Summary
The levator ani muscle of the rat was examined by correlated light and electron microscopic morphometry. Corrections were made for shrinkage, compression, and differences in stretching. Age, castration, and subsequent testosterone treatment do not affect the fiber number, the filament lattice, and the size of the filaments and myonuclei. The fibers in intact growing males increase in width and length. The number of myonuclei rises, although relatively slower than the amount of contractile material.
Castration, performed at six weeks, partially suppresses fiber growth. The increase of mean fiber width is more strongly inhibited than that of fiber length. Myonuclear multiplication is almost completely arrested in castrates, and the amount of contractile material per myonucleus is lower than in intact males of equal age.
Testosterone, administered at about two months following orchidectomy, highly accelerates the transversal fiber growth, but fiber length is not significantly influenced. Between the fourth and seventh day of treatment a marked increase in myonuclear number occurs.
Analysis of the frequency distribution of the individual fiber widths, which is logarithmic-normal in intact males, revealed that the hormonal influence on the net result of protein anabolism and catabolism markedly differs in the various fibers of a single muscle.
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With the technical assistance of Tineke J. Hoogenboezem.
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Galavazi, G., Szirmai, J.A. Cytomorphometry of skeletal muscle: The influence of age and testosterone on the rat M. levator ani. Z.Zellforsch 121, 507–530 (1971). https://doi.org/10.1007/BF00560157
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DOI: https://doi.org/10.1007/BF00560157