[Changes in the oxygen tension of rat cerebral cortex subsequent to hyperoxia and the protective effect of urea]

When breathing with air, pO2 in anesthetized rats was 24.1+/-1.8 mm Hg, while after urea administration it was 19.4+/-1.7 mm Hg. A sharp increase in pO2 was revealed in hyperoxia(911+/-48 mm Hg at 6 atm during first 5 min, and 924+/-38 mm Hg--by the 7th min). The high pO2 was only reduced in 10-15 min after decompression. At a combined action of urea and hyperoxia, pO2 was significantly lower (714+/-52 mm Hg); pO2 in successive cortical layers (0-2400 mcm with a 200-mcm step) was progressively decreasing (from 40.7+/-4.9 mm Hg to 16.0+/-1.0 mm Hg in control, and from 928+/-35 mm Hg to 274+/-64 mm Hg in hyperoxia).