Effect of Infection on Skeletal Muscle Ribosomes in Rats Fed Adequate or Low Protein

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Abstract
The effect of Salmonella typhimurium infection on protein metabolism in the skeletal muscle of the hind leg was studied in rats in 2 experiments. In experiment 1 rats were fed an adequate-protein diet and killed at zero, 1, 2, 3, and 5 days after infection. In vivo uptake of 14C-leucine by muscle ribosomes into nascent peptides was measured; and ribosomes were studied by sucrose gradient analysis. Infection reduced the uptake of radioactivity by ribosomes and resulted in lowered levels of heavy polyribosomes and increased proportions of the light ribosome species. In experiment 2 weanling rats were prefed a low protein or adequate-protein diet for 9 days and then infected. In vivo and in vitro synthetic capacity of muscle ribosomes was studied at zero, 1, 2, 3, or 7 days after infection. The in vivo and in vitro protein-synthesizing capacity of the ribosomes was reduced by the infection in both dietary groups. Clear-cut differences in the variables studied were not observed between the dietary groups during the first 3 days after infection. The changes are discussed in relation to the metabolic nitrogen loss occurring during infection.