Effect of hypoxia and ischemia on the activity of glucose 6-phosphatase in the guinea-pig brain

The effect of ischemia and pharmacological treatment evaluated on synaptosomes and purified mitochondria from rat cerebral cortex

Changes in the maximal rate of some cerebral enzymatic activities related to energy transduction (lactate dehydrogenase; citrate synthase and malate dehydrogenase; total NADH-cytochrome c reductase and cytochrome oxidase) as well as both glutamate dehydrogenase and acetylcholine esterase were assayed in the purified mitochondrial fraction or in crude synaptosomal fraction from cerebral cortex. The evaluations were performed in rats before and after a postdecapitative normothermic ischemia of 5, 10, 20 and 40 min duration. The ischemic damage resulted in a decrease in the activity of mitochondrial malate dehydrogenase and total NADH-cytochrome c reductase, and of synaptosomal acetylcholine esterase. The biochemical evaluations were performed also after an i.p. pretreatment with vincamine, trimetazidine and suloctidil (50 mg/kg). The drugs induced different changes in enzyme activities as a function of the ischemia duration. These various interferences are discussed with regard to the possible drugs mode of action.

The interaction of transport and metabolism on brain glucose utilization: a reevaluation of the lumped constant

The relative cerebral cortical metabolism of glucose (GLU) and 2-deoxy-D-glucose (DG) was measured in vivo in control and insulin-treated hypoglycemic rats. The ratio of the utilization rate constants for the two hexoses, i.e., KDG/KGLU is defined as the Hexose Utilization Index (HUI). The HUI was found to be invariant in rats whose cerebral glucose content exceeded 1 mumol . g-1 wet weight (HUI = 0.48 +/- 0.07). Severe hypoglycemia (plasma glucose less than 2 mM) effected a shift in the HUI to 1.04 +/- 0.21. The results are consistent with a model in which the interpretation of the HUI is determined by the rate of transport into brain, or subsequent phosphorylation, as the rate-limiting step for hexose utilization.

Effect of hypoxia and ischemia on the distribution of protein in brain cellular fractions

The effect of postdecapitative ischemia (5 min at 37 degrees) and hypoxia (5% O2, 95% N2, 30 min) on the distribution of protein radioactivity in the cellular fractions of guinea pig cerebral cortex was studied. Ischemic conditions resulted in the increase of total radioactivity level and protein content in the mitochondrial fraction. In the cytosol the opposite effect was observed; the radioactivity and protein content were decreased. The amino acid analysis of microsomal proteins and the distribution of glucose-6-phosphatase activity, differing from those in control animals, suggest structural disturbances in the microsomal fraction. The results indicate a different sedimentation of proteins in the given experimental conditions. After hypoxia such effects were not observed.