THE GASEOUS METABOLISM OF THE BRAIN OF THE MONKEY

Abstract

Cerebral arterial inflow was measured directly in lightly anesthetized rhesus and spider monkeys while arterial and cerebral venous blood samples were collected for estimation of their O2 and CO2 contents. The "normal" values for cerebral O2 uptake were: mean 3.7, minimum 2.5 and maximum 4.5 ml./100 g. wet brain/min.; cerebral O2 uptake accounted for about 10% of the total O2 absorbed. Cerebral metabolism varied directly and consistently with cerebral functional activity, whether the changes occurred spontaneously or were induced by hemorrhage, transfusion, or injns. of drugs (epinephrine, metrazol, picrotoxin, nikethamide, pentothal, etc.); the "physiological" range (i.e., that compatible with prompt and complete recovery) was from about half to nearly double the resting "normal." Severe cerebral anoxia could be produced either by reducing the available supply of O2 below the existing demand (by hemorrhage) or by increasing the demand above the available supply (by convulsant drugs); in either case cerebral O2 uptake underwent a marked and prolonged fall. Of the 3 possible correlations among (a) cerebral A-V oxygen difference, (b) cerebral blood flow and (c) cerebral O2 uptake, that between (a) and (b) was the least, that between (a) and (c) intermediate, and that between (b) and (c) the highest. This order is believed to signify that the cerebral circulation is automatically adjusted to the metabolic requirements of the brain; changes in the A-V difference therefore indicate only that the adjustment has been imperfect and cannot measure changes either in cerebral metabolism or blood flow. The highest "normal" value for cerebral Qo was 13.5, which is very close to that reported for brain cortex in vitro but considerably lower than previous values obtained in vivo. The former agreement is probably fortuitous because these expts. deal with the whole brain, not with cortex exclusively. The latter discrepancy is attributed to overestimation of cerebral blood flow in earlier expts. since an isolated cerebral circulation was not available.