Senescent changes in rodent hepatic epoxide metabolism.

Age-related alterations in epoxide metabolism were examined in subcellular fractions of liver from 3-, 12- and over 24-month-old male rats and mice. Using styrene oxide as the substrate, glutathione-S-transferase activity remained unchanged while the activity of epoxide hydrase increased with age in both species. The microsomally-mediated binding of benzo[a]pyrene to DNA was also increased in the old animals. Thus, senescent rodents retain or increase their ability to metabolize epoxides. The effect on epoxide metabolism of pretreatment of the senescent rodents with polychlorinated biphenyls was also examined. Glutathione-S-transferase activity was induced only in old animals. However, epoxide hydrase activity, while inducible in all age groups of rats, increased only in young mice. Therefore, there is an age-related difference in response of epoxide metabolizing enzymes to polychlorinated biphenyl treatments between rats and mice.