Recovery of ¹⁵N in Liver, Muscle Tissue, and in the Lens of the Eye after Administration of ¹⁵N-Ammonium Acetate to Rats and Rabbits

Abstract

¹⁵N-ammonium acetate was injected into rats and rabbits. The ¹⁵N excess was determined in protein and NPN from muscle tissue and plasma and/or from liver and lens. In liver and plasma protein the incorporation values were already high one day after administration and decreased rapidly during the time of investigation, 9 to 13 days. In protein and NPN from muscle tissue the ¹⁵N excess increased up to the 4th day, whereafter it decreased slowly. In lens protein the excess also rose during 4 days but did not reach values exceeding about one-third of those from muscle protein and one-tenth of the values from plasma and liver protein. The ¹⁵N in lens NPN remained considerably higher than in protein in spite of a rapid decrease. The results indicate that muscle protein has a much lower turnover rate than plasma and liver protein, and that intracellular amino acids are utilized for muscle protein synthesis. They also confirm that a considerable part of the lens protein has a very slow turnover.

Key Words:

• Amino acid distribution
• intracellular NPN
• lens protein
• liver protein
• ¹⁵N metabolism
• muscle protein
• non-protein nitrogen turnover
• protein turnover