Rates of lactic acid permeation and utilization in the isolated dog brain

The rate of lactic acid (LA) permeation from brain tissue to venous blood and utilization in brain tissue was investigated in 13 isolated dog brains before and after an ischemic period of 3 min. LA concentration in the brain, cerebral blood flow, as well as the arteriovenous differneces of LA, glucose, and O2 were determined. LA concentration in cerebral tissue increased from a control value of 254 +/- 42 to 1,606 +/- 177 mumol/100 g brain tissue in the 2nd min after ischemia (mean values +/- SE). Before ischemia no release of LA was found, whereas in the 2nd min after ischemia LA permeation rate had increased to 25.1 +/- 8.5 mumol/100 g brain tissue per minute (P less than 0.005). Up to the 4th min after ischemia no net LA utilization was observed. Thereafter LA utilization increased rapidly and exceeded the LA permeation rate by a ratio of maximally 10:1 between the 12th and 21st min after ischemia. The O2 equivalent of the cerebral metabolic rate for lactate maximally amounted to 2.82 +/- 0.42 mumol-min-1-g-1 or 181 +/- 28%. LA output may be limited by passage of LA across the brain cell and the blood-brain barrier.