Hypoxic survival of normoglycaemic young adult and adult mice in relation to cerebral metabolic rates.

Abstract

AbstractThe hypoxic tolerance and the cerebral metabolic rates (CMR) of young adult mice (20 to 25 g, 4 to 5 weeks old) and adult mice (30 g and above, 6 to 7 weeks old), respectively, were determined and their interrelationship was evaluated. CMRs increased from 25 mmol ‐ P/kg.min to 38 mmol/kg.min as the animals grew older from young to full adulthood. Concurrently the tolerance to aerogcnic hypoxia (5% O2‐95%j N2) declined. The effects of hypoxia on the cerebral energy metabolism were greater in adult than in young adult animals. It is concluded that the full metabolic maturation of the brain is reached in adult animals only. They become more dependent on an adequate oxygen supply as the aerobic activity of the energy metabolism of the brain is further increasing.Hypoxic gasping occurred while the pool of cerebral energy reserves was still far from being depleted. A failure to utilize energy reserves rather than their exhaustion is suggested as the ultimate cause of death from hypoxia. An acid‐soluble form of glycogen or related polyglucan was found in addition to the usual amounts of insoluble glycogen. It was utilizcd rapidly during hypoxia and ischaemic anoxia and it may, therefore, constitute an additional source of carbohydrate substrates in thc brain.