Metabolic State and Blood Flow in Rat Cerebral Cortex, Cerebellum and Brainstem in Hypoxic Hypoxia

In order to study the effect of hypoxic hypoxia upon regional cerebral metabolism and blood flow the arterial Po a of lightly anaesthetized rats was lowered to about 35, 29 and 23 mm Hg, respectively, with subsequent measurements of labile metabolites and of blood flow in cerebral cortex, cerebellum and brain stem. The metabolites, which included organic phosphates, carbohydrate substrates and amino acids, were measured with enzymatic, fluorometric techniques after freezing the tissue in situ and the regional blood flow was estimated from the tissue uptake of 14 C‐ethanol. In all 3 regions marked hypoxia (Po a 23) gave rise to small increases in the ADP concentration, but since neither ATP nor AMP was changed from the normal it is concluded that the energy state remained essentially unaltered. The increase in lactate concentration was similar in all three regions and the substrate patterns were essentially the same. Since the regional blood flow also increased to a similar extent in the three regions it is concluded that brain regions show similar metabolic and circulatory changes in hypoxic hypoxia. The results thus give no support to the view that different brain areas show selective vulnerability to hypoxia, at least not in forms of hypoxia that are uncomplicated by absolute or relative ischemia.