The influence of hypoxia on the concentrations of cyclic nucleotides in the rat brain.

In order to study the influence of hypoxia on cyclic nucleotides in the brain, we reduced arterial Po(2) for 15-30 min in lightly anaesthetised and artificially ventilated rats to obtain values ranging from about 45 to about 10 mm Hg. In an additional group (arterial Po(2) 18-22 mm Hg), the tissue hypoxia was aggravated by moderate arterial hypotension (mean arterial blood pressure about 80 mm Hg). In all animals, electrocortical activity was recorded. Cyclic GMP concentrations in cerebral cortex were unchanged in all groups but one. In that group, in which tissue hypoxia was severe enough to induce a suppression-burst EEG pattern and a measurable reduction in the adenylate energy charge, cyclic GMP concentrations were slightly increased (p less than 0.05). Cyclic AMP concentrations remained unaltered at all degrees of hypoxia studied. It is concluded that changes in cyclic nucleotides in brain tissue occur first at such severe degrees of hypoxia of the duration studied that function and metabolism are profoundly altered.