Effects of hypoxia and recovery on brain eicosanoids and carbohydrate metabolites in rat brain cortex

Brain fixation for analysis of brain lipid-mediators of signal transduction and brain eicosanoids requires head-focused microwave irradiation: an historical perspective

To microwave or not to microwave, that is the question that has confounded the neurochemist as the quest for reducing changes in neurochemicals associated with post-mortem delay has evolved over the years. Rapid changes in brain constituents during the post-mortem delay have been recognized for years as a problem. What is real and what is artifact? What are true basal levels of molecules found in the brain? In the 1920s, neurochemists recognized this issue and determined freezing of the brain was most advantageous for halting rapid breakdown of some molecules and rapid formation of others. By the early 1970s, a number of laboratories noted that freezing the brain in situ or upon removing it from the cranial vault was not sufficient to reduce alterations in brain chemistry. Groups began experimenting with two different techniques to attack this problem, freeze-blowing and head-focused microwave irradiation. My laboratory and others have found that the utilization of head-focused microwave irradiation to halt enzymic alterations in lipids is an essential tool to limit alterations post-mortem. Recently, we and others have demonstrated that this technique is essential in reliably assessing brain eicosanoid levels, without such fixation true basal levels of eicosanoids are impossible to determine and the high concentrations seen in some paradigms may be merely an artifact produced during handling of the brain. Thus, for eicosanoid analysis and other applications in measuring brain lipid levels, head-focused microwave irradiation is an essential tool for the lipid neurochemist.

An imbalance between prostacyclin and thromboxane in relation to cerebral blood flow in neonates with maternal preeclampsia

OBJECTIVE

A disturbance of prostacyclin (PGI2) and thromboxane A2 (TXA2) balance has been reported in preeclampsia. However, little is known about the concentrations of these prostanoids in neonates born to preeclamptic pregnant women. The purpose of this study is to determine whether the PGI2 and TXA2 concentrations are altered and whether the prostanoid balance correlates to the cerebral blood flow in neonates born to preeclampsia.

METHODS

Spontaneously voided urine samples were collected from 20 neonates of normotensive and 16 neonates of preeclamptic women during the first 24 h after birth. We measured by radioimmunoassay the concentrations of urinary 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) and 11-dehydro-thromboxane B2 (11-dehydro-TXB2), respectively. Blood flow velocity in the middle cerebral artery was studied by pulsed Doppler ultrasonography in the neonates between 17 and 38 h after birth.

RESULTS

There was no significant difference between the urinary 6-keto-PGF1alpha in the neonates of mothers with and without preeclampsia (median, 5.3 vs. 3.6 ng/mg of creatinine). In contrast, the urinary 11-dehydro-TXB2 and the ratio of 11-dehydro-TXB2 to 6-keto-PGF1alpha in the neonates of mothers with preeclampsia were significantly lower as compared with the neonates without preeclampsia, respectively (13.7 vs. 20.6 ng/mg of creatinine and 3.0 vs. 5.2, median). The resistance index in the middle cerebral artery was significantly reduced in the neonates with preeclampsia than without preeclampsia (0.67 +/- 0.01 vs. 0.74 +/- 0.02, mean +/- SEM).

CONCLUSIONS

There was an association between maternal preeclampsia and the imbalance in the neonatal urinary excretion of PGI2 and TXA2 metabolites. This imbalance may contribute to the regulation of cerebral blood flow.

Metabolismo da glicose cerebral no trauma crânio-encefálico: uma avaliação

Os autores apresentam revisão geral da distribuição e metabolização da glicose, com ênfase para os distúrbios que ocorrem no trauma crânio-encefálico, como a hiperglicemia que ocorre na fase aguda. Finalizando, são feitos comentários sobre as possíveis conseqüências desses conhecimentos sobre os procedimentos atuais, que aconselham a restrição na oferta de glicose a pacientes com catabolismo acentuado e que necessitam poupar o contingente de proteína corporal.

Acute intrauterine hypoxia increases amniotic fluid prostaglandin F metabolites in the pregnant sheep

OBJECTIVE

Amniotic fluid infection promotes cytokine release, prostaglandin production, and premature labor. In several tissues local hypoxia also activates the secretion of cytokines. Many patients initially seen in premature labor carry small-for-gestational-age fetuses, a condition associated with intrauterine hypoxia. The purpose of our study was to determine whether a reduction in placental blood flow and subsequent acute hypoxia affects prostaglandin secretion by the placenta.

STUDY DESIGN

We chronically catheterized six pregnant sheep at 120 days of gestation. We placed catheters in the maternal and fetal femoral arteries and in the amniotic fluid cavity. A flow probe and snare were placed around the common uterine artery.

RESULTS

A 30-minute uterine circulation occlusion of 30% of its control value produced an increase in prostaglandin F metabolite from 790 +/- 157 to 944 +/- 184 pg/ml within 10 minutes (p < 0.01). Additional uterine blood flow reduction to 60% of control increased the amniotic fluid prostaglandin F metabolites concentration to 894 +/- 202 (p < 0.05, analysis of variance). No increase in mean intrauterine pressure was detected (p > 0.1).

CONCLUSIONS

We speculate that the prostaglandin increase in amniotic fluid in response to intrauterine hypoxia could eventually lead to premature labor. Whether the increase in prostaglandins is mediated by changes in cytokines is unknown at the present time.

Inhibition of sodium-potassium-ATPase: a potentially ubiquitous mechanism contributing to central nervous system neuropathology

Direct and indirect evidence suggests that Na+/K(+)-ATPase activity is reduced or insufficient to maintain ionic balances during and immediately after episodes of ischemia, hypoglycemia, epilepsy, and after administration of excitotoxins (glutamate agonists). Recent results show that inhibition of this enzyme results in neuronal death, and thus a hypothesis is proposed that a reduction and/or inhibition of this enzyme contributes to producing the central neuropathy found in the above disorders, and identifies potential mechanisms involved. While the extent of inhibition of Na+/K(+)-ATPase during ischemia, hypoglycemia and epilepsy may be insufficient to cause neuronal death by itself, unless the inhibition is severe and prolonged, there are a number of interactions which can lead to a potentiation of the neurotoxic actions of glutamate, a prime candidate for causing part of the damage following trauma. Presynaptically, inhibition of the Na+/K(+)-ATPase destroys the sodium gradient which drives the uptake of acidic amino acids and a number of other neurotransmitters. This results in both a block of reuptake and a stimulation of the release not only of glutamate but also of other neurotransmitters which modulate the neurotoxicity of glutamate. An exocytotic release of glutamate can also occur as inhibition of the enzyme causes depolarization of the membrane, but exocytosis is only possible when ATP levels are sufficiently high. Postsynaptically, the depolarization could alleviate the magnesium block of NMDA receptors, a major mechanism for glutamate-induced neurotoxicity, while massive depolarization results in seizure activity. With less severe inhibition, the retention of sodium results in osmotic swelling and possible cellular lysis. A build-up of intracellular calcium also occurs via voltage-gated calcium channels following depolarization and as a consequence of a failure of the sodium-calcium exchange system, maintained by the sodium gradient.

Effect of stimulation of the nucleus basalis of Meynert on blood flow and extracellular lactate in the cerebral cortex with special reference to the effect of noxious stimulation of skin and hypoxia

Cerebral blood flow (CBF) and extracellular lactate in the parietal cortex were simultaneously measured in halothane-anesthetized rats. Focal electrical stimulation of the magnocellular nucleus of the basal forebrain (nucleus basalis of Meynert; NBM) for 10 min produced a significant increase in cortical CBF without any significant changes in extracellular lactate in the parietal cortex or in systemic arterial blood pressure (BP). Cutaneous pinching of a hindpaw for 10 min increased cortical CBF and BP, but did not influence extracellular cortical lactate. Systemic hypoxia for 10 min reducing the end-tidal O2 concentration from 18% to 6-8% produced a remarkable increase in extracellular cortical lactate. It was suggested that the increased cortical CBF following either NBM stimulation or pinching of a hindpaw was not due to metabolic changes in the cortical neurons of anesthetized rats.

Accumulation of arachidonic acid cyclo- and lipoxygenase products in rat brain during ischemia and reperfusion: effects of treatment with GM1-lactone

The aim of our study was to investigate the changes of various biochemical parameters (concentrations of lactate, free arachidonate, cyclo- and lipoxygenase products) in rat brain after ischemia and reperfusion and the effects of pretreatment with the ganglioside derivative GM1-lactone on the same parameters. Ischemia was induced by reversible occlusion of common carotid arteries for 20 min, which included a final 5 min of respiration of 5% oxygen in nitrogen. Reperfusion was obtained by removing the occlusion. Pre-ischemic conditions were obtained on sham-operated animals. Animals were killed by microwave irradiation of their heads. Brain levels of lactate and of free arachidonate were markedly increased after ischemia and returned to normal values at 5 min of reperfusion. Levels of the cyclooxygenase metabolites prostaglandin F2 alpha, 6-keto-prostaglandin F1 alpha, and thromboxane B2 were increased after ischemia, whereas levels of the lipoxygenase metabolite leukotriene C4 (LTC4) did not change. After reperfusion, a very marked increase of the cyclooxygenase products occurred but not of LTC4. Treatment with GM1-lactone prevented the elevation of cyclo- and lipoxygenase metabolites especially during reperfusion, with limited effects on lactate and free arachidonate levels.

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.

The carbochromene derivative AD6 reduces the TxB2/6-keto-PGF1 alpha ratio in cerebral cortex during hypoxia and recovery and leukotriene synthesis in brain tissue, in the rat

Pretreatments of rats with the Carbochromene derivative AD6 (4 mg/kg i.p., 2 h before sacrifice) resulted in elevation of brain levels of 6-keto-PGF1 alpha in cerebral cortex under physiological conditions, had no effect on levels of TxB2 and 6-Keto-PGF1 alpha at 30 min of hypoxia (respiration of 5% O2 in N2) and prevented the accumulation of TxB2 occurring in brain at 5 min of recovery after hypoxia. In addition, the accumulation of LTC4 and B4 in brain slices incubated in the presence of the Ca++ ionophore A23187 and arachidonic acid, was reduced in samples obtained from pretreated rats. The drug, thus, had favourable effects on the 6-keto-PGF1 alpha/TxB2 ratio in normal conditions, as well as in conditions of altered oxygen supply. In addition it reduced the formation of compounds, the leukotrienes, which may exert pro-inflammatory activities on the cerebral microcirculation.