Antioxidant capacity in different tissues of young and old rats.

The antioxidant capacity in heart, liver, lung, and kidney was studied in young (6 months) and old (22 months) male Fischer 344 rats, using the oxygen radical absorbance capacity (ORAC) assay system with two different reactive oxygen species (ROS) generators. The results indicated that liver in old rats had significantly lower peroxyl radical absorbance capacity (ORACROO), units/g wet wt), but higher hydroxyl radical absorbance capacity (ORACOH), units/mg protein) than in young rats. The decreased liver ORACROO in the old rats was mainly due to the loss of cytosol protein, while the increased liver ORACOH in the old rats was a result of an increased resistance of cytosol proteins to the attack of ROS. This conclusion was further supported by the finding that the contribution of nonprotein fraction of liver cytosol to the ORACOH of the cytosol decreased with age. No effect of age was found on either ORACROO or ORACOH in other tissues. The antioxidant capacity for both ORACROO and ORACOH, was usually high in liver and kidney but low in lung and heart.