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 rats at various developmental stages. Total fiber number in plantaris (PLA) muscles increased gradually between 2 and 10 weeks of age (ca. 300 g BW), and then remained constant thereafter. In contrast, proliferating cells labeled by bromodeoxyuridine decreased gradually during the same period, and were hardly evident after 10 wk. In the growth curves for the body weight, lower hindlimb length, muscle weight, and length of the EDL muscle, turning points were observed at 10 wk (300 g BW), 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 wk, including the turning point. Therefore it is suggested that the development of muscle weigth from 2 to 10 wk depends mainly on the increment of fiber number (hyperplasia), whereas development after 10 wk 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 wk of age and 300 g BW. This should be considered when investigating muscle hypertrophy or hyperplasia. Verf.-Referat