Aging has been associated with an increase in muscle dysfunction and weakness. We found a decrease in muscle carnitine with age [Biochem. Biophys. Res. Commun., 161 (1989) 1135-1143], Prolonged oral administration to both young (2-month-old) and adult (7-month-old) mice with l-carnitine increased its content in blood by 50%. The levels of carnitine in skeletal and heart muscle of old treated animals became higher than in untreated mice of the same age. However, this extensive restoration did not reach the maximum values present in skeletal muscle of young mice. Our findings indicate that an alteration of the carnitine carrier in the sarcolemma could be responsible for the decrease with age of carnitine in skeletal but not in heart muscle.
