Does Reduced Blood Flow Affect the Rate of Muscle Loss in Rats Post Spinal Cord Injury

Abstract

Muscle atrophy is a major sequela occurring after spinal cord injury (SCI) that results from disuse. Additionally, other secondary complications of SCI (e.g., alterations in muscle blood flow) may contribute to muscle loss. PURPOSE: To determine the time course of muscle blood flow changes in relation to muscle atrophy in a rodent severe contusion SCI model. METHODS: Sixty-three 4-months-old (skeletally-mature) male Sprague-Dawley rats received SHAM surgery (T9 laminectomy) or severe (250 kdyne) contusion SCI using a computer-guided impactor. At 1-, 2-, and 4-weeks (wk) post-surgery, an intravenous catheter was implanted into the tail vein of SHAM and SCI animals. Colored microspheres (15μm diameter) were then infused into the circulation, allowing for the measurement of regional blood flow (ml/min/g tissue mass). Subsequently, the animals were euthanized and the mass of the dissected right and left soleus, gastrocnemius, and plantaris were taken. Concentrations of the colored microspheres within each muscle were determined via spectrophotometry, following chemical digestion of the muscle. Muscle blood flow calculations were then averaged across the contralateral hindlimbs for the aforementioned muscles. SCI vs SHAM comparisons were made at each time point using independent samples t-tests and Pearson’s correlation coefficients. RESULTS: SCI animals exhibited 23-41% lower soleus mass, 17-27% lower gastrocnemius mass, and 16-29% lower plantaris mass vs SHAM, at all time points (p<0.001). Soleus and gastrocnemius blood flow (corrected for tissue mass, ml/min/g) was 51% lower (p<0.001) and 25% lower (p<0.05) after SCI, respectfully, at 1-wk only. Additionally, a positive relationship between soleus mass and blood flow (corrected for mass) was identified at 1-wk (r= 0.687, p<0.01). No significant alterations in plantaris blood flow were identified at any time point. CONCLUSION: Hindlimb muscle atrophy and reduced muscle blood flow occurred within 1-wk of severe contusion SCI. Thereafter, muscle blood renormalized in comparison with SHAM animals. Further research is needed to determine whether the reductions in muscle blood flow occurring after SCI contribute to muscle loss and/or whether prevention of blood flow deficits preserves muscle mass.