Effect of Dietary Protein Restriction or Food Restriction on Oxygen Consumption and Mitochondrial Distribution in Cardiac and Red and White Skeletal Muscle of Rats

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Abstract
The effects of food restriction and dietary protein restriction on the oxygen consumption of three types of muscle in the rat were compared. Control rats were fed a diet containing 27% casein. Two groups of protein-restricted rats were fed isoenergy diets containing 15% or 8% casein. Two groups of food-restricted rats were fed either the 27% or 15% casein diets in amounts equivalent to 35% of the intake of energy. Oxygen consumption was measured in papillary muscle and in fibers from the red (high oxidative) and white (low oxidative) portions of the quadriceps with pyruvate and malate as substrates. Control values (µlO2/g dry wt/min) were 35.2 + 1.5 (papillary), 20.7 ± 1.9 (red), and 7.8 ± 0.7 (white). Restriction of dietary protein content failed to alter the oxygen consumption of any of the muscle types. In contrast, involuntary food restriction, combined with a reduction in protein content, caused a reduction in the oxygen consumption of papillary and white skeletal muscle, but the metabolism of red skeletal muscle was not affected. No differences were found in the appearance and distribution of mitochondria in cardiac or red skeletal muscle after examination by electron microscopy, but a depletion of subsarcolemmal mitochondria was evident in white muscle from the food-restricted rats.