The relative hyperoxia-induced ROS formation in the lungs, as compared with the brain is not known nor has the duration of hyperoxia exposure been carefully quantified. The purpose of this study was to examine the behaviour of glutathione peroxidase (GPx) activity and free radicals (FR) production in brain and lung during graded hyperoxia. Twenty four adult male rats (188.4±2.9 g wt) were assigned to four groups. A control group and three test-groups; exposed to hyperoxia for 24, 48, and 72 hr, respectively. Following the exposure period, animals were killed and both lungs and brain tissues were homogenized for GPx and FR determinations; by Randox protocol (Randox, UK) and d-ROM method (H&D, Italy) respectively. Data are expressed as means±S.D. and tested for significant differences (P<0.05) with ANOVA, and the post hoc Tukey-Kramer test as appropriate.

Lung GPx activity increased during hyperoxia exposure for 24; then dropped to during hyperoxia exposure for 48 and 72hr. Whereas brain GPx activity increased during hyperoxia exposure for 24 and 48hr then dropped during 72hr exposure. This indicated prolonged protection against ROS in brain. Lung FR increased during hyperoxia exposure for all durations. The FR production in the brain increased during exposure for 24hr, and then dropped during 48 and 72hr. The lungs were found to have higher rate of FR at all levels of hyperoxia exposures, which suggest more mechanisms that had contributed to FR formation in pnueumocyte, compared to neurocyte. It is also concluded that antioxidant supplements are recommended for brain and lung injuries.