Altered metabolic enzyme activities in fast and slow twitch muscles due to induced sciatic neuropathy in the rat

A pilot study was conducted to examine enzymatic and metabolic alterations in end organs as a consequence of neuropathy. Silastic pellets were implanted transverse to the sciatic nerve of rats. Neurobehavioral evaluations based on hind limb gait were conducted at 2 and 4 weeks postoperatively. Four-week values demonstrated facilitated utilization of the neuropathic limb in three of five animals, as compared to the normal contralateral limb and normal animals. Nerve electrophysiology and quantitative muscle enzymology were observed at 4 weeks postoperatively. Relative to control animals, the experimental group exhibited decreased nerve conduction velocity, decreased glycolytic enzyme activity in both fast and slow twitch muscle and increased malate dehydrogenase activity in the flexor digitorum longus (FDL). Muscle weight/body weight ratios for control and experimental animals suggest an increase for experimental animals, especially of the FDL. This change was not due to increased muscle proteins for the experimental group as determined on homogenates. Muscle homogenate protein values were actually significantly lower than those of the control group for FDL and soleus. For this reason, when enzyme activities were compared on an equal protein basis, most significant differences were obscured. Only aldolase remained significantly less for the experimental group (p less than 0.01). It is concluded that muscle metabolism is subject to change when confronted with mildly neuropathic innervation. Of particular interest is the uniform direction of change. Both fast and slow twitch muscles exhibited a metabolic shift in the direction of slow twitch muscle.