The maximal rate of some cerebral enzymatic activities related to energy transduction (hexokinase; phosphofructokinase; lactate dehydrogenase; citrate synthase; malate dehydrogenase; total NADH-cytochrome c reductase; cytochrome oxidase), amino acid metabolism (glutamate decarboxylase; glutamate dehydrogenase) and cholinergic metabolism (acetylcholine esterase) were tested in the cerebral cortex and in sub-cortical area of rats. The evaluations were performed both in the homogenate in toto and in the crude mitochondrial fraction, before and after a postdecapitative normothermic ischemia of 5, 10, 20, and 40 min duration. The results are discussed also with respect to the pharmacological pretreatment with two biological substances which may modulate amino acid (L-alanine) and phospholipid metabolism (CDP-choline). The analysis of the present data suggests the occurrence in brain tissue of a variety of interrelated factors implicated in the ischemia-induced changes of the maximal rate of the enzymatic activities related to the energy transduction. These include: (a) rearrangement of the enzymatic activities because of the changed metabolic and chemico-physical condition; (b) decrease in the activity of enzymes related to the electron transfer chain and glycolysis; (c) changes in enzymes related to mitochondrial membranes. The effects of in vivo administration of alanine or CDP-choline, even if significant, are not consistent throughout the time period studied
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