Metabolite Changes in Aged Muscle During Stimulation

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Abstract
Metabolite concentrations of adenosine-5′-phosphate, phosphocreatine, and lactate were compared in adult and aged rat soleus and superficial, medial and deep, lateral gastrocnemius muscles after 3 min of moderate or intense stimulation in situ. The concentration of phosphocreatine in all muscles progressively decreased as contractile frequency increased. In most muscles, lactate increased coincident with greater contractile frequency. These changes were greater in aged muscles. Decreases in the concentration of adenosine-5′-phosphate with stimulation, where evident, were also greater in aged muscles. Metabolite levels in nonstimulated muscles were effected minimally by age. The cytochrome-c concentration was reduced with age in each muscle section. The results indicate that aged skeletal muscle has a lesser ability than adult skeletal muscle to maintain energy balance during contraction.