Abstract
The present experiment was conducted in chicks to compare the effects of excessive amounts of leucine, lysine, phenylalanine and methionine supplemented isonitrogenously on plasma amino acid (PAA) concentrations at postprandial and after fasting, and to investigate whether the specific amino acids that alleviate the toxicity of excess amino acids could be predicted from PAA concentrations, PAA ratio and PAA score. Supplementation of excess amino acids significantly increased the plasma concentrations of the corresponding amino acids and their metabolites at postprandial (3-hour fasting), and the increase rates were much greater in the toxic amino acids such as methionine and phenylalanine than in the less toxic amino acids such as leucine and lysine. However, such accumulations diminished after 24-hour fasting.
The antagonistic interactions between lysine and arginine, and among leucine, isoleucine and valine were recognized in the postprandial plasma, whereas the significant reduction by feeding excess methionine of threonine, serine and glycine which were known to have an alleviatory effect on methionine toxicity was observed in the fasting plasma. These results indicated that amino acids alleviating the adverse effect due to excess amino acids could be predicted from PAA concentrations when amino acid analysis was made for the blood plasma which was taken afer fasting as well as at postprandial. Excess phenylalanine had little effect on PAA concentrations but the concentrations of threonine and glutamic acid after fasting were significantly decreased. PAA ratio and PAA score did not provide the useful indications to predict the specific amino acids that alleviate the amino acid toxicity.
