Glucose level, metabolism, and response to electrical impulses in cerebral tissues from man and laboratory animals

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Abstract
Respiration of human and other cerebral tissues examined as slices in nutrient salines, fell by 9-12% when glucose was lowered from 5-15 mM to 0.5-1.5 mM. This is the range of blood glucose levels in which hypoglycemic changes including a large fall in respiration, become evident in vivo. Sensitivity of the tissues to low glucose was not increased by replacing O2 by air, nor by lowering concn. of inorganic phosphate in surrounding media. Electrical stimulation of the metabolism of separated tissues rendered them much more susceptible to a fall in glucose level. Respiration of stimulated human cerebral cortex was lower by 30% at 0.5-1.5 mM than at 5-15 mM. Prepns. of rabbit sera rendered the electrically stimulated respiration of rabbit cerebral tissues still more susceptible to lowered glucose levels. The aerobic accumulation of lactic acid in glucose-containing saline media also became more susceptible to lowered glucose levels when the tissues were subjected to electrical impulses. Respiration with lactate as substrate increased between 2 and 6 mM in absence of stimulation, and at substrate concns. up to 20 mM with applied impulses. With fructose as substrate both the respiration and the accumulation of lactic acid increased with increasing fructose level up to at least 10 mM, in the presence and absence of applied impulses.