Free amino acid levels in the blood of patients undergoing parenteral alimentation.

Free amino acid levels were determined in the blood of patients undergoing parenteral alimentation. During amino acid infusions, alanine, valine, glycine, isoleucine, leucine, proline, threonine, serine, methionine, phenylalanine, and lysine levels increased. Bivariate regression analysis was then done to determine the average rise in each amino acid when 1 mmole/hr of that amino acid was infused and when 1 mmole/hr of glucose was infused. This analysis was done on both arterial plasma and arterial wh-le blood increments. The average rise in the amino acid level with 1 mmole of infusion per hour varied from 32 to 133 mumole/liter. Only alanine levels were positively correlated with glucose infusion, while the branched chain levels were all negatively correlated. In no instance could a significant positive arteriovenous difference across the forearm be correlated with the infusion of an amino acid, despite amino acid levels as much as five times normal. Methionine, proline, valine, threonine, and lysine showed the greatest rise in blood concentration per millimole of amino acid infused per hour suggesting that their degradation or use in protein synthesis was limited. While the blood concentration rise in glycine was only about half as much per millimole per hour infused as was found in the previously mentioned group of amino acids, high rates of infusion of this amino acid resulted in large increments inglycine levels. It may be desirable to reduce the amounts of these amino acids in parenteral amino acid formulations.