Effect of 8 hours oxygen breathing at 2 atmosphere on glucose utilization in the rat

The regional cerebral metabolic rate for glucose (rCMRg1) was previously measured by [1$C] 2-deoxyglucose autoradiographic method in conscious rats exposed to 2 atmosphere absolute oxygen (ATA O2) up to 4 hours, and during various pre-convulsive periods of brain oxygen toxicity at 3 and 5 ATA O2. The exposures at 2 ATA O2 did not produce any visible signs of pulmonary or brain oxygen toxicity as judged by lack of changes in the respiratory pattern and normal behavior. However, 1 h exposure to 2 ATA O2 produced significant increases in rCMRg1 in various neuroanatomical structures. These increases were diminished following 4 h exposure to 2 ATA O2. In the present study the exposure time for rCMRg1 measurement was extended to 8 h oxygen breathing at 2 ATA O2, when obvious signs of respiratory distress developed. The data demonstrate no changes in rCMRg1 of the 28 neuroanatomical structures examined during oxygen breathing and normoxia at 2 ATA as compared to air breathing rats at 1 ATA. Thus, the early increases in rCMRg1 at 2 ATA O2 seem to be a transient physiological phenomenon. It is concluded that unlike exposures to 3 and 5 ATA O2, the respiratory system at 2 ATA O2 in conscious rats is more sensitive to the toxic effects of oxygen than the central nervous system