Postnatal growth of fibres on M. gracilis (pars caudalis) in both sexes of rat

Abstract

Measurements of cross sectional area on individual fibres of M. gracilis (pars caudalis) of Wistar rats of both sexes of different ages were done. Growth equations pattern and growth rates equations pattern of each muscle fibre type were also determined. In rats 12 days old, muscle fibres present a somewhat uniform SDH activity. By 23 days and thereafter, SDH technique revealed a mixed population of red, intermediate and white fibres. There was a close relationship between cross sectional area and age, where each fibre type presents a distinct exponential growth curve pattern. The highest growth rates were observed at 23 and 45 days. After this age, a marked fall in growth rates occurs, except for white fibres, where this decrease was less intense. Red and intermediate muscle fibers tend to stabilize their growth earlier than white fibres.