Objective: 

Hyperbaric oxygen (HBO) is known to cause oxidative stress. Previous studies with single HBO exposure had shown that HBO-induced oxidative stress is proportional to both its exposure pressure and duration. However, HBO treatments commonly depend on longer periods including repetitive exposures. In a series of studies we investigated the interactions of oxidant/antioxidant system markers in erythrocytes, lung and brain tissues of rats exposed to HBO from 5 up to 40 sessions.

Methods: 

Adult male rats were allotted into six study (n=8 for each) plus one control group (n=12). The study groups were exposed to 5, 10, 15, 20, 30, and 40 daily consecutive 2.8 ATA/90 min HBO sessions. Animals were sacrificed 24 h after the final session. Malonyldialdehyde and carbonylated protein levels were determined as measures of oxidative stress; superoxide dismutase and glutathione peroxidase activities were used to reflect the antioxidant status.

Results: 

In the erythrocytes, oxidative stress markers tended to increase at the early stages of repetitive HBO exposures and declined to their control values at the end of the 40-session procedure. In the lung tissue, lipid and protein oxidation products began to increase after 20 HBO exposures and then continued to increase. The increase of oxidation products was simultaneously accompanied by the antioxidant enzymes' activities. In the brain tissue (cerebral cortex, white matter and cerebellum), no alteration was recorded in any of the measured parameters.

Conclusions: 

These findings provided evidence for an oxidative effect of HBO exposure which is limited successfully via the endogenous antioxidant systems. The brain tissue represented a more resistant state against HBO-induced oxidative stress than the lungs and erythrocytes.