Abstract
Blood plasma and tissue free amino acid levels were measured at intervals in rats fasted after they had been fed a 18% casein diet for a week. Most of the plasma free amino acid levels increased remarkably at 4 hours after feeding. Plasma levels of dietary amino acids during the absorptive period were 2 to 6 times as high as those during the postabsorptive period, and the pattern of changes in those appeared to result from a reflection of amino acid composition of dietary protein. Muscle free amino acid levels also increased during the absorptive period. In contrast with these changes, the levels of the branched chain- and aromatic amino acids and also arginine in liver scarcely increased during the absorptive period, although the levels of nonessential amino acids, lysine, histidine and threonine increased. It is considered that the synthesis and degradation of tissue protein and amino acids has a more influence on the free amino acid levels in liver than in blood plasma or in muscle.
