Öter S, Topal T, Sadir S, Özler M, Uysal B, Ay H, Yaren H, Korkmaz A, Akin A. Oxidative stress levels in rats following exposure to oxygen at 3 atm for 0–120 min. Aviat Space Environ Med 2007; 78:1108–13. Background: Hyperbaric oxygen (HBO) is known to cause oxidative stress in several organs and tissues. We previously defined the pressure-related oxidative effects of HBO in several tissues of rats. This study was performed to elucidate the relationship of HBO exposure time to its oxidative effects. Methods: A total of 49 rats were randomly divided into 5 groups. Study groups were subjected to 3 atm HBO for 30, 60, 90, and 120 min except the control group. Their blood and lungs were removed immediately after exposure and used for analysis. Thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) levels were determined to reflect oxidant and antioxidant status. Results: TBARS levels were found to increase in a time-dependent manner in both erythrocytes [median (min–max); from 0.65 (0.39–0.84) with 30 min HBO exposure up to 1.26 (1.00–1.44) nmol · g⁻¹ hemoglobin after 120 min] and lung tissue [from 2140 (1550–2510) up to 5465 (5090–5950) nmol · g⁻¹ protein]. Similarly, SOD activity also presented a dose-dependent course from 0.06 (0.05–0.10) to 0.18 (0.14–0.26) U · g⁻¹ hemoglobin in erythrocytes and from 16,660 (3479–25,994) to 52,522.5 (41,362–65,799) U · g⁻¹ protein in lung tissue. In contrast, GSH-Px activity reflected an irregular trend; its levels were mostly found to be increased, but they were decreased at one stage (in the erythrocytes of 30-min exposed rats). Conclusions: The results of this study exhibited a clear relationship of HBO-induced oxidative action to exposure time. This action was most pronounced from 90 to 120 min of exposure.