Lactate dehydrogenase forms in denervation and disuse atrophy of red and white muscle

RANVIER'S early observations in rabbit revealed the existence of two types of skeletal muscle (red and white) whose difference in color paralleled morphological and functional differences as well.' Histologically, two main types of fibers can be distinguished in most skeletal muscles; the predominance of either type is responsible for the muscle's color.2 Muscles mostly consisting of white fibers generally have a higher speed of contraction and of relaxation than those in which red fibers predominate.3 White muscles possess a higher glycolytic and a lower oxidative enzyme activity than red ones.4 Lactate dehydrogenase (LDH) is known to exist in two principal forms, each being a tetrameric molecule consisting of four identical polypeptide subunits. In addition, three hybrid tetramers, containing different proportions of the two basic subunits, have been found in various tissues..5.c The names of muscle and heart LDH have been used to describe the two basic types of the enzyme. It has been observed that the two foims differ in their degree of inhibition by pyruvate. Muscle LDH maintains its activity in the presence of relatively high levels of this substance, whereas heart LDH is strongly inhibited under the same conditions.5 Skeletal muscles contain different proportions of LDH forms. I n general, heart LDH predominates in red muscles and muscle LDH in white ones.Ci Characteristic changes in these enzvme forms have been described in deneivhave very differently under various pathological conditions. Denelvation appears to cause a rapid atrophy of the white fibers and little or no change in the diameter of the red ones.' The reverse pattern is seen in tenotomized muscle.8 Selective atrophy of the red fibers has been observed in cases of Werdnig-Hoffmaim disease and of amyotrophic lateral sclerosis."*" There is very little information about specific biochemical differences between the two types of muscle in denervation or in disuse atrophy. The present work concerns LDH changes in denervated red and white muscles and provides new data regarding the effects of immobilization and of compensatory phenomena in these. Rabbit soleus, a red (tonic or slow) muscle, and gastrocnemius, a white (phasic or fast) one, have been chosen for this study.