Succinic dehydrogenase activity of forelimb and hindlimb muscles of the dystrophic mouse.

The activity of succinic dehydrogenase (SDH) was determined in muscles of normal and dystrophic mice. In contradistinction to reports based solely upon histochemical examination, we were unable to observe increased activity in fast-twitch muscles of dystrophic mice. Because dystrophic muscles contain large amounts of connective tissue, two reference bases for expression of enzyme activity were compared. SDH activity was expressed either per micromole of creatine or per milligram of "true muscle fibre weight." The latter was obtained by determining the proportion of the whole muscle occupied by muscle fibres using an image analyzer with photographs of muscle cross section. It appears that the use of creatine content as an index of muscle mass may not be valid for pathological tissue, as the concentration of creatine in some dystrophic muscles differed from that of control muscles. Hindlimb muscles of dystrophic mice exhibit continuous spontaneous activity. To determine the effects of this on oxidative enzyme activity two fast-twitch muscles from the forelimb were also examined. Although they showed histochemical changes comparable to those seen in hindlimb muscles, there was no increase in SDH activity. The only dystrophic muscle examined which showed a change in SDH activity was the soleus in which a decrease was observed.