CALORIC RESTRICTION REDUCES FIBER LOSS AND MITOCHONDRIAL ABNORMALITIES IN AGED RAT MUSCLE

The influence of caloric restriction (CR) initiated at 17 months of ag e was investigated on selected age-associated measures in skeletal mus cle. Tissue from young (3-4 months) ad libitum-fed, old (30-32 months) restricted (35% and 50% CR, designated CR35 and CR50, respectively), and old ad libitum-fed rats (29 months) was studied. CR preserved fibe r number and fiber type composition in the vastus lateralis muscle of the CR50 rats. In the old rats from all groups, individual fibers were found with either no detectable cytochrome c oxidase activity (COX-), hyperreactivity for succinate dehydrogenase activity (SDH++; also kno wn as ragged red fibers [RRF]), or both COX- and SDH++. Muscle from th e CR50 rats contained significantly fewer COX- and SDH++ fibers than d id the muscle from CR35 rats. CR50 rats also had significantly lower n umbers of mtDNA deletion products in two (adductor longus and soleus) of the four muscles examined compared to CR35 rats. These data indicat e that CR begun in late middle age can retard age-associated fiber los s and fiber type changes, as well as increases in the number of skelet al muscle fibers showing mitochondrial enzyme abnormalities. CR also d ecreased the accumulation of mtDNA deletions.