Effect of Prior High Protein Intake on Food Intake, Serine Dehydratase Activity and Plasma Amino Acids of Rats Fed Amino Acid-imbalanced Diets

Abstract

Relationships among food intake, growth, liver serine-threonine dehydratase activity (S-TDH) and plasma amino acid concentrations were studied in rats adapted to low or high protein diets at intervals after feeding them imbalanced diets containing 5% casein and 6, 12 or 18% of an amino acid mixture devoid of histidine (AA—His). When rats adapted to the low protein diet were fed the 6% AA—His-imbalanced diet, S-TDH was low; total plasma amino acid concentrations increased; plasma histidine, food intake and growth decreased. As time progressed S-TDH increased slowly; plasma serine plus threonine concentration fell; food intake and growth began to rise. When rats adapted to the high protein diet were fed the 6% AA—His-imbalanced diet, S-TDH decreased rapidly, but food intake remained constant until S-TDH had decreased considerably and plasma serine plus threonine had risen. When rats adapted to the high protein diet were fed the more severely imbalanced diets their diminishing ability to degrade amino acids was apparently exceeded; plasma amino acids rose; food intake and growth decreased. Both alterations in food intake and amino acid-degrading capacity appear to contribute to the ability of the rat to adjust to dietary imbalances of amino acids.