Figure 7. Differential changes of metabolites in skeletal and cardiac muscle from young and old mice. (A) Decreased citrate concentration in the old heart. (B) Decreased mRNA expression of citrate synthase (CS) in old heart. (C) Increased branched chain amino acid (BCAA) in old skeletal muscle. (D) Increased ceramide in old skeletal muscle. Values are means±SEM for 6 young and 5 old mice in each group. *P < 0.05. **P < 0.01.