Oxidative stress, antioxidant defenses and nitric oxide production following hyperoxic exposures

Little data exist on the dose-response relationship between the partial pressure of inspired oxygen (PiO2) and the cellular oxidative stress response in humans. The objective of this study was to determine the effects of PiO2 on lipid peroxidation, antioxidant enzyme activity and nitric oxide (NO) production. Twelve healthy male divers breathed 100% O2 in a hyperbaric chamber for two hours at 1 (101 kPa), 1.5 (152 kPa) and 2 (203 kPa) atmospheres absolute (atm abs). Venous blood was collected pre-, within 15 minutes post-, one and two hours post-hyperoxic exposures to determine changes in plasma and erythrocyte lipid peroxidation (thiobarbituric acid reactive substances-TBARS), antioxidant enzyme activity (superoxide dismutase-SOD), catalase-CAT, glutathione peroxidase-GPx), and plasma NO production (L-arginine [L-Arg], asymmetric dimethylarginine-ADMA, and nitrites). There were minor changes in TBARS and mixed responses in plasma and erythrocyte CAT and GPx activity. Plasma L-Arg increased following 1 and 1.5 atm abs exposures, yet ADMA and nitrites were unchanged. Only erythrocyte CAT and plasma GPx activity, and plasma L-Arg/ADMA demonstrated a significant PiO2 dose-dependent relationship. Two-hour hyperoxic exposures at 1-2 atm abs of O2 results in mixed oxidant-antioxidant responses and unaltered NO production. Moreover, there does not appear to be a strong systemic dose-dependent oxidative stress response at these hyperoxic exposures.