Lysine-Arginine-Electrolyte Relationships in the Rat

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Abstract
Lysine (1.5, 3, and 6% of diet) fed to weanling rats caused graded depressions in growth rates when added to an 18% casein diet and slight depressions when added to stock or isolated soy protein rations. Supplementation with 1% L-arginine eliminated the growth depression caused by 1.5 and 3% lysine and reduced that caused by 6% lysine. Changes in pancreatic trypsinogen or procarboxypeptidase B activities in animals fed lysine or ε-aminocaproic acid (in vitro enzyme inhibitors) could not be correlated with growth rates. After 14 days of supplementary lysine, cellular K in muscle decreased (not reversed by arginine) but cellular Na and bone composition were unchanged; concentrations of free lysine in plasma and muscle and of free arginine in muscle increased. These observations, data on plasma lysine and arginine concentrations after shorter test intervals, and data on urinary excretion of lysine and arginine indicate that competition for transport between lysine and arginine at the gut, tissue, or kidney is not the cause of the antagonism. Growth and food consumption curves of rats kept conventionally or at 4°, or previously protein-depleted, indicated that the growth depression was not due solely to decreased food consumption and that rats fed lysine were less efficient. It is suggested that lysine exerts its adverse effects by altering the intermediary metabolism of arginine.