Plasma free amino acid levels in uremic rats given high and low protein diets or intravenous infusions of amino acid solutions.

Plasma free amino acids were measured in uremic and sham-operated rats fed for 10 days a high (24%) or a low (6%) protein diet or given total parenteral nutrition, either with a complete amino acid solution or a solution containing only the amino acids considered to be indispensible in uremia. The plasma levels of citrulline, glycine, hydroxyproline, and 1- and 3-methylhistidine were elevated in all uremic rats compared with the corresponding controls. Plasma tryptophan was reduced in three out of four uremic groups and the brached-chain amino acids and tyrosine were reduced in plasma of orally fed uremic rats but not after intravenous infusion. Plasma serine increased with increased plasma glycine levels. The ratio serine:glycine was, however, significantly smaller in the uremic rats. The ratios of plasma valtine:glycine and indispensable:dispensable amino acids were affected by nitrogen intake as well as by uremia, whereas plasma citrulline:tryptophan was influenced only by the uremic state. This ratio was markedly elevated in all uremic groups. The alterations observed in the plasma free amino acid levels and ratios of the uremic rats were similar to those reported from clinical observations on patients with chronic renal failure.