Amino Acid Levels in Plasma and Muscle of Rats after Intravenous Administration of Different Amino Acid Infusions

Studies were conducted on the participation of specific amino acids in the alterations of their levels in plasma and muscle of rats after short term intravenous infusion. Sufficient amounts of amino acids and glucose were used as a basal solution, and the levels in plasma and muscle were determined 30 min after the end of infusion. When an infusion solution devoid of one of the essential amino acids from the basal solution, ‐Leu, ‐He, ‐Lys or ‐Thr, was administered, the plasma and muscle levels of the deleted amino acids decreased in different degrees. With infusion of the deficient solutions except for the ‐Leu, no significant changes were observed in aminoacids other than those deleted, although occasional changes were noted. On the other hand, the infusion of the ‐Leu resulted in significant increase of isoleucine and valine levels, and a moderate increase of many other amino acids both in plasma and in muscle. In contrast, when leucine was administered singly in an amount equivalent to that in the basal solution, isoleucine and valine decreased significantly. Most of the other amino acids also decreased markedly after the infusion of leucine alone. These results suggest that, in intravenous infusion, leucine plays a specific role on amino acid levels in plasma and muscle of rats.