Effect of arterial hypoxia on the cerebrocortical redox state, vascular volume, oxygen tension, electrical activity and potassium ion concentration.

The effect of different degrees of arterial hypoxia on cerebrocortical NAD/NADH redox state, reflectance, oxygen tension, extracellular potassium ion concentration, ECoG and arterial blood pressure was investigated in rats. The results may be summarized as follows. a) The decrease of cortical pO2 preceded the dilatation of cortical vessels by 15-20 sec but the changes in cortical extracellular potassium ion concentration, ECoG and arterial blood pressure started later than the vasodilatation. These results give further support to the regulatory role of cortical pO2 decrease in the initiation of cerebrocortical vasodilatation during arterial hypoxia. b) Since the K+ concentration of the brain cortex and the ECoG did not change in mild arterial hypoxia, the significant NAD reduction obtained in this experimental group is likely to be of cytoplasmic origin. The same conclusion applies to the initial periods of severe arterial hypoxia. On the basis of the extent of NAD reduction during various degrees of arterial hypoxia it is concluded that about 30% of the NAD reduction occurring in anoxia is of cytoplasmic origin. c) When the animals were ventilated with a gas mixture containing 4-7% oxygen, the brain cortex became nearly anoxic, partly because of the gradual decrease of arterial blood pressure. Finally, the mechanism of potassium leakage is identical under prolonged severe arterial hypoxaemia and on anoxic terminal depolarization.