Studies in vivo of ribonucleic acid turnover in mice (strain C57 BL/6J) homozygous and heterozygous for the dystrophic gene, dy2J

Additional biochemical criteria in the differential diagnosis of myositis

Thirty-six biopsy specimens of human biceps and vastus lateralis muscles were examined by histometric analysis and determination of enzyme activities (phosphorylase, triosephosphate dehydrogenase, 3-hydroxacyl-CoA-dehydrogenase, lactate dehydrogenase, hexose isomerase, citrate synthetase, 6-phosphogluconate dehydrogenase). The series included 13 specimens from patients suffering from a benign form of muscular dystrophy (limb girdle and Becker type of muscular dystrophy) and 12 specimens from patients with an acute (n = 5) or chronic (n = 7) form of myositis. Muscle fibres were atrophic in myositis and hypertrophic (with an increased variation of fibre diameters) in muscular dystrophies, as has been shown previously. When myositis samples were compared with either normal or dystrophic muscles, a highly significant lowering of glycolytic enzyme activity was found in chronic myositis, while the activity of 6-phosphogluconate dehydrogenase was elevated to highly significant levels. Measurements of the latter enzyme's activity might be of additional value in differentiating chronic forms of myositis from benign muscular dystrophies.

Connective tissue metabolism in normal and atrophic skeletal muscle

The first two enzymes of the pentose-phosphate pathway (G6PD and 6PGD) were studied in rabbit skeletal muscle. Their activities closely paralleled the connective tissue levels in each individual muscle, and they increased in atrophying muscles at the same rate as connective tissue. Skeletal muscle tendons and subcutaneously implanted polyvinyl sponges, both of which consist of relatively pure connective tissue, displayed much higher activity of these enzymes than the muscle homogenates. These results suggest that pentose synthesis in muscle is mostly confined to its connective tissue elements, raising the possibility of a role for connective tissue in the biosynthetic processes of skeletal muscle. The contribution of connective tissue to the results of muscle quantitative studies may be significant, and even overshadow other values in atrophic muscles, where the muscle cell population may be greatly reduced. The interpretation of quantitative biochemical studies on pathological muscle samples should take this factor into consideration.

In vitro radioisotope precursor incorporation into ribonucleic acid and protein in dystrophic mouse gastrocnemius muscle (C57 BL/6J dy2J/dy2J)

An in vitro tissue slice technique has been developed and used to compare radioisotope precurosr incorporation into RNA and protein in normal and dystrophic mouse gastrophic muscle. Significant differences are observed with both RNA and protein when incorporation is measured on a fresh weight of muscle basis. Specific activity comparisons show significantly increased incorporation with protein but not with RNA. A comparison of the results with in vivo studies has been made. The in vitro system developed is applicable to the study of macromolecular metabolism in normal and diseased human muscle tissue.