Daily variations in the concentrations of individual amino acids in rat plasma

Abstract

Daily rhythms have been described in the plasma concentrations of tyrosine and phenylalanine in the rat (1), and of tryptophan and total amino acids in the mouse (2,3). However, no data appear to be available on daily variations in the concentrations of other plasma amino acids except in the chicken and the human (4,5,6,7). The determination of whether diurnal rhythmicity is common to the plasma levels of most amino acids, and most mammals, or whether such temporal changes are associated in rats only with tyrosine and phenylalanine is essential for the characterization of the physiological mechanisms that control plasma amino acid levels. It would also be useful in assessing the significance of changes in plasma amino acid levels observed in rats several hours after particular experimental manipulations. This study describes the daily rhythmic changes that occur in the concentrations of 12 amino acids in rat plasma.