Age-related changes in lipid metabolism in rats: the consequence of moderate food restriction.

Male Sprague-Dawley rats, 3 weeks of age, received one of the four following dietary manipulations until 9 months of age: group AD, fed ad libitum; group R, restricted to 75% of food intake of group AD; group RAD, restricted until 5 months of age and then fed ad libitum; group ADR, fed ad libitum until 5 months of age and then restricted. The concentration of serum total and HDL cholesterol tended to be higher in group AD than in all groups that had experienced food restriction. Liver cholesterol was higher in groups AD and RAD than in groups R and ADR. Activity of hepatic microsomal hydroxymethylglutaryl-CoA reductase was comparable, whereas sterol synthesis from mevalonate was significantly higher in groups R and ADR than in groups AD and RAD. Cholesterol 7 alpha-hydroxylase activity also tended to be higher in groups R and ADR. It seems likely that hepatic cholesterol homeostasis functions effectively even when moderate food restriction was started after the growing period. In addition, food restriction reduced the ratio of arachidonate to linoleate, suggesting inhibition of the desaturation system.