Histoenzymatic and morphometric analysis of muscle fiber type transformation during the postnatal development of the chronically food-deprived rat.

We analyze the effect of chronic undernourishment on extensor digitorum longus (EDL) muscle maturation in the rat. Cytochrome c oxidase (COX) and alkaline ATPase histoenzymatic techniques were used to determine the relative proportion of different fiber types (oxidative/glycolytic and type I, IIa/IId, or IIb, respectively) and their cross-sectional area in control and undernourished EDL muscles at several postnatal (PN) ages. From PN days 15 to 45, undernourished EDL muscles showed predominance of oxidative and type IIa/IId fibers, but from PN days 60 to 90, there were a larger proportion of oxidative fibers and an equal proportion of type IIa/IId and IIb fibers.