Age-related changes in cholesterol and bile acid metabolism in rats.

Age-related changes in serum and liver cholesterol, phospholipid and triglyceride levels, serum lipoproteins, biliary secretion of cholesterol, phospholipid and bile acids, and fecal excretion of sterols and bile acids were examined in Sprague-Dawley and Wistar strain male rats, 7 to 106 weeks in age. Serum and liver lipid levels increased with age in both strains but the liver phospholipid level remained unchanged. The proportion of serum alpha-lipoprotein increases and that of beta- and prebeta-lipoproteins slightly decreased. Cholesterol and phospholipids in low density lipoprotein and cholesterol in high density lipoprotein fractions also increased with age. Bile flow and biliary secretion of cholesterol and bile acids decreased in aged rats, but when they were expressed in terms of units per rat they were almost constant without regard to age. Pool size, synthesis, secretion, and turnover frequency of bile acids also did not change when they were expressed per rat, though 7-week-old rats showed a low value for turnover frequency. Biliary secretion of phospholipid, however, increased in aged rats. Biliary secretion of chenodeoxycholic and alpha-muricholic acids decreased but that of cholic and hyodeoxycholic acids increased. Daily excretion of feces and fecal neutral sterols decreases in aged rats but the excretion of bile acids remained constant regardless of age. The ratio of coprostanol and cholesterol in the total sterols was not affected. Fecal lithocholic, beta-muricholic and P10 (probably omega-muricholic) acids were decreased with age but the other bile acid components were not changed or were slightly increased.