired before and throughout the first 10 rnin of complete cerebral ischemia. The surgical preparation, protocol to induce ischemia, and "P NMR data acquisition and signal processing were the same as described in detail previously (Corbett et al, 1992). The experimental protocol consisted of acquiring control NMR spectra and systemic physiologic data, followed by sequential NMR data collection after inducing complete cerebral ischemia via KC1-induced cardiac arrest.…”

“…Polygraph traces of heart rate and mean arterial pressure were recorded continuously during the experiment to determine the exact point at which ischemia began. Several of the animals reported here were also part of a study (Corbett et al, 1992) to measure the dependency of acid production on blood plasma glucose concentration ([glucose],,,,,,). Hence, some piglets received either a continuous intravenous infusion of glucose (10-30 mg/kg/min) for 20-30 rnin or bolus intravenous injection of insulin (1-2 lU/kg), to alter [~~ucos~],,~~,, in the range of 1-30 mM.…”

Reproducibility of high spatial resolution proton magnetic resonance spectroscopic imaging in the human brain

“…CA), operating SAKE spectroscopy software. Each raw data set was treated with a Fermi filter (radius 7. width 1) in the spatial dimension and a negative exponential filter in the chemical-shift dimension equivalent to 1 Hz of line broadening. After a 3D fast-Fourier transform, the data were automatically phase corrected by selection of the NAA resonance by the computer and application of a zero-order phase correction, based on maximization of the magnitude of the real component.…”