| Morphological Studies on the Effects of Lidocaine and Tetracaine on Rat Gracilis Muscle. |
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Chung Hyun Cho |
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Department of Anesthesiology,Yonsei University College of Medicine, Seoul, Korea. |
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| Abstract |
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It has long been known that skeletal muacle undergoes atrophy following permanent interruption of the motor nerve supply. Also many local anesthetic agents are known to damage skeletal muscle following local injection. Reviews of the literature reveal that ralatively few studies have been done on the histopathological effects of local anesthetics on ske eltal muscle (Benoit, 1971). The agents used and examination of tissue varied widely, and before 1970, the majority of investigators reported muscle degeneration or necrosis only. Except for bupivacaine, there haa been relatively little systematic work documenting the myotoxic effects of a single dose of local anesthetics. In this study, the myotoxicity of the local anesthetics, lidocaine (Xylocaine) and tetracaine (Pontocaine) was evaluated in the rat gracilis muscle via morphological and histopathological changes. The results are summarized as follows: 1) After one to three days of treatment, a marked atrophy of the gracilis posticus muscle was observed. The wet weight of the muscle was reduced to about 60 to 70% of the contralateral untreated muscle. After 15 to 20 the days muscle returned to normal size. 2) One to 3 days after injection, macrophage appeared in the dsmaged myofibers, and the plasma membrane was irregular, nuclei with densely clumped chromatin were observed in the atrcphied muscle fibers. After 15 to 25 days the histological pictures had refurned to almost normaL 3) Mean diameter of muscle fibers were reduced to about 45 to 64% of that of the control fibers 4) Type g fibers appeared more susceptible to the damage than type I fibers to these drugs. 5) Tetracaine caused move muscle damage than lidocaine and regeneration was delayed. In conclusion, although there were small differences in degree of changes, lidocaine and tetracaine appear to effect upon rat gracilis muscle and cause rapid destruction of skeletal muscle fibers which is then followed by regeneration of new fibers in the affected area. Also Type g fibers appear more susceptible to these drugs. |
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