Acetyl-1- 14 C-l-carnitine oxidation, carnitine acetyltransferase activity, and CoA content in skeletal muscle mitochondria from normal and dystrophic mice (strain 129)

Mitochondria isolated from the hind leg muscle of normal and dystrophic mice (strain 129) were compared in their capacity to oxidize acetyl-1-14C-l-carnitine. Oxidation in the mitochondria from dystrophic animals was reduced by 80%. Carnitine acetyltransferase (EC 2.3.1.7) activity in the mitochondria was determined and showed a 35% reduction in the mitochondria from dystrophic muscle. A larger decrease (55%) was observed in the mitochondrial content of acid-soluble CoA. Although the combined decreases in carnitine acetyltransferase and CoA can largely account for the observed decrease in acetylcarnitine oxidation in the mitochondria isolated from dystrophic muscle, it is conceivable that some defect may still exist in the utilization of acetyl groups in the tricarboxylic acid cycle.

Palmitic acid-1- 14 C oxidation by skeletal muscle mitochondria of dystrophic mice

Cofactor requirements for the oxidation of palmitate-1-14C by 600 × g supernatant fraction of mouse skeletal muscle homogenate and by skeletal muscle mitochondria are described. Optimal oxidation of palmitate-1-14C by skeletal muscle mitochondria requires the presence of carnitine, ATP, CoA, and a Krebs cycle intermediate (e.g. succinate). Succinate, malate, alpha-ketoglutarate, and oxaloacetate are all equally effective in supporting the oxidation, but isocitrate is less effective. The oxidation of palmitate-1-14C by 600 × g supernatant fraction of muscle homogenate as well as by skeletal muscle mitochondria from dystrophic mice is significantly decreased compared with that of the normal littermate controls. The present results, together with the previous findings, suggest that the decrease in oxidation of palmitate-1-14C by the dystrophic muscle preparations is most likely due to a defect in one or more of the steps of the Krebs cycle.

Hypothalamic obesity in weanling rats

Bilateral hypothalamic lesions were placed in the ventromedial nuclei of 15 male weanling rats. Nine male littermates were used as controls. Food intake, body weight, and nose-occipital (N-O) length were followed for 90 days. Rats were killed on the 90th postoperative day and stomach weight, body fat content, and femur length were then measured. Although the daily food intake and the rate of body weight gain of the rats with lesions were comparable to those of their controls, all 15 operated rats became obese and their N-O and femur lengths were significantly shorter. It is concluded that hypothalamic obesity of weanling rats is associated with growth impairment.