The Mechanism of the Lysine-Arginine Antagonism in the Chick: Effect of lysine on digestion, kidney arginase, and liver transamidinase

Abstract

Experiments were performed in chicks to determine the mechanism by which excess dietary L-lysine alters arginine metabolism. Excess lysine also decreased growth and plasma arginine level when a mixture of crystalline amino acids was used to simulate the composition of the basal 18% casein-10% gelatin ration. The postprandial increase in plasma arginine level was comparable in lysine-fed and control chicks. Thus, lysine does not alter arginine metabolism by affecting a digestive or absorptive process. In chicks fed crystalline amino acid diets with varied concentrations of lysine and arginine, changes in growth and plasma lysine and arginine concentrations showed a direct relationship between excess dietary lysine and arginine metabolism. A decrease in plasma arginine level caused by adding 4% L-aspartic acid to the basal ration was reversed by increasing dietary pyridoxine·HCl from 1.6 to 3.2 mg/100 g of ration. The depressed plasma arginine level in chicks fed 2% L-lysine was not altered by 1% creatine but the creatine partially eliminated the growth depression. Lysine also decreased the liver transamidinase level; therefore, this enzyme is probably not implicated in the disposal of arginine. Plasma arginine level decreased significantly within 6 hours after chicks ate diets containing excess lysine; the kidney arginase response — an increase to 5 to 10 times control values — occurred 2 to 4 days later. Because of its time relationship the arginase response is probably not physiologically significant. It is postulated that lysine causes an immediate loss of arginine from tissue, of undetermined nature, and that the increase in arginase is caused by removal of product repression.