Effect of denervation on the red and white fibres of the pectoralis muscle of the pigeon.

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Abstract
A histochemical study of the localization of glycogen, fat, phosphorylase, succinlc dehydrogenase (SDH), pentose cycle dehydrogenases, [beta]-hydroxybutyric dehydrogenase, acid and alkaline phosphatases, lipase and esterase in denervated pigeon breast muscle was undertaken to demonstrate the effect of de-nervationi on red and white fibers. A shift of metabolism was shown by the red fibers acquiring more glycogen and phosphorylase and the white fibers losing these compounds. Little fat was demonstrated in the muscle cells but considerable accumulations of fat were seen in the inter-fascicular spaces of the muscle. A few red fibers, however, were loaded with fat. Since the activity of the pentose cycle dehydrogenases was increased, it was inferred that in atrophic muscle there is an increased synthesis of fat. This fat, which is not utilized by the muscle accumulates in the muscle cells as well as in the intercellular spaces. The increase seen in [beta]-hydroxybutyric dehydrogenase is probably due to an increased lipogenesis. Lipase activity decreased and Tween 20 esterase increased. Discrepancies between biochemical data and these histochemical findings were attributed to the substrate specificity of "true" lipase. Acid and alkaline phosphatase activities were found to be low in the atrophied fibers as well as in the connective tissues surrounding them. Some of the hydrolytic enzymes and NADP-linked dehydrogenases are active in the connective tissue. Denervation results in a drastic change in intracellular metabolism of red and white muscle fibers. The majority of the red fibers are adapted to a glycolytic metabolism and fat synthesis increases in the muscle as a whole. With complete inactivation of the muscle, in the white fibers there is structural breakdown accompanied by biochemical changes while in the red fibers biochemical changes occur and structural integrity becomes lost towards the final stages of a trophy. These biochemical changes were shown to be due to a shift in metabolism from aerobic to anaerobic in the red fibers and anaerobic to aerobic in the white fibers.