Dexamethasone-induced hyposensitivity to rocuronium in rat diaphragm associated with muscle-fiber transformation

The aim of the current study was to investigate the effect of chronic dexamethasone (Dex) administration on rat diaphragm function and sensitivity to rocuronium and muscle-fiber transformation. Adult male Sprague-Dawley rats were randomized to receive a daily intraperitoneal injection of Dex to evaluate whether alterations in diaphragm function and susceptibility to rocuronium would be induced. In addition, diaphragm contractile properties, histopathology and isometric twitch tensions of nerve-hemidiaphragm preparations were evaluated. Dex administration led to impaired diaphragm force generation, increased fatigue resistance and a prolonged half-relaxation time, as well as time-to-peak tension. Dex treatment led to desensitization of the rat diaphragm to rocuronium, as demonstrated by a shift of the rocuronium concentration-twitch tension curves to the right. Histochemical analysis of adenosine triphosphatase revealed that the distribution and cross-sectional area of type II fibers were decreased in rats exposed to Dex. The present study indicates that chronic Dex treatment induced alterations in muscle function and that susceptibility to rocuronium is associated with muscle fiber-type transformation, which may aid in directing future administration of muscle relaxants.