Histomorphological assessment of a rat model of skeletal muscle injury induced by local injection of bupivacaine

Chen Yu-pei; Liu Tong; Zou De-hui; Zhang Li; Mao Ying-qiu; Huo Ze-jun

doi:10.3969/j.issn.2095-4344.2016.18.005

Abstract：BACKGROUND: The neurotoxicity and cardiotoxicity of bupivacaine have been reported frequently. However, the studies on bupivacaine-induced muscle toxicity are few. <br> OBJECTIVE: To establish and evaluate local intramuscular injection of bupivacaine on the changes in histomorphology and ultrastructure of rat multifidus muscle at various time points. <br> METHODS: A total of 54 male Sprague-Dawley rats weighing 280-320 g were randomly divided into black group (n=18), model group (n=18) and model control group (n=18). Each group was then equal y subdivided into three subgroups according to time points (4, 7 and 14 days) (n=6). Both sides of multifidus muscle of the rats (L4 and L5) were injected with 0.5% bupivacaine. The morphological and ultrastructural changes of multifidus muscle were observed and analyzed with light microscope and transmission electron microscope at 4, 7 and 14 days after model establishment. <br> RESULTS AND CONCLUSION: (1) A single intramuscular injection of 0.5% bupivacaine induced muscular damage. (2) Hematoxylin-eosin staining results showed fiber necrosis, inflammatory cel infiltration, and a smal amount of macrophages in local skeletal muscle. (3) Under the transmission electron microscope, the structure of myofibrils was destroyed or disintegrated; kinds of bands and lines were indistinct, disrupted or disappeared; the structure of mitochondria was abnormal, the mitochondrial cristae were reduced or disappeared. In the 7- and 14-day groups, multifidus muscle proliferated and repaired. (4) Ultrastructural change scores in skeletal muscle were significantly higher in the model group than in the blank and model control groups (P < 0.05). Above scores were significantly greater in the 4-day group than in the 7- and 14-day groups (P < 0.05), and higher in the 7-day group than in the 14-day group (P < 0.05). (5) Results suggest that a single intramuscular injection of 0.5% bupivacaine can result in pathological changes of skeletal muscle from morphology and ultrastructure. This method can establish a suitable model of skeletal muscle injury.