Synthesis and Accumulation of Protein and Nucleic Acid in Rat Gastrocnemius Muscles during Normal Growth, Restricted Growth, and Recovery from Restricted Growth

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Abstract
Rates of synthesis and accumulation of DNA, RNA and protein in rat gastrocnemius muscles were measured during normal and restricted growth and during recovery from restricted growth. Growth was restricted by limiting food availability to 50 to 60% of ad libitum intake. Recovery growth was induced by refeeding ad libitum after 3 weeks of restricted feeding. The amounts of DNA, RNA and protein in muscles from rats killed at intervals were measured to determine rates of accumulation. Rates of synthesis were measured in vivo as 32P-orthophosphate incorporation into DNA and RNA and L-14C-leucine incorporation into protein. Rates of protein synthesis were measured in vitro as L-14C-leucine incorporation by muscle microsomes. Food restriction inhibited synthesis and accumulation of nucleic acids and protein. Rates of DNA and RNA synthesis during recovery growth were greater than normal. Recovery of protein synthesis after restriction was delayed for several days and there was no compensatory acceleration in protein synthesis and accumulation during recovery growth. Rate of muscle protein synthesis appeared to be determined by both the amount and the activity of RNA in muscle. The results are discussed in relation to the differential responses of DNA, RNA and protein metabolism during the initiation of compensatory growth of muscle tissue.