Cholesterol Metabolism in Normo and Genetically Hyperlipidemic Rats in Aging

The changes of cholesterol metabolism in aging was studied in normolipidemic (Brown Norway strain) and in spontaneously hyperlipidemic rats (Yoshida strain). Plasma and hepatic lipid levels and the activity of HMGCoA reductase, cholesterol 7α-hydroxylase were measured at the age of 2, 6 and 18 months. The effect of cholestyramine and simvastatin was also considered. Plasma cholesterol and triglyceride levels were higher in Yoshida and increased with aging. The raise of plasma lipid levels with increasing age was not evident in Brown Norway rats. HMGCoA reductase was higher in Yoshida as compared to Brown Norway, and decreased with aging in both groups. Cholesterol 7α-hydroxylase was higher in Yoshida with respect to Brown Norway and no variation of the activity was observed in aging. Cholestyramine induced HFMGCoA reductase and cholesterol 7α-hydroxylase activity in both groups, the stimulation of the enzymes being more pronounced in Brown Norway rats. Treatment with simvastatin reduced HMGCoA reductase activity to the same extent (50%) in both groups at the different ages.