ABSTRACT
The first Total parenteral nutrition (TPN) preparations used casein hydrolysates as a source of amino acids. The maturation of three pathways of amino acid metabolism appears especially relevant to total parenteral nutrition. The metabolism of phenylalanine and tyrosine illustrates the potential for amino acids to be both trophic and toxic, given the appropriate circumstances. The role of tyrosine in neonatal nutrition has been paradoxical because in some situations it appears that nutrition may result in an excess of this amino acid which may have long- term consequences with respect to the outcome of the infants. In other nutritional situations, especially TPN, a deficiency of tyrosine appears to occur, suggesting a requirement for this amino acid. In order to study the effects of TPN on infants, in particular to put the findings about plasma in the context of events in the tissues, a suitable animal was necessary.
