Sex-difference in the age related change of cholesterol metabolism in rats.

In Sprague-Dawley rats at the ages of 5 weeks (young) and 9 months (adult), the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in age-matched animals was significantly higher in females than in males. The magnitude of the age-related decrease in the reductase activity was also greater in female rats. When rats were fed a cholesterol-enriched (1%) diet for 30 h as cholesterol challenge, the reduction of reductase activity depended more on sex than on age. The activity of cholesterol 7 alpha-hydroxylase was also higher in female than in male rats and it apparently remained unchanged with age in female rats while it decreased in male rats. With a cholesterol-enriched diet, the hydroxylase exhibited a significant age- and sex-dependent difference and it increased only in young males and adult females. In male rats, the concentration of hepatic cholesterol was significantly higher in adult than in young rats while it was comparable in female rats. The increase in hepatic cholesterol with dietary cholesterol was observed only in male adult rats. A significant age-related difference was observed in the concentration of serum cholesterol. The results suggest an existence of sex-dependent compensatory mechanism for maintenance of hepatic cholesterol homeostasis with age.