Changes in RNA, DNA and protein content and the rates of protein synthesis and degradation during hypertrophy of the anterior latissimus dorsi muscle of the adult fowl (Gallus domesticus).

Hypertrophy of the anterior latissimus dorsi muscle of the adult fowl was induced by attaching a weight to one wing and after 2, 6 and 14 days the muscle wet weight, as well as protein, RNA and DNA contents were measured. After 6 days of hypertrophy the wet weight of the muscle had increased by 74%, the protein content by 44%, RNA by 203% and DNA by 83% compared with the contralateral control. Average rates of protein synthesis and degradation were measured over the 14 days of hypertrophy from the rate of loss of radioactivity in the muscle protein after pulse labelling using 3H-leucine. Results were compatible with a 50% increase in the protein synthesis rate with no detectable change in the degradation rate. The increase in synthesis rate was paralleled by a similar rise in the RNA concentration. The DNA content indicated that this increase in RNA resulted from an increased RNA production per nucleus as well as from an increased number of nuclei. The kinetics of the loss of total radioactivity from the muscle protein and the amount of free 3H-leucine remaining in the muscle free amino acid pool during hypertrophy indicated that reutilization of 3H-leucine was extensive. This was in spite of attempts aimed at minimizing reutilization by feeding fowls a high protein diet plus a daily supplement of unlabelled leucine.