Internal redistribution of tissue protein synthesis in uremia

Abstract

Tissue composition and in vivo tissue protein synthesis were altered by acute uremia, induced in rats by bilateral nephrectomy. Net protein synthesis (anabolism minus catabolism) was increased in liver and heart and decreased in skeletal muscle, as judged from changes in total organ weight, ratios of protein: DNA and RNA: DNA, and leucine-¹⁴C incorporation into trichloroacetic acid (TCA)-insoluble, nucleic acid-free material. Concentration of free lysine, a major constituent of histones and ribonucleoproteins, also was increased in liver and decreased in skeletal muscle, a finding suggesting lysine shifted from muscle to liver in association with the changes in protein synthesis. Acute uremia also altered tissue levels of other amino acids. Hepatic concentrations and liver:blood concentration ratios tended to be increased for the essential, but not for the nonessential amino acids. Moreover, the phenylalanine:tyrosine concentration ratio, which reflects activity of the enzyme phenylalanine hydroxylase, was increased in blood, muscle, and liver. These findings indicate uremia selectively alters tissue composition and protein synthesis in different organs and may modify intermediary metabolism of some individual amino acids.