Protection against oxidative stress in liver of four different vertebrates.

The possible relation between respiratory capacity and antioxidant capacity and susceptibility to oxidative stress of the liver has been investigated in Rattus norvegicus, Gallus gallus domesticus, Lacerta s. sicula, and Rana esculenta. Accordingly, we measured oxygen consumption and cytochrome oxidase activity, glutathione peroxidase and glutathione reductase activity and overall antioxidant capacity, and lipid peroxidation and response to oxidative stress in vitro in liver. The order of liver oxygen consumption and cytochrome oxidase activity among the different species was rat > chick > lizard > frog. The antioxidant defenses supplied by the combined action of glutathione peroxidase and glutathione reductase were not adapted to the respiratory capacities. In particular, there was no correlation either between the activities of two enzymes or between their activities and oxygen consumption. In contrast, the overall antioxidant capacity of the liver appeared to be related to its oxidative capacity, and the malondialdehyde formation, an indirect measure of lipid peroxidation, was inversely related to antioxidant capacity. The response to oxidative stress in vitro indicated that the liver susceptibility to oxidative challenge is higher in ectothermic than in endothermic species. Such higher susceptibility appeared to depend on both lower antioxidant capacity and higher levels of free radical producing species. This finding is apparently in contrast with a higher content of cytochromes in endotherms, which are able to determine both respiratory characteristics and sensitivity to pro-oxidants. However, it could indicate the existence of species-related differences in the tissue content of either preventive antioxidants or hemoproteins able to trap the radicals produced at their active center. J. Exp. Zool. 284:610-616, 1999.