Relationship between age-related increases in rat liver lipid peroxidation and bile canalicular plasma membrane fluidity.

Aging is associated with increased cellular levels of lipid peroxides and reactive oxygen species. This increase in the radical species may affect membrane fluidity and consequently membrane functions. We attempted to determine whether age-related increases in lipid peroxide and reactive oxygen species levels affect the annular fluidity of the bile canalicular plasma membrane in young (2-3 weeks old), adult (20 weeks old) and old (100 weeks old) rats. Hepatic levels of lipid peroxides measured with thiobarbituric acid reactive substances (TBARS), reactive oxygen species and reduced glutathione were significantly higher in the old rats than in the young and adult rats. Arachidonic acid (AA) levels increased and docosahexaenoic acid (DHA) levels decreased in the isolated canalicular plasma membrane of the old rats, and the ratio of DHA to AA thus decreased significantly with rat aging. Hepatic TBARS levels correlated negatively with molar ratios of DHA to AA. The annular fluidity of the bile canalicular plasma membrane decreased significantly in the old rats compared with that in the young and adult rats. These results suggest that the age-related decrease in DHA content of the bile canalicular plasma membrane and the molar ratio of DHA to AA may be associated with age-related deterioration of membrane annular fluidity.