Changes in the numbers of proliferating cells and muscle fibers in growing rat skeletal muscle / 体力科学

ABSTRACT

Changes in the numbers of muscle fibers and proliferating cells detected by immunohistochemistry were studied in correlation with various growth parameters including changes in body weight, lower hindlimb length, muscle length, muscle weight and age in Wistar-strain rats at various developmental stages. The total fiber number in plantaris (PLA) muscles increased gradually between 2 weeks and 10 weeks of age (about 300g body weight), and then remained constant between 10, 000 and 11, 000 these after. In contrast, proliferating cells labeled by bromodeoxyuridine decreased gradually during the same period, and were hardly evident after 10 weeks. In the growth curves for the body weight, lower hindlimb length, muscle weight, and the length of the extensor digitorum longus (EDL) muscle, turning points were observed at 10 weeks (300 g body weight), respectively, suggesting that the turning point between growth in length and growth in width occurred at this point. Furthermore, the growth curves for the body weight and PLA muscle weight were correlated between 2 and 20 weeks, including the turning point. Therefore it is suggested that the development of muscle weight from 2 to 10 weeks depends mainly on the increment of fiber number (hyperplasia), whereas development after 10 weeks depends on the increment of individual fiber diameter (hypertrophy), in relation to the tendency for an increase in fiber number and a decrease in proliferating cells. These results indicate that maturation of skeletal muscle in male Wistar rats occurs at 10 weeks of age and a body weight of 300g. Accordingly, these facts should be considered when investigating muscle hypertrophy or hyperplasia.