The incorporation of radioactively labelled amino acids into skeletal muscle protein by Pietrain and Large White pigs

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Abstract
The changes in muscle protein and plasma radioactivity with time have been observed in anaesthetized pigs receiving constant infusions of [14C]glycine and [3H]tyrosine. The specific radioactivity of muscle protein was found to increase linearly with time. However, it was not possible to calculate absolute rates of muscle protein synthesis for the plasma radioactivity had not reached a plateau after 8 h infusion.The specific radioactivities of Pietrain muscle protein increased more rapidly than those of Large Whites when animals of the same lean mass, receiving the same dietary amino acid supply per unit of lean mass, were compared. However, when considered with respect to published biochemical data, these results support the hypothesis that the differences arise from inequalities in plasma specific radioactivities; which appeared to be related to differences in blood volumes, between pigs of the two breeds, at the same age. When plasma specific radioactivity/time relationships were adjusted so as to account for this variation no significant differences were found, indicating that muscle protein synthesis and muscle growth proceed at similar rates in the two breeds.
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