The effect of electrocortical state on cerebral carbohydrate metabolism in fetal sheep

We measured hemispherical cerebral blood flow and arteriovenous differences across the cerebral cortex for glucose, oxygen, and lactate during the two primary electroencephalographic patterns (high and low voltage) in unanesthetized, near-term fetal sheep. Oxygen consumption was 127 mumol/min/100 g brain in high voltage and was 14% higher in low voltage. Glucose uptake was 19 mumol/min/100 g and was 37% higher in low voltage. Cerebral blood flow was 112 ml/min/100 g and was 29% higher in low voltage. The glucose:oxygen quotient increased from 0.91 in high voltage to 1.08 in low voltage. There was a net lactate efflux of 3.2 mumol/min/100 g during low voltage compared to a net influx of 3.3 mumol/min/100 g in high voltage. During high voltage the fetal brain uses a small amount of lactate for oxidative metabolism. During low voltage, glucose uptake exceeds the oxygen uptake needed for completely aerobic consumption, and a portion of the energy utilized by the brain is produced anaerobically.     

Cerebral carbohydrate metabolism during hypoglycemia and anoxia in newborn rats

The cerebral metabolic responses to perinatal hypoglycemia and anoxia were studied in newborn rats given regular insulin (30 units per kilogram of body weight). Animals were observed for up to 2 hours with no apparent ill effects in spite of blood glucose concentrations of 0.75 mmol per liter. When exposed to 100% nitrogen at 37°C, hypoglycemic animal survived only one-tenth as long as littermate controls with normal blood glucose levels (4.7 mmol/L). Pretreatment of hypoglycemic rats with glucose (10 mmol/kg) 10 and 30 minutes prior to nitrogen exposure nearly completely reversed the anoxic vulnerability. Hypoglycemia led to progressive reductions in crebral glycogen and glucose; however, only glucose reverted to normal levels 20 minutes after systemic glucose administration. The glycolytic intermediates glucose 6-phosphate and lactate were also lower during hypoglycemia. Brain glucose levels below 0.1 mmol per kilogram were associated with a disrupted cerebral energy state, reflected by declines in phosphocreatine (33%) and adenosine triphosphate (ATP) (10%). Cerebral energy utilization (metabolic rate) was minimally reduced (?7.2%) by hypoglycemia and returned to the control value (2.36 mmol ～ P/kg/min) with glucose treatment. The cerebral energy reserves ATP, adenosine diphosphate, and phosphocreatine delined more rapidly and to a lower level in hypoglycemic rats subjected to 2 1/2 minutes of anoxia than in normoglycemic animals rendered similarly hypoxic. The findings suggest that decreased anoxic resistance of hypoglycemic newborn rats is not primarily a function of reduced brain glycogen or altered cerebral metabolic rate. The presence of endogenous cerebral glucose stores combined with continued circulating glucose (cerebrovascular perfusion) appear to be critical factors for maintaining perinatal hypoxic survival.     

Cerebral carbohydrate metabolism during acute carbon monoxide intoxication.

The cerebral metabolic effects of 2.5, 5, 7.5, 10, 20, 30 and 60 min exposure to 1% CO were studied in lightly anesthetized rats by measurement of cerebral cortical contents of selected glycolytic and citric acid cylce intermediates, as well as tissue energy phosphates. The initial change in the glycolytic sequence occurred at 2.5 min with decreases in tissue glucose and glucose-6-phosphate and increases in fructose-1-6-diphosphate which indicated an activation of phosphofructokinase and hexokinase. The "crossover" pattern between glucose-6-phosphate and fructose-1,6-diphosphate was present at 5, 7.5 and 10 min, but not at 20, 30 and 60 min and thus confirmed previous observations that detection of phosphofructokinase activation in acute unifactorial cerebral hypoxia requires tissue study during the early phases of the experimental exposure. The initial activation of phosphofructokinase occurred in the absence of detectable changes in the tissue content of ATP, ADP, AMP or phosphocreatine and therefore suggested that an imbalance of tissue energy homeostasis is not a prerequisite for the activation of glycolysis in CO intoxication. One percent CO resulted in an increasing malate/oxaloacetate ratio at 5 min, followed by a decrease in alpha-ketoglutarate and aspartate at 7.5 min which suggested a shift in the aspartate aminotransferase reaction towards the replenishment of oxaloacetate removed via the malate dehydrogenase reaction. Subsequent increases in alpha-ketoglutarate at 10, 20, 30 and 60 min were associated with increases in alanine, indicating a contributing role for a secondary shift of the alanine aminotransferase reaction in the replenishment of alpha-ketoglutarate. A comparison of the CO induced changes in the glycolytic and citric acid cycle pathways with those seen in acute hypoxemia indicates no basic qualitative differences in the metabolic responses of brain tissue to the two conditions.     

Cerebral oxygenation during postasphyxial seizures in near-term fetal sheep.

After exposure to asphyxia, infants may develop both prolonged, clinically evident seizures and shorter, clinically silent seizures; however, their effect on cerebral tissue oxygenation is unclear. We therefore examined the hypothesis that the increase in oxygen delivery during postasphyxial seizures might be insufficient to meet the needs of increased metabolism, thus causing a fall in tissue oxygenation, in unanesthetized near-term fetal sheep in utero (gestational age 125+/-1 days). Fetuses were administered an infusion of the specific adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine, followed by 10 mins of asphyxia induced by complete umbilical cord occlusion. The fetuses then recovered for 3 days. Sixty-one episodes of electrophysiologically defined seizures were identified in five fetuses. Tissue PO(2) (tPO(2)) did not change significantly during short seizures (<3.5 mins), 5.2+/-0.2 versus baseline 5.6+/-0.1 mm Hg (NS), but fell to 2.2+/-0.2 mm Hg during seizures lasting more than 3.5 mins (P<0.001). During prolonged seizures, cortical blood flow did not begin to increase until tPO(2) had begun to fall, and then rose more slowly than the increase in metabolism, with a widening of the brain to blood temperature gradient. In conclusion, in the immature brain, during prolonged, but not short seizures, there is a transient mismatch between cerebral blood flow and metabolism leading to significant cerebral deoxygenation.     

Cerebral oxygen transport and metabolism during graded isovolemic hemodilution in experimental global ischemia

To verify the optimal hematocrit (Hct) level in the treatment of cerebral ischemia, cerebral oxygen transport (CTO₂) and cerebral oxygen metabolism (CMRO₂) in graded isovolemic hemodilution were evaluated during cerebral ischemia. Isovolemic hemodilution with low molecular weight dextran to stepwise lower Hct from 43% to 36%, 31%, and 26% was carried out in 13 splenectomized dogs, 6 h after global cerebral ischemia. Global ischemia of the animals was produced by multiple intra- and extracranial ligations of cerebral arteries. Cerebral blood flow (CBF) was measured with radioisotope labeled microspheres. CTO₂, CMRO₂, and oxygen extraction fraction (OEF) were calculated from CBF, arterial oxygen content (CaO₂), and venous oxygen content (CvO₂). In dogs with global cerebral ischemia, CBF increased with graded isovolemic hemodilution (r=−0.73, P<0.05). CTO₂ reached its highest value at a Hct level of 31.3%. CTO₂ at Hct of 36.1% and 31.3% was statistically different from the value measured at a Hct of 43.3%, and there was a decrease when Hct was lowered to 25.9%. CMRO₂ was the highest when Hct was at 31.3% and differed significantly from the value measured at a Hct of 43.3%. There was a 10% increase of OEF when Hct was at 25.9%; however this change was not statistically significant compared with the OEF at Hct of 36.1% and 31.3%, respectively. These findings indicate that CTO₂ and CMRO₂ were the highest when Hct was reduced to 31% in hemodilution. Hct at 31% is the optimum for cerebral metabolism in ischemic status. Uncoupling of CTO₂, CMRO₂ with CaO₂ was also observed in this study. This phenomenon suggests that hemodilution to augment cerebral circulation may be at least partially attributed to the beneficial effects of hemorheologic improvement in the microcirculation of the ischemic brain.     

Cerebral phosphoinositide, triacylglycerol and energy metabolism during severe hypoxia and recovery

The cerebral concentrations of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidic acid (PA), triacylglycerol (TAG) and free fatty acids (FFA), as well as cerebral metabolites, were measured in rats subjected to 10 min of hypoxia and subsequent recovery of 7 or 30 min duration. The experiments were carried out with control of physiological variables. Hypoxia (paO2 values of about 15 mm Hg) caused a decrease in PI, whereas PIP and PIP2 did not change significantly. A two-fold increase of total FFA was noted, mainly comprising stearic and arachidonic acids. TAG-arachidonate tended to increase, but the other species in TAG decreased. Adenosine triphosphate (ATP) and energy charge (EC) decreased slightly and there was a marked lactate accumulation. PA did not change throughout the experiment. With recovery of 7 min duration, PI decreased further and total FFA continued to increase. TAG-arachidonate increased significantly. ATP remained depressed but EC recovered to the control range. Both tissue and plasma glucose increased. Tissue lactate remained elevated and systemic acidosis occurred. After a recovery period of 30 min, all lipids normalized and the energy state returned toward control. The data suggest that the phosphoinositide alterations during hypoxia are metabolically linked to changes in FFA and the lipid changes are accompanied by alterations in cerebral energy and carbohydrate metabolism. The selective increase in TAG-arachidonate may represent an incorporation of arachidonic acid into TAG, which may serve to reduce the free arachidonic acid level in the brain.     

Cerebral metabolism in newborn dogs during reversible asphyxia

Acute, systemic asphyxia was induced in paralyzed, lightly anesthetized 1- to 2-day-old dogs by respiratory arrest. Measurements of arterial blood pressure, acid-base balance, and concentrations of pyruvate, lactate, and glucose in blood were correlated with electroencephalographic activity and with concentrations of high-energy phosphates and glycolytic substrates in the cerebral cortex. Most animals tolerated 15 minutes, but not 20 minutes, of asphyxia with apparently normal behavioral recovery. Asphyxia was always accompanied by bradycardia, systemic hypotension, and a progressive decline in arterial pH; the concentration of blood lactate and the lactate/pyruvate ratio rose. Blood glucose levels were unaffected, at least during the first 10 minutes. Concentrations of glucose and phosphocreatine in cerebral cortex declined rapidly during asphyxia to low levels, but levels of adenosine triphosphate remained within normal limits for up to 5 minutes despite the fact that electrical activity in brain ceased within 2 minutes. The intravenous injection of carbon black into animals asphyxiated for 2^1/2, 5, 10, or 15 minutes revealed substantial reductions in blood flow to brain during asphyxia; however, relative to the cerebral cortex, brainstem structures received a preferential blood supply.     

White matter protection with insulin-like growth factor 1 and hypothermia is not additive after severe reversible cerebral ischemia in term fetal sheep

Moderate cerebral hypothermia significantly improves survival without disability from perinatal hypoxia-ischemia. However, protection is partial. Insulin-like growth factor 1 (IGF-1) plays a key role in oligodendrocyte survival and myelination. The purpose of this study was to test the hypothesis that the combination of IGF-1 plus hypothermia could reduce postischemic white matter damage compared with hypothermia alone. Unanesthetized near-term fetal sheep received 30 min of cerebral ischemia, followed by either an infusion of 3 μg of IGF-1 intracerebroventricularly from 4.5 to 5.5 h plus cooling from 5.5 to 72 h (IGF-1 + hypothermia; n = 8), vehicle infusion plus cooling from 5.5 to 72 h (vehicle + hypothermia; n = 12), sham cooling plus sham infusion (ischemia control; n = 12) or sham ischemia (n = 5). The fetal extradural temperature was reduced from 39.4 ± 0.1°C to between 30 and 33°C. White matter was assessed after 5 days. Ischemia was associated with severe loss of CNPase-positive oligodendrocytes in white matter compared with sham ischemia (380 ± 138 vs. 1,180 ± 152 cells/field; mean ± SD; p < 0.001). Delayed hypothermia reduced cell loss (847 ± 297 cells/field, p < 0.01, vs. ischemia control), but there was no significant difference between vehicle + hypothermia and IGF-1 + hypothermia (1,015 ± 211 cells/field; NS). Ischemia was associated with increased caspase 3 expression in white matter (216 ± 41 vs. 19 ± 18 cells/field; p < 0.001). Hypothermia reduced numbers of activated caspase 3-positive cells (116 ± 81 cells/field; p < 0.05), with no significant difference between vehicle + hypothermia and IGF-1 + hypothermia (91 ± 27 cells/field; NS). In conclusion, delayed cotreatment with IGF-1 plus hypothermia after ischemia was associated with an improvement in white matter damage similar to that achieved by hypothermia alone.     

Cardiac vagal action during hypoxia in adult and fetal sheep

The effects of hypoxia on the potential for the vagus to slow the heart, and on resting heart rate, were compared in anesthetized, vagotomized adult and fetal sheep, and in a chronically catheterized fetus in utero. In adults, the action of the cardiac vagus was potentiated at and below an arterial pO2 in the range 13-27 mm Hg. In contrast, in the fetus and the neonate, vagal action was not potentiated as pO2 fell through this range to 10-12 mm Hg. Below 10-12 mm Hg baseline heart rate fell markedly, and the effect of the cardiac vagus on heart rate was diminished, but its effect on pulse interval was not consistently changed. It is concluded that potentiation of vagal action during hypoxia occurs in adult but not fetal sheep and the bradycardia seen in the fetus during severe hypoxia is probably due to direct myocardial depression.     

Cerebral perfusion and metabolism in resuscitated patients with severe post-hypoxic encephalopathy

Positron emission tomography (PET) was used for the study of regional cerebral perfusion and metabolism in eight patients with severe post-hypoxic encephalopathy, caused by cardiac arrest and resulting in a coma lasting for at least 24 h. Using this method, we aimed to identify regional vulnerability, which was hypothesized to provide (i) insight in pathogenic mechanisms and (ii) early prognostic parameters. On day 1 post-resuscitation, 18-Fluor deoxyglucose ([F18]-FDG) indicated a marked decrease of cerebral metabolic activity. Gray matter glucose consumption was 54% of normal values, whereas white matter uptake was 70% of normal. Regional differences followed a pattern of neuronal density rather than specific patterns of functionally or biochemically defined regions or of vascular territories. In contrast to [F18]-FDG, the distribution of 15-oxygen labeled water ([O-15]-water) showed a better demarcation between gray and white matter, whereas focal deficit was not observed. In some patients, hyperperfusion relative to regional glucose consumption was observed in the occipital poles and basal ganglia. This suggests loss of vascular tone, i.e. vascular paralysis, in the basilar artery territory. CT and MRI scanning did not show any major change with respect to the hypoxic injury. In the small group studied, all patients had a poor outcome. The comparison between survivors and nonsurvivors did not reveal obvious differences in PET data, suggesting that this technique does not provide major prognostic clues adding to the prognostic information derived from serial neurological assessment in the restricted patient group characterized by prolonged coma.     

Cerebral 11C-glucose metabolism during human sleep

Some reports have suggested that there is no difference in cerebral metabolic rates between wakefulness and sleep. However recently Kennedy et al. and Heiss et al. reported a decrease in cerebral glucose utilization during NREM sleep measured by the using deoxyglucose method. We used a 11C-glucose method for positron emission tomography (PET) while estimating cerebral glucose metabolism during human sleep with polysomnography (PSG). This PET and PSG study was carried out on 11 healthy male volunteers ranging in age from 18 to 26 years. In order to facilitate the onset of sleep, the subjects were deprived of sleep, under observation in the lab, for a period of approximately 20 hours prior to the PSG and PET examination. All experiments were performed in the early morning, most often between 4 and 10 AM. The subjects' sleep was monitored by PSG, i.e. electroencephalogram, electrooculogram and a submental electroencephalogram, electrooculogram and a submental electromyogram. The 11C-glucose used in the experiment was prepared by the biosynthetic method developed by Lifton and Welch, using 11C produced by a baby cyclotron. The 11C-glucose solution, containing about 20 mCi of 11C activity was administered orally to the subjects. The time course of the 11C activity in the blood following the administration was determined by drawing 1 ml of blood from the antecubital vein once every 10 minutes. These samples were assayed for 11C activity in a NaI well counter. The PET images of a horizontal cross-section of the brain at 45 mm above the orbito-meatal line, were used for the analysis of the glucose metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral ketone metabolism during development and injury

Cerebral metabolism of ketones is a normal part of the process of brain development. While the mature brain relies on glucose as a primary fuel source, metabolism of ketone bodies remains an alternative energy source under conditions of starvation. The neuroprotective properties of brain ketone metabolism make this alternative substrate a viable therapeutic option for various pathologies. Since the ability to revert to utilizing ketones as an alternative substrate is greatest in the younger post-weaned brain, this particular therapeutic approach remains an untapped resource particularly for pediatric pathological conditions.     

Susceptibility of feline spinal cord energy metabolism to severe incomplete ischemia

Feline spinal cords were subjected to 10 to 30 minutes of severe incomplete ischemia (average reduction in blood flow of 92%) with and without 90 minutes of recirculation, and the L-2 segment was analyzed for high-energy phosphates and certain glycolytic metabolites. Spinal cord tissue lactic acid levels were stepwise elevated, and adenosine triphosphate (ATP), phosphocreatine (P-creatine), and glucose were progressively consumed by increasing durations of ischemia. However, upon restoration of blood flow, there was extensive recovery of energy metabolites and normalized lactic acid, demonstrating resumption of mitochondrial oxidative metabolism. These data indicate that the spinal cord can tolerate at least 30 minutes of severely reduced blood flow before recovery of energy metabolism is significantly impaired upon restitution of blood flow.     

Brain polyphosphoinositide metabolism during focal ischemia in rat cortex.

Using a rat model of stroke, we examined the effects of focal cerebral ischemia on the metabolism of polyphosphoinositides by injecting 32Pi into both the left and right cortices. After equilibration of the label for 2-3 hours, ischemia induced a significant decrease (p less than 0.001) in the concentrations of labeled phosphatidyl 4,5-bisphosphates (66-78%) and phosphatidylinositol 4-phosphate (64-67%) in the right middle cerebral artery cortex of four rats. The phospholipid labeling pattern in the left middle cerebral artery cortex, which sustained only mild ischemia and no permanent tissue damage, was not different from that of two sham-operated controls. However, when 32Pi was injected 1 hour after the ischemic insult, there was a significant decrease (p less than 0.01) in the incorporation of label into the phospholipids in both cortices of four ischemic rats compared with four sham-operated controls. Furthermore, differences in the phospholipid labeling pattern were observed in the left cortex compared with the sham-operated controls. The change in labeling pattern was attributed to the partial reduction in blood flow following ligation of the common carotid arteries. We provide a sensitive procedure for probing the effects of focal cerebral ischemia on the polyphosphoinositide signaling pathway in the brain, which may play an important role in the pathogenesis of tissue injury.     

Regulatory role of zinc during aluminium-induced altered carbohydrate metabolism in rat brain

Aluminium is considered an environmental neurotoxicant and causes many neurological disorders, whereas zinc is vital for many biological functions. The present study was carried out to investigate the role of Zn, if any, in mitigating the adverse effects inflicted by Al on carbohydrate metabolism in rat brain. Male Sprague-Dawley rats weighing 140-160 g were divided into four different groups: normal control, Al-treated (100 mg/kg b.w./day in drinking water via oral gavage), Zn-treated (227mg/liter in drinking water), and combined Al- and Zn-treated rats. All the treatments were continued for 2 months, and their effects on carbohydrate-metabolizing enzymes were studied. Additionally, expressions of the proteins glycogen synthase kinase-3 (GSK3) and protein phosphatase (PP1), which help in regulating carbohydrate energy metabolism, were also studied. Al treatment resulted in increased activities of the glucose-6-phosphatase (G6P), glucose-6-isomerase (G6I), and lactate dehydrogenase (LDH), whereas the activities of hexokinase and succinate dehydrogenase (SDH) and glycogen content were decreased. Moreover, no significant change was observed in the biochemical parameters upon Zn supplementation alone. However, Zn supplementation to Al-treated rats was able to reduce significantly the Al-induced increased activities of G6P, G6I, and LDH, but it elevated the levels of hexokinase, SDH, and glycogen. Furthermore, Al treatment increased the protein expression of GSK3 and decreased the PP1 expression, which were found to be reversed upon Zn administration. Hence, Zn is effective in regulating theAl-induced alterations in carbohydrate metabolism.     

Cerebral blood flow, glucose metabolism and tunel-positive cells in the development of ischemia

Few in vivo studies were available about the relation between cerebral blood flow, glucose metabolism and the appearance of apoptotic cells in the development of cerebral infarct. To investigate this, we measured local cerebral blood flow (lCBF), local cerebral metabolic rate in glucose (lCMRglc), and histopathology in transient focal cerebral ischemia in the rat. A unilateral middle cerebral artery occlusion (MCAO) was induced for 2 h in Wistar-ST rats (n = 42). A histopathological study with hematoxylin-eosin staining and the TdT-mediated dUTP-biotin nick-end labeling (TUNEL) method was performed. lCBF was measured by means of the (14)C-iodoantipyrine autoradiography technique during MCAO (n = 6), and 1, 22 and 70 h after reperfusion. lCMRglc was also measured by autoradiography with (14)C-2-deoxyglucose in the animals 22 h after reperfusion. These parameters were assessed in each region of interest: the ischemic core, boundary zones (BZ-I and BZ-II) and remote area. The boundary zones were defined as the area based on TUNEL positivity (more than 5/field) at 22 h after reperfusion (BZ-I) and at 70 h after reperfusion (BZ-II). In the BZ-I, lCBF was decreased to 18% of the control during MCAO, and lCBF and lCMRglc showed 44 and 62% of the control, respectively, 22 h after reperfusion. In this area, TUNEL-positive cells increased at 22 h, then markedly decreased 70 h after reperfusion. In the BZ-II, lCBF decreased to 39% of the control during MCAO, then returned to about 90% of the control 22 h after reperfusion. lCMRglc was maintained near its normal range (82% of the control) 22 h after reperfusion. Histopathology of BZ-II was normal 22 h after reperfusion. The TUNEL positivity of neurons in our study was assumed to be a marker of apoptotic cells. Our data suggested that the apoptotic process plays an important role in the maturation of a cerebral infarct. Both lCBF and lCMRglc were maintained with only a mild reduction in the predisposing phase of apoptosis, suggesting that sufficient blood supply and glucose metabolism are required to promote the process of apoptosis.