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Journal of Nutrition Vol. 101 No. 4 April 1971, pp. 485-494
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Concentrations of Selected Enzymes and Metabolites in Rat Skeletal Muscle: Effects of Food Restriction

R. E. Howarth1 and R. L. Baldwin

Department of Animal Science, University of California, Davis, California 95616

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.

1 Present address: Biochemistry Department, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.

Manuscript received 14 September 1970.




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