Incorporation of radioisotopically labelled L-leucine into skeletal muscle proteins was measured in vivo and in vitro, and into liver proteins in vivo in three groups of sheep: (1) infected by Trichostrongylus colubriformis, (2) uninfected, pair-fed with the infected animals, (3) uninfected, fed ad lib. Incorporation of [14C]L-leucine by an homogenate of wool follicles from infected and uninfected sheep was also measured. Incorporation of leucine by muscle, and hence muscle protein synthesis, was equally depressed in the anorexic infected sheep losing weight, and in pair-fed animals, whether measured in vivo or in vitro, or expressed in terms of either RNA or DNA. Incorporation into protein was elevated equally in vivo in the livers of the infected and pair-fed sheep when expressed in terms of content of tissue nitrogen, but not in terms of cither nucleic acid. Incorporation by the wool follicular homogenate was appreciably depressed by the infection and is consistent with the poor wool growth in nematode infections. These results show that the same depression of skeletal muscle and, possibly, elevation of liver protein synthesis occur in a ruminant as were reported earlier for laboratory monogastric animals with intestinal nematode infections. Pair-feeding uninfected animals in both this and the earlier experiments emphasized the importance of anorexia as a major cause of these effects on protein synthesis. The importance of these effects upon production is discussed briefly.
Effects of the hepatotoxic agents retrorsine and aflatoxin B1 on hepatic protein synthesis in the rat