Decreased phosphorylative capacity and respiratory rate of rabbit skeletal muscle mitochondria in vitamin E dystrophy.

i. Lfltrastructurai and biochemical changes occurring in mitochondria of skeletal muscil: of vitamin E deficient rabbits and the extent of repair of the mitochondria after oral administration of the vitamin to the deficient rabbits have been studied. 2. Muscle of the dystrophic rabbits showed structural changes typtcai of the myopathic state. and these were reversed in the rehabilitated rabbits. 3. State 3 respiratory rate of the dystrophic mitochondria was severely reduced when measured tn the presence or absence of albumin in the assay medium. 4. The ADP.0 ratlo of the dystrophic mltochondria utilizing glutamate malate uas reduced by one-third when albumin was absent from the assay medium but was similar to the ratio of the control and reh~ibilitated mito~h~)ndria when albumin was present. 5. This result suggested that skeletal muscle mitochondria of dystrophic rabbits had a decreased ADP 0 ratio ict rim. The lesions of vitamin E dystraphy in skeletal muscle of the rabbit are characterized in the early stages by mitochondrial swelling. f~gm~ntation of the cristae and accumulation of dense granules within the mitochondria (van Vleet er ul., 1967; 1968). Later changes. such as myofibrillar disruption. accumulation of lipid droplets in the sarcoplasm and intra-mitochondria~ calcification. are considered to be secondary in nature (Mason. 1973). The lesions are generally regarded as being myogenic in origin. Biochemical studies of vitamin E deficient rabbit muscle indicate that increased oxygen uptake by skeletal muscle represents a primary response to the vitamin deficiency whereas other biochemical changes are secondary to this or some other metaboIic disturbance (Mason, 1973: Victor. 1934). Increased oxygen uptake usually precedes the appearance of the histological lesions in rabbits and can be restored to normal within a few hours of intravenous administration of I>L-r-tocopherol (Hummel & Melville. 1951). These studies suggest that vitamin E deficiency leads in some manner to increased mitochondri~l oxygen consumption. Although this may be due in part to the increased energy demands of accelerated protein synthesis, the ultrastructural observations indicate that the major *All correspondence should be addressed to: Dr J. J. A. Heffron. Department of Biochemistry, University College of Cork. Cork. Ireland. ’ Scientific Journal Series. Paper No. 9782 Minnesota Agricultural Experimental Station. Abbreviations. ADP, Adenosine-S-diphosphate; FAD, Flavin adenine dinucleotide: NAD, Nicotinamide adenine dinucleotide proportion of the increased oxygen consumption may be due to a loss of respiratory control or to uncoupling of oxidative phosphoryfatjon or a combination of both of these factors. In the present study we have attempted to correlate the ultrastructural damage and biochemical changes occurring in the mitochondria of skeletal muscle of vitamin E deficient rabbits. The extent of repair of the mitochondria after oral administration of vitamin E to the dystrophic animals has not been studied. Therefore, the correlation of biochemical and structural properties of the mitochondria in the rehabilitated muscle has not been determined. MATER I.4LS AND i%lETNODS Four male New Zealand white rabbits (Or~~crolugtrs cuniculu.s ~/~lo,ttr.sticus). body weight 1.3 kg, were fed a diet deficient in vitamin E for 4 weeks. The composition of the diet and the rationale for inducing acute dystrophy in a 4 week experimental period are explained elsewhere (Ghan & Hegarty. 1977). At the end of the 4 week period on the vitamin E deficient diet. two of the rabbits were given an oral dose of 50mg uL-z-tocopherol acetate and then fed a diet containing vitamin E for about 4 weeks after which time the animals’ body weight had returned to that of control animals. Rabbits were then killed by injection of potassium chloride into the heart. and the gastrocnemius muscles were excised immediately and placed in ice-cold 0.15 M NaC1. Muscles were obtained from 3 control animals in the same way. Elrcrrou rt7icrosc~op~ Muscles samples from the control. dystrophic and rehabilitated animals were processed for electron microscopy as previously described (Hegarty PI ai., 1973). Bricffy, the