Background: This study aimed to examine the effects of a new hind limb disuse model on the morphology and fiber type distribution of the extensor digitorum longus (EDL) of rats. Quicker onset of disuse atrophy would reduce the amount of time the animals have to be subjected to tail suspension.
Methods: The new hind limb disuse mode was achieved by tail suspension (TS) and one hind limb fixed by plaster-casting (tail suspension-immobilization, TS+Im). There were 42 female Sprague-Dawley rats randomly divided into 7 groups (6 rats in each group) and exposed to the conditions for 0-6 wk, respectively. The cross-sectional area (CSA) and the types of muscle fiber of the rats' EDL were measured and classified by histochemical staining.
Results: The decrease of EDL's CSA caused by TS+Im was more obvious (significant change was observed after 4 wk and Type I fiber's CSA decreased 27.3% after 6 wk) than that caused by TS only (significant change occurred after 6 wk and Type I fiber's CSA diminished 18.01% at that time). TS lead to the transition of Type IIB fibers to Type I and IIA fibers while TS+Im led to Type I and IIA fibers getting converted to Type IIB fibers.
Discussion: When compared to TS only, TS+Im caused faster and greater reduction of the EDL's CSA in rats. TS+Im can also lead to a shift from oxidative to glycolytic metabolism of the EDL muscle fiber. Tail suspension-immobilization is a new hind limb disuse model for the EDL and may be more effective.