Hyperoxia-induced protection against rat's renal ischemic damage: relation to oxygen exposure time

Pre-exposure to hyperoxic gas (>or= 95%) has been shown to protect the heart and central nervous system from ischemia-reperfusion injury. In the present study, we investigated whether oxygen pretreatment induces delayed renal protection in rats. The possible role of some renal antioxidant agents was also investigated.

Adult male Wistar rats were kept in a hyperoxic (HO) (>or= 95% O(2)) environment for 0.5 h, 1 h, 2 h, 3 h, 6 h, and 2 h/day for three consecutive days and 4 h/day for six consecutive days, and control group (IR) animals were kept in the cage with no HO, one day before subjecting their kidney to 40 minutes of ischemia and 24h of reperfusion. Renal function was assessed by comparing plasma creatinine (Cr), blood urea nitrogen (BUN), creatinine clearance (CLCr), and fractional excretion of sodium (FENa%). Histopathological injury score was also determined according to the Jablonski method. To examine the antioxidant system induction by hyperoxia, we measured renal catalase and superoxide dismutase activity, and renal glutathione and malondialdehyde content.

Our data demonstrated that only in 4 h/day HO for six consecutive days, the renal function tests (Cr, CLCr, BUN, and FENa%) and Jablonski histological injury were better than control group (p < 0.05). The beneficial effect of oxygen pretreatment in this group was associated with increased renal catalase activity compared with those obtained from control group (p < 0.05).

The present study demonstrates that repeated exposure to hyperoxic (>or= 95% O(2)) environment can reduce subsequent rat's renal ischemia-reperfusion damage. Induction of endogenous antioxidant system may partially explain this beneficial effect of hyperoxic preconditioning.