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Age-Related Changes in Ribosomal Profiles and in Vitro Protein Synthesis in Skeletal Muscle during Fasting and Subsequent Refeeding of Rats¹

Department of Pathology, University of South Florida, College of Medicine, Tampa, Florida 33612

Age-dependent changes in ribosomal profiles and in in vitro protein synthesis in skeletal muscle (gastrocnemius muscle) were studied in rats subjected to fasting and subsequent refeeding. Male rats of 4, 7, and 21 weeks of age were used. Incorporation of ¹⁴C-leucine into protein in vitro using skeletal muscle ribosomes from fed rats decreased with the age of the animals. Sucrose density gradient analyses of ribosomal profiles revealed that the changes in protein synthesis were accompanied by progressive declines in the concentrations of polyribosomes and total RNA in skeletal muscle. After fasting for 1 or 2 days, protein synthesis in muscle of young rats dropped markedly and this change could be attributed to the fall in the concentrations of polyribosomes. Also, the concentration and total RNA in the muscles of the young rats decreased. During refeeding of rats after fasting for 2 days, the incorporation of ¹⁴C-amino acid into protein recovered more efficiently using ribosomes of skeletal muscle of young animals compared with using those of older animals. This rapid increase in the protein synthesizing activity of skeletal muscle may be related to the efficient recovery of the ribosomes toward heavier aggregates. The results indicate that young animals adapt more efficiently to fasting and refeeding than do older animals.

KEY WORDS: • age effects • skeletal muscle • ribosomes • protein synthesis • fasting • refeeding after fasting

¹ Supported by U.S. Public Health Service Research Grants AM-10530 from the National Institute of Arthritis. Metabolism and Digestive Diseases and CA-14156 from the National Cancer Institute.

² Dr. Nakano's present address is Laboratory of Nutritional Regulation. Institute for Biochemical Regulation, Nagoya University, Chikusa, Nagoya, 464 Japan.

³ Dr. Sidransky's present address is Department of Pathology. The George Washington University Medical Center, 2300 Eye Street, N.W., Washington, D.C. 20037. Reprint requests should be sent to Dr. Sidransky at this address.

Manuscript received 3 August 1977.