The effect of storage on rat tissues and human plasma amino acid levels determined by HPLC.

Tissue concentrations of the amino acids tryptophan, methionine, valine, phenylalanine, isoleucine and leucine were determined in rat liver, skeletal muscle and brain tissue and human plasma. The effect of storage at -20 degrees C for up to 21 days was examined. Significantly elevated levels after 7 and 21 days of storage were observed in liver and brain tissue but no changes were found in muscle and plasma. Minimal changes occurred in liver tissue stored up to 6 hours at -4 degrees C. This study emphasizes the need for rapid deproteinization of tissues to avoid changes in the free pool of amino acids.