Cerebral Oxidative Metabolism and Blood Flow During Acute Hypoglycemia and Recovery in Unanesthetized Rats

Abstract: Progressive neurological depression leading to coma was produced in unanesthetized rats at a constant level of hypoglycemia induced by insulin. High-energy phosphate concentrations in brain remained normal during hypoglycemic lethargy, but ATP declined by 6% during stupor and by 40% during coma that was characterized by an isoelectric EEG. Cerebral blood flow (CBF) remained normal during hypoglycemia whereas the cerebral metabolic rates for oxygen (CMRo₂) and glucose (CMR_glucose) decreased by 45 and 73%, respectively, indicating oxidation of nonglucose fuels. A plot of CMRo₂ and CMR_glucose versus plasma glucose indicated increasing oxidation of alternate substrates (elevated CMRo²/CMR_glucose) at plasma glucose concentrations below 2.5 mm . The cerebral uptake of β-hydroxybutyrate increased during hypoglycemic stupor and its complete oxidation could account for the CMRo₂ in excess of glucose utilization. Brain ammonia, a byproduct of amino acid metabolism, reached a level during hypoglycemic coma sufficient to produce coma in normoglycemic animals. The rate and degree of recovery after glucose administration depended on the duration of hypoglycemia and the pretreatment neurological state of the animal. Following 10 min of glucose infusion, ATP levels that were modestly depressed in stuporous rats recovered fully, paralleling the animals' apparently full neurological recovery. Rats that had been in hypoglycemic coma for 1 min or less fully recovered high-energy phosphate concentrations in brain. However, when normalization of plasma glucose was delayed for more than 1 min of coma, the CMRo₂ remained depressed, CBF decreased to 40% of control, and high-energy substrates failed to normalize. In keeping with the depression of oxidative metabolism and blood flow, neurological function and the EEG remained abnormal even after 1 h of glucose infusion. The findings suggest that irreversible brain injury may develop within the first minutes of hypoglycemic coma.     

Cerebral Phosphoinositide and Energy Metabolism During and After Insulin-Induced Hypoglycemia

During and after insulin-induced hypoglycemia, changes in levels of cerebral phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidic acid (PA), triacylglycerol (TAG), diacylglycerol (DAG), and free fatty acids (FFAs) as well as the cerebral energy state were studied in relation to the EEG. In hypoglycemic rats with an EEG pattern of quasiperiodic sharp or slow sharp waves, which preceded the development of an isoelectric EEG, PIP2 levels increased significantly, together with a slight decrease in PI content. Levels of the other lipids did not change during this period. The cerebral energy state was affected only slightly in spite of profound decreases in plasma and tissue glucose levels. With 30 min of an isoelectric EEG, levels of all phosphoinositides and PA decreased significantly; total FFA and DAG contents increased seven- and twofold, respectively; the TAG-palmitate level decreased, and that of TAG-arachidonate increased. Plasma and tissue glucose were nearly depleted, and the cerebral energy state deteriorated severely. The increment in fatty acids in the DAG and FFA pools was less than their loss from phosphoinositides and PA, an observation suggesting vascular washout or oxidation of a portion of the FFAs produced. Following 90 min of glucose infusion, PIP and PA levels recovered to control values; however, the PIP2 content exceeded control levels, and that of PI remained below control levels. DAG and FFA contents returned to normal.(ABSTRACT TRUNCATED AT 250 WORDS)     

妊娠期糖代谢异常对新生儿出生结局的影响

目的:探讨妊娠期不同程度的糖代谢异常对胎儿发育及结局的影响。方法:前瞻性收集我院2009年1月至2010年1月分娩的糖代谢异常的331例单胎妊娠孕妇,分为糖筛查异常组69例、糖耐量异常组126例、妊娠期糖尿病(Gestaional DiabetesMellitus,GDM)组136例,并选择同期糖代谢正常的751例单胎孕妇为对照组,比较四组新生儿出生的最终结局。结果:糖筛查异常组与对照组新生儿结局差异无显著性意义(P>0.05);糖耐量异常组中巨大儿及新生儿窒息、早产儿的发生率与对照组差异有显著性意义(P<0.05);GDM组与对照组差异有显著性意义(P<0.05)。结论:母亲妊娠期不同程度的糖代谢异常对新生儿影响不同。口服葡萄糖耐量试验(Oral Glucose Tolerance Test,OGTT)异常与GDM一样对新生儿发育及结局均有影响,可使巨大儿、新生儿窒息、早产儿的发生率增高。     

妊娠期糖代谢异常对新生儿出生结局的影响

目的：探讨妊娠期不同程度的糖代谢异常对胎儿发育及结局的影响。方法：前瞻性收集我院2009年1月至2010年1月分娩的糖代谢异常的331例单胎妊娠孕妇,分为糖筛查异常组69例、糖耐量异常组126例、妊娠期糖尿病（Gestaional DiabetesMellitus,GDM）组136例,并选择同期糖代谢正常的751例单胎孕妇为对照组,比较四组新生儿出生的最终结局。结果：糖筛查异常组与对照组新生儿结局差异无显著性意义（P〉0.05）;糖耐量异常组中巨大儿及新生儿窒息、早产儿的发生率与对照组差异有显著性意义（P〈0.05）;GDM组与对照组差异有显著性意义（P〈0.05）。结论：母亲妊娠期不同程度的糖代谢异常对新生儿影响不同。口服葡萄糖耐量试验（Oral Glucose Tolerance Test,OGTT）异常与GDM一样对新生儿发育及结局均有影响,可使巨大儿、新生儿窒息、早产儿的发生率增高。     

Regional Cerebral Glucose Utilization During Insulin-Induced Hypoglycemia in Unanesthetized Rats

Regional cerebral glucose utilization (rCMRgl) was studied during insulin-induced hypoglycemia in unanesthetized rats. Rats were surgically prepared using halothane and nitrous oxide anesthesia and allowed 5 h to recover from the anesthesia before rCMRgl was measured. The rCMRgl was measured using [6-14C]glucose in a normoglycemic control group and two hypoglycemic groups, A (30 min after insulin injection) and B (2 h after insulin injection). The mean plasma glucose level was 7.03 mumol/ml in the normoglycemic group, 1.96 mumol/ml in hypoglycemic group A, and 1.40 mumol/ml in hypoglycemic group B. The rCMRgl in hypoglycemic group A decreased 8-18% in 17 brain regions measured; five changes were statistically significant. The rCMRgl in hypoglycemic group B decreased significantly in all but one of the brain regions measured; the decrease ranged from 15% in the pyramidal tract to 36% in the motor and auditory cortices. The rCMRgl in every brain region decreased when the plasma glucose level fell below 1.5-2.5 mumol/ml. No brain region could maintain rCMRgl at plasma glucose concentrations lower than predicted by regional glucose influx described in previous studies. Glucose utilization in all brain regions appears to be limited by the influx of glucose.     

Cerebral Blood Flow and Oxidative Metabolism in Conscious Fischer-344 Rats of Different Ages

Abstract: The cerebral metabolic rates for O₂ and for glucose were measured in conscious, fasted male Fischer-344 rats at the ages of 3, 12, and 24 months, and cerebral blood flow was determined with ¹⁴C-iodoantipyrine. The metabolic rates for oxygen and glucose were obtained by multiplying blood flow by the O₂ and glucose concentration differences, respectively, between blood in the femoral artery and in the superior sagittal sinus. Mean cerebral blood flow and the metabolic rates for oxygen and glucose did not differ significantly (p > 0.05) between 3 and 12 or between 12 and 24 months. Nor did the arteriovenous differences for O₂ and for glucose change significantly with age. Because the superior sagittal sinus drains blood mainly from the cerebral cortex, the results indicate that average cerebral cortical oxidative metabolism, and the coupling ratios between the cerebral metabolic rate for oxygen and cerebral blood flow and between the cerebral metabolic rate for glucose and cerebral blood flow, do not change significantly with age in the Fischer-344 rat.     

Regional Cerebral Glucose Metabolism and Blood Flow During the Silent Phase of Methylmercury Neurotoxicity in Rats

Methylmercuric chloride was given to rats in a neurotoxic dose regimen (six daily doses of 8 mg kg-1 p.o.). During the silent (asymptomatic) phase of intoxication, the rates of cerebral glucose influx and cerebral glucose phosphorylation were measured simultaneously using 2-deoxyglucose. Regional cerebral blood flow was also measured using iodoantipyrine. The unidirectional flux of glucose into brain was not affected by methylmercury, and differences in the rates of glucose phosphorylation from region to region remained coupled to the regional cerebral blood flow. However, the blood flow was reduced throughout the brain, an observation suggesting that the operational level of metabolically regulated blood flow had been reset. Thus, in spite of a generalised reduction in blood flow, there was no indication of impaired cerebral glucose supply or utilization during the silent phase of methylmercury intoxication.     

Accumulation of Cyclooxygenase Products of Arachidonic Acid Metabolism in Gerbil Brain During Reperfusion After Bilateral Common Carotid Artery Occlusion

: Several of the cyclooxygenase products of arachidonic acid were measured in the cerebral hemispheres of gerbils subjected to transient interruption of the cerebral circulation. The levels of PGD₂, PGF₂α, PGE₂, TXB₂, 13,14-H₂-15-keto-PGE₂, and the stable nonenzymic product of prostacyclin, 6-keto-PGF₁α, were not altered at the end of a 5-min period of ischemia. However, the onset of reperfusion was accompanied by a rapid accumulation of these products. Levels were highest during the initial period of reperfusion, then decreased to approach control levels after 120 min. PGD₂, PGF₂α, and PGE₂ were the predominant metabolites detected. This postischemic accumulation of arachidonic acid metabolites could be blocked by prior administration of inhibitors of cyclooxygenase activity.     

Effects of Intracisternally Injected Serotonin on Cerebral Blood Flow in Cats During Winter and Summer,and After Dark Exposure

This investigation reports on two experiments: (a) The examination of the effects of intracisternally injected serotonin on cerebral blood flow and systemic pressure in cats during winter (1/10–3/7) and summer (7/6–9/3) at a latitude of 39' 40, and (b) the effects of similarly injected serotonin on the same parameters in 11 cats after exposure to 3 days of continuous darkness during the summer months. Serotonin (5 mg) injected intracisternally produced significant decreases in cerebral blood flow and systemic pressure that lasted from 60 to 180 min after injection. Blood flow decreases, expressed as percentage change from baseline, seen during winter (n = 24) periods were significantly greater [analysis of variance (ANOVA), p < 0.02] from decreases seen during summer (n = 25) periods. Following serotonin injection, systemic pressure decreases between the winter and summer cats were not significantly different. Eleven summer cats were subjected to 3 days of continuous darkness before being injected with serotonin. Blood flow decreases in the dark-exposed cats were significantly (p < 0.05) greater than those seen in normal light-exposed cats, whereas systemic pressure changes were not different. These studies suggest that the seasonal photoperiod may affect the sensitivity of cerebral vessels to intracisternally injected serotonin in cats.     

一氧化氮对脑血流的调节

一氧化氮是近年来发现的一种重要的血管活性因子,它通过激活平滑肌细胞内水溶性鸟苷酸环化酶,而产生血管舒张作用,在正常生理条件下,ＮＯ不仅对外因管有作用,对脑血管也有作用,但关于它在低氧和高二氧化碳条件下脑血管是否具有调节作用还存在着争议。     

Rat Brain Protein Synthesis Declines During Postdevelopmental Aging

Using improved methods to measure brain protein synthesis in vivo (Dunlop et al., 1975) we have established that brain protein synthesis significantly declines in forebrain, cerebellum and brain stem when mature rats (3 months old) are compared to old rats (22.5 months old). The incorporation of (3H) L-lysine into forebrain protein is reduced 11% in 10.5 month old rats compared to 3 month old rats. A further reduction of 9% occurred between 16.5 months and 22.5 months. Our data suggest that reduced levels of protein synthesis initiation may be responsible, at least in part, for this age-related decline.     

PET脑血流量测量方法和临床应用进展

脑血流量测量对于脑血管疾病、脑肿瘤诊断和疗效评估具有重要的临床价值。PET是基于正电子示剂技术无创性、精确测量脑血流量的方法,正日益广泛地应用于临床。按照PET测量脑血流量的方法和使用的正电子示踪剂不同,其测量方法分为平衡法、放射自显影法和动力学方法三种。18O-H2O示踪剂PET测量脑血流量被认为测量脑血流方法的"金标准"。随着PET设备分辨率提高、新的图像重建方法使用和PET与MRI图像融合技术不断成熟,18F-FDG首次通过、采用图像衍生动脉输入函数(imagederived arterial input function,IDAIF)替代动脉抽血样精确测量脑血量方法受到广泛重视,有可能逐步取代高成本的18O-H2O测量脑血流量。PET无创、方便和精确测量脑血流量的方法在临床应使用有助于脑血管性疾病、脑肿瘤和脑退行性病变早期诊断、鉴别诊断和个性化医疗。本文介绍PET脑血流量测量原理、方法和临床应用进展。     

Effects of Metabotropic Glutamate Receptor Stimulation on Cerebral O2 Consumption and Blood Flow During Focal Cerebral Ischemia in Rats

This investigation was performed to evaluate the effects of ACPD [(1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid], a metabotropic glutamate receptor agonist, on cerebral O₂ consumption during focal cerebral ischemia. Male Wistar rats were placed in control (n = 7) and ACPD (n = 7) groups under isoflurane anesthesia. Twenty minutes after middle cerebral artery (MCA) occlusion, gauze sponges with 10^–5 M ACPD or normal saline were placed on the ischemic cortex (IC) for a period of 40 min and were changed every 10 min. One hour after MCA occlusion, regional cerebral blood flow (rCBF) was determined using the C¹⁴-iodoantipyrine autoradiographic technique. Regional arterial and venous oxygen saturation were determined using microspectrophotometry. There were no statistical differences in vital signs, blood gases, and hemoglobin between the groups. In the control group, the cerebral blood flow and oxygen consumption of the IC were significantly lower than the contralateral cortex (rCBF: 45 ± 11 vs. 110 ± 11 ml/min/100 g, O₂ consumption: 2.9 ± 0.4 vs. 5.4 ± 1.1 ml O₂/min/100 g). ACPD did not change regional cerebral blood flow of the IC, but did significantly increase the oxygen extraction (7.8 ± 0.2 vs. 6.9 ± 0.3 ml O₂/100 ml) and oxygen consumption of the IC (4.3 ± 1.5 vs. 2.9 ± 0.4) compared to the control IC. Our data demonstrated that topical application of 10^–25 M ACPD to the ischemic area worsened cerebral O₂ balance. These data suggest that metabotropic glutamate receptors are not maximally activated during ischemia in the temporal cortex.     

Effect of 7-Nitroindazole Sodium on the Cellular Distribution of Neuronal Nitric Oxide Synthase in the Cerebral Cortex of Hypoxic Newborn Piglets

Cerebral hypoxia results in generation of nitric oxide (NO) free radicals by Ca⁺⁺-dependent activation of neuronal nitric oxide synthase (nNOS). The present study tests the hypothesis that the hypoxia-induced increased expression of nNOS in cortical neurons is mediated by NO. To test this hypothesis the cellular distribution of nNOS was determined immunohistochemically in the cerebral cortex of hypoxic newborn piglets with and without prior exposure to the selective nNOS inhibitor 7-nitroindazole sodium (7-NINA). Studies were conducted in newborn piglets, divided into normoxic (n = 6), normoxic treated with 7-NINA (n = 6), hypoxic (n = 6) and hypoxic pretreated with 7-NINA (n = 6). Hypoxia was induced by lowering the FiO₂ to 0.05–0.07 for 1 h. Cerebral tissue hypoxia was documented by decrease of ATP and phosphocreatine levels in both the hypoxic and 7-NINA pretreated hypoxic groups (P < 0.01). An increase in the number of nNOS immunoreactive neurons was observed in the frontal and parietal cortex of the hypoxic as compared to the normoxic groups (P < 0.05) which was attenuated by pretreatment with 7-NINA (P < 0.05 versus hypoxic). 7-NINA affected neither the cerebral energy metabolism nor the cellular distribution of nNOS in the cerebral cortex of normoxic animals. We conclude that nNOS expression in cortical neurons of hypoxic newborn piglets is NO-mediated. We speculate that nNOS inhibition by 7-NINA will protect against hypoxia-induced NO-mediated neuronal death.     

Cerebral Cortex Ammonia and Glutamine Metabolism During Liver Insufficiency-Induced Hyperammonemia in the Rat

Hyperammonemia has been suggested to induce enhanced cerebral cortex ammonia uptake, subsequent glutamine synthesis and accumulation, and finally net glutamine release into the blood stream, but this has never been confirmed in liver insufficiency models. Therefore, cerebral cortex ammonia- and glutamine-related metabolism was studied during liver insufficiency-induced hyperammonemia by measuring plasma flow and venous-arterial concentration differences of ammonia and amino acids across the cerebral cortex (enabling estimation of net metabolite exchange), 1 day after portacaval shunting and 2, 4, and 6 h after hepatic artery ligation (or in controls). The intra-organ effects were investigated by measuring cerebral cortex tissue ammonia and amino acids 6 h after liver ischemia induction or in controls. Arterial ammonia and glutamine increased in portacaval-shunted rats versus controls, and further increased during liver ischemia. Cerebral cortex net ammonia uptake, observed in portacaval-shunted rats, increased progressively during liver ischemia, but net glutamine release was only observed after 6 h of liver ischemia. Cerebral cortex tissue glutamine, gamma-aminobutyric acid, most other amino acids, and ammonia levels were increased during liver ischemia. Glutamate was equally decreased in portacaval-shunted and liver-ischemia rats. The observed net cerebral cortex ammonia uptake, cerebral cortex tissue ammonia and glutamine accumulation, and finally glutamine release into the blood suggest that the rat cerebral cortex initially contributes to net ammonia removal from the blood during liver insufficiency-induced hyperammonemia by augmenting tissue glutamine and ammonia pools, and later by net glutamine release into the blood. The changes in cerebral cortex glutamate and gamma-aminobutyric acid could be related to altered ammonia metabolism.     

Regional Acetylcholine Metabolism in Brain During Acute Hypoglycemia and Recovery

Insulin-induced hypoglycemia in normothermic rats caused progressive neurological depression and differentially altered regional cerebral acetylcholine metabolism. Reductions of plasma glucose from 7.7 mM (control) to 2.5-1.7 mM (moderate hypoglycemia associated with decreased motor activity) or 1.5 mM (severe hypoglycemia with lethargy progressing to stupor) decreased glucose concentrations in the cerebral cortex, striatum, and hippocampus to less than 10% of control. Moderate hypoglycemia diminished acetylcholine concentrations in cortex and striatum (21% and 45%, respectively) and reduced [1-2H2, 2-2H2]choline incorporation into acetylcholine (62% and 41%, respectively). Severe hypoglycemia did not reduce the acetylcholine concentration or synthesis in cortex and striatum further. The concentrations of choline rose in the cortex (+53%) and striatum (+130%) of animals that became stuporous but a similar rise in [1-2H2, 2-2H2]choline left the specific activities of choline in these structures unchanged. Even severe hypoglycemia did not alter the hippocampal cholinergic system. In rats that developed hypoglycemic stupor and were then treated with glucose, the animals recovered apparently normal behavior, and the concentrations of acetylcholine and the incorporation of [1-2H2, 2-2H2]-choline into acetylcholine returned to control values in the striatum but not in the cerebral cortex. Thus, impaired acetylcholine metabolism in selected regions of the brain may contribute to the early symptoms of neurological dysfunction in hypoglycemia.     

Relations between Blood Glucose and Hepatic Glucose Production in Newborn Dogs

No correlation was found between the concentration of glucose in blood plasma and the rate of hepatic glucose production in newborn pups aged 2½-112 hours. During the first few hours of life the hypoglycaemic response to insulin was small or absent. Later the response seemed exaggerated mainly owing to a slow recovery to normoglycaemia. This latter observation can be entirely accounted for by the lack of a feedback mechanism between the plasma concentration and the hepatic rate of production of glucose.     

Angiotensin and Cerebral Blood Flow

1.General properties of the cerebral circulation.2.Cerebral blood flow autoregulation in hypertension, in stroke, and during the aging process.3.The Angiotensin system.4.Angiotensin receptor subtypes.5.Angiotensin receptors and actions of Angiotensin II in the brain: interactions between the brain and circulating Angiotensin II.6.The cerebrovascular Angiotensin system.7.Effects of Angiotensin II on cerebrovascular reactivity.8.Angiotensin and cerebrovascular flow.9.Effects of therapeutic modulation of the Angiotensin II system on cerebrovascular regulation in health and disease.10.Conclusions.     

Turnaround of Axoplasmic Transport of Selected Particle-Specific Enzymes at an Injury in Control and Diisopropylphosphorofluoridate-Treated Rats

: Reversal of direction (turnaround) of axonal transport of particle specific enzyme activities was studied at a ligature placed on rat sciatic nerve. In the principal experiment, the ligature remained on the nerve in vivo several hours, allowing enzyme activities (acetylcholinesterase, acid phosphatase, and monoamine oxidase) to accumulate immediately proximal to the tie. The nerve was then tied a second time, proximal to the first tie, and incubated in vitro for several more hours. Accumulation of enzyme activities just distal to the second tie was measured. This second accumulation, of activities traveling in the retrograde direction, was shown to be the result of turnaround in several ways. (1) The increase in activity distal to the second tie was equal to the decrease in activity proximal to the first. (2) The increase in enzyme activities distal to the second tie was greatly reduced when the accumulation proximal to the first tie was trapped by placing a third tie between the first and second ties. (3) It was shown that the activity that accumulated distal to the second tie could not have been in retrograde motion at the time of the first tie. (4) Accumulation distal to the second tie was not a function of the length of nerve segment included between the two ties. In contrast to the consistent occurrence of turnaround of orthograde flow, turnaround of retrograde flow could not be demonstrated. Turnaround transport was blocked by incubation in the cold and in the presence of NaCN or vinblastine. The turnaround process operated on all three enzymes studied, suggesting that it operates on lysosomes and mitochondria, as well as on the endoplasmic reticulum-like material bearing acetylcholinesterase. Evidence for the participation of the transport process in the renewal of AChE in the distal portions of the axon was obtained in experiments using diisopropylphosphorofluoridate and cycloheximide.     

The Effect of Morphine on Regional Cerebral Blood Flow Measured by 99mTc-ECD SPECT in Dogs

To gain insights into the working mechanism of morphine, regional cerebral blood flow (rCBF) patterns after morphine administration were assessed in dogs. In a randomized cross-over experimental study, rCBF was estimated with ^99mTc-Ethylcysteinate Dimer single photon emission computed tomography in 8 dogs at baseline, at 30 minutes and at 120 minutes after a single bolus of morphine. Perfusion indices (PI) in the frontal, parietal, temporal and occipital cortex and in the subcortical and cerebellar region were calculated. PI was significantly decreased 30 min after morphine compared to baseline in the right frontal cortex. The left parietal cortex and subcortical region showed a significantly increased PI 30 min after morphine compared to baseline. No significant differences were noted for the other regions or at other time points. In conclusion, a single bolus of morphine generated a changing rCBF pattern at different time points.