Systemic low-grade inflammation does not decrease skeletal muscle mass and protein synthesis in old rats

Age-associated low-grade systemic inflammation may contribute to sarcopenia. We hypothesized that skeletal muscle mass and protein synthesis rate would be reduced in old rats exhibiting persistent low-grade inflammation compared to age-matched controls. Male 24-month-old Wistar rats exhibiting a low-grade systemic inflammation for at least one month (LGI group) were compared to non-inflamed rats (C group). Tissue protein synthesis rates were quantified using the L-[1-(13)C]-valine flooding dose method. Body weight, gastrocnemius muscle and spleen weights were not significantly different between groups, but liver and small intestine weights were 13 and 14% higher in LGI than in C. Fractional and absolute protein synthesis rates were not significantly different between groups for gastrocnemius, spleen and small intestine, but higher for liver in LGI than in C. Despite an increase in liver protein synthesis, low-grade inflammation did not reduce skeletal muscle mass, suggesting that age-associated low-grade systemic inflammation occurs independently of sarcopenia.