Stretch-induced growth in chicken wing muscles: biochemical and morphological characterization.

Skeletal muscle growth induced by passive stretch was characterized in chicken wing muscles. Within 24 h after installing the stretch apparatus on the birds, the sarcomere length of the stretched patagialis was 40% greater than control. This was accompanied by increasing muscle wet weight, protein content, DNA and RNA concentrations. Sarcomere length returned to near control values by 3 days, but muscle wet weight and protein content continued to increase through 10 days. DNA and RNA concentrations reached a peak after 5-7 days and began to decline. Histological examination after 7 days revealed no change in the concentration of nuclei inside the basement membrane surrounding the muscle fibers, but the concentration of nuclei outside the basement membrane had increased. Therefore, the ratio of protein to DNA can be a poor index of muscle fiber DNA unit size. Additionally, no evidence of new muscle fiber formation was found. Electron microscopy demonstrated that passive stretch destroyed sarcomere registration between adjacent myofibrils. We concluded that passive stretch is a powerful inducer of muscle growth.