Age-related changes in cerebral energy utilization were examined in swine, a species whose maximal rate of development is known to occur in the perinatal period. Interleaved in vivo 31P and 1H nuclear magnetic resonance spectroscopy was used to measure the rates of change in cerebral concentrations of phosphocreatine (PCr), nucleoside triphosphates, and lactate following complete ischemia, induced via cardiac arrest, in a total of 19 newborn, 10-day-old, and 1-month-old piglets. Preischemic concentrations of these three metabolites plus glucose and glycogen were determined in a separate experiment on 12 piglets whose brains were funnel-frozen in situ. The rate constants for the PCr and ATP decline and lactate increase were determined by nonlinear regression fits to the experimental data, assuming first-order kinetics. The rate constants and preischemic metabolite concentrations were used to calculate the initial flux of high-energy phosphate equivalents (approximately P), which was used as an estimate of cerebral energy utilization at the point when ischemia was initiated. Cerebral energy utilization equaled 6.5 +/- 1.9, 9.5 +/- 3.2, and 15.1 +/- 3.2 mumol approximately P/g/min in newborn, 10-day-old, and 1-month-old piglets, respectively. Within each age group the energy utilization rate was not altered by hyperglycemia-induced increases in cerebral energy reserves, but during hypoglycemia cerebral energy utilization rates decrease. The slope of approximately P versus time decreased with the duration of ischemia, indicating that cerebral energy utilization rates decrease after the first few minutes of ischemia. Newborn piglets had higher cerebral energy utilization rates compared with literature values for newborn rats and mice. This is consistent with the concept that newborns from a species with a perinatal stage of maximal growth and development will have higher cerebral energy demands compared with newborns from a species such as rodents, whose maximal growth occurs postnatally. However, this conclusion remains tentative because literature cerebral utilization rates estimated from the initial slope of approximately P-versus-time plots tend to underestimate the true rate, since the assumption of continued linearity may not be valid for the interval chosen.

Background and Purpose: During global brain ischemia or hypoxia-ischemia in adults, hyperglycemia is deleterious to the brain. In contrast, similar adverse effects have not been found in neonatal animals. This investigation examined neonatal piglets to determine if there were specific alterations of ischemic brain metabolism associated with different systemic glucose concentrations and to potentially clarify the effects of hyperglycemia during ischemia in neonates.Methods: Two groups of animals (n=12 in each group) were studied during partial ischemia to compare the effects of hyperglycemia (plasma glucose concentration, 258+97 mg% [mean±SD]) with modest hypoglycemia (plasma glucose concentration, 62 ±23 mg%). A broad spectrum of cerebral blood flow reduction was achieved by combining inflation of a cervical pressure cuff with varying degrees of hemorrhagic hypotension. High-energy phosphorylated metabolites, intracellular pH, and cerebral blood flow were simultaneously measured using a magnetic resonance spectroscopic technique. Brain metabolic variables (/J-ATP, inorganic phosphorus, phosphocreatine, intracellular pH) were plotted as a function of blood flow reduction during partial ischemia for each group.Results: During ischemia values of cerebral blood flow were comparably distributed between groups and ranged from 15% to 110% of those of control. At a given reduction of cerebral blood flow, hyperglycemic piglets maintained a higher concentration of/J-ATP (p=0.011) and had a smaller increase in inorganic phosphorus (p<0.001). At cerebral blood flow <50% of control, the intracellular pH of piglets with modest hypoglycemia during partial ischemia was never reduced to <6.46, whereas intracellular pH fell as low as 5.97 for hyperglycemic animals.Conclusions: ATP preservation may account for the differing effects of glucose during ischemia in neonates compared with adults, provided that the accentuated brain acidosis is not deleterious to neonatal brain tissue. (Stroke 1992;23:1504-1511 KEY WORDS • cerebral ischemia • cerebral metabolism • glucose • nuclear magnetic resonance • pigs

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.

Background and Purpose: Our investigation sought to determine whether neonatal brain ischemic vascular and metabolic effects were altered by repeated episodes of ischemia.Methods: We studied twelve piglets using in vivo magnetic resonance spectroscopy to obtain multiple, simultaneous measurements of cerebral blood flow and phosphorylated metabolites from the same tissue volume. The relationship between cerebral blood flow and energy metabolism was examined over a range of reduced cerebral blood flow (90-10% of control). Three episodes of partial ischemia were studied, each lasting 10 minutes and separated by 45 minutes.Results: During each interval of ischemia, plots of the percent reduction in cerebral blood flow versus the percent change in phosphorylated metabolites (phosphocreatine, inorganic phosphorus) or unit change in intracellular pH did not differ in slope and intercept. The relationship between /3-ATP and cerebral blood flow during repeated ischemia revealed similar slopes, but a lower intercept during the third interval of ischemia (p=0.029). After ischemia, cerebral blood flow was reduced as a function of the severity of the preceding ischemia. After each interval of ischemia, phosphocreatine and intracellular pH were unchanged from preischemic values. Inorganic phosphorus remained elevated after ischemia (117±16 and 118±11% of control, p<0.005, following the first and second intervals of ischemia), and /3-ATP was restored to progressively lower values (92±10 and 83±11% of control, p<0.025). Calculated free ADP decreased after ischemia and correlated with the postischemic level of/3-ATP (r=0.63,p=0.001).Conclusions: These results demonstrate that the relationship between cerebral blood flow and metabolism was reasonably preserved during repeated partial ischemia. However, following ischemia, alterations occurred in both cerebral blood flow and metabolism. These alterations may reflect a relative inhibition of ATP production by metabolic regulators such as ADP on either glycolysis or oxidative phosphorylation or both. (Stroke 1992;23:380-387) KEY WORDS • cerebral blood flow • cerebral ischemia • metabolism • pigs

ABSTRACT. The purpose of this study was to investigate Abbreviations the effect of plasma glucose concentration on cerebral agonal glycolytic rates in piglets of different ages. Twenty-AGR, initial agonal glycolytic rate four piglets were divided into four different age groups [glu~ose],~,,,,, arterial blood plasma glucose concentration corresponding to 113, 121, 128, and 145 d postconception 'H NMR, proton nuclear magnetic resonance (normal gestation = 115 d). For each group the agonal k, first order rate constant for lactate accumulation Km, blood plasma glucose concentration at which the glycolytic rate was measured by monitoring the rate of glycolytic rate is half maximal cerebral lactate accumulation after total ischemia. Ische-[la~tate]~,,~, final postmortem brain lactate concentration mia was induced by cardiac arrest, and the rate of lactate MAP, mean arterial blood pressure formation was measured in vivo using proton nuclear mag-V, , , , maximum agonal glycolytic rate netic resonance spectroscopy. Before cardiac arrest, the blood plasma glucose concentration for individual piglets was adjusted to a specific value in the range 1-30 mM. The dependence of agonal glycolytic rate upon blood glucose concentration was analyzed for each age group, usingThe role of glucose status in immature animals exposed to the ~i~h~~l i~-~~~~~~ equation to evaluate v,,,, the max-hypoxic-ischemia insults is controversial (1). In adults, an eleimal rate of glucose utilization, and K~ the concentration vated blood glucose concentration during cerebral ischemia is of plasma glucose at which the half maximal rate of detrimental to the recovery of normal brain function and strucutilization occurs. V,,, for the two youngest age groups of ture. A detrimental role for elevated glucose is based on the piglets had significantly different ( p < 0.05) values presumption that there is excessive lactate production during pared with each other (1.38 f 0.17 and 1.92 f 0.64 pmol. hyperglycemic hypoxia-ischemia compared with when glucose is g -~, min-~, respectively) and with the two older groups of not elevated. Support for this comes from studies of juvenile animals (2.99 f 0.52 and 3.42 f 0.65 pmo1.g-' .min-', monkeys (2) and adult rats (3, 4) that were made hyperglycemic respectively). The Km values determined for the two young-before or during ischemia or anoxia and showed increased morphologic brain damage and poorer clinical recovery compared est age piglets. During combined anaerobic glycolysis, with glucose being converted to lactate and hypergl~cemia and severe ischemia, newborns will not be concurrent production of H+ (5, 7). Several clinical studies have levels lactate as as reported that adult stroke patients with elevated blood glucose 2-to 4-wk-old ~iglets. However, despite the differences in have a poorer prognosis than their normoglycemic counterparts glycolytic rates, all four age groups showed similar poten-(8). tials to generate high cerebral lactate concentrations. FurIn contrast, administration of glucose improves the "su...