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Effect of hypoenergetic feeding on muscle oxidative phosphorylation and mitochondrial complex I–IV activities in rats^1,2,3

¹ From the Department of Medicine, University of Toronto.

Background: Previous studies showed that malnutrition reduces the activity of complexes I, II, and III in the mitochondria of skeletal muscle.

Objective: We hypothesized that malnutrition would influence oxidative phosphorylation and mitochondrial complex activity in the skeletal muscle of rats.

Design: Thirty-two rats were assigned either to a control group with an ad libitum intake of 364 kJ/d or to a hypoenergetic group with an intake of 92 kJ/d. Eleven of these rats received the hypoenergetic diet for 10 d, 2 for 5 d, 2 for 6 d, 2 for 7 d, and 1 each for 8 and 11 d to achieve a distributed weight loss. Ten controls were fed for 10 d, 2 for 7 d, and 1 for 5 d, to match day 10, day 5, and the midpoint (day 7) of 6–8 d of hypoenergetic feeding. The 2 diets provided the same volume, electrolytes, vitamins, and trace elements but different amounts of energy.

Results: A significant relation was observed between weight loss and the state 4 and 3 oxidation rates with pyruvate + malate and for state 3 glutamate + malate and succinate + rotenone but not with tetramethyl-p-phenylenediamine + ascorbate + antimycin A (TMPD). Similarly, a significant relation was observed between the degree of weight loss and complex I and III activities but not with complex II and IV activities.

Conclusions: The complex activities of the mitochondrial oxidative phosphorylation chain in muscle were depressed selectively with energy deprivation when compared with normally fed rats. These findings may partly explain the mechanism of reduced muscle energetics in energy malnutrition.

Key Words: Malnutrition • energy metabolism • oxidative phosphorylation • respiratory chain • hypoenergetic feeding • complex activity • rats

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