Changes in the concentration of specific amino acids in the serum of experimentally malnourished pigs

Abstract

1. The concentrations of individual free serum amino acids have been studied during the course of chronic protein malnutrition in experimentally malnourished pigs. 2. Until growth was markedly impaired, reducing the protein content of the diet had no significant effect on serum amino acid composition. 3. During the period when growth had practically ceased but kcal intake per kg body-weight was normal the concentrations of valine, leucine, isoleucine, threonine and eventually tyrosine fell, the levels of alanine and serine were above control levels and aspartic acid, glycine, methionine, phenylalanine, proline, arginine, histidine and lysine remained unaltered. 4. When the kcal intake per kg fell below control levels, owing to anorexia, and the animals began to lose weight, the levels of alanine, glycine, serine and methionine fell and valine, leucine, isoleucine, threonine and tyrosine remained well below control levels. 5. The physiological, nutritional and metabolic significance of these findings is considered. The changes in alanine and glycine concentration are discussed in terms of the regulation of gluconeogenesis. The reduction of the branched-chain amino acids is interpreted on the basis of their availability for synthetic and catabolic needs.