Cellular Response of Rat Quadriceps Muscle to Chronic Dietary Restrictions

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Abstract
The effects of 10 weeks of protein restriction (8% casein) or protein-energy restriction (15% casein, restricted intake) on quadriceps muscle were compared to well-nourished age-controls (27% casein, ad libitum). Muscle weights relative to body weights were unchanged by the dietary restrictions (0.78 g/100 g). Mean diameters of muscle fibers from the red portion were 60.2, 42.7, and 48.5 µm for controls, protein-restricted, and protein-energy restricted groups, and 59.9, 33.1, and 42.2 µm for fibers from the white portion. Although the fiber diameters tended to be smaller in the experimental, the difference was only significant for the white portion of the protein-restricted group. At the ultrastructural level, most of the fibers from both parts of the muscle were qualitatively and quantitatively normal. Diameters of the myofibrils were unchanged from controls: 695 and 852 nm for the red and white portions. A few fibers in each part of the muscle were undergoing moderate degenerative changes, however, with myofibrillar disorganization more prominent in the white portion. The changes were more widespread in the protein-energy restricted rats. A small percentage of satellite cells was found in muscle from each dietary group. It was concluded that while a few fibers are adversely affected, most of the fibers of quadriceps muscle are structurally similar to age-controls after chronic dietary restriction of protein or energy.