Concentrations of Selected Enzymes and Metabolites in Rat Skeletal Muscle: Effects of Food Restriction

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Abstract
Activities and concentrations of selected enzymes and metabolites were measured in gastrocnemius muscles from normal rats fed ad libitum; from rats whose growth was retarded by restricting food intake; and from rats recovering from a period of food restriction. The relative activities of glucose-6-P isomerase, fructose-1,6-diP aldolase and pyruvate kinase were not significantly altered by the experimental treatments. During the first day of recovery, hexokinase, glucose-P mutase and UDPG-pyrophosphorylase activities increased. These changes were accompanied by glycogen accumulation. Glucose-6-P, isocitrate (NADP), malate and lactate dehydrogenase activities were 20 to 50% of normal during growth restriction and returned to normal within 7 days after refeeding. There were no changes in glucose, ATP, and lactate concentrations. ADP, glucose-6-P and pyruvate concentrations increased during growth restriction and returned to normal within 3 days after refeeding. AMP concentration was normal during food restriction, decreased during the first 2 days after refeeding and was normal thereafter. The results are discussed in relation to regulation of muscle growth and suggest that availability of energy-yielding metabolites and activities of oxidative enzymes are not key factors in the regulation of muscle growth.