Effect of Force-feeding of Protein-free Diets Supplemented with Sulfur-containing Amino Acids and Sulfur-compounds on Liver Fat and Urinary Nitrogen

Abstract

Experiments using rats force-fed a protein-free diet supplemented with methionine, leucine, threonine, cystine or sulfur-containing compounds were conducted to investigate the effects of sulfur-containing amino acids on fat content in the liver and on the excretion of urinary nitrogen. The addition of methionine to a protein-free diet produced fat accumulation in the liver and reduced the excretion of urinary nitrogen, but that of leucine or threonine did not affect them. The addition of methionine to the protein-free diet produced a remarkable decrease in the concentration of threonine in the liver along with the increase in the concentration of methionine. On the other hand, the further addition of leucine to the mehtionine supplemented diet apparently eliminated the nitrogen sparing action of methionine and the effect of the added methionine on the concentration of threonine in the liver, but did not bring about any changes in the fat accumulation. The addition of cystine demonstrated the effects similar to that of methionine on the fat content in the liver and the excretion of urinary nitrogen, and showed a clear increase in the concentration of methionine and a great decrease in that of threonine, without changes in that of cystine, in the liver. However, fat accumulation of rats given the protein-free diet supplemented with cystine was not eliminated with the further addition of threonine to this diet. The addition of neither cysteic acid nor thioglycerol affected the free-amino acid concentration in the liver, but the latter produced the fat accumulation in the liver.