Amino Acid Regulation of Albumin Synthesis

Abstract

The effects of amino acids on albumin synthesis were measured in 47 studies using the isolated perfused rabbit liver. Carbon-14 carbonate was used to label the hepatic intracellular arginine pool, and hence, the carbon of urea and the guanido carbon of arginine. Amino acid levels in the perfusate and in the liver were determined. All studies were run for 2.5 hours to assure release of labeled albumin. Livers obtained from fasted rabbits synthesized 18 ± 1.1 mg of albumin 117 ± 8 mg of urea. The addition of methionine, lysine, leucine, valine, or threonine, at 10 μmoles/ml, failed to alter albumin synthesis. Tryptophan at 0.05 to 10.0 μmoles/ml increased albumin synthesis 138 to 175%, and urea synthesis by 56%. The addition of isoleucine also resulted in an 89% increase in albumin synthesis, and both isoleucine and tryptophan resulted in ribosomal reaggregation. When the donor rabbits were fed, albumin synthesis averaged 33 mg, and no increase was observed with tryptophan or isoleucine. Results of these studies are compatible with the concept that tryptophan stimulates the ribosomal reaggregation with enhanced albumin production. Isoleucine, while effecting reaggregation, may be either less efficient in this regard or less specific for albumin.