Morphology of the cells of normal, testosterone‐deprived and testosterone‐stimulated levator ani muscles

The atrophy of the levator ani following castration of an adult mouse or rat results from the dissolution of the myofilaments from myofibrils and eventual loss of two‐thirds of the sarcoplasm. Within 45 days the atrophy ceases. The morphology of the now smaller muscle fibers is indistinguishable from those from intact males. Treatment of the stable neuter with testosterone produces rapid enlargement of the muscle fibers, but neglegible changes in the morphological patterns of the sarcoplasm. Observations indicate that new myofilaments form in register along the myofibrils, the enlarging myofibrils being divided to maintain a diameter between 0.5 and 1.5 μ. The cytology of each of the five cell types common to the primary bundles is described. Satellite cells of the muscle fibers are a consistent component, but do not contribute to the processes of atrophy or hypertrophy.