The oxygen-adapted rat model: Tolerance to oxygen at 1.5 and 2 ATA.

The effect of pre-exposure to graded hyperoxia on subsequent survival under hyperbaric conditions was investigated in 250-300 g male Sprague-Dawley rats. The average survival of normal rats was approximately 4 d in 1 ATA O2, 1 d in 1.5 ATA O2, and 16 h in 2 ATA O2. Rats pre-exposed to O2 at 0.8 ATA for 1 week became O2 tolerant and survived a subsequent 1 week in O2 at 1 ATA with zero mortality. These O2-tolerant rats had a three-fold increase of survival duration in O2 at 1.5 ATA, but showed no significant prolongation of survival in 2 ATA O2. Pre-exposure to 0.8 ATA O2 for 2 weeks had no further effect on tolerance. However, rats pre-exposed to O2 at 0.8 ATA for 1 week followed by exposure to O2 at 1 ATA for a second week demonstrated approximately a three-fold increase in subsequent survival at 2 ATA O2. The results indicate that oxygen-tolerant rats remain susceptible to mortality in 1.5-2 ATA O2 and that graded tolerance to O2 develops as a function of the oxygen exposure regimen.