THE EFFECT OF CARBON DIOXIDE TENSION ON THE METABOLISM OF CEREBRAL CORTEX AND MEDULLA OBLONGATA

Manometric measurements were made of oxygen uptake (Q (O(O2))) and aerobic lactic acid output (Q(G)) by slices of cerebral cortex and medulla oblongata of the cat in the presence of mixtures of 1, 5, and 20 volumes per cent of carbon dioxide in oxygen. The concentrations of NaHCO(3) and NaCl in the medium were varied to maintain constant pH and sodium ion concentrations. The calcium ion concentration was 0.0002 M. At pH 7.5 under these conditions, an increase in carbon dioxide from 1 per cent to 5 per cent doubled the Q(G) of both tissues but did not alter Q (O(O2)); an increase from 5 per cent to 20 per cent carbon dioxide had no further effect on Q(G) in either tissue or Q (O(O2)) of cortex, but did depress the Q (O(O2)) of medulla. At pH 8.1, an increase in carbon dioxide from 1 per cent to 5 per cent raised the Q (O(O2)) and Q(G) of cortex by about 60 per cent. Measurements at low oxygen tension carried out previously in phosphate medium were repeated in bicarbonate medium to obtain data for the combined output of lactic acid and carbon dioxide (Q(A)). When the oxygen in the gas phase was decreased from 95 to 3 volumes per cent, the lactic acid output as measured colorimetrically increased by 114 mg./gm. in cortex and by 8 mg./gm. in medulla; Q(A) increased from 12.3 to 13.5 in cortex and decreased from 5.1 to 3.8 in medulla.