Histochemical Assessment of Cytochrome Oxidase Activity for Monitoring Ischemic Muscle Injury

Electromyographic detection of increased neuromuscular conduction latency that follows electrostimulation of spinal nerves has been used widely as a clinical tool for detection of ischemic muscle injury. We hypothesized that a biochemical marker for stagnant hypoxia provides more direct evidence for evaluating severity and monitoring resolution of ischemic muscle injury than the EMG. To detect intracellular changes in oxygen use during experimental ischemia, ultrathin sections of rat gastrocnemius muscle were treated with reducing agent, 3,3′-diaminobenzidine (DAB), a histochemical marker for intramitochondrial cytochrome oxidase activity. The observed decrease in mitochondrial uptake of DAB suggested that a decrease in cytochrome oxidase activity was associated with experimental ischemia. Neuromuscular conduction latency in rat gastrocnemius muscle was also quantitated after electrostimulation of the sciatic nerve. Ligation of the femoral artery produced ischemic tissue injury, during which recordings of the EMG showed that conduction latency increased [from a mean ± SEM control value of 3.09 ± 0.13 to 3.92 ± 0.22 ms (N = 11, P \u3c 0.001).] The changes in both histochemically detectable cytochrome oxidase activity and neuromuscular conduction latency were reversed by reperfusion. Response of the rat tissue to arterial occlusion was thereby shown to be a physiologic model for skeletal muscle response to ischemia. In addition, histochemical detection of cytochrome oxidase activity was shown to be a sensitive intracellular marker for decreased oxygen use during ischemic muscle injury