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Notes: Abstract: We tested whether cerebral noradrenaline (NA) may play a central role in mediating the increased production of free fatty acids (FFAs) during cerebral ischemia. Levels of FFAs, cyclic AMP, and NA, as well as ATP, ADP, and AMP, were measured in cerebral cortex during decapitation ischemia in rats 2 weeks after unilateral locus ceruleus lesion. Comparisons were made between the results obtained from the contralateral cortex with normal NA content and the NA-depleted ipsilateral cortex. Although NA depletion was associated with a diminished transient rise of cyclic AMP in response to ischemia, it failed to influence the magnitude of FFA increase or the decline of energy state within the 15-min period of ischemia. A more than twofold increase of total FFAs (sum of palmitic, stearic, oleic, arachidonic, and docosahexaenoic acids) was observed in both hemispheres at 1 min after decapitation, when energy failure became manifest. The increased production of FFAs continued throughout the 15 min of ischemia, with a preferential rise in the levels of stearic and arachidonic acids. There was an inverse correlation between FFA levels and total adenylate pool. The results do not support a major role for NA and cyclic AMP in increasing cortical FFAs during complete ischemia. Instead, they are consistent with the view that impaired oxidative phosphorylation activates deacylating enzymes. Disturbance of reacylation due to energy depletion is probably another factor contributing to the continuous increase of FFAs during prolonged ischemia.

Notes: Abstract: 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%. The incidence of resolvable conjugated diene peaks was much greater in the reperfused groups (18 of 124 samples total; 0.25%〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:00223042:JNC268:les" location="les.gif"/〉 [CD]/[IDB] 〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:00223042:JNC268:les" location="les.gif"/〉 1.34%), compared to the nonreperfused group (1 of 38 samples; [CD]/[IDB] = 0.62%). No specific regional susceptibility to conjugated diene formation was observed. It also was shown by computer averaging over all the tissue zones sampled that, if one had used large samples consisting of pooled brain tissue for analysis of lipid peroxides and/or their reaction products, the conjugated diene peak would have been attenuated below distinctly resolvable levels. These results constitute the first demonstration of lipid peroxidation induced by reversible global ischemia. The observation that the effect is highly focal and not generalized throughout the brain suggests that special conditions of reperfusibility and reoxygenation must be satisfied for lipid peroxidation to be detectable in an ischemic milieu.

Notes: Abstract Lipid peroxides, quantitated as lipid conjugated dienes, and (Na+,K+)-ATPase activity were assayed concurrently in brains of control rats and in three groups subjected to 30 min of reversible forebrain ischemia followed by 0, 1, and 4 hr of recirculation. Multiple small samples were taken from lateral, dorsolateral and medial cortex, hippocampus, thalamus and striatum following in situ freezing. (Na+,K+)-ATPase activity was elevated in hippocampus, dorsolateral and lateral cortex (P〈0.10) and in thalamus (P〈0.05) following 30 min ischemia. ATPase activity in medial cortex continued to increase during the first 1 hr of recirculation (P〈0.10). Following 4 hr of recirculation, decreased enzyme activities were observed in all of these regions (lateral cortex and hippocampus,P〈0.10). No changes in ATPase activity were observed in samples from striatum. Of the regional samples assayed for lipid peroxide content, the incidence of conjugated dienes as a function of recirculation time was 6% (0 hr), 23% (1 hr), and 17% (4 hr). For these samples, plots of normalized ATPase activity vs. tissue conjugated diene concentration revealed that normalized ATPase activity varied with recirculation time, but was independent of the magnitude of the lipid peroxidative process (expressed in terms of tissue conjugated diene concentration). These results suggest that disturbances in membrane structure and function presumed to arise from lipid peroxidation are not responsible for the behavior of the ATPase under the current in vivo conditions.