[Effect of ageing on hepatic biotransformation function and microsomal membrane fluidity in rats]

Microsomes were isolated from livers of male Sprague-Dawley rats at 3-4, 14 and 24 months of age for each group for the determination of monooxygenase components and drug metabolism activities. Some GSH-related enzyme activities in microsomes and cytosol were also measured. DPH (1,6-diphenyl-1,3,5-hexatriene) was used to determine the microsomal membrane lipid region fluidity. Microsomal cytochrome P-450 content and NADPH-cytochrome c reductase activities remained unchanged in old rats, but there were significantly decreases in cytochrome P-450 dependent aminopyrine N-demethylase and aniline hydroxylase activities. Glutathione S-transferase (GST) in cytosol and microsomes and glutathione peroxidase (GSH-Px) in cytosol were also decreased in old rats. Simultaneously, microsomal membrane fluidity of 24-month old rats decreased (measured at 25 degrees C and 37 degrees C), accompanied by an elevation of cholesterol/phospholipid ratio. Results suggest that there might be some relationship between the lipid environment and membrane fluidity changes and the decreases of hepatic biotransformation function.