Calcium Antagonist Isradipine Reduces Metabolic Alterations in Acute Cerebral Ischemia in Spontaneously Hypertensive Rats

The present study was designed to examine the effect of a calcium antagonist isradipine (PN200-110: PN) on local cerebral blood flow and brain tissue metabolism after 1-hour supratentorial ischemia induced by bilateral carotid artery ligation (BCL) in spontaneously hypertensive rats (SHR). PN, dissolved in ethanol plus polyethylene glycol 400, diluted with saline to make the final concentration of 0.25mg/ml and 2.5mg/ml, was administered subcutaneously either 30 min prior to BCL or just after the induction of incomplete cerebral ischemia (n = 7 in each group). Vehicle injection was served as a control group (n = 7). Cerebral blood flow in the parietal cortex (CBF) and the cerebellar cortex (CeBF) was measured by hydrogen clearance technique, and the supra- and infratentorial metabolites of the brain frozen in situ were determined by the enzymatic method. Blood pressure was lowered, but CBF was increased by PN administration in pre-BCL treatment study. After 1 hour of BCL, CBF decreased to around 10% or less of the resting value, being insignificant among the groups. Brain adenosine triphosphate was better preserved in PN-administered groups. The increase in lactate level tended to reduce dose dependently by PN treatment. PN also reduced the metabolic alterations in brain tissue with significance, even when administered just after the induction of forebrain ischemia. It is considered that pre- as well as post-BCL administration of PN is beneficial to attenuate the metabolic alterations in incomplete forebrain ischemia in SHR.     

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.     

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.     

Nutritional Prevention on Hypertension, Cerebral Hemodynamics and Thrombosis in Stroke-Prone Spontaneously Hypertensive Rats

1. Stroke-prone spontaneously hypertensive rats (SHRSP/Izm), which become severely hypertensive and exhibit a very high incidence of stroke (cerebral hemorrhage and/or infarction), are used widely for the study of the hypertension and stroke. In the previous study, we indicated that high thrombotic tendency of cerebral microvessels in SHRSP/Izm compared with stroke-resistant SHR (SHR/Izm) and normotensive Wistar Kyoto rats (WKY/Izm) at aged period. 2. L-arginine, a substrate of nitric oxide (NO), and voluntary exercise reduced blood pressure and thrombotic tendency in cerebral microvessels caused by highly production of NO in vivo. Furthermore, antioxidants show that the effects of antihypertensive and antithrombosis in SHRSP/Izm. 3. Although SHRSP/Izm become genetically hypertensive and exhibit stroke, a number of nutritional factors, particularly antioxydative nutrient, have preventive effects on hypertension, cerebral blood flow dysfunction, thrombus formation, and neuronal cell death in SHRSP/Izm. Our results indicate that those treatments are beneficial in the prevention of hypertension and stroke and that the nutritional science is very important for "prediction and prevention medicine."     

Regional Cerebral Glucose Phosphorylation and Blood Flow After Insertion of a Microdialysis Fiber Through the Dorsal Hippocampus in the Rat

Local cerebral glucose metabolism (LCMRglc) and local cerebral blood flow (LCBF) were studied following implantation of a microdialysis fiber in rat dorsal hippocampus. Recovery time after implantation varied from 0 to 24 h. All rats showed pronounced disturbances in LCMRglc and LCBF during the first 2 h of implantation. The changes consisted of (a) a general decrease in blood flow and glucose phosphorylation and (b) small areas (spots) around the fiber with increased glucose phosphorylation and decreased blood flow. Animals allowed to recover for 24 h demonstrated a near normalization of LCMRglu and LCBF, and the focal disturbances (spots) of glucose phosphorylation and blood flow disappeared. The slight reduction in blood flow and glucose metabolism at this time must be accepted, because extension of the recovery period beyond 24 h may give interpretation problems due to the developing gliosis.     

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.     

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.     

Effect of Hypothermia on Brain Cell Membrane Function and Energy Metabolism in Experimental Escherichia coli Meningitis in the Newborn Piglet

We evaluated the anti-inflammatory and neuroprotective effects of hypothermia during the early phase of experimental Escherichia coli meningitis in the newborn piglet. Hypothermia significantly attenuated the meningitis-induced acute inflammatory responses such as increased intracranial pressure, decreased glucose level, increased lactate concentration, increased tumor necrosis factor- level and leukocytosis in the cerebrospinal fluid. Decreased cerebral cortical cell membrane Na⁺,K⁺-ATPase activity and increased lipid peroxidation products, indicative of meningitis-induced brain damage, were significantly improved with hypothermia. Hypothermia also significantly improved the meningitis-induced reduction in brain ATP and phosphocreatine levels. In summary, hypothermia significantly attenuated the acute inflammatory responses and the ensuing brain injury in experimental neonatal bacterial meningitis.     

Effects of Mild Hypothermia on the Release of Regional Glutamate and Glycine During Extended Transient Focal Cerebral Ischemia in Rats

The present study is to determine the effect of mild hypothermia (MHT) on the release of glutamate and glycine in rats subjected to middle cerebral artery occlusion and reperfusion. The relationship between amino acid efflux and brain infarct volume was compared in different periods during MHT. Reversible middle cerebral artery occlusion was performed in Sprague-Dawley rats using a suture model. The rats were divided into four groups including (1) MHT during ischemia (MHTi), (2) MHT during reperfusion (MHTr), (3) MHT during ischemia and reperfusion (MHTi + r), and (4) a normothermic group (NT). Extracellular concentrations of glutamate and glycine in the cortex and striatum were monitored using in vivo microdialysis and analyzed using high-performance liquid chromatography. Morphometric measurements for infarct volume were performed using 2,3,5-triphenyltetrazolium chloride staining. The increase of glutamate and glycine in the ischemic cortex of the MHTi and MHTi + r rats during ischemic and reperfusion periods was significantly less than that of the NT rats (p < 0.05). However, there was no statistical difference among these groups in the peak of glutamate and glycine release in the striatum. Infarct volume paralleled the release of glutamate and glycine. The protective effect of MHTi and MHTi + r in reducing ischemia and reperfusion brain injury may be due to the attenuation of both glutamate and glycine release during ischemia and reperfusion.     

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 AMPA on Cerebral Cortical Oxygen Balance of Ischemic Rat Brain

We tested the hypothesis that the excitatory neurotransmitter receptor agonist, alpha amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), would worsen cerebral cortical oxygen supply/consumption balance during focal ischemia. In this study, we compared regional cerebral blood flow, arterial and venous O₂ saturation, O₂ extraction and oxygen consumption of ischemic and AMPA treated ischemic and control regions of rat brain. Ischemia was induced by middle cerebral artery (MCA) occlusion in isoflurane (1.4%) anesthetized Wistar rats. Twenty minutes after MCA occlusion, 10^–5 M AMPA was applied to the ischemic cortex (IC) for a period of 40 min; the fluid was changed every 10 min. After 1 hr of ischemia, animals were sacrificed and regional cerebral blood flow (rCBF) was determined using the C¹⁴-iodoantipyrine autoradiographic technique. Regional arterial and venous oxygen saturation were determined microspectrophotometrically. In control, the cerebral blood flow and oxygen consumption of the IC were significantly lower than the contralateral cortex (rCBF: 46 ± 20 vs. 81 ± 39 ml/min/100g, O₂ consumption: 2.8 ± 1.4 vs. 3.6 ± 1.4 ml O₂/min/100g). 10^–5 M AMPA did not significantly alter regional cerebral blood flow and oxygen consumption of the IC, but did decrease the average venous O₂ saturation of the IC from 50.2 ± 3.9% to 46.7 ± 1.6%. AMPA also significantly increased the frequency of small veins with less than 45% O₂ saturation in the IC (8 out of 56 veins in IC vs. 18 out of 56 veins in AMPA treated IC). Thus, topical application of 10^–5 M AMPA to the ischemic area worsens cerebral O₂ balance and suggests that excitatory amino acids contribute to the degree of cerebral ischemia.     

Age-Related Changes in the DNA and RNA Content of the Brain in Spontaneously Hypertensive Rats

To elucidate the effects of aging accompanied with hypertension on brain nucleic acid, we measured both the DNA and RNA contents of six specific brain regions in adult (5–6 months old) and aged (18–22 months old) female spontaneously hypertensive rats (SHRs). Although no statistical difference was observed in the RNA content, the DNA content did tend to increase in the hippocampal CA1 of aged SHR (4.24 ± 0.55 ng/g protein, mean ± SD, n = 6) in comparison to that of adult SHR (3.21 ± 0.71 ng/g protein, n = 4). Hence, aged SHRs showed a significant decrease in the RNA to DNA ratio in the CA1 subfield of the hippocampus (3.79 ± 0.61) compared to adult SHR (5.27 ± 0.81). On the other hand, no other regions, except for the dorsolateral region of the striatum, showed any difference in the RNA/DNA ratio between aged and adult SHR. We therefore conclude that subtle changes in the nucleic acid occur in vulnerable regions of the brain in aged SHRs.     

Substrain Differences, Gender, and Age of Spontaneously Hypertensive Rats Critically Determine Infarct Size Produced by Distal Middle Cerebral Artery Occlusion

1. The present work discussed the effects of substrain or genetic differences, gender, and age of the rat on infarct size produced by distal middle cerebral artery occlusion (MCAO) in spontaneously hypertensive rats (SHR). 2. In SHR/Kyushu, infarct volume was significantly larger than that of SHR/Izm, while blood pressure levels were essentially the same between the two substrains. Although SHR-SP/Izm had a higher blood pressure than SHR/Kyushu, infarct volumes were the same between SHR/Kyushu and SHR-SP/Izm. These results suggest the presence of blood pressure-independent factors which affect the infarct size after MCAO. 3. Estrogen accounted the large part of greater tolerability against focal brain ischemic injury in female compared with male SHR. 4. We found age-related vulnerability to focal cerebral ischemia in female SHR. This age-related vulnerability in aged female SHR was unrelated to the blood levels of sex hormones such as estrogens and progesterone. 5. Finally, we emphasized the importance of reproducible and least invasive focal ischemia models in stroke research.     

Effects of Excitatory Amino Acids on Cerebral Oxygen Consumption and Blood Flow in Rat

This investigation tested the importance of excitatory amino acids' effects on regional cerebral O₂ consumption and the concomitant changes in cerebral blood flow (rCBF) in isoflurane anesthetized rats. In the glutamate or N-methyl-D-aspartate (NMDA) groups, 10^–2 M glutamate or NMDA was topically applied to the right cortex and the left cortex was used as a control. One mg/kg dizocilpine maleate (MK-801), a non-competitive NMDA receptor antagonist, was administered (iv) to the MK-801 group and saline was given to the control group. Cortical rCBF was determined using ¹⁴C-iodoantipyrine and regional O₂ extraction was measured microspectrophotometrically. Cerebral O₂ consumption increased 77% after glutamate (contralateral cortex: 9.0 ± 1.1 ml O₂/min/100 g, glutamate treated cortex: 15.9 ± 3.9), while a 46% increase was observed with the same concentration of NMDA (contralateral cortex: 9.8 ± 2.0, NMDA treated cortex: 14.3 ± 5.5). After MK-801, the O₂ consumption decreased to 37% of the control value (control cortex: 7.0 ± 1.3, MK-801 treated cortex: 2.6 ± 3.9). MK-801 significantly decreased cerebral O₂ extraction from 7.1 ± 1.3 ml O₂/100 ml (control cortex) to 5.3 ± 0.6 (MK-801 treated cortex). However, there was no significant difference in cerebral O₂ extraction between treated and contralateral cortex in either the glutamate or NMDA groups. The increase in O₂ consumption caused by glutamate or NMDA was coupled with increased rCBF. Glutamate increased rCBF from 95 ± 5 ml/min/100 g (contralateral cortex) to 165 ± 31 (treated cortex), while NMDA increased rCBF from 114 ± 12 (contralateral cortex) to 178 ± 60 (treated cortex). MK-801 decreased O₂ consumption with a lesser decrease of rCBF. The rCBF was 48 ± 9 in the MK-801 treated cortex and 99 ± 22 in the control cortex. Some substances produced by the activation of NMDA receptors may be related to the coupling of cerebral metabolism and blood flow, since after blockade of NMDA receptors with MK-801, this relationship is uncoupled. These findings suggest that glutamatergic processes have a major effect on cerebral O₂ consumption and that this is at least partly due to NMDA receptors.     

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。     

双侧颈总动脉结扎对大鼠学习记忆相关脑区血流量的影响

目的为建立双侧颈总动脉结扎致大鼠血管性痴呆模型,观察了大鼠双侧颈总动脉结扎后不同脑区脑血流量的影响。方法采用激光多普勒血流仪,测定麻醉大鼠双侧颈总动脉结扎后１０ｍｉｎ内不同脑区脑血流量变化。结果大鼠双侧颈总动脉结扎后,平均脑血流量减少额区６７８３％、顶区５６８２％、枕区１６１６％、Ｍｙｎｅｒｔ基底核５１２１％、尾壳核４１１８％,海马ＣＡ１５１８３和海马ＣＡ２４１２１。结论大鼠双侧颈总动脉结扎后与学习记忆有关的脑区脑血流量均显著下降     

Reduction of Blood Pressure by Soybean Saponins,Renin Inhibitors from Soybean,in Spontaneously Hypertensive Rats

The effect of commercial purified soybean saponin on renin activity and blood pressure was investigated. Soybean saponin significantly inhibited human renin in vitro with IC₅₀=59.9 μg/ml. Orally administered soybean saponin at 80 mg/kg of body weight per day to spontaneously hypertensive rats for 8 weeks significantly decreased the blood pressure.     

Relationship Between Regional Brain Angiotensinogen a Local Blood Flow and Volume in the Adrenalectomize Rat: Application of Approach to Quantification of Brain Corticosterone Receptors

Abstract: Prior studies from this laboratory have established that angiotensinogen, the prohormone of angiotensin, is unevenly distributed in the rat brain and that adrenalectomy selectively perturbs levels of the prohormone in regions associated with cardiovascular neural pathways. However, plasma angiotensinogen levies are 10²-10³ times higher in plasma than in brain, so that the observation of a unique distribution of brain angiotensinogen may reflect variable plasma contamination. Studies were therefore undertaken to establish whether adrenalectomy selectively alters regional blood flow, blood volume, or plasma contamination of brain tissue, thereby artifactitiously altering apparent angiotensinogen levels. Radioactive 2-deoxyglucose, iodoantipyrine, and inulin were employed in these analyses. We conclude that variations in blood flow do not explain the selective effects of adrenalectomy, but that a variable extent of residual plasma contamination (remaining after transcardiac perfusion) is partially reflected in our earlier data. However, after correcting for plasma contamination, we still find significant changes in selected areas of the rat brain following adrenalectomy. Finally, our results demonstrate the necessity for direct quantitation of plasma contamination of brain tissue segments. This is shown to have relevance in other situations, such as corticosterone binding globulin contamination of brain corticosterone receptor binding.     

Nicotinamide Attenuates Focal Ischemic Brain Injury in Rats: With Special Reference to Changes in Nicotinamide and NAD+ Levels in Ischemic Core and Penumbra

We investigated the neuroprotective action of nicotinamide in focal ischemia. Male spontaneously hypertensive rats (5–7 months old) were subjected to photothrombotic occlusion of the right distal middle cerebral artery (MCA). Either nicotinamide (125 or 250 mg/kg) or vehicle was injected IV before MCA occlusion. Changes in the cerebral blood flow (CBF) were monitored using laser-Doppler flowmetry, and infarct volumes were determined with TTC staining 3 days after MCA occlusion. In another set of experiments, the brain nicotinamide and nicotinamide adenine dinucleotide (NAD⁺) levels were analyzed by HPLC using the frozen samples dissected from the regions corresponding to the ischemic core and penumbra. In the 250-mg/kg nicotinamide group, the ischemic CBF was significantly increased compared to that the untreated group, and the infarct volumes were substantially attenuated (–36%). On the other hand, the ischemic CBF in the 125 mg/kg nicotinamide group was not significantly different from the untreated CBF, however, the infarct volumes were substantially attenuated (–38%). Cerebral ischemia per se did not affect the concentrations of nicotinamide and NAD⁺ both in the penumbra and ischemic core. In the nicotinamide groups, the brain nicotinamide levels increased significantly in all areas examined, and brain NAD⁺ levels increased in the penumbra but not in the ischemic core. Increased brain levels of nicotinamide are considered to be primarily important for neuroprotection against ischemia, and the protective action may be partly mediated through the increased NAD⁺ in the penumbra.