Initial Effects of Amino Acid Imbalance in the Rat

Abstract

In an attempt to distinguish the initial effects of an amino acid imbalance from the indirect effects of the depressed food intake, several biochemical changes were determined in protein-depleted rats in short-term experiments. The rats were fed for 24 hours an imbalanced diet, made by adding 3.1% of an amino acid mixture lacking threonine to a basal diet containing 10% wheat gluten supplemented with 0.8% of lysine and 0.1% of DL-threonine. In pair-feeding experiments it was observed that the protein, amino acid N and threonine content in liver of rats fed the imbalanced diet was higher than in those fed the basal diet. Relative high levels of liver protein concentration in protein-depleted rats after feeding the imbalanced diet were also observed in ad libitum experiments. These observations support the assumption that the imbalance could act initially, stimulating the liver protein synthesis. An increase in liver weight correlated with a high glycogen content was also observed in protein-depleted rats fed the imbalanced and the corrected diet (imbalanced plus 0.1% DL-threonine) both in ad libitum or in the pair-feeding experiments. These observations indicate the utilization of the excess of amino acids provided by the amino acid mixture for glyconeogenesis. As a consequence of the changes in liver and plasma concentration of threonine and amino acid N, some of the ratios that reflect their relative proportions were markedly altered. The possibility that the depression in food intake characteristic of the imbalance could be related to those changes is discussed.