Lipid Peroxidation In Vivo Induced by Reversible Global Ischemia in Rat Brain

It has been hypothesized that ischemia, followed by reperfusion, facilitates peroxidative free-radical chain processes in brain. To resolve this question, rats were subjected to reversible global ischemia. From coronal sections of brains frozen in situ, small (ca. 2 mg) amounts of tissue were sampled from neocortex, hippocampus, and thalamus of both cerebral hemispheres of four groups of rats exposed to 30 min cerebral ischemia followed by 0, 30, 60, and 240 min of reperfusion, and from a control group subjected to the same operative procedures, except for the induction of ischemia. Heptane-solubilized total lipid extracts from these samples were analyzed spectroscopically in the 190-330 nm range for content of isolated (nonconjugated) double bonds and of conjugated diene structures; the latter are formed from isolated double bonds during peroxidation of unsaturated fatty acids. Spectra derived from tissue regions of rats subjected to ischemia, or ischemia followed by reperfusion, were compared to averaged, region-specific control spectra and were normalized to the original content of isolated double bonds in the peroxidized samples. The resultant difference spectra were analyzed in terms of ratios of conjugated diene concentration to the concentration of isolated double bonds originally at risk in the specific tissue zones considered. The peak representing conjugated diene formation was centered at 238 +/- 1 nm and was usually well resolved when the molar ratio [conjugated diene]/[isolated double bonds], expressed as a percentage [( CD]/[IDB]), was greater than 0.25%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lipid Peroxides in the Free Radical Pathophysiology of Brain Diseases

1. Polyunsaturated fatty acids are essential for normal neural cell membrane functioning because many membrane properties, such as fluidity and permeability, are closely related to the presence of unsaturated and polyunsaturated side chains. Lipid peroxidation results in loss of membrane polyunsaturated fatty acids and oxidized phospholipids as polar species contributing to increased membrane rigidity.2. Polyunsaturated fatty acids are released from membrane phospholipids by a number of enzymic mechanisms involving the receptor-mediated stimulation of phospholipase A₂ and phospholipase C/diacylglycerol lipase pathways.3. The overstimulation of excitatory amino acid (EAA) receptors stimulates the activities of lipases and phospholipases, and this stimulation produces changes in membrane phospholipid composition, permeability, and fluidity, thus decreasing the integrity of plasma membranes.4. Alterations in properties of plasma membranes may be responsible for the degeneration of neurons seen in neurodegenerative diseases. Two major processes may be involved in neuronal injury caused by the overstimulation of EAA receptors. One is a large Ca²⁺ influx and the other is an accumulation of free radicals and lipid peroxides as a result of neural membrane phospholipid degradation. It is suggested that calcium and free radicals act in concert to induce neuronal injury in acute trauma (ischemia and spinal cord injury) and in neurodegenerative diseases.     

脱氧核糖核酸对过氧化脂质和脂褐素生成的影响

实验探讨了脱氧核糖核酸（DNA）对小鼠心脏、肝脏和脑组织中的过氧化脂质（LPO）和脂褐素（Lf）生成的影响。结果表明,实验条件下所使用的脱氧核糖核酸可使小鼠体内过氧化脂质的生成明显减少,对脑和肝组织中脂褐素的生成有抑制效果。     

Mitochondrial Calcium Transport and Mitochondrial Dysfunction After Global Brain Ischemia in Rat Hippocampus

Here we report effect of ischemia-reperfusion on mitochondrial Ca²⁺ uptake and activity of complexes I and IV in rat hippocampus. By performing 4-vessel occlusion model of global brain ischemia, we observed that 15 min ischemia led to significant decrease of mitochondrial capacity to accumulate Ca²⁺ to 80.8% of control whereas rate of Ca²⁺ uptake was not significantly changed. Reperfusion did not significantly change mitochondrial Ca²⁺ transport. Ischemia induced progressive inhibition of complex I, affecting final electron transfer to decylubiquinone. Minimal activity of complex I was observed 24 h after ischemia (63% of control). Inhibition of complex IV activity to 80.6% of control was observed 1 h after ischemia. To explain the discrepancy between impact of ischemia on rate of Ca²⁺ uptake and activities of both complexes, we performed titration experiments to study relationship between inhibition of particular complex and generation of mitochondrial transmembrane potential (ΔΨ_m). Generation of a threshold curves showed that complex I and IV activities must be decreased by approximately 40, and 60%, respectively, before significant decline in ΔΨ_m was documented. Thus, mitochondrial Ca²⁺ uptake was not significantly affected by ischemia-reperfusion, apparently due to excess capacity of the complexes I and IV. Inhibition of complex I is favourable of reactive oxygen species (ROS) generation. Maximal oxidative modification of membrane proteins was documented 1 h after ischemia. Although enhanced formation of ROS might contribute to neuronal injury, depressed activities of complex I and IV together with unaltered rate of Ca²⁺ uptake are conditions favourable of initiation of other cell degenerative pathways like opening of mitochondrial permeability transition pore or apoptosis initiation, and might represent important mechanism of ischemic damage to neurones.     

Thromboxane and Prostacyclin Levels in Fetal Rabbit Brain and Placenta After Intrauterine Partial Ischemic Episodes

The appearance of arachidonic acid (AA) oxidation products in fetal rabbit brain and placenta under normal or partial short-term ischemic episodes induced by placental blood vessel restriction was examined. Intracerebral administration of [3H]AA into close-to-term rabbit fetuses gave rise to radioactively labeled prostaglandin (PG) E2, thromboxane B2, and 6-keto-PGF1 alpha metabolites as detected by HPLC analysis. A significant increase of 20-30% of [3H]AA precursor into eicosanoids was detected in brain of fetuses after 2-h restriction. The thromboxane B2 and 6-keto-PGF1 alpha levels were determined by radioimmunoassay technique over a period of 48 h following ischemic episodes. Thromboxane B2 content in affected animals was higher by five- and twofold at 3 h over control fetal brain and placental tissue values, respectively, and remained significantly higher for 24 h. 6-Keto-PGF1 alpha levels reached a peak value that was greater by 2.5- and 1.5-fold at 6 h for the ischemic brain and placental tissue, respectively, compared with control fetuses. PGE2 levels were less affected, attaining a maximum of 1.9- and 1.1-fold in brain and placenta correspondingly. The thromboxane/prostacyclin ratio reached a maximum in the brain after approximately 3 h, while that in the placenta continued to rise even after 20 h. Persisting high levels of thromboxane are indicative of cerebral vasoconstriction and may suggest possible damaging effects.     

Lipid Peroxidation and Antioxidant Systems in Rat Brain: Effect of Chronic Alcohol Consumption

The effect of chronic ethanol exposure, in a liquid diet, on lipid peroxidation and some antioxidant systems of rat brain was investigated. Chronic ethanol administration induced a greater susceptibility to iron/ascorbate-induced lipid peroxidation, estimated as thiobarbituric reactive substances (TBARS) production, in the microsomal fraction, but a lower lipid peroxidation in the total homogenate. Glutathione (GSH) levels as well as GSH peroxidase and GSH reductase were unaffected, while the activity of Cu-Zn superoxide dismutase was decreased and that of catalase increased. Lipid peroxidation experiments performed in the presence of some hydroxyl radical scavengers suggested that a greater OH^· generation may be responsible of the greater TBARS production in the microsomal fraction of ethanol treated rats; differently, in total homogenate of control and ethanol rats a relationship was found between the redox state of iron and TBARS production, suggesting that the lower lipid peroxidation in treated rats may depend on a different modulation of the iron redox state.     

Antimalarial Drugs Exacerbate Rat Liver Microsomal Lipid Peroxidation in the Presence of Oxidants

The study was undertaken to evaluate the effect of prior treatment of rats with the antimalarial drugs amodiaquine (AQ) mefloquine (MQ) and halofantrine (HF) on rat liver microsomal lipid peroxidation in the presence of 1 mM FeSO4, 1 mM ascorbate and 0.2 mM H₂O₂ (oxidants). Ingestion of -tocopheral, a radical chain-breaking antioxidant was also included to assess the role of antioxidants in the drug treatment. In the presence of oxidants AQ, MQ and HF elicited 288%, 175% and 225% increases in malondialdehyde (MDA) formation while the drugs induced 125%, 63% and 31% increases in the absence of oxidants respectively. Similarly, AQ, MQ and HF induced lipid hydroperoxide formation by 380%, 256%, 360% respectively in the presence of oxidants and 172%, 136% and 92% in the absence of exogenously added oxidants respectively. -tocopherol reduced AQ, MQ and HF-induced MDA formation by 40%, 55% and 52% respectively and lipid hydroperoxide formation by 53%, 59% and 54% respectively. Similarly, -tocopherol attenuated the AQ, MQ and HF-induced MDA formation by 49%, 51% and 51% in the presence of oxidants and lipid hydroperoxide formation by 61%, 62% and 47% respectively. The results indicate that rat liver microsomal lipid peroxidation could be enhanced by antimalarial drugs in the presence of reactive oxygen species and this effect could be ameliorated by treatment with antioxidants.     

Effects of Vitamin A and Its Analogs on Nonenzymatic Lipid Peroxidation in Rat Brain Mitochondria

Vitamin A (retinol) and some of its analogs exhibited varying degrees of inhibition on induced iron and ascorbic acid lipid peroxidation of rat brain mitochondria. Malonyldialdehyde production was used as an index of the extent of in vitro lipid peroxidation. The fat-soluble vitamins retinol, retinol acetate, retinoic acid, retinol palmitate, and retinal at concentrations between 0.1 and 10.0 mmol/L inhibited brain lipid peroxidation. Retinol and retinol acetate were the most effective inhibitors. It is concluded from this study that retinol and its analogs can be considered as potential antioxidant factors, more potent than some of the well-known antioxidants such as alpha-tocopherol and butylated hydroxytoluene.     

Enhancement of ATPase Activity by a Lipid Peroxide of Arachidonic Acid in Rat Brain Microvessels

The effects of 15-hydroperoxyarachidonic acid (15-HPAA) on Na+, K+- and Mg+-ATPase activities in the blood-brain barrier (BBB) were examined using rat brain microvessels (MV). 15-HPAA markedly stimulated these ATPase activities in MV at low concentrations whereas the synaptosomal Na+, K+-ATPase activity was inhibited in a dose-dependent manner. Further neurochemical analysis revealed that this stimulatory effect of 15-HPAA in MV was not due to a simple detergent-like action of the compound on the membranes but rather to stimulation of the phospholipase A2 and lipoxygenase activity within MV. In addition, it was shown that free radical reactions were involved in the mechanism. Since such anti-edema drugs as 1,2-bis(nicotinamido)propane were proved to be potent suppressors of the enhanced ATPase activity, further speculations on the role of this effect for ischemic brain edema are offered.     

Effects of CDPcholine and CDPethanolamine on the Alterations in Rat Brain Lipid Metabolism Induced by Global Ischemia

Abstract: The fast turnover pool of rat brain lipids was labeled by intracerebral injection of [³H]acetate. Cerebral ischemia for a duration of 5 min after decapitation caused a 2.2-fold increase in radioactivity in the free fatty acids and loss of more than 20% of the radioactivity from choline and ethanolamine glycerophospholipids. An intracerebral injection of 0.6 μmol each of cytidine diphosphocholine (CDPcholine) and cytidine diphosphoethanolamine (CDPethanolamine) prevented the loss of radioactivity from the glycerophospholipids and decreased the amount of radioactivity in the free fatty acids by 59% as compared with control values and 82% as compared with ischemia values. By GLC assays of the mass of the free fatty acids, there was a threefold increase of free fatty acids in ischemic brains. Pretreatment of ischemic brains with CDPcholine and CDPethanolamine reduced the levels of unesterified fatty acids to 60% of the control values. Thus, a prior injection of cytidine nucleotides prevented the release of free fatty acids observed in ischemic brains.     

Alterations of the Eicosanoid Synthetic Capacity of Rat Brain Microvessels Following Ischemia: Relevance to Ischemic Brain Edema

To know the mechanism underlying ischemic brain edema, a time-course analysis of the eicosanoid synthetic capacity of brain microvessels was carried out using unilateral, middle cerebral artery (MCA)-occluded rats. Concomitant with the development of brain edema the synthetic capacity of all products, including cyclooxygenase and lipoxygenase products, increased significantly. Next the effects of 15-hydroperoxyarachidonic acid (15-HPAA) on the synthetic capacity of microvessels were examined. The drug caused a generalized increase of each product, the profile of which was similar to that obtained with ischemic hemispheres, although the ratios of each product differed somewhat among them. The enhanced synthesis of eicosanoids by 15-HPAA was markedly suppressed by radical scavengers such as alpha-tocopherol, hydroquinone, and 1,2-bis(nicotineamide)-propane. Furthermore, the evolution of brain edema was virtually suppressed by the systemic administration of 1,2-bis(nicotineamide)-propane. The above result suggests that the enzyme activity of the arachidonic acid (AA) cascade of microvessels is stimulated by its own products. Such a mechanism will form a vicious cycle that accelerates the accumulation of free radicals within microvessels and thus may play a role in the progressing disruption of the blood-brain barrier (BBB) following ischemia.     

Modulation of Fetal Rat Brain and Liver Phospholipid Content by Intraamniotic Ethyl Docosahexaenoate Administration

Abstract: In an attempt to elucidate the role of docosahexaenoic acid (DHA; 22:6n-3) in the developing brain, a method was devised whereby rapid enrichment of fetal brain and liver lipid with DHA was achieved. Fetal rats at 17 days of gestation were injected intraamniotically with ethyl docosahexaenoate (EtDHA). Control fetuses were administered ethyl oleate (EtOle). Brain lipid DHA content increased by almost 21% (p = 0.02) 3 days after EtDHA administration as compared with EtOle-injected fetuses, whereas liver lipid DHA content increased by almost 60% (p = 0.0002). At this time brain phosphatidylinositol content doubled, whereas phosphatidylserine (PS) content increased by >50% (p = 0.03). Increases in liver PS (+25.8%; p = 0.015) and sphingomyelin (+43.6%; p = 0.01) content were observed. A redistribution of total brain phospholipid (PL) DHA was observed following Et-DHA administration, resulting in a 56.4% increase in PS-DHA abundance (p < 0.05) and an 8.8% decrease in phosphatidylethanolamine-DHA abundance (p = 0.05). These results suggest modulation of fetal brain and liver PL and provide a method for enrichment of DHA content in discrete PLs during intrauterine life.     

Global Brain Ischemia and Reperfusion: Modifications in Eukaryotic Initiation Factors Associated with Inhibition of Translation Initiation

Abstract: We used in vitro translation and antibodies against phosphoserine and the eukaryotic initiation factors eIF-4E, eIF-4G, and eIF-2α to examine the effects of global brain ischemia and reperfusion on translation initiation and its regulation in a rat model of 10 min of cardiac arrest followed by resuscitation and 90 min of reperfusion. Translation reactions were performed on postmitochondrial supernatants from brain homogenates with and without aurintricarboxylic acid to separate incorporation due to run-off from incorporation due to peptide synthesis initiated in vitro. The rate of leucine incorporation due to in vitro-initiated protein synthesis in normal forebrain homogenates was ∼0.4 fmol of leucine/min/µg of protein and was unaffected by 10 min of cardiac arrest, but 90 min of reperfusion reduced this rate 83%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blots of these homogenates showed that neither 10 min of global brain ischemia nor 90 min of reperfusion induced significant alterations in the quantity or serine phosphorylation of eIF-4E. However, we observed in all 90-min-reperfused samples eIF-4G fragments that also bound eIF-4E. The amount of eIF-2α was not altered by ischemia or reperfusion, and immunoblotting after isoelectric focusing did not detect serine-phosphorylated eIF-2α in normal samples or in those obtained after ischemia without reperfusion. However, serine-phosphorylated eIF-2α was uniformly present after 90 min of reperfusion and represented 24 ± 3% of the eIF-2α in these samples. The serine phosphorylation of eIF-2α and partial fragmentation of eIF-4G observed after 90 min of reperfusion offer an explanation for the inhibition of protein synthesis.     

Ageing-Induced Alterations in Lipid/Phospholipid Profiles of Rat Brain and Liver Mitochondria: Implications for Mitochondrial Energy-Linked Functions

Effects of ageing on the lipid/phospholipid profile of brain and liver mitochondria from rats were examined. In the brain mitochondria the contents of total phospholipid (TPL) and cholesterol (CHL) increased with simultaneous increase in the TPL/CHL (mole:mole) ratio. The proportion and contents of lysophospholipid (Lyso), sphingomyelin (SPM), phosphatidylinositol (PI), phosphatidylserine (PS) and diphosphatidylglycerol (DPG) components increased, with maximal increases seen for PS and PI; phosphatidylcholine (PC) and phosphatidylethanolamine (PE) components registered decrease. In the liver mitochondria contents of TPL and CHL increased. However, the TPL/CHL (mole:mole) ratio was not altered. Lyso, PI and PS increased. However, the magnitude of increase was competitively lower; PE and DPG decreased. SPM and PC did not change as a consequence of ageing. These changes altered the contents of individual phospholipids in the two membrane systems. Respiration with glutamate, pyruvate + malate, succinate and ascorbate + N,N,N’,N’-tetramethyl-p-phenylenediamine was significantly impaired in brain mitochondria from old animals. For liver mitochondria the respiratory activity declined with glutamate and succinate. Correlation studies by regression analysis revealed that the lipid/phospholipid classes regulate respiratory function differently in the mitochondria from the two tissues. The respiration-related parameters in the brain mitochondria were dependent on multiple lipid/phospholipid components, and the process of regulation was complex compared to the liver mitochondrial functions.     

Hypoxia-Induced Lipid Peroxidation in Rat Brain and Protective Effect of Carnitine and Phosphocreatine

The exposure to hypobaric hypoxia increased lipid peroxidation (as indicated by thiobarbituric acid-reactive substances [TBARS] in rat brain. Plasma lactate/pyruvate ratio was used as a marker of hypoxia. We compared the protective effect of -tocopherol with the effect of l-carnitine or phosphocreatine. Rats pretreated with -tocopherol, l-carnitine, or phosphocreatine had lower TBARS levels after the exposure to hypobaric hypoxia. However, lactate/pyruvate ratio was improved only in rats pretreated with l-carnitine or phosphocreatine. We conclude from our data that, contrary to -tocopherol, protective effects of l-carnitine and phosphocreatine administrations are due to their regulation of metabolic reactions during hypobaric hypoxia rather than to their scavenger activity.     

Lipid Peroxidation in Rat Brain Cortical Slices as Measured by the Thiobarbituric Acid Test

Abstract: Malonaldehyde formation by cortical brain slices from rat brain was determined as a function of incubation time and of oxygen pressure. This substance, a byproduct of lipid peroxidation, was detected by the thiobarbituric acid test. Significant amounts of malonaldehyde were formed by brain slices during incubation in the 0.2 (air) to 10 atm oxygen range, and a portion of it was released into the medium. The rate of malonaldehyde formation was the highest during the first 10 min. Elevation of oxygen pressure above 1 atm caused further increments in malonaldehyde production with kinetic properties similar to that seen at 1 atm pressure, but the increments per additional oxygen pressure were diminishing. The formation of a given amount of malonaldehyde can be expressed as a function of atm oxygen × min. This function has the shape of a saturation curve approaching a maximum at around 300 atm × min. The results indicate extensive lipid peroxidation in brain slices under standard incubation conditions.     

A fluorescence approach of the gamma radiation effects on gramicidin A inserted in liposomes.

The fluorescence of tryptophan residues of gramicidin A (gA), bound to phosphatidylcholine liposomes contains valuable information about local changes in the environment of the molecule induced by gamma radiation. With this work, we aim to demonstrate that the gamma radiation effect on the peptide involves the action of free radicals, derived from water radiolysis and the process of lipid peroxidation. Basically, the methodology consists of the analysis of UV and fluorescence emission spectra of the peptide liposome complexes under control conditions and upon gamma irradiation. Free radical production was impaired by the removal of molecular oxygen or the presence of ethanol in the liposome suspension. The intensity of the tryptophan fluorescence was recorded as a function of the gamma radiation dose in the range of 0-250 Gy and the data were fitted with a single decay exponential function containing an additional constant term (named residual fluorescence). The correlation between the decrease in tryptophan fluorescence emission (D(c) = 80 +/- 10 Gy) and increase in gamma radiation dose indicates the partial damage of the tryptophan side chains of gA. O(2) removal or ethanol addition partially reduced the decay of the tryptophan fluorescence emission involving an indirect action of gamma radiation via a water radiolysis mechanism. The residual fluorescence emission (A(0)) increases in O(2)-free buffer (98 +/- 13) and in 10% ethanol-containing buffer (74 +/- 34) compared to control conditions (23 +/- 5). Varying the dose rate between 1-10 Gy/min at a constant dose of 50 Gy, an inverse dose-rate effect was observed. Thus, our study provides evidence for the lipid peroxidation effect on the tryptophan fluorescence. In conclusion, this article sustains the hypothesis of the connection between the lipid peroxidation and structural changes of membrane proteins induced by gamma radiation. Copyright (c) 2008 European Peptide Society and John Wiley & Sons, Ltd.     

Reduction of HSP70 and HSC70 Heat Shock mRNA Induction by Pentobarbital After Transient Global Ischemia in Gerbil Brain

Abstract: The effect of pentobarbital on the induction of heat shock protein (HSP) 70 and heat shock cognate protein (HSC) 70 mRNAs after transient global ischemia in gerbil brains was investigated by in situ hybridization using cloned cDNA probes selective for each mRNA species. In sham control brains, HSP70 mRNA was scarcely present, whereas HSC70 mRNA was present in most cell populations. After a 5-min occlusion of bilateral common carotid arteries, HSP70 and HSC70 mRNAs were induced together in several cells and were especially dense in hippocampal dentate granule cells at 3 h, but the strong hybridization of the mRNAs continued only in hippocampal CA1 cells by 2 days. At 7 days after the ischemia, CA1 neuronal cell death was apparent, and the HSP70 mRNA disappeared and HSC70 mRNA content returned to the sham level, except for in the CA1 cells. Pretreatment with pentobarbital (40 mg/kg, i.p.) greatly reduced or inhibited the induction of HSP70 and HSC70 mRNAs at both early (3-h) and late (2-day) phases after ischemia. The drug also prevented CA1 cell death at 7 days along with the maintenance of expression of HSC70 mRNA at the sham control level. Hypothermic effects of pentobarbital were noted at 30 and 60 min after the reperfusion, whereas at 2 h there was no statistical significance between the control and drug-treated groups. The great reduction of HSP70 and HSC70 mRNA induction at both early and late phases after ischemia suggests that pentobarbital reduces intra- and/or postischemic stress and may protect CA1 cells from ischemic damage. These effects of the drug may be mainly due to its specific action rather than its hypothermic effects.     

Delayed Postconditionig Initiates Additive Mechanism Necessary for Survival of Selectively Vulnerable Neurons After Transient Ischemia in Rat Brain

1. The aim of this study was to validate the role of postconditioning, used 2 days after lethal ischemia, for protection of selectively vulnerable brain neurons against delayed neuronal death.2. Eight, 10, or 15 min of transient forebrain ischemia in rat (four-vessel occlusion model) was used as initial lethal ischemia. Fluoro Jade B, the marker of neurodegeneration, and NeuN, a specific neuronal marker were used for visualization of changes 7 or 28 days after ischemia without and with delayed postconditioning.3. Our results confirm that postconditioning if used at right time and with optimal intensity can prevent process of delayed neuronal death. At least three techniques, known as preconditioners, can be used as postconditioning: short ischemia, 3-nitropropionic acid and norepinephrine. A cardinal role for the prevention of death in selectively vulnerable neurons comprises synthesis of proteins during the first 5 h after postconditioning. Ten minutes of ischemia alone is lethal for 70% of pyramidal CA1 neurons in hippocampus. Injection of inhibitor of protein synthesis (Cycloheximide), if administered simultaneously with postconditioning, suppressed beneficial effect of postconditioning and resulted in 50% of CA1 neurons succumbing to neurodegeneration. Although, when Cycloheximide was injected 5 h after postconditioning, this treatment resulted in survival of 90% of CA1 neurons.4. Though postconditioning significantly protects hippocampal CA1 neurons up to 10 min of ischemia, its efficacy at 15 min ischemia is exhausted. However, protective impact of postconditioning in less-sensitive neuronal populations (cortex and striatum) is very good after such a damaging insult like 15 min ischemia. This statement also means that up to 15 min of ischemia, postconditioning does not induce cumulation of injuries produced by the first and the second stress.     

Acute Uteroplacental Ischemic Embryo: Lactic Acid Accumulation and Prostaglandin Production in the Fetal Rat Brain

A new experimental model for studying the effects of acute ischemia on brain development in the near-term fetal rat has been devised. Ischemic conditions are achieved by complete clamping of blood vessels branching from the uterine vasculature into each individual fetus for designated times followed by removal of the clamps to permit reperfusion. Accumulation of lactic acid in the fetal brain depends on the length of the restriction period, reaching a plateau level of 29 mumol/g tissue at about 30 min. It also depends on the reperfusion time. Thus after a period of 15 min of restriction lactate levels show an increase over the next 30-min reperfusion to a value of 25.5 mumol/g followed by a rapid decrease to normal values by 3 h of reperfusion. Restriction of 15 min followed by reperfusion of 45 min causes an elevation of prostaglandin E2 (PGE2) level from 12.4 +/- 0.86 ng/g to 21.1 +/- 0.6 ng/g (p less than 0.001). This elevation in PGE2 level is less apparent after 20 min of restriction. No effects are seen on the level of PGF2 alpha. Both PGE2 and PGF2 alpha accumulate in vitro in a time-dependent manner by brain particulate fraction. In vitro synthesis of both PGE2 and PGF2 alpha is inhibited by indomethacin (100% and 68%, respectively) and AA861 (94% and 76%, respectively). BW755c and nordihydroguaiaretic acid do not affect PGE2 formation but enhance PGF2 alpha production by 112% and 152%, respectively. Particulate fractions from restricted brain produce less PGF2 alpha than control brains (6.38 +/- 1.62 versus 11.43 +/- 2.2, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)