Effect of Amino Acid Imbalance on Plasma and Tissue Free Amino Acids in the Rat

Abstract

Plasma and tissue free amino acids were measured in rats trained to eat a single meal for 1 hour daily, at intervals after they had been fed a low protein diet or an amino acid-imbalanced diet containing 5.4% of an amino acid mixture lacking threonine. The plasma concentration of the most limiting amino acid, threonine, in rats fed the imbalanced diet, fell rapidly below both the fasting value and the value for rats fed the control diet. The pattern of changes of threonine in the systemic plasma appeared to be a reflection of the changes occurring in the muscle. The pattern of changes in the liver, however, differed from those in muscle and plasma. Threonine concentration in liver of rats fed the imbalanced diet did not fall below that of the control at the 3- and 5-hour intervals. Threonine concentration of intestinal tissues of the imbalanced group was high compared with those of plasma and muscle. Plasma threonine concentration of rats fed the imbalanced diet ad libitum paralleled food intake rather closely, i.e., threonine concentration fell below that of the control when food intake was depressed, but at the end of the 22-day experimental period increased above the control value when the food intake also increased above that of the control. Plasma amino acid pattern of rats fed a protein-free diet more closely resembled that of rats fed the control diet.