Mechanism of the cerebrocortical vasodilatation during anoxia.
The possible role of cerebrocortical ion homeostasis, NAD/NADH redox state and of cortical oxygen tension was investigated in the initiation of hypoxic cortical vasodilatation. In addition, changes in cerebrocortical extracellular concentrations of Na+, K+, and Cl- during anoxia were studied. The results were as follows. a) The cerebrocortical reflectance decrease, e.g. cerebral vasodilatation, lagged behind the cortical pO2 decrease by 1-2 sec, but preceded the decrease of arterial blood pressure and ECoG as well as the extracellular Na+, K+, Cl- increases by 20-30 sec. Since the cortical pO2 decreased first and the ion changes lagged behind the onset of vasodilatation by 20-30 sec, it is suggested that the CBF increase in hypoxia is mediated via the cortical pO2 decrease. b) A significant NAD reduction was already present after 20 sec. of nitrogen breathing. Since the ECoG and MABP decreased, and K+ activity increased much later than this, it is presumed that the NAD reduction during the first 30-40 sec of anoxia indicates an increased rate of glycolysis, but not mitochondrial hypoxia. c) In the predepolarization phase a 17% K+, 4% Na+, 5% Cl- increase is probably the result of a reduction of the extracellular spaces caused by water movement and by the migration of Na+ and Cl- from the extracellular to the intracellular space. The large K+, Na+, Cl- changes during terminal depolarization can be interpreted as a result of the failure of the membrane bound Na+ -K+ pump and of the altered ion permeability of the cell membranes.
D000200:Action Potentials; D000818:Animals; D001794:Blood Pressure; D001812:Blood-Brain Barrier; D002540:Cerebral Cortex / Q000503:physiopathology; D002560:Cerebrovascular Circulation; D004569:Electroencephalography; D004573:Electrolytes / Q000378:metabolism; D002534:Hypoxia, Brain / Q000503:physiopathology*; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D009243:NAD / Q000378:metabolism; D010100:Oxygen / Q000097:blood; D051381:Rats; D014664:Vasodilation
D004573:Electrolytes; D007473:Ion Channels; D009243:NAD; D010100:Oxygen