Protein metabolism: I. Incorporation of 14C- l-leucine into skeletal muscle and liver proteins of mice and guinea pigs infected with Nematospiroides dubius and Trichostrongylus colubriformis

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The incorporation of 14C- l-leucine into skeletal muscle protein of the mouse infected with Nematospiroides dubius (Nematoda) and the guinea pig with Trichostrongylus colubriformis (Nematoda) was markedly depressed. Conversely, the 14C- l-leucine incorporated into the liver protein of the infected animals was increased. There was no change in the free 14C- l-leucine of either muscle or liver of the infected mouse. The biological half-lives of 14C- l-leucine were shorter in the muscle protein and longer in liver protein of these mice. The infected animals were losing while their controls were gaining weight. In the infected guinea pig, (1) the RNA levels were depressed in muscle and elevated in liver, (2) the polyribosomal fraction fell markedly in muscle and rose slightly in liver, while in muscle the polyribosomes were replaced by light ribosomes, (3) the DNA levels appeared to rise in both muscle and liver, (4) the ATP level was depressed in muscle and was unchanged in the liver. In general these changes are consistent with the changes in incorporation of amino acid into proteins. The weight loss of the infected mouse was closely associated with inappetance. However, in the uninfected mouse, which lost weight on a quantitatively inadequate diet, the incorporation of 14C- l-leucine into muscle protein was depressed but there was no change in the incorporation into liver protein. The changes in incorporation of 14C- l-leucine are discussed in relation to poor growth in intestinal nematode infections. Comparisons are made with bacterial infections.