Background: Periods of immobilization are often associated with pathologies and/or aging. These periods of disuse muscle atrophy could worsen the pathology or elderly frailty. Exercise, the best way to recover muscle mass, is not always applicable.  Aim of Work: This study aimed to compare the therapeutic effect of oxandrolone versus whey protein on disuse induced muscle atrophy in old aged male rats with low testosterone level and mobility limitation.
Materials and Methods: Twenty four aged male albino rats were included: 6 rats as control (group I). Eighteen rats were subjected to hind limb suspension (HLS) for 2 weeks then were divided into: 6 rats as group II (disuse atrophy) and 12 rats as group III (treated group) which was equally subdivided into: group IIIa (oxandrolone treated) and IIIb (whey protein treated) where oxandrolone 1.23 mg/kg and whey protein 9.25 gm/kg were given orally daily for 4 weeks. Rats were sacrificed after 6 weeks. Gastrocnemius muscle weight and total protein content were measured. Muscle specimens were stained with Hematoxylin and Eosin, PAS and immunohistochemical staining for Myogenin. Morphometric measurements of type I and type II fibers number and cross sectional area (CSA), number of myogenin positive cells (differentiated satellite cells) were taken and statistically analyzed.  Results: Group II showed atrophic angulated muscle fibers and significant increase in type II fibers compared to the control. Subgroup IIIa showed muscle fibers with large diameter. Many rounded vesicular nuclei were observed among muscle fibers. A significant increase in type I fibers and number of myogenin positive cells as compared to the control and subgroup IIIb.  Conclusion: Oxandrolone and whey protein treated subgroups showed improved muscle mass, CSA, total protein content, histological architecture of muscle fibers and increase of satellite cells number. However, oxandrolone showed better therapeutic potential in ameliorating disuse muscle atrophy.