Cerebral metabolic state after discontinuation of nitrous oxide supply in artificially ventilated rats

Previous results from this laboratory have shown that when administration of 70% nitrous oxide is discontinued in artificially ventilated rats, cerebral oxygen uptake increases by about 40% at 5 min and by about 80-90% at 30 min, and that this increase is blocked by previous adrenalectomy. In the present experiments, nitrous oxide was withdrawn for 45 s, 2 min 45 s, or 15 min, in non-adrenalectomized animals, and for 5 min in adrenalectomized animals, and the tissue was frozen in situ for subsequent measurements of labile phosphates, glycolytic metabolites, citric acid cycle intermediates and associated amino acids and ammonia. The results allow the conclusion that upon withdrawal of nitrous oxide in non-adrenalectomized animals, there is an increase in metabolic rate at an essentially unchanged metabolic state. In adrenalectomized animals, discontinuation of nitrous oxide supply did not induce changes in any of the tissue metabolites measured. We conclude that 70% N2O neither influences the metabolic rate of the tissue, nor its metabolic state.