Influence of diet and age on ribonucleic acid, protein and free amino acid levels of rat skeletal muscle.

The relationship of dietary protein to RNA, protein and free amino acids in the growth of rat gastrocnemii (GN) muscles over 4, 8, and 12 week periods, was investigated in male weanling rats. The N content of casein diets, C-1, C-2, and C-3 was 0.76, 1.41 and 2.88% while that of the supplemented wheat (SW) diet was 2.5%, respectively. The decrease in concentration of RNA with age was significantly influenced by diet. Accumulation of RNA over a period of time was also influenced by diet, for the C-1 diet permitted only limited accumulation and the C-2 and SW diets restricted accumulation to within 80% of that of the C-3 diet. While protein concentration was affected more by age than by diet, accumulation was influenced by diet, greatest quantities being found in C-3 and SW rats throughout the experimental period. Changes in free amino acid concentration of GN muscles also occurred with age and reflected quantitatively the C-2 and C-3 dietary amino acid patterns. The high levels of certain amino acids in C-1 rats, however, were typical of those found during periods of restrictive protein intake. All criteria of measurement indicated growth and development were greatly restricted by the C-1 diet, less restricted by the C-2 diet while the C-3 diet permitted normal growth.